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[Git][ghc/ghc][wip/T23109a] 86 commits: Driver: make MonadComprehensions imply ParallelListComp
by Simon Peyton Jones (＠simonpj) 29 Apr '25

29 Apr '25

Simon Peyton Jones pushed to branch wip/T23109a at Glasgow Haskell Compiler / GHC Commits: 34a9b55d by lazyLambda at 2025-04-04T06:22:26-04:00 Driver: make MonadComprehensions imply ParallelListComp This commit changes GHC.Driver.Flags.impliedXFlags to make the MonadComprehensions extension enable the ParallelListComp extension. Fixes #25645 - - - - - d99eb7cd by sheaf at 2025-04-04T06:23:28-04:00 NamedDefaults: handle poly-kinded unary classes With this commit, we accept named default declarations for poly-kinded classes such as Typeable, e.g. default Typeable (Char) This used to fail because we assumed the kind of the class was monomorphic, e.g. Type -> Constraint (Type -> Type) -> Constraint Nat -> Constraint Now, we can handle a simple polymorphic class such as Typeable :: forall k. k -> Constraint Note that we keep the restriction that the class must only have one visible argument. This is all explained in the new Note [Instance check for default declarations] in GHC.Tc.Gen.Default. Fixes #25882 - - - - - 4cbc90de by sheaf at 2025-04-04T11:39:05-04:00 LLVM: add type annotations to AtomicFetch_cmm.cmm - - - - - e2237305 by sheaf at 2025-04-04T11:39:05-04:00 Cmm lint: lint argument types of CallishMachOps This commit adds a new check to Cmm lint to ensure that the argument types to a CallishMachOp are correct. The lack of this check was detected in the AtomicFetch test: the literals being passed as the second arguments to operations such as 'fetch_add', 'fetch_and'... were of the wrong width, which tripped up the LLVM backend. - - - - - 9363e547 by Cheng Shao at 2025-04-04T11:39:50-04:00 ci: add ghc-wasm-meta integration testing jobs This patch adds ghc-wasm-meta integration testing jobs to the CI pipeline, which are only triggered via the `test-wasm` MR label or manually when the `wasm` label is set. These jobs will fetch the wasm bindists and test them against a variety of downstream projects, similarly to head.hackage jobs for native bindists, offering a convenient way to catch potential downstream breakage while refactoring the wasm backend. - - - - - 27029e60 by Adam Gundry at 2025-04-04T11:40:36-04:00 base: Minor fixes to GHC.Records haddocks This corrects a stale reference to OverloadedRecordFields (which should be OverloadedRecordDot), fixes the haddock link syntax and adds an @since pragma. - - - - - f827c4c6 by Rodrigo Mesquita at 2025-04-07T11:22:10-04:00 Parametrize default logger action with Handles Introduce `defaultLogActionWithHandles` to allow GHC applications to use GHC's formatting but using custom handles. `defaultLogAction` is then trivially reimplemented as ``` defaultLogActionWithHandles stdout stderr ``` - - - - - 5dade5fd by sheaf at 2025-04-07T11:23:02-04:00 Finer-grained recompilation checking for exports This commit refines the recompilation checking logic, to avoid recompiling modules with an explicit import list when the modules they import start exporting new items. More specifically, when: 1. module N imports module M, 2. M is changed, but in a way that: a. preserves the exports that N imports b. does not introduce anything that forces recompilation downstream, such as orphan instances then we no longer require recompilation of N. Note that there is more to (2a) as initially meets the eye: - if N includes a whole module or "import hiding" import of M, then we require that the export list of M does not change, - if N only includes explicit imports, we check that the imported items don't change, e.g. - if we have @import M(T(K, f), g)@, we must check that N continues to export all these identifiers, with the same Avail structure (i.e. we should error if N stops bundling K or f with T) - if we have @import M(T(..))@, we must check that the children of T have not changed See Note [When to recompile when export lists change?] in GHC.Iface.Recomp. This is all tested in the new tests RecompExports{1,2,3,4,5} Fixes #25881 - - - - - f32d6c2b by Andreas Klebinger at 2025-04-07T22:01:25-04:00 NCG: AArch64 - Add -finter-module-far-jumps. When enabled the arm backend will assume jumps to targets outside of the current module are further than 128MB away. This will allow for code to work if: * The current module results in less than 128MB of code. * The whole program is loaded within a 4GB memory region. We have seen a few reports of broken linkers (#24648) where this flag might allow a program to compile/run successfully at a very small performance cost. ------------------------- Metric Increase: T783 ------------------------- - - - - - 553c280b by Andreas Klebinger at 2025-04-07T22:02:11-04:00 Revert "rts: fix small argument passing on big-endian arch (fix #23387)" Based on analysis documented in #25791 this doesn't fully fix the big while introducing new bugs on little endian architectures. A more complete fix will have to be implemented to fix #23387 This reverts commit 4f02d3c1a7b707e609bb3aea1dc6324fa19a5c39. - - - - - b0dc6599 by Andreas Klebinger at 2025-04-07T22:02:11-04:00 Interpreter: Fixes to handling of subword value reads/writes. Load subword values as full words from the stack truncating/expanding as neccesary when dealing with subwords. This way byte order is implicitly correct. This commit also fixes the order in which we are pushing literals onto the stack on big endian archs. Last but not least we enable a test for ghci which actually tests these subword operations. - - - - - ed38c09b by Cheng Shao at 2025-04-07T22:02:53-04:00 testsuite: don't test WasmControlFlow stdout This patch solves a potential test flakiness in `WasmControlFlow` by removing `WasmControlFlow.stdout` which is not so portable/stable as it seems. See added `Note [WasmControlFlow]` for more detailed explanation. - - - - - f807c590 by Rodrigo Mesquita at 2025-04-08T17:41:51-04:00 debugger: Add docs to obtainTermFromId - - - - - 5dba052d by Rodrigo Mesquita at 2025-04-08T17:41:51-04:00 Move logic to find and set Breakpoint to GHC Breakpoints are uniquely identified by a module and an index unique within that module. `ModBreaks` of a Module contains arrays mapping from this unique breakpoint index to information about each breakpoint. For instance, `modBreaks_locs` stores the `SrcSpan` for each breakpoint. To find a breakpoint using the line number you need to go through all breakpoints in the array for a given module and look at the line and column stored in the `SrcSpan`s. Similarly for columns and finding breakpoints by name. This logic previously lived within the `GHCi` application sources, however, it is common to any GHC applications wanting to set breakpoints, like the upcoming `ghc-debugger`. This commit moves this logic for finding and setting breakpoints to the GHC library so it can be used by both `ghci` and `ghc-debugger`. - - - - - bc0b9f73 by Rodrigo Mesquita at 2025-04-08T17:41:51-04:00 Refactor and move logic for identifier breakpoints Breakpoints can be set on functions using syntax of the form `[Module.]function`. The parsing, resolution (e.g. inferring implicit module), and validation of this syntax for referring to functions was tightly coupled with its GHCi use. This commit extracts the general purpose bits of resolving this syntax into `GHC.Runtime.Debugger.Breakpoints` so it can be further used by other GHC applications and to improve the code structure of GHCi. Moreover, a few utilities that do splitting and joining of identifiers as strings were moved to `GHC.Runtime.Eval.Utils`, which also can be used in the future to clean up `GHC.Runtime.Eval` a bit. - - - - - 4f728d21 by Rodrigo Mesquita at 2025-04-08T17:41:51-04:00 debugger: derive Ord for BreakpointIds - - - - - 5528771c by Rodrigo Mesquita at 2025-04-08T17:41:51-04:00 debugger: Move context utils from GHCi to GHC Moves `enclosingTickSpan`, `getCurrentBreakSpan`, and `getCurrentBreakModule`, general utilities on the internal debugger state, into the GHC library. - - - - - 4871f543 by sheaf at 2025-04-08T17:42:43-04:00 Implicit quantification in type synonyms: add test This adds a test for ticket #24090, which involves implicit quantification in type synonyms. The underlying issue was fixed in 0d4ee209dfe53e5074d786487f531dabc36d561c. - - - - - 48917d3c by sheaf at 2025-04-08T17:42:44-04:00 Turn on implicit-rhs-quantification by default This flag was added to GHC 9.8, and will be removed in a future GHC release. In preparation, this commit adds it to the default warning flags. - - - - - 629be068 by Rodrigo Mesquita at 2025-04-08T17:43:26-04:00 debugger: Add breakpoints to every Stmt While single-stepping through a Haskell program we stop at every breakpoint. However, we don't introduce breakpoints at every single expression (e.g. single variables) because they would be too many and uninteresting. That said, in a do-block, it is expected that stepping over would break at every line, even if it isn't particularly interesting (e.g. a single arg like getArgs). Moreover, let-statements in do-blocks, despite only being evaluated once needed, lead to surprising jumps while stepping through because some have outermost (outside the let) breakpoints while others don't. This commit makes every statement in a do-block have a breakpoint. This leads to predictable stepping through in a do-block. Duplicate breakpoints in the same location are avoided using the existing blacklist mechanism, which was missing a check in one relevant place. Fixes #25932 - - - - - 99a3affd by Matthew Pickering at 2025-04-08T17:44:08-04:00 driver: refactor: Split downsweep and MakeAction into separate modules. This will facilitate using the downsweep functions in other parts of the compiler than just --make mode. Also, the GHC.Driver.Make module was huge. Now it's still huge but slightly smaller! - - - - - ecfec4df by sheaf at 2025-04-09T14:13:12-04:00 Store user-written qualification in the GhcRn AST This commit ensures we store the original user-written module qualification in the renamed AST. This allows us to take into account the user-written qualification in error messages. Fixes #25877 - - - - - 97c884e2 by sheaf at 2025-04-09T14:13:12-04:00 TcRnIllegalTermLevelUse: simpler error when possible This commit makes GHC emit a simple error message in the case of an illegal term-level use of a data constructor: we will try to report an out-of-scope error instead of a "Illegal term level use" error, as the latter might be a bit overwhelming for newcomers. We do this when we have a data constructor import suggestion to provide to the user. For example: module M where { data A = A } module N where import M(A) x = Bool -- Illegal term-level use of Bool y = A -- Data constructor not in scope: A. -- Perhaps add 'A' to the import list of 'M'. This commit also revamps the "similar names" suggestion mechanism, and in particular its treatment of name spaces. Now, which name spaces we suggest is based solely on what we are looking for, and no longer on the NameSpace of the Name we have. This is because, for illegal term-level use errors, it doesn't make much sense to change the suggestions based on the fact that we resolved to e.g. a type constructor/class; what matters is what we were expecting to see in this position. See GHC.Rename.Unbound.{suggestionIsRelevant,relevantNameSpace} as well as the new constructors to GHC.Tc.Errors.Types.WhatLooking. Fixes #23982 - - - - - bff645ab by Rodrigo Mesquita at 2025-04-09T14:13:57-04:00 driver: Split Session functions out of Main This commit moves out functions that help in creating and validating a GHC multi session from Main into the ghc library where they can be used by other GHC applications. Moreover, `Mode` processing and `checkOptions` linting were moved to separate modules within the ghc-bin executable package. In particular: - Move `Mode` types and functions (referring to the mode GHC is running on) to `ghc-bin:GHC.Driver.Session.Mode` - Move `checkOptions` and aux functions, which validates GHC DynFlags based on the mode, to `ghc-bin:GHC.Driver.Session.Lint` - Moves `initMulti`, `initMake`, and aux functions, which initializes a make/multi-unit session, into `ghc:GHC.Driver.Session.Units`. - - - - - 501b015e by Rodrigo Mesquita at 2025-04-09T14:13:57-04:00 docs: Improve haddock of ExecComplete - - - - - dea98988 by Andreas Klebinger at 2025-04-09T19:23:57-04:00 Avoid oversaturing constructor workers. Constructor applications always need to take the exact number of arguments. If we can't ensure that instead apply the constructor worker like a regular function. Fixes #23865 - - - - - f1acdd2c by sheaf at 2025-04-09T19:25:41-04:00 NamedDefaults: require the class to be standard We now only default type variables if they only appear in constraints of the form `C v`, where `C` is either a standard class or a class with an in-scope default declaration. This rectifies an oversight in the original implementation of the NamedDefault extensions that was remarked in #25775; that implementation allowed type variables to appear in unary constraints which had arbitrary classes at the head. See the rewritten Note [How type-class constraints are defaulted] for details of the implementation. Fixes #25775 Fixes #25778 - - - - - 5712e0d6 by Vladislav Zavialov at 2025-04-10T05:17:38+00:00 Retry type/class declarations and instances (#12088) Retry type/class declarations and instances to account for non-lexical dependencies arising from type/data family instances. This patch improves the kind checker's ability to use type instances in kind checking of other declarations in the same module. * Key change: tcTyAndClassDecls now does multiple passes over the TyClGroups, as long as it is able to make progress. See the new Note [Retrying TyClGroups] in GHC.Tc.TyCl * Supporting change: FVs of a TyClGroup are now recorded in its extension field, namely XCTyClGroup. See the new Note [Prepare TyClGroup FVs] in GHC.Rename.Module * Instances are no longer inserted at the earliest positions where their FVs are bound. This is a simplification. See the new Note [Put instances at the end] in GHC.Rename.Module * Automatic unpacking is now more predictable, but fewer fields get unpacked by default. Use explicit {-# UNPACK #-} pragmas instead. See the new Note [Flaky -funbox-strict-fields with type/data families] For the wide range of newly accepted programs, consult the added test cases. Fixed tickets: #12088, #12239, #14668, #15561, #16410, #16448, #16693, #19611, #20875, #21172, #22257, #25238, #25834 Metric Decrease: T8095 - - - - - bc73a78d by sheaf at 2025-04-10T15:07:24-04:00 checkFamApp: don't be so eager to cycle break As remarked in #25933, a pure refactoring of checkTyEqRhs in ab77fc8c7adebd610aa0bd99d653f9a6cc78a374 inadvertently changed behaviour, as it caused GHC to introduce cycle-breaker variables in some unnecessary circumstances. This commit refactors 'GHC.Tc.Utils.Unify.checkFamApp' in a way that should restore the old behaviour, so that, when possible, we first recur into the arguments and only introduce a cycle breaker if this recursion fails (e.g. due to an occurs check failure). Fixes #25933 - - - - - 3acd8182 by Andreas Klebinger at 2025-04-10T22:32:12-04:00 Expand docs for RTS flag `-M`. The behaviour of how/when exceptions are raised was not really covered in the docs. - - - - - 026c1a39 by Adam Sandberg Ericsson at 2025-04-10T22:32:56-04:00 add cases for more SchedulerStatus codes in rts_checkSchedStatus - - - - - 5977c6a1 by sheaf at 2025-04-10T22:33:46-04:00 Squash warnings in GHC.Runtime.Heap.Inspect There were incomplete record selector warnings in GHC.Runtime.Heap.Inspect due to the use of the partial 'dataArgs' record selector. This is fixed by passing the fields to the 'extractSubTerms' function directly, rather than passing a value of the parent data type. - - - - - 6a3e38f5 by Andreas Klebinger at 2025-04-11T15:13:53-04:00 hadrian: Make ghcWithInterpreter the universal source of truth about availability of the interpreter We were doing some ad-hoc checks in different places in hadrian to determine whether we supported the interprter or not. Now this check if confined to one function, `ghcWithInterpreter`, and all the places which use this information consult `ghcWithInterpreter` to determine what to do. Fixes #25533. - - - - - 207de6f1 by Matthew Pickering at 2025-04-11T15:14:37-04:00 testsuite: Fix running TH tests with profiled dynamic compiler Previously, I had failed to update the ghc_th_way_flags logic for the profiled dynamic compiler. In addition to this `ghc_dynamic` was incorrectly set for profiled dynamic compiler. I also updated MultiLayerModulesTH_OneShot test to work for any compiler linkage rather than just dynamic. Fixes #25947 ------------------------- Metric Decrease: MultiLayerModulesTH_Make ------------------------- - - - - - 5455f2b9 by Matthew Pickering at 2025-04-12T08:31:36-04:00 driver: Add support for "Fixed" nodes in the ModuleGraph A fixed node in the module graph is one which we presume is already built. It's therefore up to the user to make sure that the interface file and any relevant artifacts are available for a fixed node. Fixed/Compile nodes are represented by the ModuleNodeInfo type, which abstracts the common parts of Fixed/Compile nodes with accessor functions of type `ModuleNodeInfo -> ...`. Fixed nodes can only depend on other fixed nodes. This invariant can be checked by the function `checkModuleGraph` or `mkModuleGraphChecked`. --make mode is modified to work with fixed mode. In order to "compile" a fixed node, the artifacts are just loaded into the HomePackageTable. Currently nothing in the compiler will produce Fixed nodes but this is tested with the FixedNodes GHC API test. In subsequent patches we are going to remove the ExternalModuleGraph and use Fixed nodes for modules in the module graph in oneshot mode. Fixes #25920 - - - - - ad64d5c2 by Cheng Shao at 2025-04-12T08:32:19-04:00 ci: remove manual case of ghc-wasm-meta downstream testing jobs This patch removes the manual case of ghc-wasm-meta downstream testing jobs; now the only way of including them in the pipeline and running them is via the test-wasm label. The reason of the removal is it proves to be problematic for MRs with only the wasm label; the wasm job would succeed, then the pipeline status would be waiting for manual action instead of succeeding. There needs to be separate jobs for the label-triggered and manual-triggered cases, but I don't think it's worth that extra complexity, the label-triggered case is already sufficient. - - - - - b34890c7 by Vladislav Zavialov at 2025-04-13T01:08:21+03:00 Fix EmptyCase panic in tcMatches (#25960) Due to faulty reasoning in Note [Pattern types for EmptyCase], tcMatches was too keen to panic. * Old (incorrect) assumption: pat_tys is a singleton list. This does not hold when \case{} is checked against a function type preceded by invisible forall. See the new T25960 test case. * New (hopefully correct) assumption: vis_pat_tys is a singleton list. This should follow from: checkArgCounts :: MatchGroup GhcRn ... -> TcM VisArity checkArgCounts (MG { mg_alts = L _ [] }) = return 1 ... - - - - - 84806ebc by Vladislav Zavialov at 2025-04-13T11:40:08-04:00 Remove unused type: TokenLocation - - - - - 05eb50df by Vladislav Zavialov at 2025-04-13T19:16:38-04:00 Register EpToken in Parser.PostProcess.Haddock (#22558) This change allows us to reject more badly placed Haddock comments. Examples: module -- | Bad comment for the module T17544_kw where data Foo -- | Bad comment for MkFoo where MkFoo :: Foo newtype Bar -- | Bad comment for MkBar where MkBar :: () -> Bar class Cls a -- | Bad comment for clsmethod where clsmethod :: a - - - - - 01944e5e by Vladislav Zavialov at 2025-04-13T19:17:21-04:00 Reject puns in T2T (#24153) This patch implements pun detection in T2T. Consider: x = 42 f, g :: forall a -> ... f (type x) = g x In accordance with the specification, the `g x` function call is renamed as a term, so `x` refers to the top-level binding `x = 42`, not to the type variable binding `type x` as one might expect. This is somewhat counterintuitive because `g` expects a type argument. Forbidding puns in T2T allows us to produce a helpful error message: Test.hs:5:16: error: [GHC-09591] Illegal punned variable occurrence in a required type argument. The name ‘x’ could refer to: ‘x’ defined at Test.hs:3:1 ‘x’ bound at Test.hs:5:9 This commit is a follow up to 0dfb1fa799af254c8a1e1045fc3996af2d57a613 where checking for puns was left as future work. - - - - - cc580552 by Vladislav Zavialov at 2025-04-13T19:18:02-04:00 Additional test cases for #12088, #13790 Extract more test cases from ticket discussions, including multi-module examples. Follow up to 5712e0d646f611dfbfedfd7ef6dff3a18c016edb - - - - - d47bf776 by Matthew Pickering at 2025-04-14T16:44:41+01:00 driver: Use ModuleGraph for oneshot and --make mode This patch uses the `hsc_mod_graph` field for both oneshot and --make mode. Therefore, if part of the compiler requires usage of the module graph, you do so in a uniform way for the two different modes. The `ModuleGraph` describes the relationship between the modules in the home package and units in external packages. The `ModuleGraph` can be queried when information about the transitive closure of a package is needed. For example, the primary use of the ModuleGraph from within the compiler is in the loader, which needs to know the transitive closure of a module so it can load all the relevant objects for evaluation. In --make mode, downsweep computes the ModuleGraph before any compilation starts. In oneshot mode, a thunk is created at the start of compilation, which when forced will compute the module graph beneath the current module. The thunk is only forced at the moment when the user uses Template Haskell. Finally, there are some situations where we need to discover what dependencies to load but haven't loaded a module graph at all. In this case, there is a fallback which computes the transitive closure on the fly and doesn't cache the result. Presumably if you are going to call getLinkDeps a lot, you would compute the right ModuleGraph before you started. Importantly, this removes the ExternalModuleGraph abstraction. This was quite awkward to work with since it stored information about the home package inside the EPS. This patch will also be very useful when implementing explicit level imports, which requires more significant use of the module graph in order to determine which level instances are available at. Towards #25795 ------------------------- Metric Decrease: MultiLayerModulesTH_Make MultiLayerModulesTH_OneShot ------------------------- - - - - - 395e0ad1 by sheaf at 2025-04-16T12:33:26-04:00 base: remove .Internal modules (e.g. GHC.TypeLits) This commit removes the following internal modules from base, as per CLC proposal 217: - GHC.TypeNats.Internal - GHC.TypeLits.Internal - GHC.ExecutionStack.Internal Fixes #25007 - - - - - e0f3ff11 by Patrick at 2025-04-17T04:31:12-04:00 Refactor Handling of Multiple Default Declarations Fixes: #25912, #25914, #25934 Previously, GHC discarded all loaded defaults (tcg_default) when local defaults were encountered during typechecking. According to the exportable-named-default proposal (sections 2.4.2 and 2.4.3), local defaults should be merged into tcg_default, retaining any defaults already present while overriding where necessary. Key Changes: * Introduce DefaultProvenance to track the origin of default declarations (local, imported, or built-in), replacing the original cd_module in ClassDefaults with cd_provenance :: DefaultProvenance. * Rename tcDefaults to tcDefaultDecls, limiting its responsibility to only converting renamed class defaults into ClassDefaults. * Add extendDefaultEnvWithLocalDefaults to merge local defaults into the environment, with proper duplication checks: - Duplicate local defaults for a class trigger an error. - Local defaults override imported or built-in defaults. * Update and add related notes: Note [Builtin class defaults], Note [DefaultProvenance]. * Add regression tests: T25912, T25914, T25934. Thanks sam and simon for the help on this patch. Co-authored-by: sheaf <sam.derbyshire(a)gmail.com> - - - - - 386f1854 by Teo Camarasu at 2025-04-17T04:31:55-04:00 template-haskell: Remove `addrToByteArrayName` and `addrToByteArray` These were part of the implementation of the `Lift ByteArray` instance and were errornously exported because this module lacked an explicit export list. They have no usages on Hackage. Resolves #24782 - - - - - b96e2f77 by Sylvain Henry at 2025-04-18T20:46:33-04:00 RTS: remove target info and fix host info (#24058) The RTS isn't a compiler, hence it doesn't have a target and we remove the reported target info displayed by "+RTS --info". We also fix the host info displayed by "+RTS --info": the host of the RTS is the RTS-building compiler's target, not the compiler's host (wrong when doing cross-compilation). - - - - - 6d9965f4 by Sylvain Henry at 2025-04-18T20:46:33-04:00 RTS: remove build info As per the discussion in !13967, there is no reason to tag the RTS with information about the build platform. - - - - - d52e9b3f by Vladislav Zavialov at 2025-04-18T20:47:15-04:00 Diagnostics: remove the KindMismatch constructor (#25957) The KindMismatch constructor was only used as an intermediate representation in pretty-printing. Its removal addresses a problem detected by the "codes" test case: [GHC-89223] is untested (constructor = KindMismatch) In a concious deviation from the usual procedure, the error code GHC-89223 is removed entirely rather than marked as Outdated. The reason is that it never was user-facing in the first place. - - - - - e2f2f9d0 by Vladislav Zavialov at 2025-04-20T10:53:39-04:00 Add name for -Wunusable-unpack-pragmas This warning had no name or flag and was triggered unconditionally. Now it is part of -Wdefault. In GHC.Tc.TyCl.tcTyClGroupsPass's strict mode, we now have to force-enable this warning to ensure that detection of flawed groups continues to work even if the user disables the warning with the -Wno-unusable-unpack-pragmas option. Test case: T3990c Also, the misnamed BackpackUnpackAbstractType is now called UnusableUnpackPragma. - - - - - 6caa6508 by Adam Gundry at 2025-04-20T10:54:22-04:00 Fix specialisation of incoherent instances (fixes #25883) GHC normally assumes that class constraints are canonical, meaning that the specialiser is allowed to replace one dictionary argument with another provided that they have the same type. The `-fno-specialise-incoherents` flag alters INCOHERENT instance definitions so that they will prevent specialisation in some cases, by inserting `nospec`. This commit fixes a bug in 7124e4ad76d98f1fc246ada4fd7bf64413ff2f2e, which treated some INCOHERENT instance matches as if `-fno-specialise-incoherents` was in effect, thereby unnecessarily preventing specialisation. In addition it updates the relevant `Note [Rules for instance lookup]` and adds a new `Note [Canonicity for incoherent matches]`. - - - - - 0426fd6c by Adam Gundry at 2025-04-20T10:54:23-04:00 Add regression test for #23429 - - - - - eec96527 by Adam Gundry at 2025-04-20T10:54:23-04:00 user's guide: update specification of overlapping/incoherent instances The description of the instance resolution algorithm in the user's guide was slightly out of date, because it mentioned in-scope given constraints only at the end, whereas the implementation checks for their presence before any of the other steps. This also adds a warning to the user's guide about the impact of incoherent instances on specialisation, and more clearly documents some of the other effects of `-XIncoherentInstances`. - - - - - a00eeaec by Matthew Craven at 2025-04-20T10:55:03-04:00 Fix bytecode generation for `tagToEnum# <LITERAL>` Fixes #25975. - - - - - 2e204269 by Andreas Klebinger at 2025-04-22T12:20:41+02:00 Simplifier: Constant fold invald tagToEnum# calls to bottom expr. When applying tagToEnum# to a out-of-range value it's best to simply constant fold it to a bottom expression. That potentially allows more dead code elimination and makes debugging easier. Fixes #25976 - - - - - 7250fc0c by Matthew Pickering at 2025-04-22T16:24:04-04:00 Move -fno-code note into Downsweep module This note was left behind when all the code which referred to it was moved into the GHC.Driver.Downsweep module - - - - - d2dc89b4 by Matthew Pickering at 2025-04-22T16:24:04-04:00 Apply editing notes to Note [-fno-code mode] suggested by sheaf These notes were suggested in https://gitlab.haskell.org/ghc/ghc/-/merge_requests/14241 - - - - - 91564daf by Matthew Pickering at 2025-04-24T00:29:02-04:00 ghci: Use loadInterfaceForModule rather than loadSrcInterface in mkTopLevEnv loadSrcInterface takes a user given `ModuleName` and resolves it to the module which needs to be loaded (taking into account module renaming/visibility etc). loadInterfaceForModule takes a specific module and loads it. The modules in `ImpDeclSpec` have already been resolved to the actual module to get the information from during renaming. Therefore we just need to fetch the precise interface from disk (and not attempt to rename it again). Fixes #25951 - - - - - 2e0c07ab by Simon Peyton Jones at 2025-04-24T00:29:43-04:00 Test for #23298 - - - - - 0eef99b0 by Sven Tennie at 2025-04-24T07:34:36-04:00 RV64: Introduce J instruction (non-local jumps) and don't deallocate stack slots for J_TBL (#25738) J_TBL result in local jumps, there should not deallocate stack slots (see Note [extra spill slots].) J is for non-local jumps, these may need to deallocate stack slots. - - - - - 1bd3d13e by fendor at 2025-04-24T07:35:17-04:00 Add `UnitId` to `EvalBreakpoint` The `EvalBreakpoint` is used to communicate that a breakpoint was encountered during code evaluation. This `EvalBreakpoint` needs to be converted to an `InternalBreakpointId` which stores a `Module` to uniquely find the correct `Module` in the Home Package Table. The `EvalBreakpoint` used to store only a `ModuleName` which is then converted to a `Module` based on the currently active home unit. This is incorrect in the face of multiple home units, the break point could be in an entirely other home unit! To fix this, we additionally store the `UnitId` of the `Module` in `EvalBreakpoint` to later reconstruct the correct `Module` All of the changes are the consequence of extending `EvalBreakpoint` with the additional `ShortByteString` of the `UnitId`. For performance reasons, we store the `ShortByteString` backing the `UnitId` directly, avoiding marshalling overhead. - - - - - fe6ed8d9 by Sylvain Henry at 2025-04-24T18:04:12-04:00 Doc: add doc for JS interruptible calling convention (#24444) - - - - - 6111c5e4 by Ben Gamari at 2025-04-24T18:04:53-04:00 compiler: Ensure that Panic.Plain.assertPanic' provides callstack In 36cddd2ce1a3bc62ea8a1307d8bc6006d54109cf @alt-romes removed CallStack output from `GHC.Utils.Panic.Plain.assertPanic'`. While this output is redundant due to the exception backtrace proposal, we may be bootstrapping with a compiler which does not yet include this machinery. Reintroduce the output for now. Fixes #25898. - - - - - 217caad1 by Matthew Pickering at 2025-04-25T18:58:42+01:00 Implement Explicit Level Imports for Template Haskell This commit introduces the `ExplicitLevelImports` and `ImplicitStagePersistence` language extensions as proposed in GHC Proposal #682. Key Features ------------ - `ExplicitLevelImports` adds two new import modifiers - `splice` and `quote` - allowing precise control over the level at which imported identifiers are available - `ImplicitStagePersistence` (enabled by default) preserves existing path-based cross-stage persistence behavior - `NoImplicitStagePersistence` disables implicit cross-stage persistence, requiring explicit level imports Benefits -------- - Improved compilation performance by reducing unnecessary code generation - Enhanced IDE experience with faster feedback in `-fno-code` mode - Better dependency tracking by distinguishing compile-time and runtime dependencies - Foundation for future cross-compilation improvements This implementation enables the separation of modules needed at compile-time from those needed at runtime, allowing for more efficient compilation pipelines and clearer code organization in projects using Template Haskell. Implementation Notes -------------------- The level which a name is availble at is stored in the 'GRE', in the normal GlobalRdrEnv. The function `greLevels` returns the levels which a specific GRE is imported at. The level information for a 'Name' is computed by `getCurrentAndBindLevel`. The level validity is checked by `checkCrossLevelLifting`. Instances are checked by `checkWellLevelledDFun`, which computes the level an instance by calling `checkWellLevelledInstanceWhat`, which sees what is available at by looking at the module graph. Modifications to downsweep -------------------------- Code generation is now only enabled for modules which are needed at compile time. See the Note [-fno-code mode] for more information. Uniform error messages for level errors --------------------------------------- All error messages to do with levels are now reported uniformly using the `TcRnBadlyStaged` constructor. Error messages are uniformly reported in terms of levels. 0 - top-level 1 - quote level -1 - splice level The only level hard-coded into the compiler is the top-level in GHC.Types.ThLevelIndex.topLevelIndex. Uniformly refer to levels and stages ------------------------------------ There was much confusion about levels vs stages in the compiler. A level is a semantic concept, used by the typechecker to ensure a program can be evaluated in a well-staged manner. A stage is an operational construct, program evaluation proceeds in stages. Deprecate -Wbadly-staged-types ------------------------------ `-Wbadly-staged-types` is deprecated in favour of `-Wbadly-levelled-types`. Lift derivation changed ----------------------- Derived lift instances will now not generate code with expression quotations. Before: ``` data A = A Int deriving Lift => lift (A x) = [| A $(lift x) |] ``` After: ``` lift (A x) = conE 'A `appE` (lift x) ``` This is because if you attempt to derive `Lift` in a module where `NoImplicitStagePersistence` is enabled, you would get an infinite loop where a constructor was attempted to be persisted using the instance you are currently defining. GHC API Changes --------------- The ModuleGraph now contains additional information about the type of the edges (normal, quote or splice) between modules. This is abstracted using the `ModuleGraphEdge` data type. Fixes #25828 ------------------------- Metric Increase: MultiLayerModulesTH_Make ------------------------- - - - - - 7641a74a by Simon Peyton Jones at 2025-04-26T22:05:19-04:00 Get a decent MatchContext for pattern synonym bindings In particular when we have a pattern binding K p1 .. pn = rhs where K is a pattern synonym. (It might be nested.) This small MR fixes #25995. It's a tiny fix, to an error message, removing an always-dubious `unkSkol`. The bug report was in the context of horde-ad, a big program, and I didn't manage to make a small repro case quickly. I decided not to bother further. - - - - - ce616f49 by Simon Peyton Jones at 2025-04-27T21:10:25+01:00 Fix infelicities in the Specialiser On the way to #23109 (unary classes) I discovered some infelicities (or maybe tiny bugs, I forget) in the type-class specialiser. I also tripped over #25965, an outright bug in the rule matcher Specifically: * Refactor: I enhanced `wantCallsFor`, whih previously always said `True`, to discard calls of class-ops, data constructors etc. This is a bit more efficient; and it means we don't need to worry about filtering them out later. * Fix: I tidied up some tricky logic that eliminated redundant specialisations. It wasn't working correctly. See the expanded Note [Specialisations already covered], and (MP3) in Note [Specialising polymorphic dictionaries]. See also the new top-level `alreadyCovered` function, which now goes via `GHC.Core.Rules.ruleLhsIsMoreSpecific` I also added a useful Note [The (CI-KEY) invariant] * Fix #25965: fixed a tricky bug in the `go_fam_fam` in `GHC.Core.Unify.uVarOrFam`, which allows matching to succeed without binding all type varibles. I enhanced Note [Apartness and type families] some more * #25703. This ticket "just works" with -fpolymorphic-specialisation; but I was surprised that it worked! In this MR I added documentation to Note [Interesting dictionary arguments] to explain; and tests to ensure it stays fixed. - - - - - 22d11fa8 by Simon Peyton Jones at 2025-04-28T18:05:19-04:00 Track rewriter sets more accurately in constraint solving The key change, which fixed #25440, is to call `recordRewriter` in GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant that we were secretly rewriting a Wanted with a Wanted, but not really noticing; and that led to a very bad error message, as you can see in the ticket. But of course that led me into rabbit hole of other refactoring around the RewriteSet code: * Improve Notes [Wanteds rewrite Wanteds] * Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors. This is tidier anyway (e.g. de-clutters debug output), and helps with the next point. * In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint with no rewriters with an equal constraint that has many. See See (CE4) in Note [Combining equalities] * Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into GHC.Tc.Zonk.TcType, where they properly belong. A handful of tests get better error messages. For some reason T24984 gets 12% less compiler allocation -- good Metric Decrease: T24984 - - - - - 865ba1a8 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Improve the Simplifier While working on #23109, I made two improvements to the Simplifier * I found that the Simplifier was sometimes iterating more than it should. I fixed this by improving postInlineUnconditionally. * I refactored tryCastWorkerWrapper. It is now clearer, and does less repeated work. This allowed me to call it from makeTrivial, which again does a bit more in one pass, elminating a potential extra Simplifier iteration - - - - - bad1623f by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 More care in postInline Don't inline data con apps so vigorously needs more docs - - - - - b2cb2e32 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Wibbles - - - - - 486e9265 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Be more careful in mkDupableContWithDmds to not create a binding that will immediately be inlined - - - - - 02627f29 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Do post-inline used-once bindings This makes cacheprof not regress and seems generally a good plan - - - - - 07daeae0 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 More eperiments * Don't inline toplevel things so much * Don't float constants so vigorously in the first float-out - - - - - 783cb70d by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Comments only - - - - - 9b0f654c by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Refator GHC.Core.Opt.SetLevels.notWorthFloating I refactored `notWorthFloating` while I was doing something else. I don't think there's a change in behaviour, but if so it's very much a corner case. - - - - - 6b7a63b3 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Always float bottoming expressions to the top ...regardless of floatConsts - - - - - b6c5dc5a by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Comments only - - - - - c7564d28 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Wibble SetLevels - - - - - ee8e7442 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Specialise the (higher order) showSignedFloat - - - - - d39ff923 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Eta reduce augment and its rules ... to match foldr. I found this reduced some simplifer iterations - - - - - 4245bf67 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Try getting rid of this early-phase business - - - - - b3cb6109 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Don't float PAPs to top level ...and treat case alternatives as strict contexts - - - - - 63c39e03 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Wibble to postInlineUnconditionally - - - - - 46bca683 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Small wibbles Don't make error calls interesting. Literals say True too isSaturatedConApp - - - - - 432f7c05 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Import wibble - - - - - d884af50 by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Fix `augment`! - - - - - 536aa79d by Simon Peyton Jones at 2025-04-29T11:19:58+01:00 Tiny change to saves_alloc Float lambdas (and PAPs) out of lambdas to top level This improves spectral/cse But the old comment was -- is_con_app: don't float PAPs to the top; they may well end -- up getting eta-expanded and re-inlined -- E.g. f = \x -> (++) ys -- If we float, then eta-expand we get -- lvl = (++) ys -- f = \x \zs -> lvl zs -- and now we'll inline lvl. Silly. Let's see what CI says - - - - - 656 changed files: - .gitlab-ci.yml - compiler/GHC.hs - compiler/GHC/ByteCode/Asm.hs - compiler/GHC/ByteCode/Instr.hs - compiler/GHC/ByteCode/Types.hs - compiler/GHC/Cmm/Lint.hs - compiler/GHC/Cmm/MachOp.hs - compiler/GHC/Cmm/Type.hs - compiler/GHC/CmmToAsm/AArch64/CodeGen.hs - compiler/GHC/CmmToAsm/Config.hs - compiler/GHC/CmmToAsm/RV64/CodeGen.hs - compiler/GHC/CmmToAsm/RV64/Instr.hs - compiler/GHC/CmmToAsm/RV64/Ppr.hs - compiler/GHC/Core/Coercion.hs - compiler/GHC/Core/InstEnv.hs - compiler/GHC/Core/Opt/ConstantFold.hs - compiler/GHC/Core/Opt/OccurAnal.hs - compiler/GHC/Core/Opt/Pipeline.hs - compiler/GHC/Core/Opt/SetLevels.hs - compiler/GHC/Core/Opt/Simplify/Env.hs - compiler/GHC/Core/Opt/Simplify/Iteration.hs - compiler/GHC/Core/Opt/Simplify/Utils.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/Core/Utils.hs - compiler/GHC/CoreToStg.hs - compiler/GHC/Data/Graph/Directed/Reachability.hs - compiler/GHC/Driver/Backpack.hs - compiler/GHC/Driver/Config/CmmToAsm.hs - + compiler/GHC/Driver/Downsweep.hs - compiler/GHC/Driver/DynFlags.hs - compiler/GHC/Driver/Env.hs - compiler/GHC/Driver/Env/Types.hs - compiler/GHC/Driver/Errors/Ppr.hs - compiler/GHC/Driver/Errors/Types.hs - compiler/GHC/Driver/Flags.hs - compiler/GHC/Driver/Main.hs - compiler/GHC/Driver/Make.hs - + compiler/GHC/Driver/MakeAction.hs - compiler/GHC/Driver/MakeFile.hs - + compiler/GHC/Driver/Messager.hs - compiler/GHC/Driver/Pipeline.hs - compiler/GHC/Driver/Pipeline.hs-boot - compiler/GHC/Driver/Pipeline/Execute.hs - compiler/GHC/Driver/Session.hs - + compiler/GHC/Driver/Session/Units.hs - compiler/GHC/Hs/Decls.hs - compiler/GHC/Hs/Expr.hs - compiler/GHC/Hs/Extension.hs - compiler/GHC/Hs/ImpExp.hs - compiler/GHC/Hs/Instances.hs - compiler/GHC/Hs/Pat.hs - compiler/GHC/Hs/Type.hs - compiler/GHC/Hs/Utils.hs - compiler/GHC/HsToCore/Breakpoints.hs - compiler/GHC/HsToCore/Match.hs - compiler/GHC/HsToCore/Quote.hs - compiler/GHC/HsToCore/Ticks.hs - 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+ compiler/GHC/Runtime/Eval/Utils.hs - compiler/GHC/Runtime/Heap/Inspect.hs - compiler/GHC/Runtime/Interpreter.hs - compiler/GHC/Runtime/Loader.hs - compiler/GHC/StgToByteCode.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Deriv/Generate.hs - compiler/GHC/Tc/Deriv/Utils.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/Default.hs - compiler/GHC/Tc/Gen/Export.hs - compiler/GHC/Tc/Gen/Expr.hs - compiler/GHC/Tc/Gen/Head.hs - compiler/GHC/Tc/Gen/HsType.hs - compiler/GHC/Tc/Gen/Match.hs - compiler/GHC/Tc/Gen/Pat.hs - compiler/GHC/Tc/Gen/Splice.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Tc/Plugin.hs - compiler/GHC/Tc/Solver.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Dict.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/TyCl.hs - compiler/GHC/Tc/TyCl/Instance.hs - compiler/GHC/Tc/TyCl/PatSyn.hs - 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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/ce5db8f652b48a613e55d0738bcc7a… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/ce5db8f652b48a613e55d0738bcc7a… You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc][wip/andreask/spec_tyfams] 7 commits: Doc: add doc for JS interruptible calling convention (#24444)
by Simon Peyton Jones (＠simonpj) 29 Apr '25

29 Apr '25

Simon Peyton Jones pushed to branch wip/andreask/spec_tyfams at Glasgow Haskell Compiler / GHC Commits: fe6ed8d9 by Sylvain Henry at 2025-04-24T18:04:12-04:00 Doc: add doc for JS interruptible calling convention (#24444) - - - - - 6111c5e4 by Ben Gamari at 2025-04-24T18:04:53-04:00 compiler: Ensure that Panic.Plain.assertPanic' provides callstack In 36cddd2ce1a3bc62ea8a1307d8bc6006d54109cf @alt-romes removed CallStack output from `GHC.Utils.Panic.Plain.assertPanic'`. While this output is redundant due to the exception backtrace proposal, we may be bootstrapping with a compiler which does not yet include this machinery. Reintroduce the output for now. Fixes #25898. - - - - - 217caad1 by Matthew Pickering at 2025-04-25T18:58:42+01:00 Implement Explicit Level Imports for Template Haskell This commit introduces the `ExplicitLevelImports` and `ImplicitStagePersistence` language extensions as proposed in GHC Proposal #682. Key Features ------------ - `ExplicitLevelImports` adds two new import modifiers - `splice` and `quote` - allowing precise control over the level at which imported identifiers are available - `ImplicitStagePersistence` (enabled by default) preserves existing path-based cross-stage persistence behavior - `NoImplicitStagePersistence` disables implicit cross-stage persistence, requiring explicit level imports Benefits -------- - Improved compilation performance by reducing unnecessary code generation - Enhanced IDE experience with faster feedback in `-fno-code` mode - Better dependency tracking by distinguishing compile-time and runtime dependencies - Foundation for future cross-compilation improvements This implementation enables the separation of modules needed at compile-time from those needed at runtime, allowing for more efficient compilation pipelines and clearer code organization in projects using Template Haskell. Implementation Notes -------------------- The level which a name is availble at is stored in the 'GRE', in the normal GlobalRdrEnv. The function `greLevels` returns the levels which a specific GRE is imported at. The level information for a 'Name' is computed by `getCurrentAndBindLevel`. The level validity is checked by `checkCrossLevelLifting`. Instances are checked by `checkWellLevelledDFun`, which computes the level an instance by calling `checkWellLevelledInstanceWhat`, which sees what is available at by looking at the module graph. Modifications to downsweep -------------------------- Code generation is now only enabled for modules which are needed at compile time. See the Note [-fno-code mode] for more information. Uniform error messages for level errors --------------------------------------- All error messages to do with levels are now reported uniformly using the `TcRnBadlyStaged` constructor. Error messages are uniformly reported in terms of levels. 0 - top-level 1 - quote level -1 - splice level The only level hard-coded into the compiler is the top-level in GHC.Types.ThLevelIndex.topLevelIndex. Uniformly refer to levels and stages ------------------------------------ There was much confusion about levels vs stages in the compiler. A level is a semantic concept, used by the typechecker to ensure a program can be evaluated in a well-staged manner. A stage is an operational construct, program evaluation proceeds in stages. Deprecate -Wbadly-staged-types ------------------------------ `-Wbadly-staged-types` is deprecated in favour of `-Wbadly-levelled-types`. Lift derivation changed ----------------------- Derived lift instances will now not generate code with expression quotations. Before: ``` data A = A Int deriving Lift => lift (A x) = [| A $(lift x) |] ``` After: ``` lift (A x) = conE 'A `appE` (lift x) ``` This is because if you attempt to derive `Lift` in a module where `NoImplicitStagePersistence` is enabled, you would get an infinite loop where a constructor was attempted to be persisted using the instance you are currently defining. GHC API Changes --------------- The ModuleGraph now contains additional information about the type of the edges (normal, quote or splice) between modules. This is abstracted using the `ModuleGraphEdge` data type. Fixes #25828 ------------------------- Metric Increase: MultiLayerModulesTH_Make ------------------------- - - - - - 7641a74a by Simon Peyton Jones at 2025-04-26T22:05:19-04:00 Get a decent MatchContext for pattern synonym bindings In particular when we have a pattern binding K p1 .. pn = rhs where K is a pattern synonym. (It might be nested.) This small MR fixes #25995. It's a tiny fix, to an error message, removing an always-dubious `unkSkol`. The bug report was in the context of horde-ad, a big program, and I didn't manage to make a small repro case quickly. I decided not to bother further. - - - - - ce616f49 by Simon Peyton Jones at 2025-04-27T21:10:25+01:00 Fix infelicities in the Specialiser On the way to #23109 (unary classes) I discovered some infelicities (or maybe tiny bugs, I forget) in the type-class specialiser. I also tripped over #25965, an outright bug in the rule matcher Specifically: * Refactor: I enhanced `wantCallsFor`, whih previously always said `True`, to discard calls of class-ops, data constructors etc. This is a bit more efficient; and it means we don't need to worry about filtering them out later. * Fix: I tidied up some tricky logic that eliminated redundant specialisations. It wasn't working correctly. See the expanded Note [Specialisations already covered], and (MP3) in Note [Specialising polymorphic dictionaries]. See also the new top-level `alreadyCovered` function, which now goes via `GHC.Core.Rules.ruleLhsIsMoreSpecific` I also added a useful Note [The (CI-KEY) invariant] * Fix #25965: fixed a tricky bug in the `go_fam_fam` in `GHC.Core.Unify.uVarOrFam`, which allows matching to succeed without binding all type varibles. I enhanced Note [Apartness and type families] some more * #25703. This ticket "just works" with -fpolymorphic-specialisation; but I was surprised that it worked! In this MR I added documentation to Note [Interesting dictionary arguments] to explain; and tests to ensure it stays fixed. - - - - - 22d11fa8 by Simon Peyton Jones at 2025-04-28T18:05:19-04:00 Track rewriter sets more accurately in constraint solving The key change, which fixed #25440, is to call `recordRewriter` in GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant that we were secretly rewriting a Wanted with a Wanted, but not really noticing; and that led to a very bad error message, as you can see in the ticket. But of course that led me into rabbit hole of other refactoring around the RewriteSet code: * Improve Notes [Wanteds rewrite Wanteds] * Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors. This is tidier anyway (e.g. de-clutters debug output), and helps with the next point. * In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint with no rewriters with an equal constraint that has many. See See (CE4) in Note [Combining equalities] * Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into GHC.Tc.Zonk.TcType, where they properly belong. A handful of tests get better error messages. For some reason T24984 gets 12% less compiler allocation -- good Metric Decrease: T24984 - - - - - 1fb071db by Andreas Klebinger at 2025-04-29T10:17:02+01:00 Try to relax specialization requirements we put on args. Dont make comment seem like haddock Test things Wibble Try simons version of isInterestingDict Disable trace for ci checks use inscope set Add test cases Polishing up from Simon Rmoved accidentally committed traces and add missing import Typos Remove a special case that appears to do nothing See the commented-out block of `specCase` Wibbles Another subtle wibble: (ID8) - - - - - 302 changed files: - compiler/GHC.hs - compiler/GHC/Core/Coercion.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Predicate.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/Data/Graph/Directed/Reachability.hs - compiler/GHC/Driver/Backpack.hs - compiler/GHC/Driver/Downsweep.hs - compiler/GHC/Driver/DynFlags.hs - compiler/GHC/Driver/Flags.hs - compiler/GHC/Driver/Make.hs - compiler/GHC/Driver/MakeFile.hs - compiler/GHC/Driver/Pipeline.hs - compiler/GHC/Driver/Pipeline/Execute.hs - compiler/GHC/Driver/Session.hs - compiler/GHC/Hs/ImpExp.hs - compiler/GHC/Iface/Recomp.hs - compiler/GHC/Iface/Tidy.hs - 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testsuite/tests/typecheck/should_fail/T18851.stderr - utils/check-exact/ExactPrint.hs - utils/count-deps/Main.hs - utils/haddock/haddock-api/src/Haddock/Backends/Hyperlinker/Parser.hs The diff was not included because it is too large. View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/dc677e8d65cec9787d22d5742bc146… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/dc677e8d65cec9787d22d5742bc146… You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc][wip/T26003] 4 commits: Fix infelicities in the Specialiser
by Simon Peyton Jones (＠simonpj) 29 Apr '25

29 Apr '25

Simon Peyton Jones pushed to branch wip/T26003 at Glasgow Haskell Compiler / GHC Commits: ce616f49 by Simon Peyton Jones at 2025-04-27T21:10:25+01:00 Fix infelicities in the Specialiser On the way to #23109 (unary classes) I discovered some infelicities (or maybe tiny bugs, I forget) in the type-class specialiser. I also tripped over #25965, an outright bug in the rule matcher Specifically: * Refactor: I enhanced `wantCallsFor`, whih previously always said `True`, to discard calls of class-ops, data constructors etc. This is a bit more efficient; and it means we don't need to worry about filtering them out later. * Fix: I tidied up some tricky logic that eliminated redundant specialisations. It wasn't working correctly. See the expanded Note [Specialisations already covered], and (MP3) in Note [Specialising polymorphic dictionaries]. See also the new top-level `alreadyCovered` function, which now goes via `GHC.Core.Rules.ruleLhsIsMoreSpecific` I also added a useful Note [The (CI-KEY) invariant] * Fix #25965: fixed a tricky bug in the `go_fam_fam` in `GHC.Core.Unify.uVarOrFam`, which allows matching to succeed without binding all type varibles. I enhanced Note [Apartness and type families] some more * #25703. This ticket "just works" with -fpolymorphic-specialisation; but I was surprised that it worked! In this MR I added documentation to Note [Interesting dictionary arguments] to explain; and tests to ensure it stays fixed. - - - - - 22d11fa8 by Simon Peyton Jones at 2025-04-28T18:05:19-04:00 Track rewriter sets more accurately in constraint solving The key change, which fixed #25440, is to call `recordRewriter` in GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant that we were secretly rewriting a Wanted with a Wanted, but not really noticing; and that led to a very bad error message, as you can see in the ticket. But of course that led me into rabbit hole of other refactoring around the RewriteSet code: * Improve Notes [Wanteds rewrite Wanteds] * Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors. This is tidier anyway (e.g. de-clutters debug output), and helps with the next point. * In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint with no rewriters with an equal constraint that has many. See See (CE4) in Note [Combining equalities] * Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into GHC.Tc.Zonk.TcType, where they properly belong. A handful of tests get better error messages. For some reason T24984 gets 12% less compiler allocation -- good Metric Decrease: T24984 - - - - - 4ab20fe4 by Simon Peyton Jones at 2025-04-29T09:36:41+01:00 Wip on #26003 - - - - - c31925a1 by Simon Peyton Jones at 2025-04-29T10:04:02+01:00 Wibbles - - - - - 27 changed files: - compiler/GHC/Core/Coercion.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/InertSet.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Zonk/TcType.hs - compiler/GHC/Tc/Zonk/Type.hs - compiler/GHC/Types/Basic.hs - testsuite/tests/indexed-types/should_fail/T3330c.stderr - testsuite/tests/indexed-types/should_fail/T4174.stderr - testsuite/tests/indexed-types/should_fail/T8227.stderr - + testsuite/tests/simplCore/should_compile/T25703.hs - + testsuite/tests/simplCore/should_compile/T25703.stderr - + testsuite/tests/simplCore/should_compile/T25703a.hs - + testsuite/tests/simplCore/should_compile/T25703a.stderr - + testsuite/tests/simplCore/should_compile/T25965.hs - testsuite/tests/simplCore/should_compile/all.T - testsuite/tests/typecheck/should_compile/T25266a.stderr - testsuite/tests/typecheck/should_fail/T18851.stderr Changes: ===================================== compiler/GHC/Core/Coercion.hs ===================================== @@ -120,7 +120,7 @@ module GHC.Core.Coercion ( multToCo, mkRuntimeRepCo, - hasCoercionHoleTy, hasCoercionHoleCo, hasThisCoercionHoleTy, + hasHeteroKindCoercionHoleTy, hasHeteroKindCoercionHoleCo, setCoHoleType ) where @@ -2795,24 +2795,12 @@ has_co_hole_co :: Coercion -> Monoid.Any -- | Is there a hetero-kind coercion hole in this type? -- (That is, a coercion hole with ch_hetero_kind=True.) -- See wrinkle (EIK2) of Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality -hasCoercionHoleTy :: Type -> Bool -hasCoercionHoleTy = Monoid.getAny . has_co_hole_ty +hasHeteroKindCoercionHoleTy :: Type -> Bool +hasHeteroKindCoercionHoleTy = Monoid.getAny . has_co_hole_ty -- | Is there a hetero-kind coercion hole in this coercion? -hasCoercionHoleCo :: Coercion -> Bool -hasCoercionHoleCo = Monoid.getAny . has_co_hole_co - -hasThisCoercionHoleTy :: Type -> CoercionHole -> Bool -hasThisCoercionHoleTy ty hole = Monoid.getAny (f ty) - where - (f, _, _, _) = foldTyCo folder () - - folder = TyCoFolder { tcf_view = noView - , tcf_tyvar = const2 (Monoid.Any False) - , tcf_covar = const2 (Monoid.Any False) - , tcf_hole = \ _ h -> Monoid.Any (getUnique h == getUnique hole) - , tcf_tycobinder = const2 - } +hasHeteroKindCoercionHoleCo :: Coercion -> Bool +hasHeteroKindCoercionHoleCo = Monoid.getAny . has_co_hole_co -- | Set the type of a 'CoercionHole' setCoHoleType :: CoercionHole -> Type -> CoercionHole ===================================== compiler/GHC/Core/Opt/Specialise.hs ===================================== @@ -1243,14 +1243,15 @@ specExpr env (Let bind body) -- Note [Fire rules in the specialiser] fireRewriteRules :: SpecEnv -> InExpr -> [OutExpr] -> (InExpr, [OutExpr]) fireRewriteRules env (Var f) args - | Just (rule, expr) <- specLookupRule env f args InitialPhase (getRules (se_rules env) f) + | let rules = getRules (se_rules env) f + , Just (rule, expr) <- specLookupRule env f args activeInInitialPhase rules , let rest_args = drop (ruleArity rule) args -- See Note [Extra args in the target] zapped_subst = Core.zapSubst (se_subst env) expr' = simpleOptExprWith defaultSimpleOpts zapped_subst expr -- simplOptExpr needed because lookupRule returns -- (\x y. rhs) arg1 arg2 - , (fun, args) <- collectArgs expr' - = fireRewriteRules env fun (args++rest_args) + , (fun', args') <- collectArgs expr' + = fireRewriteRules env fun' (args'++rest_args) fireRewriteRules _ fun args = (fun, args) -------------- @@ -1620,7 +1621,7 @@ specCalls :: Bool -- True => specialising imported fn -- This function checks existing rules, and does not create -- duplicate ones. So the caller does not need to do this filtering. --- See 'already_covered' +-- See `alreadyCovered` type SpecInfo = ( [CoreRule] -- Specialisation rules , [(Id,CoreExpr)] -- Specialised definition @@ -1644,15 +1645,13 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs = -- pprTrace "specCalls: some" (vcat -- [ text "function" <+> ppr fn - -- , text "calls:" <+> ppr calls_for_me - -- , text "subst" <+> ppr (se_subst env) ]) $ + -- , text "calls:" <+> ppr calls_for_me + -- , text "subst" <+> ppr (se_subst env) ]) $ foldlM spec_call ([], [], emptyUDs) calls_for_me | otherwise -- No calls or RHS doesn't fit our preconceptions - = warnPprTrace (not (exprIsTrivial rhs) && notNull calls_for_me && not (isClassOpId fn)) + = warnPprTrace (not (exprIsTrivial rhs) && notNull calls_for_me) "Missed specialisation opportunity for" (ppr fn $$ trace_doc) $ - -- isClassOpId: class-op Ids never inline; we specialise them - -- through fireRewriteRules. So don't complain about missed opportunities -- Note [Specialisation shape] -- pprTrace "specCalls: none" (ppr fn <+> ppr calls_for_me) $ return ([], [], emptyUDs) @@ -1664,6 +1663,10 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs fn_unf = realIdUnfolding fn -- Ignore loop-breaker-ness here inl_prag = idInlinePragma fn inl_act = inlinePragmaActivation inl_prag + is_active = isActive (beginPhase inl_act) :: Activation -> Bool + -- is_active: inl_act is the activation we are going to put in the new + -- SPEC rule; so we want to see if it is covered by another rule with + -- that same activation. is_local = isLocalId fn is_dfun = isDFunId fn dflags = se_dflags env @@ -1674,16 +1677,6 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs (rhs_bndrs, rhs_body) = collectBindersPushingCo rhs -- See Note [Account for casts in binding] - already_covered :: SpecEnv -> [CoreRule] -> [CoreExpr] -> Bool - already_covered env new_rules args -- Note [Specialisations already covered] - = isJust (specLookupRule env fn args (beginPhase inl_act) - (new_rules ++ existing_rules)) - -- Rules: we look both in the new_rules (generated by this invocation - -- of specCalls), and in existing_rules (passed in to specCalls) - -- inl_act: is the activation we are going to put in the new SPEC - -- rule; so we want to see if it is covered by another rule with - -- that same activation. - ---------------------------------------------------------- -- Specialise to one particular call pattern spec_call :: SpecInfo -- Accumulating parameter @@ -1717,8 +1710,12 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs -- , ppr dx_binds ]) $ -- return () + ; let all_rules = rules_acc ++ existing_rules + -- all_rules: we look both in the rules_acc (generated by this invocation + -- of specCalls), and in existing_rules (passed in to specCalls) ; if not useful -- No useful specialisation - || already_covered rhs_env2 rules_acc rule_lhs_args + || alreadyCovered rhs_env2 rule_bndrs fn rule_lhs_args is_active all_rules + -- See (SC1) in Note [Specialisations already covered] then return spec_acc else do { -- Run the specialiser on the specialised RHS @@ -1780,7 +1777,7 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs spec_fn_details = case idDetails fn of JoinId join_arity _ -> JoinId (join_arity - join_arity_decr) Nothing - DFunId is_nt -> DFunId is_nt + DFunId unary -> DFunId unary _ -> VanillaId ; spec_fn <- newSpecIdSM (idName fn) spec_fn_ty spec_fn_details spec_fn_info @@ -1804,6 +1801,8 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs , ppr spec_fn <+> dcolon <+> ppr spec_fn_ty , ppr rhs_bndrs, ppr call_args , ppr spec_rule + , text "acc" <+> ppr rules_acc + , text "existing" <+> ppr existing_rules ] ; -- pprTrace "spec_call: rule" _rule_trace_doc @@ -1812,19 +1811,35 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs , spec_uds `thenUDs` uds_acc ) } } +alreadyCovered :: SpecEnv + -> [Var] -> Id -> [CoreExpr] -- LHS of possible new rule + -> (Activation -> Bool) -- Which rules are active + -> [CoreRule] -> Bool +-- Note [Specialisations already covered] esp (SC2) +alreadyCovered env bndrs fn args is_active rules + = case specLookupRule env fn args is_active rules of + Nothing -> False + Just (rule, _) + | isAutoRule rule -> -- Discard identical rules + -- We know that (fn args) is an instance of RULE + -- Check if RULE is an instance of (fn args) + ruleLhsIsMoreSpecific in_scope bndrs args rule + | otherwise -> True -- User rules dominate + where + in_scope = substInScopeSet (se_subst env) + -- Convenience function for invoking lookupRule from Specialise -- The SpecEnv's InScopeSet should include all the Vars in the [CoreExpr] specLookupRule :: SpecEnv -> Id -> [CoreExpr] - -> CompilerPhase -- Look up rules as if we were in this phase + -> (Activation -> Bool) -- Which rules are active -> [CoreRule] -> Maybe (CoreRule, CoreExpr) -specLookupRule env fn args phase rules +specLookupRule env fn args is_active rules = lookupRule ropts in_scope_env is_active fn args rules where dflags = se_dflags env in_scope = substInScopeSet (se_subst env) in_scope_env = ISE in_scope (whenActiveUnfoldingFun is_active) ropts = initRuleOpts dflags - is_active = isActive phase {- Note [Specialising DFuns] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -2323,21 +2338,24 @@ This plan is implemented in the Rec case of specBindItself. Note [Specialisations already covered] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We obviously don't want to generate two specialisations for the same -argument pattern. There are two wrinkles - -1. We do the already-covered test in specDefn, not when we generate -the CallInfo in mkCallUDs. We used to test in the latter place, but -we now iterate the specialiser somewhat, and the Id at the call site -might therefore not have all the RULES that we can see in specDefn - -2. What about two specialisations where the second is an *instance* -of the first? If the more specific one shows up first, we'll generate -specialisations for both. If the *less* specific one shows up first, -we *don't* currently generate a specialisation for the more specific -one. (See the call to lookupRule in already_covered.) Reasons: - (a) lookupRule doesn't say which matches are exact (bad reason) - (b) if the earlier specialisation is user-provided, it's - far from clear that we should auto-specialise further +argument pattern. Wrinkles + +(SC1) We do the already-covered test in specDefn, not when we generate + the CallInfo in mkCallUDs. We used to test in the latter place, but + we now iterate the specialiser somewhat, and the Id at the call site + might therefore not have all the RULES that we can see in specDefn + +(SC2) What about two specialisations where the second is an *instance* + of the first? It's a bit arbitrary, but here's what we do: + * If the existing one is user-specified, via a SPECIALISE pragma, we + suppress the further specialisation. + * If the existing one is auto-generated, we generate a second RULE + for the more specialised version. + The latter is important because we don't want the accidental order + of calls to determine what specialisations we generate. + +(SC3) Annoyingly, we /also/ eliminate duplicates in `filterCalls`. + See (MP3) in Note [Specialising polymorphic dictionaries] Note [Auto-specialisation and RULES] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -2800,12 +2818,10 @@ non-dictionary bindings too. Note [Specialising polymorphic dictionaries] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - Note June 2023: This has proved to be quite a tricky optimisation to get right see (#23469, #23109, #21229, #23445) so it is now guarded by a flag `-fpolymorphic-specialisation`. - Consider class M a where { foo :: a -> Int } @@ -2845,11 +2861,26 @@ Here are the moving parts: function. (MP3) If we have f :: forall m. Monoid m => blah, and two calls - (f @(Endo b) (d :: Monoid (Endo b)) - (f @(Endo (c->c)) (d :: Monoid (Endo (c->c))) + (f @(Endo b) (d1 :: Monoid (Endo b)) + (f @(Endo (c->c)) (d2 :: Monoid (Endo (c->c))) we want to generate a specialisation only for the first. The second is just a substitution instance of the first, with no greater specialisation. - Hence the call to `remove_dups` in `filterCalls`. + Hence the use of `removeDupCalls` in `filterCalls`. + + You might wonder if `d2` might be more specialised than `d1`; but no. + This `removeDupCalls` thing is at the definition site of `f`, and both `d1` + and `d2` are in scope. So `d1` is simply more polymorphic than `d2`, but + is just as specialised. + + This distinction is sadly lost once we build a RULE, so `alreadyCovered` + can't be so clever. E.g if we have an existing RULE + forall @a (d1:Ord Int) (d2: Eq a). f @a @Int d1 d2 = ... + and a putative new rule + forall (d1:Ord Int) (d2: Eq Int). f @Int @Int d1 d2 = ... + we /don't/ want the existing rule to subsume the new one. + + So we sadly put up with having two rather different places where we + eliminate duplicates: `alreadyCovered` and `removeDupCalls`. All this arose in #13873, in the unexpected form that a SPECIALISE pragma made the program slower! The reason was that the specialised @@ -2947,16 +2978,29 @@ data CallInfoSet = CIS Id (Bag CallInfo) -- The list of types and dictionaries is guaranteed to -- match the type of f -- The Bag may contain duplicate calls (i.e. f @T and another f @T) - -- These dups are eliminated by already_covered in specCalls + -- These dups are eliminated by alreadyCovered in specCalls data CallInfo - = CI { ci_key :: [SpecArg] -- All arguments + = CI { ci_key :: [SpecArg] -- Arguments of the call + -- See Note [The (CI-KEY) invariant] + , ci_fvs :: IdSet -- Free Ids of the ci_key call -- /not/ including the main id itself, of course -- NB: excluding tyvars: -- See Note [Specialising polymorphic dictionaries] } +{- Note [The (CI-KEY) invariant] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Invariant (CI-KEY): + In the `ci_key :: [SpecArg]` field of `CallInfo`, + * The list is non-empty + * The least element is always a `SpecDict` + +In this way the RULE has as few args as possible, which broadens its +applicability, since rules only fire when saturated. +-} + type DictExpr = CoreExpr ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet @@ -3045,10 +3089,7 @@ mkCallUDs' env f args ci_key :: [SpecArg] ci_key = dropWhileEndLE (not . isSpecDict) $ zipWith mk_spec_arg args pis - -- Drop trailing args until we get to a SpecDict - -- In this way the RULE has as few args as possible, - -- which broadens its applicability, since rules only - -- fire when saturated + -- Establish (CI-KEY): drop trailing args until we get to a SpecDict mk_spec_arg :: OutExpr -> PiTyBinder -> SpecArg mk_spec_arg arg (Named bndr) @@ -3086,34 +3127,76 @@ site, so we only look through ticks that RULE matching looks through -} wantCallsFor :: SpecEnv -> Id -> Bool -wantCallsFor _env _f = True - -- We could reduce the size of the UsageDetails by being less eager - -- about collecting calls for LocalIds: there is no point for - -- ones that are lambda-bound. We can't decide this by looking at - -- the (absence of an) unfolding, because unfoldings for local - -- functions are discarded by cloneBindSM, so no local binder will - -- have an unfolding at this stage. We'd have to keep a candidate - -- set of let-binders. - -- - -- Not many lambda-bound variables have dictionary arguments, so - -- this would make little difference anyway. - -- - -- For imported Ids we could check for an unfolding, but we have to - -- do so anyway in canSpecImport, and it seems better to have it - -- all in one place. So we simply collect usage info for imported - -- overloaded functions. - -{- Note [Interesting dictionary arguments] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Consider this - \a.\d:Eq a. let f = ... in ...(f d)... -There really is not much point in specialising f wrt the dictionary d, -because the code for the specialised f is not improved at all, because -d is lambda-bound. We simply get junk specialisations. - -What is "interesting"? Just that it has *some* structure. But what about -variables? We look in the variable's /unfolding/. And that means -that we must be careful to ensure that dictionaries have unfoldings, +-- See Note [wantCallsFor] +wantCallsFor _env f + = case idDetails f of + RecSelId {} -> False + DataConWorkId {} -> False + DataConWrapId {} -> False + ClassOpId {} -> False + PrimOpId {} -> False + FCallId {} -> False + TickBoxOpId {} -> False + CoVarId {} -> False + + DFunId {} -> True + VanillaId {} -> True + JoinId {} -> True + WorkerLikeId {} -> True + RepPolyId {} -> True + +{- Note [wantCallsFor] +~~~~~~~~~~~~~~~~~~~~~~ +`wantCallsFor env f` says whether the Specialiser should collect calls for +function `f`; other thing being equal, the fewer calls we collect the better. It +is False for things we can't specialise: + +* ClassOpId: never inline and we don't have a defn to specialise; we specialise + them through fireRewriteRules. +* PrimOpId: are never overloaded +* Data constructors: we never specialise them + +We could reduce the size of the UsageDetails by being less eager about +collecting calls for some LocalIds: there is no point for ones that are +lambda-bound. We can't decide this by looking at the (absence of an) unfolding, +because unfoldings for local functions are discarded by cloneBindSM, so no local +binder will have an unfolding at this stage. We'd have to keep a candidate set +of let-binders. + +Not many lambda-bound variables have dictionary arguments, so this would make +little difference anyway. + +For imported Ids we could check for an unfolding, but we have to do so anyway in +canSpecImport, and it seems better to have it all in one place. So we simply +collect usage info for imported overloaded functions. + +Note [Interesting dictionary arguments] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In `mkCallUDs` we only use `SpecDict` for dictionaries of which +`interestingDict` holds. Otherwise we use `UnspecArg`. Two reasons: + +* Consider this + \a.\d:Eq a. let f = ... in ...(f d)... + There really is not much point in specialising f wrt the dictionary d, + because the code for the specialised f is not improved at all, because + d is lambda-bound. We simply get junk specialisations. + +* Consider this (#25703): + f :: (Eq a, Show b) => a -> b -> INt + goo :: forall x. (Eq x) => x -> blah + goo @x (d:Eq x) (arg:x) = ...(f @x @Int d $fShowInt)... + If we built a `ci_key` with a (SpecDict d) for `d`, we would end up + discarding the call at the `\d`. But if we use `UnspecArg` for that + uninteresting `d`, we'll get a `ci_key` of + f @x @Int UnspecArg (SpecDict $fShowInt) + and /that/ can float out to f's definition and specialise nicely. + Hooray. (NB: the call can float only if `-fpolymorphic-specialisation` + is on; otherwise it'll be trapped by the `\@x -> ...`.)( + +What is "interesting"? (See `interestingDict`.) Just that it has *some* +structure. But what about variables? We look in the variable's /unfolding/. +And that means that we must be careful to ensure that dictionaries /have/ +unfoldings, * cloneBndrSM discards non-Stable unfoldings * specBind updates the unfolding after specialisation @@ -3159,7 +3242,7 @@ Now `f` turns into: meth @a dc .... When we specialise `f`, at a=Int say, that superclass selection can -nfire (via rewiteClassOps), but that info (that 'dc' is now a +fire (via rewiteClassOps), but that info (that 'dc' is now a particular dictionary `C`, of type `C Int`) must be available to the call `meth @a dc`, so that we can fire the `meth` class-op, and thence specialise `wombat`. @@ -3286,7 +3369,11 @@ dumpUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, OrdList DictBind) -- Used at a lambda or case binder; just dump anything mentioning the binder dumpUDs bndrs uds@(MkUD { ud_binds = orig_dbs, ud_calls = orig_calls }) | null bndrs = (uds, nilOL) -- Common in case alternatives - | otherwise = -- pprTrace "dumpUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs) $ + | otherwise = -- pprTrace "dumpUDs" (vcat + -- [ text "bndrs" <+> ppr bndrs + -- , text "uds" <+> ppr uds + -- , text "free_uds" <+> ppr free_uds + -- , text "dump-dbs" <+> ppr dump_dbs ]) $ (free_uds, dump_dbs) where free_uds = uds { ud_binds = free_dbs, ud_calls = free_calls } @@ -3325,20 +3412,17 @@ callsForMe fn uds@MkUD { ud_binds = orig_dbs, ud_calls = orig_calls } calls_for_me = case lookupDVarEnv orig_calls fn of Nothing -> [] Just cis -> filterCalls cis orig_dbs - -- filterCalls: drop calls that (directly or indirectly) - -- refer to fn. See Note [Avoiding loops (DFuns)] ---------------------- filterCalls :: CallInfoSet -> FloatedDictBinds -> [CallInfo] --- Remove dominated calls (Note [Specialising polymorphic dictionaries]) --- and loopy DFuns (Note [Avoiding loops (DFuns)]) +-- Remove +-- (a) dominated calls: (MP3) in Note [Specialising polymorphic dictionaries] +-- (b) loopy DFuns: Note [Avoiding loops (DFuns)] filterCalls (CIS fn call_bag) (FDB { fdb_binds = dbs }) - | isDFunId fn -- Note [Avoiding loops (DFuns)] applies only to DFuns - = filter ok_call de_dupd_calls - | otherwise -- Do not apply it to non-DFuns - = de_dupd_calls -- See Note [Avoiding loops (non-DFuns)] + | isDFunId fn = filter ok_call de_dupd_calls -- Deals with (b) + | otherwise = de_dupd_calls where - de_dupd_calls = remove_dups call_bag + de_dupd_calls = removeDupCalls call_bag -- Deals with (a) dump_set = foldl' go (unitVarSet fn) dbs -- This dump-set could also be computed by splitDictBinds @@ -3352,10 +3436,10 @@ filterCalls (CIS fn call_bag) (FDB { fdb_binds = dbs }) ok_call (CI { ci_fvs = fvs }) = fvs `disjointVarSet` dump_set -remove_dups :: Bag CallInfo -> [CallInfo] +removeDupCalls :: Bag CallInfo -> [CallInfo] -- Calls involving more generic instances beat more specific ones. -- See (MP3) in Note [Specialising polymorphic dictionaries] -remove_dups calls = foldr add [] calls +removeDupCalls calls = foldr add [] calls where add :: CallInfo -> [CallInfo] -> [CallInfo] add ci [] = [ci] @@ -3364,12 +3448,20 @@ remove_dups calls = foldr add [] calls | otherwise = ci2 : add ci1 cis beats_or_same :: CallInfo -> CallInfo -> Bool +-- (beats_or_same ci1 ci2) is True if specialising on ci1 subsumes ci2 +-- That is: ci1's types are less specialised than ci2 +-- ci1 specialises on the same dict args as ci2 beats_or_same (CI { ci_key = args1 }) (CI { ci_key = args2 }) = go args1 args2 where - go [] _ = True + go [] [] = True go (arg1:args1) (arg2:args2) = go_arg arg1 arg2 && go args1 args2 - go (_:_) [] = False + + -- If one or the other runs dry, the other must still have a SpecDict + -- because of the (CI-KEY) invariant. So neither subsumes the other; + -- one is more specialised (faster code) but the other is more generally + -- applicable. + go _ _ = False go_arg (SpecType ty1) (SpecType ty2) = isJust (tcMatchTy ty1 ty2) go_arg UnspecType UnspecType = True ===================================== compiler/GHC/Core/Rules.hs ===================================== @@ -9,7 +9,7 @@ -- The 'CoreRule' datatype itself is declared elsewhere. module GHC.Core.Rules ( -- ** Looking up rules - lookupRule, matchExprs, + lookupRule, matchExprs, ruleLhsIsMoreSpecific, -- ** RuleBase, RuleEnv RuleBase, RuleEnv(..), mkRuleEnv, emptyRuleEnv, @@ -587,8 +587,8 @@ findBest :: InScopeSet -> (Id, [CoreExpr]) findBest _ _ (rule,ans) [] = (rule,ans) findBest in_scope target (rule1,ans1) ((rule2,ans2):prs) - | isMoreSpecific in_scope rule1 rule2 = findBest in_scope target (rule1,ans1) prs - | isMoreSpecific in_scope rule2 rule1 = findBest in_scope target (rule2,ans2) prs + | ruleIsMoreSpecific in_scope rule1 rule2 = findBest in_scope target (rule1,ans1) prs + | ruleIsMoreSpecific in_scope rule2 rule1 = findBest in_scope target (rule2,ans2) prs | debugIsOn = let pp_rule rule = ifPprDebug (ppr rule) (doubleQuotes (ftext (ruleName rule))) @@ -603,15 +603,25 @@ findBest in_scope target (rule1,ans1) ((rule2,ans2):prs) where (fn,args) = target -isMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool --- The call (rule1 `isMoreSpecific` rule2) +ruleIsMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool +-- The call (rule1 `ruleIsMoreSpecific` rule2) -- sees if rule2 can be instantiated to look like rule1 --- See Note [isMoreSpecific] -isMoreSpecific _ (BuiltinRule {}) _ = False -isMoreSpecific _ (Rule {}) (BuiltinRule {}) = True -isMoreSpecific in_scope (Rule { ru_bndrs = bndrs1, ru_args = args1 }) - (Rule { ru_bndrs = bndrs2, ru_args = args2 }) - = isJust (matchExprs in_scope_env bndrs2 args2 args1) +-- See Note [ruleIsMoreSpecific] +ruleIsMoreSpecific in_scope rule1 rule2 + = case rule1 of + BuiltinRule {} -> False + Rule { ru_bndrs = bndrs1, ru_args = args1 } + -> ruleLhsIsMoreSpecific in_scope bndrs1 args1 rule2 + +ruleLhsIsMoreSpecific :: InScopeSet + -> [Var] -> [CoreExpr] -- LHS of a possible new rule + -> CoreRule -- An existing rule + -> Bool -- New one is more specific +ruleLhsIsMoreSpecific in_scope bndrs1 args1 rule2 + = case rule2 of + BuiltinRule {} -> True + Rule { ru_bndrs = bndrs2, ru_args = args2 } + -> isJust (matchExprs in_scope_env bndrs2 args2 args1) where full_in_scope = in_scope `extendInScopeSetList` bndrs1 in_scope_env = ISE full_in_scope noUnfoldingFun @@ -620,9 +630,9 @@ isMoreSpecific in_scope (Rule { ru_bndrs = bndrs1, ru_args = args1 }) noBlackList :: Activation -> Bool noBlackList _ = False -- Nothing is black listed -{- Note [isMoreSpecific] +{- Note [ruleIsMoreSpecific] ~~~~~~~~~~~~~~~~~~~~~~~~ -The call (rule1 `isMoreSpecific` rule2) +The call (rule1 `ruleIsMoreSpecific` rule2) sees if rule2 can be instantiated to look like rule1. Wrinkle: @@ -825,7 +835,7 @@ bound on the LHS: The rule looks like forall (a::*) (d::Eq Char) (x :: Foo a Char). - f (Foo a Char) d x = True + f @(Foo a Char) d x = True Matching the rule won't bind 'a', and legitimately so. We fudge by pretending that 'a' is bound to (Any :: *). ===================================== compiler/GHC/Core/Unify.hs ===================================== @@ -331,35 +331,57 @@ Wrinkles `DontBindMe`, the unifier must return `SurelyApart`, not `MaybeApart`. See `go_fam` in `uVarOrFam` -(ATF6) You might think that when /matching/ the um_fam_env will always be empty, - because type-class-instance and type-family-instance heads can't include type - families. E.g. instance C (F a) where ... -- Illegal - - But you'd be wrong: when "improving" type family constraint we may have a - type family on the LHS of a match. Consider +(ATF6) When /matching/ can we ever have a type-family application on the LHS, in + the template? You might think not, because type-class-instance and + type-family-instance heads can't include type families. E.g. + instance C (F a) where ... -- Illegal + + But you'd be wrong: even when matching, we can see type families in the LHS template: + * In `checkValidClass`, in `check_dm` we check that the default method has the + right type, using matching, both ways. And that type may have type-family + applications in it. Example in test CoOpt_Singletons. + + * In the specialiser: see the call to `tcMatchTy` in + `GHC.Core.Opt.Specialise.beats_or_same` + + * With -fpolymorphic-specialsation, we might get a specialiation rule like + RULE forall a (d :: Eq (Maybe (F a))) . + f @(Maybe (F a)) d = ... + See #25965. + + * A user-written RULE could conceivably have a type-family application + in the template. It might not be a good rule, but I don't think we currently + check for this. + + In all these cases we are only interested in finding a substitution /for + type variables/ that makes the match work. So we simply want to recurse into + the arguments of the type family. E.g. + Template: forall a. Maybe (F a) + Target: Mabybe (F Int) + We want to succeed with substitution [a :-> Int]. See (ATF9). + + Conclusion: where we enter via `tcMatchTy`, `tcMatchTys`, `tc_match_tys`, + etc, we always end up in `tc_match_tys_x`. There we invoke the unifier + but we do not distinguish between `SurelyApart` and `MaybeApart`. So in + these cases we can set `um_bind_fam_fun` to `neverBindFam`. + +(ATF7) There is one other, very special case of matching where we /do/ want to + bind type families in `um_fam_env`, namely in GHC.Tc.Solver.Equality, the call + to `tcUnifyTyForInjectivity False` in `improve_injective_wanted_top`. + Consider + of a match. Consider type family G6 a = r | r -> a type instance G6 [a] = [G a] type instance G6 Bool = Int - and the Wanted constraint [W] G6 alpha ~ [Int]. We /match/ each type instance - RHS against [Int]! So we try - [G a] ~ [Int] + and suppose we haev a Wanted constraint + [W] G6 alpha ~ [Int] +. According to Section 5.2 of "Injective type families for Haskell", we /match/ + the RHS each type instance [Int]. So we try + Template: [G a] Target: [Int] and we want to succeed with MaybeApart, so that we can generate the improvement - constraint [W] alpha ~ [beta] where beta is fresh. - See Section 5.2 of "Injective type families for Haskell". - - A second place that we match with type-fams on the LHS is in `checkValidClass`. - In `check_dm` we check that the default method has the right type, using matching, - both ways. And that type may have type-family applications in it. Example in - test CoOpt_Singletons. - -(ATF7) You might think that (ATF6) is a very special case, and in /other/ uses of - matching, where we enter via `tc_match_tys_x` we will never see a type-family - in the template. But actually we do see that case in the specialiser: see - the call to `tcMatchTy` in `GHC.Core.Opt.Specialise.beats_or_same` - - Also: a user-written RULE could conceivably have a type-family application - in the template. It might not be a good rule, but I don't think we currently - check for this. + constraint + [W] alpha ~ [beta] + where beta is fresh. We do this by binding [G a :-> Int] (ATF8) The treatment of type families is governed by um_bind_fam_fun :: BindFamFun @@ -399,6 +421,8 @@ Wrinkles Key point: when decomposing (F tys1 ~ F tys2), we should /also/ extend the type-family substitution. + (ATF11-1) All this cleverness only matters when unifying, not when matching + (ATF12) There is a horrid exception for the injectivity check. See (UR1) in in Note [Specification of unification]. @@ -595,7 +619,7 @@ tc_match_tys_x :: HasDebugCallStack -> [Type] -> Maybe Subst tc_match_tys_x bind_tv match_kis (Subst in_scope id_env tv_env cv_env) tys1 tys2 - = case tc_unify_tys alwaysBindFam -- (ATF7) in Note [Apartness and type families] + = case tc_unify_tys neverBindFam -- (ATF7) in Note [Apartness and type families] bind_tv False -- Matching, not unifying False -- Not an injectivity check @@ -1857,6 +1881,7 @@ uVarOrFam env ty1 ty2 kco = go_fam_fam tc1 tys1 tys2 kco -- Now check if we can bind the (F tys) to the RHS + -- This can happen even when matching: see (ATF7) | BindMe <- um_bind_fam_fun env tc1 tys1 rhs = -- ToDo: do we need an occurs check here? do { extendFamEnv tc1 tys1 rhs @@ -1881,11 +1906,6 @@ uVarOrFam env ty1 ty2 kco -- go_fam_fam: LHS and RHS are both saturated type-family applications, -- for the same type-family F go_fam_fam tc tys1 tys2 kco - | tcEqTyConAppArgs tys1 tys2 - -- Detect (F tys ~ F tys); otherwise we'd build an infinite substitution - = return () - - | otherwise -- Decompose (F tys1 ~ F tys2): (ATF9) -- Use injectivity information of F: (ATF10) -- But first bind the type-fam if poss: (ATF11) @@ -1902,13 +1922,19 @@ uVarOrFam env ty1 ty2 kco (inj_tys1, noninj_tys1) = partitionByList inj tys1 (inj_tys2, noninj_tys2) = partitionByList inj tys2 - bind_fam_if_poss | BindMe <- um_bind_fam_fun env tc tys1 rhs1 - = extendFamEnv tc tys1 rhs1 - | um_unif env - , BindMe <- um_bind_fam_fun env tc tys2 rhs2 - = extendFamEnv tc tys2 rhs2 - | otherwise - = return () + bind_fam_if_poss + | not (um_unif env) -- Not when matching (ATF11-1) + = return () + | tcEqTyConAppArgs tys1 tys2 -- Detect (F tys ~ F tys); + = return () -- otherwise we'd build an infinite substitution + | BindMe <- um_bind_fam_fun env tc tys1 rhs1 + = extendFamEnv tc tys1 rhs1 + | um_unif env + , BindMe <- um_bind_fam_fun env tc tys2 rhs2 + = extendFamEnv tc tys2 rhs2 + | otherwise + = return () + rhs1 = mkTyConApp tc tys2 `mkCastTy` mkSymCo kco rhs2 = mkTyConApp tc tys1 `mkCastTy` kco @@ -1993,7 +2019,7 @@ data UMState = UMState -- in um_foralls; i.e. variables bound by foralls inside the types being unified -- When /matching/ um_fam_env is usually empty; but not quite always. - -- See (ATF6) and (ATF7) of Note [Apartness and type families] + -- See (ATF7) of Note [Apartness and type families] newtype UM a = UM' { unUM :: UMState -> UnifyResultM (UMState, a) } ===================================== compiler/GHC/Tc/Errors.hs ===================================== @@ -466,13 +466,12 @@ mkErrorItem ct = do { let loc = ctLoc ct flav = ctFlavour ct - ; (suppress, m_evdest) <- case ctEvidence ct of - -- For this `suppress` stuff - -- see Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint - CtGiven {} -> return (False, Nothing) - CtWanted (WantedCt { ctev_rewriters = rewriters, ctev_dest = dest }) - -> do { rewriters' <- zonkRewriterSet rewriters - ; return (not (isEmptyRewriterSet rewriters'), Just dest) } + (suppress, m_evdest) = case ctEvidence ct of + -- For this `suppress` stuff + -- see Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint + CtGiven {} -> (False, Nothing) + CtWanted (WantedCt { ctev_rewriters = rws, ctev_dest = dest }) + -> (not (isEmptyRewriterSet rws), Just dest) ; let m_reason = case ct of CIrredCan (IrredCt { ir_reason = reason }) -> Just reason @@ -503,7 +502,7 @@ reportWanteds ctxt tc_lvl wc@(WC { wc_simple = simples, wc_impl = implics , text "tidy_errs =" <+> ppr tidy_errs ]) -- Catch an awkward (and probably rare) case in which /all/ errors are - -- suppressed: see Wrinkle (WRW2) in Note [Prioritise Wanteds with empty + -- suppressed: see Wrinkle (PER2) in Note [Prioritise Wanteds with empty -- RewriterSet] in GHC.Tc.Types.Constraint. -- -- Unless we are sure that an error will be reported some other way @@ -1788,7 +1787,8 @@ mkTyVarEqErr ctxt item casted_tv1 ty2 mkTyVarEqErr' :: SolverReportErrCtxt -> ErrorItem -> (TcTyVar, TcCoercionN) -> TcType -> TcM TcSolverReportMsg -mkTyVarEqErr' ctxt item (tv1, co1) ty2 +mkTyVarEqErr' ctxt item (tv1, _co1) ty2 + -- ToDo: eliminate _co1??? -- Is this a representation-polymorphism error, e.g. -- alpha[conc] ~# rr[sk] ? If so, handle that first. @@ -1818,11 +1818,13 @@ mkTyVarEqErr' ctxt item (tv1, co1) ty2 -- to be helpful since this is just an unimplemented feature. return main_msg +{- -- Incompatible kinds -- This is wrinkle (EIK2) in Note [Equalities with incompatible kinds] -- in GHC.Tc.Solver.Equality - | hasCoercionHoleCo co1 || hasCoercionHoleTy ty2 + | hasHeteroKindCoercionHoleCo co1 || hasHeteroKindCoercionHoleTy ty2 = return $ mkBlockedEqErr item +-} | isSkolemTyVar tv1 -- ty2 won't be a meta-tyvar; we would have -- swapped in Solver.Equality.canEqTyVarHomo @@ -2007,6 +2009,7 @@ misMatchOrCND ctxt item ty1 ty2 -- Keep only UserGivens that have some equalities. -- See Note [Suppress redundant givens during error reporting] +{- -- These are for the "blocked" equalities, as described in GHC.Tc.Solver.Equality -- Note [Equalities with incompatible kinds], wrinkle (EIK2). There should -- always be another unsolved wanted around, which will ordinarily suppress @@ -2014,6 +2017,7 @@ misMatchOrCND ctxt item ty1 ty2 -- (sigh), so we must produce a message. mkBlockedEqErr :: ErrorItem -> TcSolverReportMsg mkBlockedEqErr item = BlockedEquality item +-} {- Note [Suppress redundant givens during error reporting] ===================================== compiler/GHC/Tc/Solver/Default.hs ===================================== @@ -1081,9 +1081,9 @@ disambigProposalSequences orig_wanteds wanteds proposalSequences allConsistent ; successes <- fmap catMaybes $ nestImplicTcS fake_ev_binds_var (pushTcLevel tclvl) $ mapM firstSuccess proposalSequences - ; traceTcS "disambigProposalSequences" (vcat [ ppr wanteds - , ppr proposalSequences - , ppr successes ]) + ; traceTcS "disambigProposalSequences {" (vcat [ ppr wanteds + , ppr proposalSequences + , ppr successes ]) -- Step (4) in Note [How type-class constraints are defaulted] ; case successes of success@(tvs, subst) : rest ===================================== compiler/GHC/Tc/Solver/Equality.hs ===================================== @@ -1613,54 +1613,59 @@ canEqCanLHSHetero ev eq_rel swapped lhs1 ps_xi1 ki1 xi2 ps_xi2 ki2 -- NotSwapped: -- ev :: (lhs1:ki1) ~r# (xi2:ki2) -- kind_co :: k11 ~# ki2 -- Same orientation as ev --- type_ev :: lhs1 ~r# (xi2 |> sym kind_co) +-- new_ev :: lhs1 ~r# (xi2 |> sym kind_co) -- Swapped -- ev :: (xi2:ki2) ~r# (lhs1:ki1) -- kind_co :: ki2 ~# ki1 -- Same orientation as ev --- type_ev :: (xi2 |> kind_co) ~r# lhs1 +-- new_ev :: (xi2 |> kind_co) ~r# lhs1 +-- Note that we need the `sym` when we are /not/ swapped; hence `mk_sym_co` - = do { (kind_co, rewriters, unifs_happened) <- mk_kind_eq -- :: ki1 ~N ki2 - ; if unifs_happened - -- Unifications happened, so start again to do the zonking - -- Otherwise we might put something in the inert set that isn't inert - then startAgainWith (mkNonCanonical ev) - else - do { let lhs_redn = mkReflRedn role ps_xi1 - rhs_redn = mkGReflRightRedn role xi2 mb_sym_kind_co - mb_sym_kind_co = case swapped of - NotSwapped -> mkSymCo kind_co - IsSwapped -> kind_co - - ; traceTcS "Hetero equality gives rise to kind equality" - (ppr swapped $$ - ppr kind_co <+> dcolon <+> sep [ ppr ki1, text "~#", ppr ki2 ]) - ; type_ev <- rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn - - ; let new_xi2 = mkCastTy ps_xi2 mb_sym_kind_co - ; canEqCanLHSHomo type_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 }} - - where - mk_kind_eq :: TcS (CoercionN, RewriterSet, Bool) - -- Returned kind_co has kind (k1 ~ k2) if NotSwapped, (k2 ~ k1) if Swapped - -- Returned Bool = True if unifications happened, so we should retry - mk_kind_eq = case ev of + = case ev of CtGiven (GivenCt { ctev_evar = evar, ctev_loc = loc }) -> do { let kind_co = mkKindCo (mkCoVarCo evar) pred_ty = unSwap swapped mkNomEqPred ki1 ki2 kind_loc = mkKindEqLoc xi1 xi2 loc ; kind_ev <- newGivenEvVar kind_loc (pred_ty, evCoercion kind_co) ; emitWorkNC [CtGiven kind_ev] - ; return (givenCtEvCoercion kind_ev, emptyRewriterSet, False) } + ; finish emptyRewriterSet (givenCtEvCoercion kind_ev) } CtWanted {} - -> do { (kind_co, cts, unifs) <- wrapUnifierTcS ev Nominal $ \uenv -> - let uenv' = updUEnvLoc uenv (mkKindEqLoc xi1 xi2) - in unSwap swapped (uType uenv') ki1 ki2 - ; return (kind_co, rewriterSetFromCts cts, not (null unifs)) } - + -> do { (kind_co, cts, unifs) <- wrapUnifierTcS ev Nominal $ \uenv -> + let uenv' = updUEnvLoc uenv (mkKindEqLoc xi1 xi2) + in unSwap swapped (uType uenv') ki1 ki2 + ; if not (null unifs) + then -- Unifications happened, so start again to do the zonking + -- Otherwise we might put something in the inert set that isn't inert + startAgainWith (mkNonCanonical ev) + else + + assertPpr (not (isEmptyCts cts)) (ppr ev $$ ppr ki1 $$ ppr ki2) $ + -- The constraints won't be empty because the two kinds differ, and there + -- are no unifications, so we must have emitted one or more constraints + finish (rewriterSetFromCts cts) kind_co } + where xi1 = canEqLHSType lhs1 role = eqRelRole eq_rel + finish rewriters kind_co + = do { traceTcS "Hetero equality gives rise to kind equality" + (ppr swapped $$ + ppr kind_co <+> dcolon <+> sep [ ppr ki1, text "~#", ppr ki2 ]) + ; new_ev <- rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn + ; canEqCanLHSHomo new_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 } + + where + -- kind_co :: ki1 ~N ki2 + lhs_redn = mkReflRedn role ps_xi1 + rhs_redn = mkGReflRightRedn role xi2 sym_kind_co + new_xi2 = mkCastTy ps_xi2 sym_kind_co + + -- Apply mkSymCo when /not/ swapped + sym_kind_co = case swapped of + NotSwapped -> mkSymCo kind_co + IsSwapped -> kind_co + + canEqCanLHSHomo :: CtEvidence -- lhs ~ rhs -- or, if swapped: rhs ~ lhs -> EqRel -> SwapFlag @@ -1863,9 +1868,10 @@ canEqCanLHSFinish ev eq_rel swapped lhs rhs ----------------------- canEqCanLHSFinish_try_unification ev eq_rel swapped lhs rhs -- Try unification; for Wanted, Nominal equalities with a meta-tyvar on the LHS - | isWanted ev -- See Note [Do not unify Givens] - , NomEq <- eq_rel -- See Note [Do not unify representational equalities] + | CtWanted wev <- ev -- See Note [Do not unify Givens] + , NomEq <- eq_rel -- See Note [Do not unify representational equalities] , TyVarLHS tv <- lhs + , isEmptyRewriterSet (ctev_rewriters wev) -- Only unify if the rewriter set is empty = do { given_eq_lvl <- getInnermostGivenEqLevel ; if not (touchabilityAndShapeTest given_eq_lvl tv rhs) then if | Just can_rhs <- canTyFamEqLHS_maybe rhs @@ -2044,19 +2050,20 @@ What do we do when we have an equality where k1 and k2 differ? Easy: we create a coercion that relates k1 and k2 and use this to cast. To wit, from - [X] (tv :: k1) ~ (rhs :: k2) + [X] co1 :: (tv :: k1) ~ (rhs :: k2) (where [X] is [G] or [W]), we go to - [X] co :: k1 ~ k2 - [X] (tv :: k1) ~ ((rhs |> sym co) :: k1) + co1 = co2 ; sym (GRefl kco) + [X] co2 :: (tv :: k1) ~ ((rhs |> sym kco) :: k1) + [X] kco :: k1 ~ k2 Wrinkles: -(EIK1) When X is W, the new type-level wanted is effectively rewritten by the - kind-level one. We thus include the kind-level wanted in the RewriterSet - for the type-level one. See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. - This is done in canEqCanLHSHetero. +(EIK1) When X=Wanted, the new type-level wanted for `co` is effectively rewritten by + the kind-level one. We thus include the kind-level wanted in the RewriterSet + for the type-level one. See Note [Wanteds rewrite Wanteds] in + GHC.Tc.Types.Constraint. This is done in canEqCanLHSHetero. (EIK2) Suppose we have [W] (a::Type) ~ (b::Type->Type). The above rewrite will produce [W] w : a ~ (b |> kw) @@ -2076,13 +2083,17 @@ Wrinkles: Instead, it lands in the inert_irreds in the inert set, awaiting solution of that `kw`. - (EIK2a) We must later indeed unify if/when the kind-level wanted, `kw` gets - solved. This is done in kickOutAfterFillingCoercionHole, which kicks out + (EIK2a) We must later indeed unify if/when the kind-level wanted, `kw` gets + solved. This is done in `kickOutAfterFillingCoercionHole`, which kicks out all equalities whose RHS mentions the filled-in coercion hole. Note that it looks for type family equalities, too, because of the use of unifyTest in canEqTyVarFunEq. - (EIK2b) What if the RHS mentions /other/ coercion holes? How can that happen? The + To do this, we slightly-hackily use the `ctev_rewriters` field of the inert, + which records that `w` has been rewritten by `kw`. + See (WRW3) in Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. + + (EIK2b) What if the RHS mentions /other/ coercion holes? How can that happen? The main way is like this. Assume F :: forall k. k -> Type [W] kw : k ~ Type [W] w : a ~ F k t @@ -2093,15 +2104,32 @@ Wrinkles: rewriting. Indeed tests JuanLopez only typechecks if we do. So we'd like to treat this kind of equality as canonical. - Hence the ch_hetero_kind field in CoercionHole: it is True of constraints - created by `canEqCanLHSHetero` to fix up hetero-kinded equalities; and False otherwise: + So here is our implementation: + * The `ch_hetero_kind` field in CoercionHole identifies a coercion hole created + by `canEqCanLHSHetero` to fix up hetero-kinded equalities. + + * An equality constraint is non-canonical if it mentions a /hetero-kind/ + CoercionHole on the RHS. This (and only this) is the (TyEq:CH) invariant + for canonical equalities (see Note [Canonical equalities]) + + * The invariant is checked by the `hasHeterKindCoercionHoleCo` test in + GHC.Tc.Utils.Unify.checkCo; and not satisfying this invariant is what + `cteCoercionHole` in `CheckTyEqResult` means. - * An equality constraint is non-canonical if it mentions a hetero-kind - CoercionHole on the RHS. See the `hasCoercionHoleCo` test in GHC.Tc.Utils.checkCo. + * These special hetero-kind CoercionHoles are created by the `uType` unifier when + the parent's CtOrigin is KindEqOrigin: see GHC.Tc.Utils.TcMType.newCoercionHole + and friends. - * Hetero-kind CoercionHoles are created when the parent's CtOrigin is - KindEqOrigin: see GHC.Tc.Utils.TcMType.newCoercionHole and friends. We - set this origin, via `mkKindLoc`, in `mk_kind_eq` in `canEqCanLHSHetero`. + We set this origin, via `updUEnvLoc`, in `mk_kind_eq` in `canEqCanLHSHetero`. + + * We /also/ add the coercion hole to the `RewriterSet` of the constraint, + in `canEqCanLHSHetero` + + * When filling one of these special hetero-kind coercion holes, we kick out + any IrredCt's that mention this hole; maybe it is now canonical. + See `kickOutAfterFillingCoercionHole`. + + Gah! This is bizarrely complicated. (EIK3) Suppose we have [W] (a :: k1) ~ (rhs :: k2). We duly follow the algorithm detailed here, producing [W] co :: k1 ~ k2, and adding @@ -2576,17 +2604,17 @@ Suppose we have Then we can simply solve g2 from g1, thus g2 := g1. Easy! But it's not so simple: -* If t is a type variable, the equalties might be oriented differently: +(CE1) If t is a type variable, the equalties might be oriented differently: e.g. (g1 :: a~b) and (g2 :: b~a) So we look both ways round. Hence the SwapFlag result to inertsCanDischarge. -* We can only do g2 := g1 if g1 can discharge g2; that depends on +(CE2) We can only do g2 := g1 if g1 can discharge g2; that depends on (a) the role and (b) the flavour. E.g. a representational equality cannot discharge a nominal one; a Wanted cannot discharge a Given. The predicate is eqCanRewriteFR. -* Visibility. Suppose S :: forall k. k -> Type, and consider unifying +(CE3) Visibility. Suppose S :: forall k. k -> Type, and consider unifying S @Type (a::Type) ~ S @(Type->Type) (b::Type->Type) From the first argument we get (Type ~ Type->Type); from the second argument we get (a ~ b) which in turn gives (Type ~ Type->Type). @@ -2601,6 +2629,24 @@ But it's not so simple: So when combining two otherwise-identical equalites, we want to keep the visible one, and discharge the invisible one. Hence the call to strictly_more_visible. + +(CE4) Suppose we have this set up (#25440): + Inert: [W] g1: F a ~ a Int (arising from (F a ~ a Int) + Work item: [W] g2: F alpha ~ F a (arising from (F alpha ~ F a) + We rewrite g2 with g1, to give + [W] g2{rw:g1} : F alpha ~ a Int + Now if F is injective we can get [W] alpha~a, and hence alpha:=a, and + we kick out g1. Now we have two constraints + [W] g1 : F a ~ a Int (arising from (F a ~ a Int) + [W] g2{rw:g1} : F a ~ a Int (arising from (F alpha ~ F a) + If we end up with g2 in the inert set (not g1) we'll get a very confusing + error message that we can solve (F a ~ a Int) + arising from F a ~ F a + + TL;DR: Better to hang on to `g1` (with no rewriters), in preference + to `g2` (which has a rewriter). + + See (WRW1) in Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. -} tryInertEqs :: EqCt -> SolverStage () @@ -2646,21 +2692,27 @@ inertsCanDischarge inerts (EqCt { eq_lhs = lhs_w, eq_rhs = rhs_w loc_w = ctEvLoc ev_w flav_w = ctEvFlavour ev_w fr_w = (flav_w, eq_rel) + empty_rw_w = isEmptyRewriterSet (ctEvRewriters ev_w) inert_beats_wanted ev_i eq_rel = -- eqCanRewriteFR: see second bullet of Note [Combining equalities] - -- strictly_more_visible: see last bullet of Note [Combining equalities] fr_i `eqCanRewriteFR` fr_w - && not ((loc_w `strictly_more_visible` ctEvLoc ev_i) - && (fr_w `eqCanRewriteFR` fr_i)) + && not (prefer_wanted ev_i && (fr_w `eqCanRewriteFR` fr_i)) where fr_i = (ctEvFlavour ev_i, eq_rel) - -- See Note [Combining equalities], final bullet + -- See (CE3) in Note [Combining equalities] strictly_more_visible loc1 loc2 = not (isVisibleOrigin (ctLocOrigin loc2)) && isVisibleOrigin (ctLocOrigin loc1) + prefer_wanted ev_i + = (loc_w `strictly_more_visible` ctEvLoc ev_i) + -- strictly_more_visible: see (CE3) in Note [Combining equalities] + || (empty_rw_w && not (isEmptyRewriterSet (ctEvRewriters ev_i))) + -- Prefer the one that has no rewriters + -- See (CE4) in Note [Combining equalities] + inertsCanDischarge _ _ = Nothing @@ -3017,6 +3069,7 @@ improve_wanted_top_fun_eqs fam_tc lhs_tys rhs_ty improve_injective_wanted_top :: FamInstEnvs -> [Bool] -> TyCon -> [TcType] -> Xi -> TcS [TypeEqn] -- Interact with top-level instance declarations +-- See Section 5.2 in the Injective Type Families paper improve_injective_wanted_top fam_envs inj_args fam_tc lhs_tys rhs_ty = concatMapM do_one branches where @@ -3035,6 +3088,7 @@ improve_injective_wanted_top fam_envs inj_args fam_tc lhs_tys rhs_ty do_one branch@(CoAxBranch { cab_tvs = branch_tvs, cab_lhs = branch_lhs_tys, cab_rhs = branch_rhs }) | let in_scope1 = in_scope `extendInScopeSetList` branch_tvs , Just subst <- tcUnifyTyForInjectivity False in_scope1 branch_rhs rhs_ty + -- False: matching, not unifying = do { let inSubst tv = tv `elemVarEnv` getTvSubstEnv subst unsubstTvs = filterOut inSubst branch_tvs -- The order of unsubstTvs is important; it must be ===================================== compiler/GHC/Tc/Solver/InertSet.hs ===================================== @@ -9,9 +9,9 @@ module GHC.Tc.Solver.InertSet ( extendWorkListNonEq, extendWorkListCt, extendWorkListCts, extendWorkListCtList, extendWorkListEq, extendWorkListEqs, + extendWorkListRewrittenEqs, appendWorkList, extendWorkListImplic, workListSize, - selectWorkItem, -- * The inert set InertSet(..), @@ -172,6 +172,7 @@ See GHC.Tc.Solver.Monad.deferTcSForAllEq data WorkList = WL { wl_eqs_N :: [Ct] -- /Nominal/ equalities (s ~#N t), (s ~ t), (s ~~ t) -- with empty rewriter set + , wl_eqs_X :: [Ct] -- CEqCan, CDictCan, CIrredCan -- with empty rewriter set -- All other equalities: contains both equality constraints and @@ -179,9 +180,8 @@ data WorkList -- See Note [Prioritise equalities] -- See Note [Prioritise class equalities] - , wl_rw_eqs :: [Ct] -- Like wl_eqs, but ones that have a non-empty - -- rewriter set; or, more precisely, did when - -- added to the WorkList + , wl_rw_eqs :: [Ct] -- Like wl_eqs, but ones that may have a non-empty + -- rewriter set -- We prioritise wl_eqs over wl_rw_eqs; -- see Note [Prioritise Wanteds with empty RewriterSet] -- in GHC.Tc.Types.Constraint for more details. @@ -258,6 +258,11 @@ extendWorkListEqs rewriters new_eqs -- push_on_front puts the new equlities on the front of the queue push_on_front new_eqs eqs = foldr (:) eqs new_eqs +extendWorkListRewrittenEqs :: [EqCt] -> WorkList -> WorkList +-- Don't bother checking the RewriterSet: just pop them into wl_rw_eqs +extendWorkListRewrittenEqs new_eqs wl@(WL { wl_rw_eqs = rw_eqs }) + = wl { wl_rw_eqs = foldr ((:) . CEqCan) rw_eqs new_eqs } + extendWorkListNonEq :: Ct -> WorkList -> WorkList -- Extension by non equality extendWorkListNonEq ct wl = wl { wl_rest = ct : wl_rest wl } @@ -296,16 +301,6 @@ emptyWorkList :: WorkList emptyWorkList = WL { wl_eqs_N = [], wl_eqs_X = [] , wl_rw_eqs = [], wl_rest = [], wl_implics = emptyBag } -selectWorkItem :: WorkList -> Maybe (Ct, WorkList) --- See Note [Prioritise equalities] -selectWorkItem wl@(WL { wl_eqs_N = eqs_N, wl_eqs_X = eqs_X - , wl_rw_eqs = rw_eqs, wl_rest = rest }) - | ct:cts <- eqs_N = Just (ct, wl { wl_eqs_N = cts }) - | ct:cts <- eqs_X = Just (ct, wl { wl_eqs_X = cts }) - | ct:cts <- rw_eqs = Just (ct, wl { wl_rw_eqs = cts }) - | ct:cts <- rest = Just (ct, wl { wl_rest = cts }) - | otherwise = Nothing - -- Pretty printing instance Outputable WorkList where ppr (WL { wl_eqs_N = eqs_N, wl_eqs_X = eqs_X, wl_rw_eqs = rw_eqs ===================================== compiler/GHC/Tc/Solver/Monad.hs ===================================== @@ -150,7 +150,6 @@ import qualified GHC.Tc.Utils.Env as TcM ) import GHC.Tc.Zonk.Monad ( ZonkM ) import qualified GHC.Tc.Zonk.TcType as TcM -import qualified GHC.Tc.Zonk.Type as TcM import GHC.Driver.DynFlags @@ -475,16 +474,16 @@ kickOutAfterUnification tv_list = case nonEmpty tv_list of ; return n_kicked } kickOutAfterFillingCoercionHole :: CoercionHole -> TcS () --- See Wrinkle (EIK2a) in Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality +-- See Wrinkle (EIK2) in Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality -- It's possible that this could just go ahead and unify, but could there be occurs-check -- problems? Seems simpler just to kick out. kickOutAfterFillingCoercionHole hole = do { ics <- getInertCans ; let (kicked_out, ics') = kick_out ics - n_kicked = lengthBag kicked_out + n_kicked = length kicked_out ; unless (n_kicked == 0) $ - do { updWorkListTcS (extendWorkListCts (fmap CIrredCan kicked_out)) + do { updWorkListTcS (extendWorkListRewrittenEqs kicked_out) ; csTraceTcS $ hang (text "Kick out, hole =" <+> ppr hole) 2 (vcat [ text "n-kicked =" <+> int n_kicked @@ -493,24 +492,18 @@ kickOutAfterFillingCoercionHole hole ; setInertCans ics' } where - kick_out :: InertCans -> (Bag IrredCt, InertCans) - kick_out ics@(IC { inert_irreds = irreds }) - = -- We only care about irreds here, because any constraint blocked - -- by a coercion hole is an irred. See wrinkle (EIK2a) in - -- Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Canonical - (irreds_to_kick, ics { inert_irreds = irreds_to_keep }) + kick_out :: InertCans -> ([EqCt], InertCans) + kick_out ics@(IC { inert_eqs = eqs }) + = (eqs_to_kick, ics { inert_eqs = eqs_to_keep }) where - (irreds_to_kick, irreds_to_keep) = partitionBag kick_ct irreds - - kick_ct :: IrredCt -> Bool - -- True: kick out; False: keep. - kick_ct ct - | IrredCt { ir_ev = ev, ir_reason = reason } <- ct - , CtWanted (WantedCt { ctev_rewriters = RewriterSet rewriters }) <- ev - , NonCanonicalReason ctyeq <- reason - , ctyeq `cterHasProblem` cteCoercionHole - , hole `elementOfUniqSet` rewriters - = True + (eqs_to_kick, eqs_to_keep) = partitionInertEqs kick_out_eq eqs + + kick_out_eq :: EqCt -> Bool -- True: kick out; False: keep. + kick_out_eq (EqCt { eq_ev = ev ,eq_lhs = lhs }) + | CtWanted (WantedCt { ctev_rewriters = RewriterSet rewriters }) <- ev + , TyVarLHS tv <- lhs + , isMetaTyVar tv + = hole `elementOfUniqSet` rewriters | otherwise = False @@ -847,17 +840,15 @@ removeInertCt is ct -- | Looks up a family application in the inerts. lookupFamAppInert :: (CtFlavourRole -> Bool) -- can it rewrite the target? - -> TyCon -> [Type] -> TcS (Maybe (Reduction, CtFlavourRole)) + -> TyCon -> [Type] -> TcS (Maybe EqCt) lookupFamAppInert rewrite_pred fam_tc tys = do { IS { inert_cans = IC { inert_funeqs = inert_funeqs } } <- getInertSet ; return (lookup_inerts inert_funeqs) } where lookup_inerts inert_funeqs - | Just ecl <- findFunEq inert_funeqs fam_tc tys - , Just (EqCt { eq_ev = ctev, eq_rhs = rhs }) - <- find (rewrite_pred . eqCtFlavourRole) ecl - = Just (mkReduction (ctEvCoercion ctev) rhs, ctEvFlavourRole ctev) - | otherwise = Nothing + = case findFunEq inert_funeqs fam_tc tys of + Nothing -> Nothing + Just (ecl :: [EqCt]) -> find (rewrite_pred . eqCtFlavourRole) ecl lookupInInerts :: CtLoc -> TcPredType -> TcS (Maybe CtEvidence) -- Is this exact predicate type cached in the solved or canonicals of the InertSet? @@ -1418,62 +1409,6 @@ getInertSet = getInertSetRef >>= readTcRef setInertSet :: InertSet -> TcS () setInertSet is = do { r <- getInertSetRef; writeTcRef r is } -getTcSWorkListRef :: TcS (IORef WorkList) -getTcSWorkListRef = TcS (return . tcs_worklist) - -getWorkListImplics :: TcS (Bag Implication) -getWorkListImplics - = do { wl_var <- getTcSWorkListRef - ; wl_curr <- readTcRef wl_var - ; return (wl_implics wl_curr) } - -pushLevelNoWorkList :: SDoc -> TcS a -> TcS (TcLevel, a) --- Push the level and run thing_inside --- However, thing_inside should not generate any work items -#if defined(DEBUG) -pushLevelNoWorkList err_doc (TcS thing_inside) - = TcS (\env -> TcM.pushTcLevelM $ - thing_inside (env { tcs_worklist = wl_panic }) - ) - where - wl_panic = pprPanic "GHC.Tc.Solver.Monad.buildImplication" err_doc - -- This panic checks that the thing-inside - -- does not emit any work-list constraints -#else -pushLevelNoWorkList _ (TcS thing_inside) - = TcS (\env -> TcM.pushTcLevelM (thing_inside env)) -- Don't check -#endif - -updWorkListTcS :: (WorkList -> WorkList) -> TcS () -updWorkListTcS f - = do { wl_var <- getTcSWorkListRef - ; updTcRef wl_var f } - -emitWorkNC :: [CtEvidence] -> TcS () -emitWorkNC evs - | null evs - = return () - | otherwise - = emitWork (listToBag (map mkNonCanonical evs)) - -emitWork :: Cts -> TcS () -emitWork cts - | isEmptyBag cts -- Avoid printing, among other work - = return () - | otherwise - = do { traceTcS "Emitting fresh work" (pprBag cts) - -- Zonk the rewriter set of Wanteds, because that affects - -- the prioritisation of the work-list. Suppose a constraint - -- c1 is rewritten by another, c2. When c2 gets solved, - -- c1 has no rewriters, and can be prioritised; see - -- Note [Prioritise Wanteds with empty RewriterSet] - -- in GHC.Tc.Types.Constraint wrinkle (WRW1) - ; cts <- wrapTcS $ mapBagM TcM.zonkCtRewriterSet cts - ; updWorkListTcS (extendWorkListCts cts) } - -emitImplication :: Implication -> TcS () -emitImplication implic - = updWorkListTcS (extendWorkListImplic implic) newTcRef :: a -> TcS (TcRef a) newTcRef x = wrapTcS (TcM.newTcRef x) @@ -1532,23 +1467,6 @@ reportUnifications (TcS thing_inside) getDefaultInfo :: TcS (DefaultEnv, Bool) getDefaultInfo = wrapTcS TcM.tcGetDefaultTys -getWorkList :: TcS WorkList -getWorkList = do { wl_var <- getTcSWorkListRef - ; wrapTcS (TcM.readTcRef wl_var) } - -selectNextWorkItem :: TcS (Maybe Ct) --- Pick which work item to do next --- See Note [Prioritise equalities] -selectNextWorkItem - = do { wl_var <- getTcSWorkListRef - ; wl <- readTcRef wl_var - ; case selectWorkItem wl of { - Nothing -> return Nothing ; - Just (ct, new_wl) -> - do { -- checkReductionDepth (ctLoc ct) (ctPred ct) - -- This is done by GHC.Tc.Solver.Dict.chooseInstance - ; writeTcRef wl_var new_wl - ; return (Just ct) } } } -- Just get some environments needed for instance looking up and matching -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -1805,6 +1723,116 @@ pprKicked :: Int -> SDoc pprKicked 0 = empty pprKicked n = parens (int n <+> text "kicked out") + +{- ********************************************************************* +* * +* The work list +* * +********************************************************************* -} + + +getTcSWorkListRef :: TcS (IORef WorkList) +getTcSWorkListRef = TcS (return . tcs_worklist) + +getWorkList :: TcS WorkList +getWorkList = do { wl_var <- getTcSWorkListRef + ; readTcRef wl_var } + +getWorkListImplics :: TcS (Bag Implication) +getWorkListImplics + = do { wl_var <- getTcSWorkListRef + ; wl_curr <- readTcRef wl_var + ; return (wl_implics wl_curr) } + +updWorkListTcS :: (WorkList -> WorkList) -> TcS () +updWorkListTcS f + = do { wl_var <- getTcSWorkListRef + ; updTcRef wl_var f } + +emitWorkNC :: [CtEvidence] -> TcS () +emitWorkNC evs + | null evs + = return () + | otherwise + = emitWork (listToBag (map mkNonCanonical evs)) + +emitWork :: Cts -> TcS () +emitWork cts + | isEmptyBag cts -- Avoid printing, among other work + = return () + | otherwise + = do { traceTcS "Emitting fresh work" (pprBag cts) + ; updWorkListTcS (extendWorkListCts cts) } + +emitImplication :: Implication -> TcS () +emitImplication implic + = updWorkListTcS (extendWorkListImplic implic) + +selectNextWorkItem :: TcS (Maybe Ct) +-- Pick which work item to do next +-- See Note [Prioritise equalities] +-- +-- Postcondition: if the returned item is a Wanted equality, +-- then its rewriter set is fully zonked. +-- +-- Suppose a constraint c1 is rewritten by another, c2. When c2 +-- gets solved, c1 has no rewriters, and can be prioritised; see +-- Note [Prioritise Wanteds with empty RewriterSet] in +-- GHC.Tc.Types.Constraint wrinkle (PER1) + +-- ToDo: if wl_rw_eqs is long, we'll re-zonk it each time we pick +-- a new item from wl_rest. Bad. +selectNextWorkItem + = do { wl_var <- getTcSWorkListRef + ; wl <- readTcRef wl_var + + ; case wl of { WL { wl_eqs_N = eqs_N, wl_eqs_X = eqs_X + , wl_rw_eqs = rw_eqs, wl_rest = rest } + | ct:cts <- eqs_N -> pick_me ct (wl { wl_eqs_N = cts }) + | ct:cts <- eqs_X -> pick_me ct (wl { wl_eqs_X = cts }) + | otherwise -> try_rws [] rw_eqs + where + pick_me :: Ct -> WorkList -> TcS (Maybe Ct) + pick_me ct new_wl + = do { writeTcRef wl_var new_wl + ; return (Just ct) } + -- NB: no need for checkReductionDepth (ctLoc ct) (ctPred ct) + -- This is done by GHC.Tc.Solver.Dict.chooseInstance + + -- try_rws looks through rw_eqs to find one that has an empty + -- rewriter set, after zonking. If none such, call try_rest. + try_rws acc (ct:cts) + = do { ct' <- liftZonkTcS (TcM.zonkCtRewriterSet ct) + ; if ctHasNoRewriters ct' + then pick_me ct' (wl { wl_rw_eqs = cts ++ acc }) + else try_rws (ct':acc) cts } + try_rws acc [] = try_rest acc + + try_rest zonked_rws + | ct:cts <- rest = pick_me ct (wl { wl_rw_eqs = zonked_rws, wl_rest = cts }) + | ct:cts <- zonked_rws = pick_me ct (wl { wl_rw_eqs = cts }) + | otherwise = return Nothing + } } + + +pushLevelNoWorkList :: SDoc -> TcS a -> TcS (TcLevel, a) +-- Push the level and run thing_inside +-- However, thing_inside should not generate any work items +#if defined(DEBUG) +pushLevelNoWorkList err_doc (TcS thing_inside) + = TcS (\env -> TcM.pushTcLevelM $ + thing_inside (env { tcs_worklist = wl_panic }) + ) + where + wl_panic = pprPanic "GHC.Tc.Solver.Monad.buildImplication" err_doc + -- This panic checks that the thing-inside + -- does not emit any work-list constraints +#else +pushLevelNoWorkList _ (TcS thing_inside) + = TcS (\env -> TcM.pushTcLevelM (thing_inside env)) -- Don't check +#endif + + {- ********************************************************************* * * * The Unification Level Flag * @@ -2340,7 +2368,7 @@ wrapUnifierX ev role do_unifications ; wrapTcS $ do { defer_ref <- TcM.newTcRef emptyBag ; unified_ref <- TcM.newTcRef [] - ; rewriters <- TcM.zonkRewriterSet (ctEvRewriters ev) + ; rewriters <- TcM.liftZonkM (TcM.zonkRewriterSet (ctEvRewriters ev)) ; let env = UE { u_role = role , u_rewriters = rewriters , u_loc = ctEvLoc ev ===================================== compiler/GHC/Tc/Solver/Rewrite.hs ===================================== @@ -150,13 +150,16 @@ bumpDepth (RewriteM thing_inside) { let !env' = env { re_loc = bumpCtLocDepth (re_loc env) } ; thing_inside env' } +recordRewriter :: CtEvidence -> RewriteM () +-- Record that we have rewritten the target with this (equality) evidence -- See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint --- Precondition: the WantedCtEvidence is for an equality constraint -recordRewriter :: WantedCtEvidence -> RewriteM () -recordRewriter (WantedCt { ctev_dest = HoleDest hole }) - = RewriteM $ \env -> updTcRef (re_rewriters env) (`addRewriter` hole) -recordRewriter other = - pprPanic "recordRewriter: non-equality constraint" (ppr other) +-- Precondition: the CtEvidence is for an equality constraint +recordRewriter (CtGiven {}) + = return () +recordRewriter (CtWanted (WantedCt { ctev_dest = dest })) + = case dest of + HoleDest hole -> RewriteM $ \env -> updTcRef (re_rewriters env) (`addRewriter` hole) + other -> pprPanic "recordRewriter: non-equality constraint" (ppr other) {- Note [Rewriter EqRels] ~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -848,16 +851,18 @@ rewrite_exact_fam_app tc tys -- STEP 3: try the inerts ; flavour <- getFlavour - ; result2 <- liftTcS $ lookupFamAppInert (`eqCanRewriteFR` (flavour, eq_rel)) tc xis - ; case result2 of - { Just (redn, (inert_flavour, inert_eq_rel)) + ; mb_eq <- liftTcS $ lookupFamAppInert (`eqCanRewriteFR` (flavour, eq_rel)) tc xis + ; case mb_eq of + { Just (EqCt { eq_ev = inert_ev, eq_rhs = inert_rhs, eq_eq_rel = inert_eq_rel }) -> do { traceRewriteM "rewrite family application with inert" (ppr tc <+> ppr xis $$ ppr redn) - ; finish (inert_flavour == Given) (homogenise downgraded_redn) } - -- this will sometimes duplicate an inert in the cache, + ; recordRewriter inert_ev + ; finish (isGiven inert_ev) (homogenise downgraded_redn) } + -- This will sometimes duplicate an inert in the cache, -- but avoiding doing so had no impact on performance, and -- it seems easier not to weed out that special case where + redn = mkReduction (ctEvCoercion inert_ev) inert_rhs inert_role = eqRelRole inert_eq_rel role = eqRelRole eq_rel downgraded_redn = downgradeRedn role inert_role redn @@ -1024,11 +1029,8 @@ rewrite_tyvar2 tv fr@(_, eq_rel) -> do { traceRewriteM "Following inert tyvar" $ vcat [ ppr tv <+> equals <+> ppr rhs_ty , ppr ctev ] - ; case ctev of - CtGiven {} -> return () - CtWanted wtd -> + ; recordRewriter ctev -- See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint - recordRewriter wtd ; let rewriting_co1 = ctEvCoercion ctev rewriting_co = case (ct_eq_rel, eq_rel) of ===================================== compiler/GHC/Tc/Types/Constraint.hs ===================================== @@ -17,7 +17,7 @@ module GHC.Tc.Types.Constraint ( isUnsatisfiableCt_maybe, ctEvidence, updCtEvidence, ctLoc, ctPred, ctFlavour, ctEqRel, ctOrigin, - ctRewriters, + ctRewriters, ctHasNoRewriters, ctEvId, wantedEvId_maybe, mkTcEqPredLikeEv, mkNonCanonical, mkGivens, tyCoVarsOfCt, tyCoVarsOfCts, @@ -240,18 +240,24 @@ instance Outputable DictCt where {- Note [Canonical equalities] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An EqCt is a canonical equality constraint, one that can live in the inert set, -and that can be used to rewrite other constrtaints. It satisfies these invariants: +and that can be used to rewrite other constraints. It satisfies these invariants: + * (TyEq:OC) lhs does not occur in rhs (occurs check) Note [EqCt occurs check] + * (TyEq:F) rhs has no foralls (this avoids substituting a forall for the tyvar in other types) + * (TyEq:K) typeKind lhs `tcEqKind` typeKind rhs; Note [Ct kind invariant] + * (TyEq:N) If the equality is representational, rhs is not headed by a saturated application of a newtype TyCon. See GHC.Tc.Solver.Equality Note [No top-level newtypes on RHS of representational equalities]. (Applies only when constructor of newtype is in scope.) + * (TyEq:U) An EqCt is not immediately unifiable. If we can unify a:=ty, we will not form an EqCt (a ~ ty). + * (TyEq:CH) rhs does not mention any coercion holes that resulted from fixing up a hetero-kinded equality. See Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality, wrinkle (EIK2) @@ -534,9 +540,12 @@ cteSolubleOccurs = CTEP (bit 3) -- Occurs-check under a type function, or in -- cteSolubleOccurs must be one bit to the left of cteInsolubleOccurs -- See also Note [Insoluble mis-match] in GHC.Tc.Errors -cteCoercionHole = CTEP (bit 4) -- Coercion hole encountered +cteCoercionHole = CTEP (bit 4) -- Kind-equality coercion hole encountered + -- See (EIK2) in Note [Equalities with incompatible kinds] + cteConcrete = CTEP (bit 5) -- Type variable that can't be made concrete -- e.g. alpha[conc] ~ Maybe beta[tv] + cteSkolemEscape = CTEP (bit 6) -- Skolem escape e.g. alpha[2] ~ b[sk,4] cteProblem :: CheckTyEqProblem -> CheckTyEqResult @@ -2220,6 +2229,12 @@ ctEvRewriters :: CtEvidence -> RewriterSet ctEvRewriters (CtWanted (WantedCt { ctev_rewriters = rws })) = rws ctEvRewriters (CtGiven {}) = emptyRewriterSet +ctHasNoRewriters :: Ct -> Bool +ctHasNoRewriters ct + = case ctEvidence ct of + CtWanted (WantedCt { ctev_rewriters = rws }) -> isEmptyRewriterSet rws + CtGiven {} -> True + -- | Set the rewriter set of a Wanted constraint. setWantedCtEvRewriters :: WantedCtEvidence -> RewriterSet -> WantedCtEvidence setWantedCtEvRewriters ev rs = ev { ctev_rewriters = rs } @@ -2444,19 +2459,29 @@ We thus want Wanteds to rewrite Wanteds in order to accept more programs, but we don't want Wanteds to rewrite Wanteds because doing so can create inscrutable error messages. To solve this dilemma: -* We allow Wanteds to rewrite Wanteds, but... +* We allow Wanteds to rewrite Wanteds, but each Wanted tracks the set of Wanteds + it has been rewritten by, in its RewriterSet, stored in the ctev_rewriters + field of the CtWanted constructor of CtEvidence. (Only Wanteds have + RewriterSets.) + +* A RewriterSet is just a set of unfilled CoercionHoles. This is sufficient + because only equalities (evidenced by coercion holes) are used for rewriting; + other (dictionary) constraints cannot ever rewrite. + +* The rewriter (in e.g. GHC.Tc.Solver.Rewrite.rewrite) tracks and returns a RewriterSet, + consisting of the evidence (a CoercionHole) for any Wanted equalities used in + rewriting. -* Each Wanted tracks the set of Wanteds it has been rewritten by, in its - RewriterSet, stored in the ctev_rewriters field of the CtWanted - constructor of CtEvidence. (Only Wanteds have RewriterSets.) +* Then GHC.Tc.Solver.Solve.rewriteEvidence and GHC.Tc.Solver.Equality.rewriteEqEvidence + add this RewriterSet to the rewritten constraint's rewriter set. * In error reporting, we simply suppress any errors that have been rewritten by /unsolved/ wanteds. This suppression happens in GHC.Tc.Errors.mkErrorItem, - which uses GHC.Tc.Zonk.Type.zonkRewriterSet to look through any filled + which uses `GHC.Tc.Zonk.Type.zonkRewriterSet` to look through any filled coercion holes. The idea is that we wish to report the "root cause" -- the error that rewrote all the others. -* We prioritise Wanteds that have an empty RewriterSet: +* In error reporting, we prioritise Wanteds that have an empty RewriterSet: see Note [Prioritise Wanteds with empty RewriterSet]. Let's continue our first example above: @@ -2471,19 +2496,30 @@ Because Wanteds can rewrite Wanteds, w1 will rewrite w2, yielding The {w1} in the second line of output is the RewriterSet of w1. -A RewriterSet is just a set of unfilled CoercionHoles. This is sufficient -because only equalities (evidenced by coercion holes) are used for rewriting; -other (dictionary) constraints cannot ever rewrite. The rewriter (in -e.g. GHC.Tc.Solver.Rewrite.rewrite) tracks and returns a RewriterSet, -consisting of the evidence (a CoercionHole) for any Wanted equalities used in -rewriting. Then GHC.Tc.Solver.Solve.rewriteEvidence and -GHC.Tc.Solver.Equality.rewriteEqEvidence add this RewriterSet to the rewritten -constraint's rewriter set. +Wrinkles: + +(WRW1) When we find a constraint identical to one already in the inert set, + we solve one from the other. Other things being equal, keep the one + that has fewer (better still no) rewriters. + See (CE4) in Note [Combining equalities] in GHC.Tc.Solver.Equality. + + To this accurately we should use `zonkRewriterSet` during canonicalisation, + to eliminate rewriters that have now been solved. Currently we only do so + during error reporting; but perhaps we should change that. + +(WRW2) When zonking a constraint (with `zonkCt` and `zonkCtEvidence`) we take + the opportunity to zonk its `RewriterSet`, which eliminates solved ones. + This doesn't guarantee that rewriter sets are always up to date -- see + (WRW1) -- but it helps, and it de-clutters debug output. + +(WRW3) We use the rewriter set for a slightly different purpose, in (EIK2) + of Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality. + This is a bit of a hack. Note [Prioritise Wanteds with empty RewriterSet] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When extending the WorkList, in GHC.Tc.Solver.InertSet.extendWorkListEq, -we priorities constraints that have no rewriters. Here's why. +we prioritise constraints that have no rewriters. Here's why. Consider this, which came up in T22793: inert: {} @@ -2527,11 +2563,11 @@ GHC.Tc.Solver.InertSet.extendWorkListEq, and extendWorkListEqs. Wrinkles -(WRW1) Before checking for an empty RewriterSet, we zonk the RewriterSet, +(PER1) Before checking for an empty RewriterSet, we zonk the RewriterSet, because some of those CoercionHoles may have been filled in since we last looked: see GHC.Tc.Solver.Monad.emitWork. -(WRW2) Despite the prioritisation, it is hard to be /certain/ that we can't end up +(PER2) Despite the prioritisation, it is hard to be /certain/ that we can't end up in a situation where all of the Wanteds have rewritten each other. In order to report /some/ error in this case, we simply report all the Wanteds. The user will get a perhaps-confusing error message, but they've ===================================== compiler/GHC/Tc/Utils/TcMType.hs ===================================== @@ -49,7 +49,6 @@ module GHC.Tc.Utils.TcMType ( newCoercionHole, newCoercionHoleO, newVanillaCoercionHole, fillCoercionHole, isFilledCoercionHole, - unpackCoercionHole, unpackCoercionHole_maybe, checkCoercionHole, newImplication, @@ -115,7 +114,6 @@ import GHC.Tc.Types.CtLoc( CtLoc, ctLocOrigin ) import GHC.Tc.Utils.Monad -- TcType, amongst others import GHC.Tc.Utils.TcType import GHC.Tc.Errors.Types -import GHC.Tc.Zonk.Type import GHC.Tc.Zonk.TcType import GHC.Builtin.Names @@ -371,6 +369,7 @@ newCoercionHoleO (KindEqOrigin {}) pty = new_coercion_hole True pty newCoercionHoleO _ pty = new_coercion_hole False pty new_coercion_hole :: Bool -> TcPredType -> TcM CoercionHole +-- For the Bool, see (EIK2) in Note [Equalities with incompatible kinds] new_coercion_hole hetero_kind pred_ty = do { co_var <- newEvVar pred_ty ; traceTc "New coercion hole:" (ppr co_var <+> dcolon <+> ppr pred_ty) @@ -1583,7 +1582,7 @@ collect_cand_qtvs_co orig_ty cur_lvl bound = go_co go_co dv (SubCo co) = go_co dv co go_co dv (HoleCo hole) - = do m_co <- unpackCoercionHole_maybe hole + = do m_co <- liftZonkM (unpackCoercionHole_maybe hole) case m_co of Just co -> go_co dv co Nothing -> go_cv dv (coHoleCoVar hole) ===================================== compiler/GHC/Tc/Utils/Unify.hs ===================================== @@ -2649,8 +2649,9 @@ There are five reasons not to unify: we can fill beta[tau] := beta[conc]. This is why we call 'makeTypeConcrete' in startSolvingByUnification. -5. (COERCION-HOLE) Confusing coercion holes - Suppose our equality is +5. (COERCION-HOLE) rhs does not mention any coercion holes that resulted from + fixing up a hetero-kinded equality. This is the same as (TyEq:CH) in + Note [Canonical equalities]. Suppose our equality is (alpha :: k) ~ (Int |> {co}) where co :: Type ~ k is an unsolved wanted. Note that this equality is homogeneous; both sides have kind k. We refrain from unifying here, because @@ -3546,11 +3547,13 @@ checkCo flags co = | case conc of { CC_None -> False; _ -> True } -> return $ PuFail (cteProblem cteConcrete) +{- Trying NOT doing this -- # -- Check for coercion holes, if unifying. -- See (COERCION-HOLE) in Note [Unification preconditions] | case lc of { LC_None {} -> False; _ -> True } -- equivalent to "we are unifying"; see Note [TyEqFlags] - , hasCoercionHoleCo co + , hasHeteroKindCoercionHoleCo co -> return $ PuFail (cteProblem cteCoercionHole) +-} -- Occurs check (can promote) | OC_Check lhs_tv occ_prob <- occ ===================================== compiler/GHC/Tc/Zonk/TcType.hs ===================================== @@ -1,3 +1,5 @@ +{-# LANGUAGE DuplicateRecordFields #-} + {- (c) The University of Glasgow 2006 (c) The AQUA Project, Glasgow University, 1996-1998 @@ -36,6 +38,13 @@ module GHC.Tc.Zonk.TcType -- ** Zonking constraints , zonkCt, zonkWC, zonkSimples, zonkImplication + -- * Rewriter sets + , zonkRewriterSet, zonkCtRewriterSet, zonkCtEvRewriterSet + + -- * Coercion holes + , isFilledCoercionHole, unpackCoercionHole, unpackCoercionHole_maybe + + -- * Tidying , tcInitTidyEnv, tcInitOpenTidyEnv , tidyCt, tidyEvVar, tidyDelayedError @@ -81,7 +90,7 @@ import GHC.Core.Coercion import GHC.Core.Predicate import GHC.Utils.Constants -import GHC.Utils.Outputable +import GHC.Utils.Outputable as Outputable import GHC.Utils.Misc import GHC.Utils.Monad ( mapAccumLM ) import GHC.Utils.Panic @@ -89,6 +98,9 @@ import GHC.Utils.Panic import GHC.Data.Bag import GHC.Data.Pair +import Data.Semigroup +import Data.Maybe + {- ********************************************************************* * * Writing to metavariables @@ -366,8 +378,8 @@ checkCoercionHole cv co ; return $ assertPpr (ok cv_ty) (text "Bad coercion hole" <+> - ppr cv <> colon <+> vcat [ ppr t1, ppr t2, ppr role - , ppr cv_ty ]) + ppr cv Outputable.<> colon + <+> vcat [ ppr t1, ppr t2, ppr role, ppr cv_ty ]) co } | otherwise = return co @@ -494,9 +506,15 @@ zonkCt ct ; return (mkNonCanonical fl') } zonkCtEvidence :: CtEvidence -> ZonkM CtEvidence -zonkCtEvidence ctev - = do { pred' <- zonkTcType (ctEvPred ctev) - ; return (setCtEvPredType ctev pred') } +-- Zonks the ctev_pred and the ctev_rewriters; but not ctev_evar +-- For ctev_rewriters, see (WRW2) in Note [Wanteds rewrite Wanteds] +zonkCtEvidence (CtGiven (GivenCt { ctev_pred = pred, ctev_evar = var, ctev_loc = loc })) + = do { pred' <- zonkTcType pred + ; return (CtGiven (GivenCt { ctev_pred = pred', ctev_evar = var, ctev_loc = loc })) } +zonkCtEvidence (CtWanted wanted@(WantedCt { ctev_pred = pred, ctev_rewriters = rws })) + = do { pred' <- zonkTcType pred + ; rws' <- zonkRewriterSet rws + ; return (CtWanted (wanted { ctev_pred = pred', ctev_rewriters = rws' })) } zonkSkolemInfo :: SkolemInfo -> ZonkM SkolemInfo zonkSkolemInfo (SkolemInfo u sk) = SkolemInfo u <$> zonkSkolemInfoAnon sk @@ -530,6 +548,103 @@ win. But c.f Note [Sharing when zonking to Type] in GHC.Tc.Zonk.Type. +%************************************************************************ +%* * + Zonking rewriter sets +* * +************************************************************************ +-} + +zonkCtRewriterSet :: Ct -> ZonkM Ct +zonkCtRewriterSet ct + | isGivenCt ct + = return ct + | otherwise + = case ct of + CEqCan eq@(EqCt { eq_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CEqCan (eq { eq_ev = ev' })) } + CIrredCan ir@(IrredCt { ir_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CIrredCan (ir { ir_ev = ev' })) } + CDictCan di@(DictCt { di_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CDictCan (di { di_ev = ev' })) } + CQuantCan {} -> return ct + CNonCanonical ev -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CNonCanonical ev') } + +zonkCtEvRewriterSet :: CtEvidence -> ZonkM CtEvidence +zonkCtEvRewriterSet ev@(CtGiven {}) + = return ev +zonkCtEvRewriterSet ev@(CtWanted wtd) + = do { rewriters' <- zonkRewriterSet (ctEvRewriters ev) + ; return (CtWanted $ setWantedCtEvRewriters wtd rewriters') } + +-- | Zonk a rewriter set; if a coercion hole in the set has been filled, +-- find all the free un-filled coercion holes in the coercion that fills it +zonkRewriterSet :: RewriterSet -> ZonkM RewriterSet +zonkRewriterSet (RewriterSet set) + = nonDetStrictFoldUniqSet go (return emptyRewriterSet) set + -- This does not introduce non-determinism, because the only + -- monadic action is to read, and the combining function is + -- commutative + where + go :: CoercionHole -> ZonkM RewriterSet -> ZonkM RewriterSet + go hole m_acc = unionRewriterSet <$> check_hole hole <*> m_acc + + check_hole :: CoercionHole -> ZonkM RewriterSet + check_hole hole + = do { m_co <- unpackCoercionHole_maybe hole + ; case m_co of + Nothing -> return (unitRewriterSet hole) -- Not filled + Just co -> unUCHM (check_co co) } -- Filled: look inside + + check_ty :: Type -> UnfilledCoercionHoleMonoid + check_co :: Coercion -> UnfilledCoercionHoleMonoid + (check_ty, _, check_co, _) = foldTyCo folder () + + folder :: TyCoFolder () UnfilledCoercionHoleMonoid + folder = TyCoFolder { tcf_view = noView + , tcf_tyvar = \ _ tv -> check_ty (tyVarKind tv) + , tcf_covar = \ _ cv -> check_ty (varType cv) + , tcf_hole = \ _ -> UCHM . check_hole + , tcf_tycobinder = \ _ _ _ -> () } + +newtype UnfilledCoercionHoleMonoid = UCHM { unUCHM :: ZonkM RewriterSet } + +instance Semigroup UnfilledCoercionHoleMonoid where + UCHM l <> UCHM r = UCHM (unionRewriterSet <$> l <*> r) + +instance Monoid UnfilledCoercionHoleMonoid where + mempty = UCHM (return emptyRewriterSet) + + +{- +************************************************************************ +* * + Checking for coercion holes +* * +************************************************************************ +-} + +-- | Is a coercion hole filled in? +isFilledCoercionHole :: CoercionHole -> ZonkM Bool +isFilledCoercionHole (CoercionHole { ch_ref = ref }) + = isJust <$> readTcRef ref + +-- | Retrieve the contents of a coercion hole. Panics if the hole +-- is unfilled +unpackCoercionHole :: CoercionHole -> ZonkM Coercion +unpackCoercionHole hole + = do { contents <- unpackCoercionHole_maybe hole + ; case contents of + Just co -> return co + Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) } + +-- | Retrieve the contents of a coercion hole, if it is filled +unpackCoercionHole_maybe :: CoercionHole -> ZonkM (Maybe Coercion) +unpackCoercionHole_maybe (CoercionHole { ch_ref = ref }) = readTcRef ref + + +{- %************************************************************************ %* * Tidying ===================================== compiler/GHC/Tc/Zonk/Type.hs ===================================== @@ -28,12 +28,6 @@ module GHC.Tc.Zonk.Type ( -- ** 'ZonkEnv', and the 'ZonkT' and 'ZonkBndrT' monad transformers module GHC.Tc.Zonk.Env, - -- * Coercion holes - isFilledCoercionHole, unpackCoercionHole, unpackCoercionHole_maybe, - - -- * Rewriter sets - zonkRewriterSet, zonkCtRewriterSet, zonkCtEvRewriterSet, - -- * Tidying tcInitTidyEnv, tcInitOpenTidyEnv, @@ -55,7 +49,6 @@ import GHC.Tc.TyCl.Build ( TcMethInfo, MethInfo ) import GHC.Tc.Utils.Env ( tcLookupGlobalOnly ) import GHC.Tc.Utils.TcType import GHC.Tc.Utils.Monad ( newZonkAnyType, setSrcSpanA, liftZonkM, traceTc, addErr ) -import GHC.Tc.Types.Constraint import GHC.Tc.Types.Evidence import GHC.Tc.Errors.Types import GHC.Tc.Zonk.Env @@ -88,7 +81,6 @@ import GHC.Types.Id import GHC.Types.TypeEnv import GHC.Types.Basic import GHC.Types.SrcLoc -import GHC.Types.Unique.Set import GHC.Types.Unique.FM import GHC.Types.TyThing @@ -99,7 +91,6 @@ import GHC.Data.Bag import Control.Monad import Control.Monad.Trans.Class ( lift ) -import Data.Semigroup import Data.List.NonEmpty ( NonEmpty ) import Data.Foldable ( toList ) @@ -1956,89 +1947,3 @@ finding the free type vars of an expression is necessarily monadic operation. (consider /\a -> f @ b, where b is side-effected to a) -} -{- -************************************************************************ -* * - Checking for coercion holes -* * -************************************************************************ --} - --- | Is a coercion hole filled in? -isFilledCoercionHole :: CoercionHole -> TcM Bool -isFilledCoercionHole (CoercionHole { ch_ref = ref }) - = isJust <$> readTcRef ref - --- | Retrieve the contents of a coercion hole. Panics if the hole --- is unfilled -unpackCoercionHole :: CoercionHole -> TcM Coercion -unpackCoercionHole hole - = do { contents <- unpackCoercionHole_maybe hole - ; case contents of - Just co -> return co - Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) } - --- | Retrieve the contents of a coercion hole, if it is filled -unpackCoercionHole_maybe :: CoercionHole -> TcM (Maybe Coercion) -unpackCoercionHole_maybe (CoercionHole { ch_ref = ref }) = readTcRef ref - -zonkCtRewriterSet :: Ct -> TcM Ct -zonkCtRewriterSet ct - | isGivenCt ct - = return ct - | otherwise - = case ct of - CEqCan eq@(EqCt { eq_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CEqCan (eq { eq_ev = ev' })) } - CIrredCan ir@(IrredCt { ir_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CIrredCan (ir { ir_ev = ev' })) } - CDictCan di@(DictCt { di_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CDictCan (di { di_ev = ev' })) } - CQuantCan {} -> return ct - CNonCanonical ev -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CNonCanonical ev') } - -zonkCtEvRewriterSet :: CtEvidence -> TcM CtEvidence -zonkCtEvRewriterSet ev@(CtGiven {}) - = return ev -zonkCtEvRewriterSet ev@(CtWanted wtd) - = do { rewriters' <- zonkRewriterSet (ctEvRewriters ev) - ; return (CtWanted $ setWantedCtEvRewriters wtd rewriters') } - --- | Check whether any coercion hole in a RewriterSet is still unsolved. --- Does this by recursively looking through filled coercion holes until --- one is found that is not yet filled in, at which point this aborts. -zonkRewriterSet :: RewriterSet -> TcM RewriterSet -zonkRewriterSet (RewriterSet set) - = nonDetStrictFoldUniqSet go (return emptyRewriterSet) set - -- this does not introduce non-determinism, because the only - -- monadic action is to read, and the combining function is - -- commutative - where - go :: CoercionHole -> TcM RewriterSet -> TcM RewriterSet - go hole m_acc = unionRewriterSet <$> check_hole hole <*> m_acc - - check_hole :: CoercionHole -> TcM RewriterSet - check_hole hole = do { m_co <- unpackCoercionHole_maybe hole - ; case m_co of - Nothing -> return (unitRewriterSet hole) - Just co -> unUCHM (check_co co) } - - check_ty :: Type -> UnfilledCoercionHoleMonoid - check_co :: Coercion -> UnfilledCoercionHoleMonoid - (check_ty, _, check_co, _) = foldTyCo folder () - - folder :: TyCoFolder () UnfilledCoercionHoleMonoid - folder = TyCoFolder { tcf_view = noView - , tcf_tyvar = \ _ tv -> check_ty (tyVarKind tv) - , tcf_covar = \ _ cv -> check_ty (varType cv) - , tcf_hole = \ _ -> UCHM . check_hole - , tcf_tycobinder = \ _ _ _ -> () } - -newtype UnfilledCoercionHoleMonoid = UCHM { unUCHM :: TcM RewriterSet } - -instance Semigroup UnfilledCoercionHoleMonoid where - UCHM l <> UCHM r = UCHM (unionRewriterSet <$> l <*> r) - -instance Monoid UnfilledCoercionHoleMonoid where - mempty = UCHM (return emptyRewriterSet) ===================================== compiler/GHC/Types/Basic.hs ===================================== @@ -87,7 +87,7 @@ module GHC.Types.Basic ( CompilerPhase(..), PhaseNum, beginPhase, nextPhase, laterPhase, Activation(..), isActive, competesWith, - isNeverActive, isAlwaysActive, activeInFinalPhase, + isNeverActive, isAlwaysActive, activeInFinalPhase, activeInInitialPhase, activateAfterInitial, activateDuringFinal, activeAfter, RuleMatchInfo(..), isConLike, isFunLike, ===================================== testsuite/tests/indexed-types/should_fail/T3330c.stderr ===================================== @@ -1,16 +1,24 @@ - -T3330c.hs:25:43: error: [GHC-18872] - • Couldn't match kind ‘* -> *’ with ‘*’ - When matching types - f1 :: * -> * - f1 x :: * - Expected: Der ((->) x) (Der f1 x) - Actual: R f1 - • In the first argument of ‘plug’, namely ‘rf’ +T3330c.hs:25:38: error: [GHC-25897] + • Could not deduce ‘Der f1 ~ f1’ + from the context: f ~ (f1 :+: g) + bound by a pattern with constructor: + RSum :: forall (f :: * -> *) (g :: * -> *). + R f -> R g -> R (f :+: g), + in an equation for ‘plug'’ + at T3330c.hs:25:8-17 + Expected: x -> f1 x + Actual: x -> Der f1 x + ‘f1’ is a rigid type variable bound by + a pattern with constructor: + RSum :: forall (f :: * -> *) (g :: * -> *). + R f -> R g -> R (f :+: g), + in an equation for ‘plug'’ + at T3330c.hs:25:8-17 + • The function ‘plug’ is applied to three visible arguments, + but its type ‘Rep f => Der f x -> x -> f x’ has only two In the first argument of ‘Inl’, namely ‘(plug rf df x)’ In the expression: Inl (plug rf df x) • Relevant bindings include - x :: x (bound at T3330c.hs:25:29) df :: Der f1 x (bound at T3330c.hs:25:25) rf :: R f1 (bound at T3330c.hs:25:13) - plug' :: R f -> Der f x -> x -> f x (bound at T3330c.hs:25:1) + ===================================== testsuite/tests/indexed-types/should_fail/T4174.stderr ===================================== @@ -1,6 +1,16 @@ - -T4174.hs:45:12: error: [GHC-18872] - • Couldn't match type ‘False’ with ‘True’ - arising from a use of ‘sync_large_objects’ +T4174.hs:45:12: error: [GHC-25897] + • Couldn't match type ‘a’ with ‘SmStep’ + Expected: m (Field (Way (GHC6'8 minor) n t p) a b) + Actual: m (Field (WayOf m) SmStep RtsSpinLock) + ‘a’ is a rigid type variable bound by + the type signature for: + testcase :: forall (m :: * -> *) minor n t p a b. + Monad m => + m (Field (Way (GHC6'8 minor) n t p) a b) + at T4174.hs:44:1-63 • In the expression: sync_large_objects In an equation for ‘testcase’: testcase = sync_large_objects + • Relevant bindings include + testcase :: m (Field (Way (GHC6'8 minor) n t p) a b) + (bound at T4174.hs:45:1) + ===================================== testsuite/tests/indexed-types/should_fail/T8227.stderr ===================================== @@ -13,12 +13,3 @@ T8227.hs:24:27: error: [GHC-83865] absoluteToParam :: Scalar (V a) -> a -> Scalar (V a) (bound at T8227.hs:24:1) -T8227.hs:24:48: error: [GHC-27958] - • Couldn't match type ‘p0’ with ‘Scalar (V p0)’ - arising from a type equality Scalar (V a) ~ Scalar (V p0) -> p0 - The type variable ‘p0’ is ambiguous - • In the second argument of ‘arcLengthToParam’, namely ‘eps’ - In the expression: arcLengthToParam eps eps - In an equation for ‘absoluteToParam’: - absoluteToParam eps seg = arcLengthToParam eps eps - ===================================== testsuite/tests/simplCore/should_compile/T25703.hs ===================================== @@ -0,0 +1,7 @@ +module T25703 where + +f :: (Eq a, Show b) => a -> b -> Int +f x y = f x y + +goo :: forall x. (Eq x) => x -> Int +goo arg = f arg (3::Int) ===================================== testsuite/tests/simplCore/should_compile/T25703.stderr ===================================== @@ -0,0 +1,2 @@ +Rule fired: SPEC f @_ @Int (T25703) +Rule fired: SPEC f @_ @Int (T25703) ===================================== testsuite/tests/simplCore/should_compile/T25703a.hs ===================================== @@ -0,0 +1,69 @@ +{-# LANGUAGE DataKinds #-} +{-# LANGUAGE GADTs #-} + +{-# OPTIONS_GHC -O2 -fspecialise-aggressively #-} + +-- This pragma is just here to pretend that the function body of 'foo' is huge +-- and should never be inlined. +{-# OPTIONS_GHC -funfolding-use-threshold=-200 #-} + +module T25703a where + +import Data.Kind +import Data.Type.Equality +import Data.Proxy +import GHC.TypeNats + +-- Pretend this is some big dictionary that absolutely must get +-- specialised away for performance reasons. +type C :: Nat -> Constraint +class C i where + meth :: Proxy i -> Double +instance C 0 where + meth _ = 0.1 +instance C 1 where + meth _ = 1.1 +instance C 2 where + meth _ = 2.1 + +{-# INLINEABLE foo #-} +foo :: forall a (n :: Nat) (m :: Nat) + . ( Eq a, C n, C m ) + => a -> ( Proxy n, Proxy m ) -> Int -> Double +-- Pretend this is a big complicated function, too big to inline, +-- for which we absolutely must specialise away the 'C n', 'C m' +-- dictionaries for performance reasons. +foo a b c + = if a == a + then meth @n Proxy + fromIntegral c + else 2 * meth @m Proxy + +-- Runtime dispatch to a specialisation of 'foo' +foo_spec :: forall a (n :: Nat) (m :: Nat) + . ( Eq a, KnownNat n, KnownNat m ) + => a -> ( Proxy n, Proxy m ) -> Int -> Double +foo_spec a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @0 Proxy Proxy + = foo @a @0 @0 a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @1 Proxy Proxy + = foo @a @0 @1 a b c + | Just Refl <- sameNat @n @1 Proxy Proxy + , Just Refl <- sameNat @m @1 Proxy Proxy + = foo @a @1 @1 a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @0 @2 a b c + | Just Refl <- sameNat @n @1 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @1 @2 a b c + | Just Refl <- sameNat @n @2 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @2 @2 a b c + | otherwise + = error $ unlines + [ "f: no specialisation" + , "n: " ++ show (natVal @n Proxy) + , "m: " ++ show (natVal @m Proxy) + ] ===================================== testsuite/tests/simplCore/should_compile/T25703a.stderr ===================================== @@ -0,0 +1,6 @@ +Rule fired: SPEC foo @_ @2 @2 (T25703a) +Rule fired: SPEC foo @_ @1 @2 (T25703a) +Rule fired: SPEC foo @_ @0 @2 (T25703a) +Rule fired: SPEC foo @_ @1 @1 (T25703a) +Rule fired: SPEC foo @_ @0 @1 (T25703a) +Rule fired: SPEC foo @_ @0 @0 (T25703a) ===================================== testsuite/tests/simplCore/should_compile/T25965.hs ===================================== @@ -0,0 +1,18 @@ +{-# LANGUAGE TypeFamilies #-} +{-# OPTIONS_GHC -O -fpolymorphic-specialisation #-} + +module Foo where + +type family F a + +data T a = T1 + +instance Eq (T a) where { (==) x y = False } + +foo :: Eq a => a -> Bool +foo x | x==x = True + | otherwise = foo x + +bar :: forall b. b -> T (F b) -> Bool +bar y x = foo x + ===================================== testsuite/tests/simplCore/should_compile/all.T ===================================== @@ -543,3 +543,8 @@ test('T25883c', normal, compile_grep_core, ['']) test('T25883d', [extra_files(['T25883d_import.hs'])], multimod_compile_filter, ['T25883d', '-O -ddump-simpl -dno-typeable-binds -dsuppress-all -dsuppress-uniques', r'grep -e "y ="']) test('T25976', [grep_errmsg('Dead Code')], compile, ['-O -ddump-simpl -dsuppress-uniques -dno-typeable-binds']) + +test('T25965', normal, compile, ['-O']) +test('T25703', [grep_errmsg(r'SPEC')], compile, ['-O -fpolymorphic-specialisation -ddump-rule-firings']) +test('T25703a', [grep_errmsg(r'SPEC')], compile, ['-O -fpolymorphic-specialisation -ddump-rule-firings']) + ===================================== testsuite/tests/typecheck/should_compile/T25266a.stderr ===================================== @@ -1,16 +1,16 @@ -T25266a.hs:10:41: error: [GHC-25897] - • Could not deduce ‘p1 ~ p2’ +T25266a.hs:10:39: error: [GHC-25897] + • Could not deduce ‘p2 ~ p1’ from the context: a ~ Int bound by a pattern with constructor: T1 :: T Int, in a case alternative at T25266a.hs:10:23-24 - ‘p1’ is a rigid type variable bound by + ‘p2’ is a rigid type variable bound by the inferred type of f :: p1 -> p2 -> T a -> Int at T25266a.hs:(9,1)-(11,40) - ‘p2’ is a rigid type variable bound by + ‘p1’ is a rigid type variable bound by the inferred type of f :: p1 -> p2 -> T a -> Int at T25266a.hs:(9,1)-(11,40) - • In the expression: y + • In the expression: x In the first argument of ‘length’, namely ‘[x, y]’ In the expression: length [x, y] • Relevant bindings include ===================================== testsuite/tests/typecheck/should_fail/T18851.stderr ===================================== @@ -1,7 +1,7 @@ - T18851.hs:35:5: error: [GHC-18872] - • Couldn't match type ‘B’ with ‘A’ - arising from a superclass required to satisfy ‘C int0 A’, + • Couldn't match type ‘Bool’ with ‘B’ + arising from a superclass required to satisfy ‘C Int B’, arising from a use of ‘f’ • In the expression: f @A @B In an equation for ‘g’: g = f @A @B + View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/22070ca0b415d0f9d644033d30538f… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/22070ca0b415d0f9d644033d30538f… You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc] Pushed new branch wip/juhp-disable-hadrian-selftest
by Jens Petersen (＠juhp) 28 Apr '25

28 Apr '25

Jens Petersen pushed new branch wip/juhp-disable-hadrian-selftest at Glasgow Haskell Compiler / GHC -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/tree/wip/juhp-disable-hadrian-selftest You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc] Deleted branch wip/juhp-disable-hadrian-selftest
by Jens Petersen (＠juhp) 28 Apr '25

28 Apr '25

Jens Petersen deleted branch wip/juhp-disable-hadrian-selftest at Glasgow Haskell Compiler / GHC -- You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc] Pushed new branch wip/juhp-disable-hadrian-selftest
by Jens Petersen (＠juhp) 28 Apr '25

28 Apr '25

Jens Petersen pushed new branch wip/juhp-disable-hadrian-selftest at Glasgow Haskell Compiler / GHC -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/tree/wip/juhp-disable-hadrian-selftest You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc][wip/T26003] Wibbles
by Simon Peyton Jones (＠simonpj) 28 Apr '25

28 Apr '25

Simon Peyton Jones pushed to branch wip/T26003 at Glasgow Haskell Compiler / GHC Commits: 22070ca0 by Simon Peyton Jones at 2025-04-28T23:47:19+01:00 Wibbles - - - - - 2 changed files: - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/Monad.hs Changes: ===================================== compiler/GHC/Tc/Solver/Equality.hs ===================================== @@ -1627,11 +1627,7 @@ canEqCanLHSHetero ev eq_rel swapped lhs1 ps_xi1 ki1 xi2 ps_xi2 ki2 kind_loc = mkKindEqLoc xi1 xi2 loc ; kind_ev <- newGivenEvVar kind_loc (pred_ty, evCoercion kind_co) ; emitWorkNC [CtGiven kind_ev] - ; let kind_co = givenCtEvCoercion kind_ev - new_xi2 = mkCastTy ps_xi2 (mk_sym_co kind_co) - ; new_ev <- do_rewrite emptyRewriterSet kind_co - -- In the Given case, `new_ev` is canonical, so carry on - ; canEqCanLHSHomo new_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 } + ; finish emptyRewriterSet (givenCtEvCoercion kind_ev) } CtWanted {} -> do { (kind_co, cts, unifs) <- wrapUnifierTcS ev Nominal $ \uenv -> @@ -1646,28 +1642,28 @@ canEqCanLHSHetero ev eq_rel swapped lhs1 ps_xi1 ki1 xi2 ps_xi2 ki2 assertPpr (not (isEmptyCts cts)) (ppr ev $$ ppr ki1 $$ ppr ki2) $ -- The constraints won't be empty because the two kinds differ, and there -- are no unifications, so we must have emitted one or more constraints - do { new_ev <- do_rewrite (rewriterSetFromCts cts) kind_co - -- The rewritten equality `new_ev` is non-canonical, - -- so put it straight in the Irreds - ; finishCanWithIrred (NonCanonicalReason (cteProblem cteCoercionHole)) new_ev } } + finish (rewriterSetFromCts cts) kind_co } where xi1 = canEqLHSType lhs1 role = eqRelRole eq_rel - -- Apply mkSymCo when /not/ swapped - mk_sym_co co = case swapped of - NotSwapped -> mkSymCo co - IsSwapped -> co - - do_rewrite rewriters kind_co + finish rewriters kind_co = do { traceTcS "Hetero equality gives rise to kind equality" (ppr swapped $$ ppr kind_co <+> dcolon <+> sep [ ppr ki1, text "~#", ppr ki2 ]) - ; rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn } + ; new_ev <- rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn + ; canEqCanLHSHomo new_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 } + where -- kind_co :: ki1 ~N ki2 lhs_redn = mkReflRedn role ps_xi1 - rhs_redn = mkGReflRightRedn role xi2 (mk_sym_co kind_co) + rhs_redn = mkGReflRightRedn role xi2 sym_kind_co + new_xi2 = mkCastTy ps_xi2 sym_kind_co + + -- Apply mkSymCo when /not/ swapped + sym_kind_co = case swapped of + NotSwapped -> mkSymCo kind_co + IsSwapped -> kind_co canEqCanLHSHomo :: CtEvidence -- lhs ~ rhs ===================================== compiler/GHC/Tc/Solver/Monad.hs ===================================== @@ -480,7 +480,7 @@ kickOutAfterFillingCoercionHole :: CoercionHole -> TcS () kickOutAfterFillingCoercionHole hole = do { ics <- getInertCans ; let (kicked_out, ics') = kick_out ics - n_kicked = length kicked_outo + n_kicked = length kicked_out ; unless (n_kicked == 0) $ do { updWorkListTcS (extendWorkListRewrittenEqs kicked_out) View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/22070ca0b415d0f9d644033d30538f0… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/22070ca0b415d0f9d644033d30538f0… You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc] Pushed new branch wip/T26003
by Simon Peyton Jones (＠simonpj) 28 Apr '25

28 Apr '25

Simon Peyton Jones pushed new branch wip/T26003 at Glasgow Haskell Compiler / GHC -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/tree/wip/T26003 You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc][master] Track rewriter sets more accurately in constraint solving
by Marge Bot (＠marge-bot) 28 Apr '25

28 Apr '25

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: 22d11fa8 by Simon Peyton Jones at 2025-04-28T18:05:19-04:00 Track rewriter sets more accurately in constraint solving The key change, which fixed #25440, is to call `recordRewriter` in GHC.Tc.Solver.Rewrite.rewrite_exact_fam_app. This missing call meant that we were secretly rewriting a Wanted with a Wanted, but not really noticing; and that led to a very bad error message, as you can see in the ticket. But of course that led me into rabbit hole of other refactoring around the RewriteSet code: * Improve Notes [Wanteds rewrite Wanteds] * Zonk the RewriterSet in `zonkCtEvidence` rather than only in GHC.Tc.Errors. This is tidier anyway (e.g. de-clutters debug output), and helps with the next point. * In GHC.Tc.Solver.Equality.inertsCanDischarge, don't replace a constraint with no rewriters with an equal constraint that has many. See See (CE4) in Note [Combining equalities] * Move zonkRewriterSet and friends from GHC.Tc.Zonk.Type into GHC.Tc.Zonk.TcType, where they properly belong. A handful of tests get better error messages. For some reason T24984 gets 12% less compiler allocation -- good Metric Decrease: T24984 - - - - - 16 changed files: - compiler/GHC/Core/Coercion.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Solver/Default.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Tc/Solver/Monad.hs - compiler/GHC/Tc/Solver/Rewrite.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Zonk/TcType.hs - compiler/GHC/Tc/Zonk/Type.hs - testsuite/tests/indexed-types/should_fail/T3330c.stderr - testsuite/tests/indexed-types/should_fail/T4174.stderr - testsuite/tests/indexed-types/should_fail/T8227.stderr - testsuite/tests/typecheck/should_compile/T25266a.stderr - testsuite/tests/typecheck/should_fail/T18851.stderr Changes: ===================================== compiler/GHC/Core/Coercion.hs ===================================== @@ -120,7 +120,8 @@ module GHC.Core.Coercion ( multToCo, mkRuntimeRepCo, - hasCoercionHoleTy, hasCoercionHoleCo, hasThisCoercionHoleTy, + hasHeteroKindCoercionHoleTy, hasHeteroKindCoercionHoleCo, + hasThisCoercionHoleTy, setCoHoleType ) where @@ -2795,12 +2796,12 @@ has_co_hole_co :: Coercion -> Monoid.Any -- | Is there a hetero-kind coercion hole in this type? -- (That is, a coercion hole with ch_hetero_kind=True.) -- See wrinkle (EIK2) of Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality -hasCoercionHoleTy :: Type -> Bool -hasCoercionHoleTy = Monoid.getAny . has_co_hole_ty +hasHeteroKindCoercionHoleTy :: Type -> Bool +hasHeteroKindCoercionHoleTy = Monoid.getAny . has_co_hole_ty -- | Is there a hetero-kind coercion hole in this coercion? -hasCoercionHoleCo :: Coercion -> Bool -hasCoercionHoleCo = Monoid.getAny . has_co_hole_co +hasHeteroKindCoercionHoleCo :: Coercion -> Bool +hasHeteroKindCoercionHoleCo = Monoid.getAny . has_co_hole_co hasThisCoercionHoleTy :: Type -> CoercionHole -> Bool hasThisCoercionHoleTy ty hole = Monoid.getAny (f ty) ===================================== compiler/GHC/Tc/Errors.hs ===================================== @@ -466,13 +466,12 @@ mkErrorItem ct = do { let loc = ctLoc ct flav = ctFlavour ct - ; (suppress, m_evdest) <- case ctEvidence ct of - -- For this `suppress` stuff - -- see Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint - CtGiven {} -> return (False, Nothing) - CtWanted (WantedCt { ctev_rewriters = rewriters, ctev_dest = dest }) - -> do { rewriters' <- zonkRewriterSet rewriters - ; return (not (isEmptyRewriterSet rewriters'), Just dest) } + (suppress, m_evdest) = case ctEvidence ct of + -- For this `suppress` stuff + -- see Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint + CtGiven {} -> (False, Nothing) + CtWanted (WantedCt { ctev_rewriters = rws, ctev_dest = dest }) + -> (not (isEmptyRewriterSet rws), Just dest) ; let m_reason = case ct of CIrredCan (IrredCt { ir_reason = reason }) -> Just reason @@ -503,7 +502,7 @@ reportWanteds ctxt tc_lvl wc@(WC { wc_simple = simples, wc_impl = implics , text "tidy_errs =" <+> ppr tidy_errs ]) -- Catch an awkward (and probably rare) case in which /all/ errors are - -- suppressed: see Wrinkle (WRW2) in Note [Prioritise Wanteds with empty + -- suppressed: see Wrinkle (PER2) in Note [Prioritise Wanteds with empty -- RewriterSet] in GHC.Tc.Types.Constraint. -- -- Unless we are sure that an error will be reported some other way @@ -1821,7 +1820,7 @@ mkTyVarEqErr' ctxt item (tv1, co1) ty2 -- Incompatible kinds -- This is wrinkle (EIK2) in Note [Equalities with incompatible kinds] -- in GHC.Tc.Solver.Equality - | hasCoercionHoleCo co1 || hasCoercionHoleTy ty2 + | hasHeteroKindCoercionHoleCo co1 || hasHeteroKindCoercionHoleTy ty2 = return $ mkBlockedEqErr item | isSkolemTyVar tv1 -- ty2 won't be a meta-tyvar; we would have ===================================== compiler/GHC/Tc/Solver/Default.hs ===================================== @@ -1081,9 +1081,9 @@ disambigProposalSequences orig_wanteds wanteds proposalSequences allConsistent ; successes <- fmap catMaybes $ nestImplicTcS fake_ev_binds_var (pushTcLevel tclvl) $ mapM firstSuccess proposalSequences - ; traceTcS "disambigProposalSequences" (vcat [ ppr wanteds - , ppr proposalSequences - , ppr successes ]) + ; traceTcS "disambigProposalSequences {" (vcat [ ppr wanteds + , ppr proposalSequences + , ppr successes ]) -- Step (4) in Note [How type-class constraints are defaulted] ; case successes of success@(tvs, subst) : rest ===================================== compiler/GHC/Tc/Solver/Equality.hs ===================================== @@ -1613,54 +1613,63 @@ canEqCanLHSHetero ev eq_rel swapped lhs1 ps_xi1 ki1 xi2 ps_xi2 ki2 -- NotSwapped: -- ev :: (lhs1:ki1) ~r# (xi2:ki2) -- kind_co :: k11 ~# ki2 -- Same orientation as ev --- type_ev :: lhs1 ~r# (xi2 |> sym kind_co) +-- new_ev :: lhs1 ~r# (xi2 |> sym kind_co) -- Swapped -- ev :: (xi2:ki2) ~r# (lhs1:ki1) -- kind_co :: ki2 ~# ki1 -- Same orientation as ev --- type_ev :: (xi2 |> kind_co) ~r# lhs1 +-- new_ev :: (xi2 |> kind_co) ~r# lhs1 +-- Note that we need the `sym` when we are /not/ swapped; hence `mk_sym_co` - = do { (kind_co, rewriters, unifs_happened) <- mk_kind_eq -- :: ki1 ~N ki2 - ; if unifs_happened - -- Unifications happened, so start again to do the zonking - -- Otherwise we might put something in the inert set that isn't inert - then startAgainWith (mkNonCanonical ev) - else - do { let lhs_redn = mkReflRedn role ps_xi1 - rhs_redn = mkGReflRightRedn role xi2 mb_sym_kind_co - mb_sym_kind_co = case swapped of - NotSwapped -> mkSymCo kind_co - IsSwapped -> kind_co - - ; traceTcS "Hetero equality gives rise to kind equality" - (ppr swapped $$ - ppr kind_co <+> dcolon <+> sep [ ppr ki1, text "~#", ppr ki2 ]) - ; type_ev <- rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn - - ; let new_xi2 = mkCastTy ps_xi2 mb_sym_kind_co - ; canEqCanLHSHomo type_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 }} - - where - mk_kind_eq :: TcS (CoercionN, RewriterSet, Bool) - -- Returned kind_co has kind (k1 ~ k2) if NotSwapped, (k2 ~ k1) if Swapped - -- Returned Bool = True if unifications happened, so we should retry - mk_kind_eq = case ev of + = case ev of CtGiven (GivenCt { ctev_evar = evar, ctev_loc = loc }) -> do { let kind_co = mkKindCo (mkCoVarCo evar) pred_ty = unSwap swapped mkNomEqPred ki1 ki2 kind_loc = mkKindEqLoc xi1 xi2 loc ; kind_ev <- newGivenEvVar kind_loc (pred_ty, evCoercion kind_co) ; emitWorkNC [CtGiven kind_ev] - ; return (givenCtEvCoercion kind_ev, emptyRewriterSet, False) } + ; let kind_co = givenCtEvCoercion kind_ev + new_xi2 = mkCastTy ps_xi2 (mk_sym_co kind_co) + ; new_ev <- do_rewrite emptyRewriterSet kind_co + -- In the Given case, `new_ev` is canonical, so carry on + ; canEqCanLHSHomo new_ev eq_rel NotSwapped lhs1 ps_xi1 new_xi2 new_xi2 } CtWanted {} - -> do { (kind_co, cts, unifs) <- wrapUnifierTcS ev Nominal $ \uenv -> - let uenv' = updUEnvLoc uenv (mkKindEqLoc xi1 xi2) - in unSwap swapped (uType uenv') ki1 ki2 - ; return (kind_co, rewriterSetFromCts cts, not (null unifs)) } - + -> do { (kind_co, cts, unifs) <- wrapUnifierTcS ev Nominal $ \uenv -> + let uenv' = updUEnvLoc uenv (mkKindEqLoc xi1 xi2) + in unSwap swapped (uType uenv') ki1 ki2 + ; if not (null unifs) + then -- Unifications happened, so start again to do the zonking + -- Otherwise we might put something in the inert set that isn't inert + startAgainWith (mkNonCanonical ev) + else + + assertPpr (not (isEmptyCts cts)) (ppr ev $$ ppr ki1 $$ ppr ki2) $ + -- The constraints won't be empty because the two kinds differ, and there + -- are no unifications, so we must have emitted one or more constraints + do { new_ev <- do_rewrite (rewriterSetFromCts cts) kind_co + -- The rewritten equality `new_ev` is non-canonical, + -- so put it straight in the Irreds + ; finishCanWithIrred (NonCanonicalReason (cteProblem cteCoercionHole)) new_ev } } + where xi1 = canEqLHSType lhs1 role = eqRelRole eq_rel + -- Apply mkSymCo when /not/ swapped + mk_sym_co co = case swapped of + NotSwapped -> mkSymCo co + IsSwapped -> co + + do_rewrite rewriters kind_co + = do { traceTcS "Hetero equality gives rise to kind equality" + (ppr swapped $$ + ppr kind_co <+> dcolon <+> sep [ ppr ki1, text "~#", ppr ki2 ]) + ; rewriteEqEvidence rewriters ev swapped lhs_redn rhs_redn } + where + -- kind_co :: ki1 ~N ki2 + lhs_redn = mkReflRedn role ps_xi1 + rhs_redn = mkGReflRightRedn role xi2 (mk_sym_co kind_co) + + canEqCanLHSHomo :: CtEvidence -- lhs ~ rhs -- or, if swapped: rhs ~ lhs -> EqRel -> SwapFlag @@ -2044,19 +2053,20 @@ What do we do when we have an equality where k1 and k2 differ? Easy: we create a coercion that relates k1 and k2 and use this to cast. To wit, from - [X] (tv :: k1) ~ (rhs :: k2) + [X] co1 :: (tv :: k1) ~ (rhs :: k2) (where [X] is [G] or [W]), we go to - [X] co :: k1 ~ k2 - [X] (tv :: k1) ~ ((rhs |> sym co) :: k1) + co1 = co2 ; sym (GRefl kco) + [X] co2 :: (tv :: k1) ~ ((rhs |> sym kco) :: k1) + [X] kco :: k1 ~ k2 Wrinkles: -(EIK1) When X is W, the new type-level wanted is effectively rewritten by the - kind-level one. We thus include the kind-level wanted in the RewriterSet - for the type-level one. See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. - This is done in canEqCanLHSHetero. +(EIK1) When X=Wanted, the new type-level wanted for `co` is effectively rewritten by + the kind-level one. We thus include the kind-level wanted in the RewriterSet + for the type-level one. See Note [Wanteds rewrite Wanteds] in + GHC.Tc.Types.Constraint. This is done in canEqCanLHSHetero. (EIK2) Suppose we have [W] (a::Type) ~ (b::Type->Type). The above rewrite will produce [W] w : a ~ (b |> kw) @@ -2076,13 +2086,17 @@ Wrinkles: Instead, it lands in the inert_irreds in the inert set, awaiting solution of that `kw`. - (EIK2a) We must later indeed unify if/when the kind-level wanted, `kw` gets - solved. This is done in kickOutAfterFillingCoercionHole, which kicks out + (EIK2a) We must later indeed unify if/when the kind-level wanted, `kw` gets + solved. This is done in `kickOutAfterFillingCoercionHole`, which kicks out all equalities whose RHS mentions the filled-in coercion hole. Note that it looks for type family equalities, too, because of the use of unifyTest in canEqTyVarFunEq. - (EIK2b) What if the RHS mentions /other/ coercion holes? How can that happen? The + To do this, we slightly-hackily use the `ctev_rewriters` field of the inert, + which records that `w` has been rewritten by `kw`. + See (WRW3) in Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. + + (EIK2b) What if the RHS mentions /other/ coercion holes? How can that happen? The main way is like this. Assume F :: forall k. k -> Type [W] kw : k ~ Type [W] w : a ~ F k t @@ -2093,15 +2107,32 @@ Wrinkles: rewriting. Indeed tests JuanLopez only typechecks if we do. So we'd like to treat this kind of equality as canonical. - Hence the ch_hetero_kind field in CoercionHole: it is True of constraints - created by `canEqCanLHSHetero` to fix up hetero-kinded equalities; and False otherwise: + So here is our implementation: + * The `ch_hetero_kind` field in CoercionHole identifies a coercion hole created + by `canEqCanLHSHetero` to fix up hetero-kinded equalities. + + * An equality constraint is non-canonical if it mentions a /hetero-kind/ + CoercionHole on the RHS. This (and only this) is the (TyEq:CH) invariant + for canonical equalities (see Note [Canonical equalities]) + + * The invariant is checked by the `hasHeterKindCoercionHoleCo` test in + GHC.Tc.Utils.Unify.checkCo; and not satisfying this invariant is what + `cteCoercionHole` in `CheckTyEqResult` means. - * An equality constraint is non-canonical if it mentions a hetero-kind - CoercionHole on the RHS. See the `hasCoercionHoleCo` test in GHC.Tc.Utils.checkCo. + * These special hetero-kind CoercionHoles are created by the `uType` unifier when + the parent's CtOrigin is KindEqOrigin: see GHC.Tc.Utils.TcMType.newCoercionHole + and friends. - * Hetero-kind CoercionHoles are created when the parent's CtOrigin is - KindEqOrigin: see GHC.Tc.Utils.TcMType.newCoercionHole and friends. We - set this origin, via `mkKindLoc`, in `mk_kind_eq` in `canEqCanLHSHetero`. + We set this origin, via `updUEnvLoc`, in `mk_kind_eq` in `canEqCanLHSHetero`. + + * We /also/ add the coercion hole to the `RewriterSet` of the constraint, + in `canEqCanLHSHetero` + + * When filling one of these special hetero-kind coercion holes, we kick out + any IrredCt's that mention this hole; maybe it is now canonical. + See `kickOutAfterFillingCoercionHole`. + + Gah! This is bizarrely complicated. (EIK3) Suppose we have [W] (a :: k1) ~ (rhs :: k2). We duly follow the algorithm detailed here, producing [W] co :: k1 ~ k2, and adding @@ -2576,17 +2607,17 @@ Suppose we have Then we can simply solve g2 from g1, thus g2 := g1. Easy! But it's not so simple: -* If t is a type variable, the equalties might be oriented differently: +(CE1) If t is a type variable, the equalties might be oriented differently: e.g. (g1 :: a~b) and (g2 :: b~a) So we look both ways round. Hence the SwapFlag result to inertsCanDischarge. -* We can only do g2 := g1 if g1 can discharge g2; that depends on +(CE2) We can only do g2 := g1 if g1 can discharge g2; that depends on (a) the role and (b) the flavour. E.g. a representational equality cannot discharge a nominal one; a Wanted cannot discharge a Given. The predicate is eqCanRewriteFR. -* Visibility. Suppose S :: forall k. k -> Type, and consider unifying +(CE3) Visibility. Suppose S :: forall k. k -> Type, and consider unifying S @Type (a::Type) ~ S @(Type->Type) (b::Type->Type) From the first argument we get (Type ~ Type->Type); from the second argument we get (a ~ b) which in turn gives (Type ~ Type->Type). @@ -2601,6 +2632,24 @@ But it's not so simple: So when combining two otherwise-identical equalites, we want to keep the visible one, and discharge the invisible one. Hence the call to strictly_more_visible. + +(CE4) Suppose we have this set up (#25440): + Inert: [W] g1: F a ~ a Int (arising from (F a ~ a Int) + Work item: [W] g2: F alpha ~ F a (arising from (F alpha ~ F a) + We rewrite g2 with g1, to give + [W] g2{rw:g1} : F alpha ~ a Int + Now if F is injective we can get [W] alpha~a, and hence alpha:=a, and + we kick out g1. Now we have two constraints + [W] g1 : F a ~ a Int (arising from (F a ~ a Int) + [W] g2{rw:g1} : F a ~ a Int (arising from (F alpha ~ F a) + If we end up with g2 in the inert set (not g1) we'll get a very confusing + error message that we can solve (F a ~ a Int) + arising from F a ~ F a + + TL;DR: Better to hang on to `g1` (with no rewriters), in preference + to `g2` (which has a rewriter). + + See (WRW1) in Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint. -} tryInertEqs :: EqCt -> SolverStage () @@ -2646,21 +2695,27 @@ inertsCanDischarge inerts (EqCt { eq_lhs = lhs_w, eq_rhs = rhs_w loc_w = ctEvLoc ev_w flav_w = ctEvFlavour ev_w fr_w = (flav_w, eq_rel) + empty_rw_w = isEmptyRewriterSet (ctEvRewriters ev_w) inert_beats_wanted ev_i eq_rel = -- eqCanRewriteFR: see second bullet of Note [Combining equalities] - -- strictly_more_visible: see last bullet of Note [Combining equalities] fr_i `eqCanRewriteFR` fr_w - && not ((loc_w `strictly_more_visible` ctEvLoc ev_i) - && (fr_w `eqCanRewriteFR` fr_i)) + && not (prefer_wanted ev_i && (fr_w `eqCanRewriteFR` fr_i)) where fr_i = (ctEvFlavour ev_i, eq_rel) - -- See Note [Combining equalities], final bullet + -- See (CE3) in Note [Combining equalities] strictly_more_visible loc1 loc2 = not (isVisibleOrigin (ctLocOrigin loc2)) && isVisibleOrigin (ctLocOrigin loc1) + prefer_wanted ev_i + = (loc_w `strictly_more_visible` ctEvLoc ev_i) + -- strictly_more_visible: see (CE3) in Note [Combining equalities] + || (empty_rw_w && not (isEmptyRewriterSet (ctEvRewriters ev_i))) + -- Prefer the one that has no rewriters + -- See (CE4) in Note [Combining equalities] + inertsCanDischarge _ _ = Nothing ===================================== compiler/GHC/Tc/Solver/Monad.hs ===================================== @@ -150,7 +150,6 @@ import qualified GHC.Tc.Utils.Env as TcM ) import GHC.Tc.Zonk.Monad ( ZonkM ) import qualified GHC.Tc.Zonk.TcType as TcM -import qualified GHC.Tc.Zonk.Type as TcM import GHC.Driver.DynFlags @@ -475,10 +474,14 @@ kickOutAfterUnification tv_list = case nonEmpty tv_list of ; return n_kicked } kickOutAfterFillingCoercionHole :: CoercionHole -> TcS () --- See Wrinkle (EIK2a) in Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality +-- See Wrinkle (EIK2) in Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality -- It's possible that this could just go ahead and unify, but could there be occurs-check -- problems? Seems simpler just to kick out. kickOutAfterFillingCoercionHole hole + | not (isHeteroKindCoHole hole) + = return () -- Only hetero-kind coercion holes provoke kick-out; + -- see (EIK2b) in Note [Equalities with incompatible kinds] + | otherwise = do { ics <- getInertCans ; let (kicked_out, ics') = kick_out ics n_kicked = lengthBag kicked_out @@ -497,14 +500,14 @@ kickOutAfterFillingCoercionHole hole kick_out ics@(IC { inert_irreds = irreds }) = -- We only care about irreds here, because any constraint blocked -- by a coercion hole is an irred. See wrinkle (EIK2a) in - -- Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Canonical + -- Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality (irreds_to_kick, ics { inert_irreds = irreds_to_keep }) where (irreds_to_kick, irreds_to_keep) = partitionBag kick_ct irreds - kick_ct :: IrredCt -> Bool - -- True: kick out; False: keep. - kick_ct ct + kick_ct :: IrredCt -> Bool -- True: kick out; False: keep. + kick_ct ct -- See (EIK2) in Note [Equalities with incompatible kinds] + -- for this very specific kick-ot stuff | IrredCt { ir_ev = ev, ir_reason = reason } <- ct , CtWanted (WantedCt { ctev_rewriters = RewriterSet rewriters }) <- ev , NonCanonicalReason ctyeq <- reason @@ -847,17 +850,15 @@ removeInertCt is ct -- | Looks up a family application in the inerts. lookupFamAppInert :: (CtFlavourRole -> Bool) -- can it rewrite the target? - -> TyCon -> [Type] -> TcS (Maybe (Reduction, CtFlavourRole)) + -> TyCon -> [Type] -> TcS (Maybe EqCt) lookupFamAppInert rewrite_pred fam_tc tys = do { IS { inert_cans = IC { inert_funeqs = inert_funeqs } } <- getInertSet ; return (lookup_inerts inert_funeqs) } where lookup_inerts inert_funeqs - | Just ecl <- findFunEq inert_funeqs fam_tc tys - , Just (EqCt { eq_ev = ctev, eq_rhs = rhs }) - <- find (rewrite_pred . eqCtFlavourRole) ecl - = Just (mkReduction (ctEvCoercion ctev) rhs, ctEvFlavourRole ctev) - | otherwise = Nothing + = case findFunEq inert_funeqs fam_tc tys of + Nothing -> Nothing + Just (ecl :: [EqCt]) -> find (rewrite_pred . eqCtFlavourRole) ecl lookupInInerts :: CtLoc -> TcPredType -> TcS (Maybe CtEvidence) -- Is this exact predicate type cached in the solved or canonicals of the InertSet? @@ -1467,8 +1468,8 @@ emitWork cts -- c1 is rewritten by another, c2. When c2 gets solved, -- c1 has no rewriters, and can be prioritised; see -- Note [Prioritise Wanteds with empty RewriterSet] - -- in GHC.Tc.Types.Constraint wrinkle (WRW1) - ; cts <- wrapTcS $ mapBagM TcM.zonkCtRewriterSet cts + -- in GHC.Tc.Types.Constraint wrinkle (PER1) + ; cts <- liftZonkTcS $ mapBagM TcM.zonkCtRewriterSet cts ; updWorkListTcS (extendWorkListCts cts) } emitImplication :: Implication -> TcS () @@ -2340,7 +2341,7 @@ wrapUnifierX ev role do_unifications ; wrapTcS $ do { defer_ref <- TcM.newTcRef emptyBag ; unified_ref <- TcM.newTcRef [] - ; rewriters <- TcM.zonkRewriterSet (ctEvRewriters ev) + ; rewriters <- TcM.liftZonkM (TcM.zonkRewriterSet (ctEvRewriters ev)) ; let env = UE { u_role = role , u_rewriters = rewriters , u_loc = ctEvLoc ev ===================================== compiler/GHC/Tc/Solver/Rewrite.hs ===================================== @@ -150,13 +150,16 @@ bumpDepth (RewriteM thing_inside) { let !env' = env { re_loc = bumpCtLocDepth (re_loc env) } ; thing_inside env' } +recordRewriter :: CtEvidence -> RewriteM () +-- Record that we have rewritten the target with this (equality) evidence -- See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint --- Precondition: the WantedCtEvidence is for an equality constraint -recordRewriter :: WantedCtEvidence -> RewriteM () -recordRewriter (WantedCt { ctev_dest = HoleDest hole }) - = RewriteM $ \env -> updTcRef (re_rewriters env) (`addRewriter` hole) -recordRewriter other = - pprPanic "recordRewriter: non-equality constraint" (ppr other) +-- Precondition: the CtEvidence is for an equality constraint +recordRewriter (CtGiven {}) + = return () +recordRewriter (CtWanted (WantedCt { ctev_dest = dest })) + = case dest of + HoleDest hole -> RewriteM $ \env -> updTcRef (re_rewriters env) (`addRewriter` hole) + other -> pprPanic "recordRewriter: non-equality constraint" (ppr other) {- Note [Rewriter EqRels] ~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -848,16 +851,18 @@ rewrite_exact_fam_app tc tys -- STEP 3: try the inerts ; flavour <- getFlavour - ; result2 <- liftTcS $ lookupFamAppInert (`eqCanRewriteFR` (flavour, eq_rel)) tc xis - ; case result2 of - { Just (redn, (inert_flavour, inert_eq_rel)) + ; mb_eq <- liftTcS $ lookupFamAppInert (`eqCanRewriteFR` (flavour, eq_rel)) tc xis + ; case mb_eq of + { Just (EqCt { eq_ev = inert_ev, eq_rhs = inert_rhs, eq_eq_rel = inert_eq_rel }) -> do { traceRewriteM "rewrite family application with inert" (ppr tc <+> ppr xis $$ ppr redn) - ; finish (inert_flavour == Given) (homogenise downgraded_redn) } - -- this will sometimes duplicate an inert in the cache, + ; recordRewriter inert_ev + ; finish (isGiven inert_ev) (homogenise downgraded_redn) } + -- This will sometimes duplicate an inert in the cache, -- but avoiding doing so had no impact on performance, and -- it seems easier not to weed out that special case where + redn = mkReduction (ctEvCoercion inert_ev) inert_rhs inert_role = eqRelRole inert_eq_rel role = eqRelRole eq_rel downgraded_redn = downgradeRedn role inert_role redn @@ -1024,11 +1029,8 @@ rewrite_tyvar2 tv fr@(_, eq_rel) -> do { traceRewriteM "Following inert tyvar" $ vcat [ ppr tv <+> equals <+> ppr rhs_ty , ppr ctev ] - ; case ctev of - CtGiven {} -> return () - CtWanted wtd -> + ; recordRewriter ctev -- See Note [Wanteds rewrite Wanteds] in GHC.Tc.Types.Constraint - recordRewriter wtd ; let rewriting_co1 = ctEvCoercion ctev rewriting_co = case (ct_eq_rel, eq_rel) of ===================================== compiler/GHC/Tc/Types/Constraint.hs ===================================== @@ -240,18 +240,24 @@ instance Outputable DictCt where {- Note [Canonical equalities] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ An EqCt is a canonical equality constraint, one that can live in the inert set, -and that can be used to rewrite other constrtaints. It satisfies these invariants: +and that can be used to rewrite other constraints. It satisfies these invariants: + * (TyEq:OC) lhs does not occur in rhs (occurs check) Note [EqCt occurs check] + * (TyEq:F) rhs has no foralls (this avoids substituting a forall for the tyvar in other types) + * (TyEq:K) typeKind lhs `tcEqKind` typeKind rhs; Note [Ct kind invariant] + * (TyEq:N) If the equality is representational, rhs is not headed by a saturated application of a newtype TyCon. See GHC.Tc.Solver.Equality Note [No top-level newtypes on RHS of representational equalities]. (Applies only when constructor of newtype is in scope.) + * (TyEq:U) An EqCt is not immediately unifiable. If we can unify a:=ty, we will not form an EqCt (a ~ ty). + * (TyEq:CH) rhs does not mention any coercion holes that resulted from fixing up a hetero-kinded equality. See Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality, wrinkle (EIK2) @@ -534,9 +540,12 @@ cteSolubleOccurs = CTEP (bit 3) -- Occurs-check under a type function, or in -- cteSolubleOccurs must be one bit to the left of cteInsolubleOccurs -- See also Note [Insoluble mis-match] in GHC.Tc.Errors -cteCoercionHole = CTEP (bit 4) -- Coercion hole encountered +cteCoercionHole = CTEP (bit 4) -- Kind-equality coercion hole encountered + -- See (EIK2) in Note [Equalities with incompatible kinds] + cteConcrete = CTEP (bit 5) -- Type variable that can't be made concrete -- e.g. alpha[conc] ~ Maybe beta[tv] + cteSkolemEscape = CTEP (bit 6) -- Skolem escape e.g. alpha[2] ~ b[sk,4] cteProblem :: CheckTyEqProblem -> CheckTyEqResult @@ -2444,19 +2453,29 @@ We thus want Wanteds to rewrite Wanteds in order to accept more programs, but we don't want Wanteds to rewrite Wanteds because doing so can create inscrutable error messages. To solve this dilemma: -* We allow Wanteds to rewrite Wanteds, but... +* We allow Wanteds to rewrite Wanteds, but each Wanted tracks the set of Wanteds + it has been rewritten by, in its RewriterSet, stored in the ctev_rewriters + field of the CtWanted constructor of CtEvidence. (Only Wanteds have + RewriterSets.) + +* A RewriterSet is just a set of unfilled CoercionHoles. This is sufficient + because only equalities (evidenced by coercion holes) are used for rewriting; + other (dictionary) constraints cannot ever rewrite. -* Each Wanted tracks the set of Wanteds it has been rewritten by, in its - RewriterSet, stored in the ctev_rewriters field of the CtWanted - constructor of CtEvidence. (Only Wanteds have RewriterSets.) +* The rewriter (in e.g. GHC.Tc.Solver.Rewrite.rewrite) tracks and returns a RewriterSet, + consisting of the evidence (a CoercionHole) for any Wanted equalities used in + rewriting. + +* Then GHC.Tc.Solver.Solve.rewriteEvidence and GHC.Tc.Solver.Equality.rewriteEqEvidence + add this RewriterSet to the rewritten constraint's rewriter set. * In error reporting, we simply suppress any errors that have been rewritten by /unsolved/ wanteds. This suppression happens in GHC.Tc.Errors.mkErrorItem, - which uses GHC.Tc.Zonk.Type.zonkRewriterSet to look through any filled + which uses `GHC.Tc.Zonk.Type.zonkRewriterSet` to look through any filled coercion holes. The idea is that we wish to report the "root cause" -- the error that rewrote all the others. -* We prioritise Wanteds that have an empty RewriterSet: +* In error reporting, we prioritise Wanteds that have an empty RewriterSet: see Note [Prioritise Wanteds with empty RewriterSet]. Let's continue our first example above: @@ -2471,19 +2490,30 @@ Because Wanteds can rewrite Wanteds, w1 will rewrite w2, yielding The {w1} in the second line of output is the RewriterSet of w1. -A RewriterSet is just a set of unfilled CoercionHoles. This is sufficient -because only equalities (evidenced by coercion holes) are used for rewriting; -other (dictionary) constraints cannot ever rewrite. The rewriter (in -e.g. GHC.Tc.Solver.Rewrite.rewrite) tracks and returns a RewriterSet, -consisting of the evidence (a CoercionHole) for any Wanted equalities used in -rewriting. Then GHC.Tc.Solver.Solve.rewriteEvidence and -GHC.Tc.Solver.Equality.rewriteEqEvidence add this RewriterSet to the rewritten -constraint's rewriter set. +Wrinkles: + +(WRW1) When we find a constraint identical to one already in the inert set, + we solve one from the other. Other things being equal, keep the one + that has fewer (better still no) rewriters. + See (CE4) in Note [Combining equalities] in GHC.Tc.Solver.Equality. + + To this accurately we should use `zonkRewriterSet` during canonicalisation, + to eliminate rewriters that have now been solved. Currently we only do so + during error reporting; but perhaps we should change that. + +(WRW2) When zonking a constraint (with `zonkCt` and `zonkCtEvidence`) we take + the opportunity to zonk its `RewriterSet`, which eliminates solved ones. + This doesn't guarantee that rewriter sets are always up to date -- see + (WRW1) -- but it helps, and it de-clutters debug output. + +(WRW3) We use the rewriter set for a slightly different purpose, in (EIK2) + of Note [Equalities with incompatible kinds] in GHC.Tc.Solver.Equality. + This is a bit of a hack. Note [Prioritise Wanteds with empty RewriterSet] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When extending the WorkList, in GHC.Tc.Solver.InertSet.extendWorkListEq, -we priorities constraints that have no rewriters. Here's why. +we prioritise constraints that have no rewriters. Here's why. Consider this, which came up in T22793: inert: {} @@ -2527,11 +2557,11 @@ GHC.Tc.Solver.InertSet.extendWorkListEq, and extendWorkListEqs. Wrinkles -(WRW1) Before checking for an empty RewriterSet, we zonk the RewriterSet, +(PER1) Before checking for an empty RewriterSet, we zonk the RewriterSet, because some of those CoercionHoles may have been filled in since we last looked: see GHC.Tc.Solver.Monad.emitWork. -(WRW2) Despite the prioritisation, it is hard to be /certain/ that we can't end up +(PER2) Despite the prioritisation, it is hard to be /certain/ that we can't end up in a situation where all of the Wanteds have rewritten each other. In order to report /some/ error in this case, we simply report all the Wanteds. The user will get a perhaps-confusing error message, but they've ===================================== compiler/GHC/Tc/Utils/TcMType.hs ===================================== @@ -49,7 +49,6 @@ module GHC.Tc.Utils.TcMType ( newCoercionHole, newCoercionHoleO, newVanillaCoercionHole, fillCoercionHole, isFilledCoercionHole, - unpackCoercionHole, unpackCoercionHole_maybe, checkCoercionHole, newImplication, @@ -115,7 +114,6 @@ import GHC.Tc.Types.CtLoc( CtLoc, ctLocOrigin ) import GHC.Tc.Utils.Monad -- TcType, amongst others import GHC.Tc.Utils.TcType import GHC.Tc.Errors.Types -import GHC.Tc.Zonk.Type import GHC.Tc.Zonk.TcType import GHC.Builtin.Names @@ -371,6 +369,7 @@ newCoercionHoleO (KindEqOrigin {}) pty = new_coercion_hole True pty newCoercionHoleO _ pty = new_coercion_hole False pty new_coercion_hole :: Bool -> TcPredType -> TcM CoercionHole +-- For the Bool, see (EIK2) in Note [Equalities with incompatible kinds] new_coercion_hole hetero_kind pred_ty = do { co_var <- newEvVar pred_ty ; traceTc "New coercion hole:" (ppr co_var <+> dcolon <+> ppr pred_ty) @@ -1583,7 +1582,7 @@ collect_cand_qtvs_co orig_ty cur_lvl bound = go_co go_co dv (SubCo co) = go_co dv co go_co dv (HoleCo hole) - = do m_co <- unpackCoercionHole_maybe hole + = do m_co <- liftZonkM (unpackCoercionHole_maybe hole) case m_co of Just co -> go_co dv co Nothing -> go_cv dv (coHoleCoVar hole) ===================================== compiler/GHC/Tc/Utils/Unify.hs ===================================== @@ -2649,8 +2649,9 @@ There are five reasons not to unify: we can fill beta[tau] := beta[conc]. This is why we call 'makeTypeConcrete' in startSolvingByUnification. -5. (COERCION-HOLE) Confusing coercion holes - Suppose our equality is +5. (COERCION-HOLE) rhs does not mention any coercion holes that resulted from + fixing up a hetero-kinded equality. This is the same as (TyEq:CH) in + Note [Canonical equalities]. Suppose our equality is (alpha :: k) ~ (Int |> {co}) where co :: Type ~ k is an unsolved wanted. Note that this equality is homogeneous; both sides have kind k. We refrain from unifying here, because @@ -3549,7 +3550,7 @@ checkCo flags co = -- Check for coercion holes, if unifying. -- See (COERCION-HOLE) in Note [Unification preconditions] | case lc of { LC_None {} -> False; _ -> True } -- equivalent to "we are unifying"; see Note [TyEqFlags] - , hasCoercionHoleCo co + , hasHeteroKindCoercionHoleCo co -> return $ PuFail (cteProblem cteCoercionHole) -- Occurs check (can promote) ===================================== compiler/GHC/Tc/Zonk/TcType.hs ===================================== @@ -1,3 +1,5 @@ +{-# LANGUAGE DuplicateRecordFields #-} + {- (c) The University of Glasgow 2006 (c) The AQUA Project, Glasgow University, 1996-1998 @@ -36,6 +38,13 @@ module GHC.Tc.Zonk.TcType -- ** Zonking constraints , zonkCt, zonkWC, zonkSimples, zonkImplication + -- * Rewriter sets + , zonkRewriterSet, zonkCtRewriterSet, zonkCtEvRewriterSet + + -- * Coercion holes + , isFilledCoercionHole, unpackCoercionHole, unpackCoercionHole_maybe + + -- * Tidying , tcInitTidyEnv, tcInitOpenTidyEnv , tidyCt, tidyEvVar, tidyDelayedError @@ -81,7 +90,7 @@ import GHC.Core.Coercion import GHC.Core.Predicate import GHC.Utils.Constants -import GHC.Utils.Outputable +import GHC.Utils.Outputable as Outputable import GHC.Utils.Misc import GHC.Utils.Monad ( mapAccumLM ) import GHC.Utils.Panic @@ -89,6 +98,9 @@ import GHC.Utils.Panic import GHC.Data.Bag import GHC.Data.Pair +import Data.Semigroup +import Data.Maybe + {- ********************************************************************* * * Writing to metavariables @@ -366,8 +378,8 @@ checkCoercionHole cv co ; return $ assertPpr (ok cv_ty) (text "Bad coercion hole" <+> - ppr cv <> colon <+> vcat [ ppr t1, ppr t2, ppr role - , ppr cv_ty ]) + ppr cv Outputable.<> colon + <+> vcat [ ppr t1, ppr t2, ppr role, ppr cv_ty ]) co } | otherwise = return co @@ -494,9 +506,15 @@ zonkCt ct ; return (mkNonCanonical fl') } zonkCtEvidence :: CtEvidence -> ZonkM CtEvidence -zonkCtEvidence ctev - = do { pred' <- zonkTcType (ctEvPred ctev) - ; return (setCtEvPredType ctev pred') } +-- Zonks the ctev_pred and the ctev_rewriters; but not ctev_evar +-- For ctev_rewriters, see (WRW2) in Note [Wanteds rewrite Wanteds] +zonkCtEvidence (CtGiven (GivenCt { ctev_pred = pred, ctev_evar = var, ctev_loc = loc })) + = do { pred' <- zonkTcType pred + ; return (CtGiven (GivenCt { ctev_pred = pred', ctev_evar = var, ctev_loc = loc })) } +zonkCtEvidence (CtWanted wanted@(WantedCt { ctev_pred = pred, ctev_rewriters = rws })) + = do { pred' <- zonkTcType pred + ; rws' <- zonkRewriterSet rws + ; return (CtWanted (wanted { ctev_pred = pred', ctev_rewriters = rws' })) } zonkSkolemInfo :: SkolemInfo -> ZonkM SkolemInfo zonkSkolemInfo (SkolemInfo u sk) = SkolemInfo u <$> zonkSkolemInfoAnon sk @@ -530,6 +548,103 @@ win. But c.f Note [Sharing when zonking to Type] in GHC.Tc.Zonk.Type. +%************************************************************************ +%* * + Zonking rewriter sets +* * +************************************************************************ +-} + +zonkCtRewriterSet :: Ct -> ZonkM Ct +zonkCtRewriterSet ct + | isGivenCt ct + = return ct + | otherwise + = case ct of + CEqCan eq@(EqCt { eq_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CEqCan (eq { eq_ev = ev' })) } + CIrredCan ir@(IrredCt { ir_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CIrredCan (ir { ir_ev = ev' })) } + CDictCan di@(DictCt { di_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CDictCan (di { di_ev = ev' })) } + CQuantCan {} -> return ct + CNonCanonical ev -> do { ev' <- zonkCtEvRewriterSet ev + ; return (CNonCanonical ev') } + +zonkCtEvRewriterSet :: CtEvidence -> ZonkM CtEvidence +zonkCtEvRewriterSet ev@(CtGiven {}) + = return ev +zonkCtEvRewriterSet ev@(CtWanted wtd) + = do { rewriters' <- zonkRewriterSet (ctEvRewriters ev) + ; return (CtWanted $ setWantedCtEvRewriters wtd rewriters') } + +-- | Zonk a rewriter set; if a coercion hole in the set has been filled, +-- find all the free un-filled coercion holes in the coercion that fills it +zonkRewriterSet :: RewriterSet -> ZonkM RewriterSet +zonkRewriterSet (RewriterSet set) + = nonDetStrictFoldUniqSet go (return emptyRewriterSet) set + -- This does not introduce non-determinism, because the only + -- monadic action is to read, and the combining function is + -- commutative + where + go :: CoercionHole -> ZonkM RewriterSet -> ZonkM RewriterSet + go hole m_acc = unionRewriterSet <$> check_hole hole <*> m_acc + + check_hole :: CoercionHole -> ZonkM RewriterSet + check_hole hole + = do { m_co <- unpackCoercionHole_maybe hole + ; case m_co of + Nothing -> return (unitRewriterSet hole) -- Not filled + Just co -> unUCHM (check_co co) } -- Filled: look inside + + check_ty :: Type -> UnfilledCoercionHoleMonoid + check_co :: Coercion -> UnfilledCoercionHoleMonoid + (check_ty, _, check_co, _) = foldTyCo folder () + + folder :: TyCoFolder () UnfilledCoercionHoleMonoid + folder = TyCoFolder { tcf_view = noView + , tcf_tyvar = \ _ tv -> check_ty (tyVarKind tv) + , tcf_covar = \ _ cv -> check_ty (varType cv) + , tcf_hole = \ _ -> UCHM . check_hole + , tcf_tycobinder = \ _ _ _ -> () } + +newtype UnfilledCoercionHoleMonoid = UCHM { unUCHM :: ZonkM RewriterSet } + +instance Semigroup UnfilledCoercionHoleMonoid where + UCHM l <> UCHM r = UCHM (unionRewriterSet <$> l <*> r) + +instance Monoid UnfilledCoercionHoleMonoid where + mempty = UCHM (return emptyRewriterSet) + + +{- +************************************************************************ +* * + Checking for coercion holes +* * +************************************************************************ +-} + +-- | Is a coercion hole filled in? +isFilledCoercionHole :: CoercionHole -> ZonkM Bool +isFilledCoercionHole (CoercionHole { ch_ref = ref }) + = isJust <$> readTcRef ref + +-- | Retrieve the contents of a coercion hole. Panics if the hole +-- is unfilled +unpackCoercionHole :: CoercionHole -> ZonkM Coercion +unpackCoercionHole hole + = do { contents <- unpackCoercionHole_maybe hole + ; case contents of + Just co -> return co + Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) } + +-- | Retrieve the contents of a coercion hole, if it is filled +unpackCoercionHole_maybe :: CoercionHole -> ZonkM (Maybe Coercion) +unpackCoercionHole_maybe (CoercionHole { ch_ref = ref }) = readTcRef ref + + +{- %************************************************************************ %* * Tidying ===================================== compiler/GHC/Tc/Zonk/Type.hs ===================================== @@ -28,12 +28,6 @@ module GHC.Tc.Zonk.Type ( -- ** 'ZonkEnv', and the 'ZonkT' and 'ZonkBndrT' monad transformers module GHC.Tc.Zonk.Env, - -- * Coercion holes - isFilledCoercionHole, unpackCoercionHole, unpackCoercionHole_maybe, - - -- * Rewriter sets - zonkRewriterSet, zonkCtRewriterSet, zonkCtEvRewriterSet, - -- * Tidying tcInitTidyEnv, tcInitOpenTidyEnv, @@ -55,7 +49,6 @@ import GHC.Tc.TyCl.Build ( TcMethInfo, MethInfo ) import GHC.Tc.Utils.Env ( tcLookupGlobalOnly ) import GHC.Tc.Utils.TcType import GHC.Tc.Utils.Monad ( newZonkAnyType, setSrcSpanA, liftZonkM, traceTc, addErr ) -import GHC.Tc.Types.Constraint import GHC.Tc.Types.Evidence import GHC.Tc.Errors.Types import GHC.Tc.Zonk.Env @@ -88,7 +81,6 @@ import GHC.Types.Id import GHC.Types.TypeEnv import GHC.Types.Basic import GHC.Types.SrcLoc -import GHC.Types.Unique.Set import GHC.Types.Unique.FM import GHC.Types.TyThing @@ -99,7 +91,6 @@ import GHC.Data.Bag import Control.Monad import Control.Monad.Trans.Class ( lift ) -import Data.Semigroup import Data.List.NonEmpty ( NonEmpty ) import Data.Foldable ( toList ) @@ -1956,89 +1947,3 @@ finding the free type vars of an expression is necessarily monadic operation. (consider /\a -> f @ b, where b is side-effected to a) -} -{- -************************************************************************ -* * - Checking for coercion holes -* * -************************************************************************ --} - --- | Is a coercion hole filled in? -isFilledCoercionHole :: CoercionHole -> TcM Bool -isFilledCoercionHole (CoercionHole { ch_ref = ref }) - = isJust <$> readTcRef ref - --- | Retrieve the contents of a coercion hole. Panics if the hole --- is unfilled -unpackCoercionHole :: CoercionHole -> TcM Coercion -unpackCoercionHole hole - = do { contents <- unpackCoercionHole_maybe hole - ; case contents of - Just co -> return co - Nothing -> pprPanic "Unfilled coercion hole" (ppr hole) } - --- | Retrieve the contents of a coercion hole, if it is filled -unpackCoercionHole_maybe :: CoercionHole -> TcM (Maybe Coercion) -unpackCoercionHole_maybe (CoercionHole { ch_ref = ref }) = readTcRef ref - -zonkCtRewriterSet :: Ct -> TcM Ct -zonkCtRewriterSet ct - | isGivenCt ct - = return ct - | otherwise - = case ct of - CEqCan eq@(EqCt { eq_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CEqCan (eq { eq_ev = ev' })) } - CIrredCan ir@(IrredCt { ir_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CIrredCan (ir { ir_ev = ev' })) } - CDictCan di@(DictCt { di_ev = ev }) -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CDictCan (di { di_ev = ev' })) } - CQuantCan {} -> return ct - CNonCanonical ev -> do { ev' <- zonkCtEvRewriterSet ev - ; return (CNonCanonical ev') } - -zonkCtEvRewriterSet :: CtEvidence -> TcM CtEvidence -zonkCtEvRewriterSet ev@(CtGiven {}) - = return ev -zonkCtEvRewriterSet ev@(CtWanted wtd) - = do { rewriters' <- zonkRewriterSet (ctEvRewriters ev) - ; return (CtWanted $ setWantedCtEvRewriters wtd rewriters') } - --- | Check whether any coercion hole in a RewriterSet is still unsolved. --- Does this by recursively looking through filled coercion holes until --- one is found that is not yet filled in, at which point this aborts. -zonkRewriterSet :: RewriterSet -> TcM RewriterSet -zonkRewriterSet (RewriterSet set) - = nonDetStrictFoldUniqSet go (return emptyRewriterSet) set - -- this does not introduce non-determinism, because the only - -- monadic action is to read, and the combining function is - -- commutative - where - go :: CoercionHole -> TcM RewriterSet -> TcM RewriterSet - go hole m_acc = unionRewriterSet <$> check_hole hole <*> m_acc - - check_hole :: CoercionHole -> TcM RewriterSet - check_hole hole = do { m_co <- unpackCoercionHole_maybe hole - ; case m_co of - Nothing -> return (unitRewriterSet hole) - Just co -> unUCHM (check_co co) } - - check_ty :: Type -> UnfilledCoercionHoleMonoid - check_co :: Coercion -> UnfilledCoercionHoleMonoid - (check_ty, _, check_co, _) = foldTyCo folder () - - folder :: TyCoFolder () UnfilledCoercionHoleMonoid - folder = TyCoFolder { tcf_view = noView - , tcf_tyvar = \ _ tv -> check_ty (tyVarKind tv) - , tcf_covar = \ _ cv -> check_ty (varType cv) - , tcf_hole = \ _ -> UCHM . check_hole - , tcf_tycobinder = \ _ _ _ -> () } - -newtype UnfilledCoercionHoleMonoid = UCHM { unUCHM :: TcM RewriterSet } - -instance Semigroup UnfilledCoercionHoleMonoid where - UCHM l <> UCHM r = UCHM (unionRewriterSet <$> l <*> r) - -instance Monoid UnfilledCoercionHoleMonoid where - mempty = UCHM (return emptyRewriterSet) ===================================== testsuite/tests/indexed-types/should_fail/T3330c.stderr ===================================== @@ -1,16 +1,24 @@ - -T3330c.hs:25:43: error: [GHC-18872] - • Couldn't match kind ‘* -> *’ with ‘*’ - When matching types - f1 :: * -> * - f1 x :: * - Expected: Der ((->) x) (Der f1 x) - Actual: R f1 - • In the first argument of ‘plug’, namely ‘rf’ +T3330c.hs:25:38: error: [GHC-25897] + • Could not deduce ‘Der f1 ~ f1’ + from the context: f ~ (f1 :+: g) + bound by a pattern with constructor: + RSum :: forall (f :: * -> *) (g :: * -> *). + R f -> R g -> R (f :+: g), + in an equation for ‘plug'’ + at T3330c.hs:25:8-17 + Expected: x -> f1 x + Actual: x -> Der f1 x + ‘f1’ is a rigid type variable bound by + a pattern with constructor: + RSum :: forall (f :: * -> *) (g :: * -> *). + R f -> R g -> R (f :+: g), + in an equation for ‘plug'’ + at T3330c.hs:25:8-17 + • The function ‘plug’ is applied to three visible arguments, + but its type ‘Rep f => Der f x -> x -> f x’ has only two In the first argument of ‘Inl’, namely ‘(plug rf df x)’ In the expression: Inl (plug rf df x) • Relevant bindings include - x :: x (bound at T3330c.hs:25:29) df :: Der f1 x (bound at T3330c.hs:25:25) rf :: R f1 (bound at T3330c.hs:25:13) - plug' :: R f -> Der f x -> x -> f x (bound at T3330c.hs:25:1) + ===================================== testsuite/tests/indexed-types/should_fail/T4174.stderr ===================================== @@ -1,6 +1,16 @@ - -T4174.hs:45:12: error: [GHC-18872] - • Couldn't match type ‘False’ with ‘True’ - arising from a use of ‘sync_large_objects’ +T4174.hs:45:12: error: [GHC-25897] + • Couldn't match type ‘a’ with ‘SmStep’ + Expected: m (Field (Way (GHC6'8 minor) n t p) a b) + Actual: m (Field (WayOf m) SmStep RtsSpinLock) + ‘a’ is a rigid type variable bound by + the type signature for: + testcase :: forall (m :: * -> *) minor n t p a b. + Monad m => + m (Field (Way (GHC6'8 minor) n t p) a b) + at T4174.hs:44:1-63 • In the expression: sync_large_objects In an equation for ‘testcase’: testcase = sync_large_objects + • Relevant bindings include + testcase :: m (Field (Way (GHC6'8 minor) n t p) a b) + (bound at T4174.hs:45:1) + ===================================== testsuite/tests/indexed-types/should_fail/T8227.stderr ===================================== @@ -13,12 +13,3 @@ T8227.hs:24:27: error: [GHC-83865] absoluteToParam :: Scalar (V a) -> a -> Scalar (V a) (bound at T8227.hs:24:1) -T8227.hs:24:48: error: [GHC-27958] - • Couldn't match type ‘p0’ with ‘Scalar (V p0)’ - arising from a type equality Scalar (V a) ~ Scalar (V p0) -> p0 - The type variable ‘p0’ is ambiguous - • In the second argument of ‘arcLengthToParam’, namely ‘eps’ - In the expression: arcLengthToParam eps eps - In an equation for ‘absoluteToParam’: - absoluteToParam eps seg = arcLengthToParam eps eps - ===================================== testsuite/tests/typecheck/should_compile/T25266a.stderr ===================================== @@ -1,16 +1,16 @@ -T25266a.hs:10:41: error: [GHC-25897] - • Could not deduce ‘p1 ~ p2’ +T25266a.hs:10:39: error: [GHC-25897] + • Could not deduce ‘p2 ~ p1’ from the context: a ~ Int bound by a pattern with constructor: T1 :: T Int, in a case alternative at T25266a.hs:10:23-24 - ‘p1’ is a rigid type variable bound by + ‘p2’ is a rigid type variable bound by the inferred type of f :: p1 -> p2 -> T a -> Int at T25266a.hs:(9,1)-(11,40) - ‘p2’ is a rigid type variable bound by + ‘p1’ is a rigid type variable bound by the inferred type of f :: p1 -> p2 -> T a -> Int at T25266a.hs:(9,1)-(11,40) - • In the expression: y + • In the expression: x In the first argument of ‘length’, namely ‘[x, y]’ In the expression: length [x, y] • Relevant bindings include ===================================== testsuite/tests/typecheck/should_fail/T18851.stderr ===================================== @@ -1,7 +1,7 @@ - T18851.hs:35:5: error: [GHC-18872] - • Couldn't match type ‘B’ with ‘A’ - arising from a superclass required to satisfy ‘C int0 A’, + • Couldn't match type ‘Bool’ with ‘B’ + arising from a superclass required to satisfy ‘C Int B’, arising from a use of ‘f’ • In the expression: f @A @B In an equation for ‘g’: g = f @A @B + View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/22d11fa818fae2c95c494fc0fac1f8c… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/22d11fa818fae2c95c494fc0fac1f8c… You're receiving this email because of your account on gitlab.haskell.org.

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[Git][ghc/ghc][master] Fix infelicities in the Specialiser
by Marge Bot (＠marge-bot) 28 Apr '25

28 Apr '25

Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC Commits: ce616f49 by Simon Peyton Jones at 2025-04-27T21:10:25+01:00 Fix infelicities in the Specialiser On the way to #23109 (unary classes) I discovered some infelicities (or maybe tiny bugs, I forget) in the type-class specialiser. I also tripped over #25965, an outright bug in the rule matcher Specifically: * Refactor: I enhanced `wantCallsFor`, whih previously always said `True`, to discard calls of class-ops, data constructors etc. This is a bit more efficient; and it means we don't need to worry about filtering them out later. * Fix: I tidied up some tricky logic that eliminated redundant specialisations. It wasn't working correctly. See the expanded Note [Specialisations already covered], and (MP3) in Note [Specialising polymorphic dictionaries]. See also the new top-level `alreadyCovered` function, which now goes via `GHC.Core.Rules.ruleLhsIsMoreSpecific` I also added a useful Note [The (CI-KEY) invariant] * Fix #25965: fixed a tricky bug in the `go_fam_fam` in `GHC.Core.Unify.uVarOrFam`, which allows matching to succeed without binding all type varibles. I enhanced Note [Apartness and type families] some more * #25703. This ticket "just works" with -fpolymorphic-specialisation; but I was surprised that it worked! In this MR I added documentation to Note [Interesting dictionary arguments] to explain; and tests to ensure it stays fixed. - - - - - 11 changed files: - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/Tc/Solver/Equality.hs - compiler/GHC/Types/Basic.hs - + testsuite/tests/simplCore/should_compile/T25703.hs - + testsuite/tests/simplCore/should_compile/T25703.stderr - + testsuite/tests/simplCore/should_compile/T25703a.hs - + testsuite/tests/simplCore/should_compile/T25703a.stderr - + testsuite/tests/simplCore/should_compile/T25965.hs - testsuite/tests/simplCore/should_compile/all.T Changes: ===================================== compiler/GHC/Core/Opt/Specialise.hs ===================================== @@ -1243,14 +1243,15 @@ specExpr env (Let bind body) -- Note [Fire rules in the specialiser] fireRewriteRules :: SpecEnv -> InExpr -> [OutExpr] -> (InExpr, [OutExpr]) fireRewriteRules env (Var f) args - | Just (rule, expr) <- specLookupRule env f args InitialPhase (getRules (se_rules env) f) + | let rules = getRules (se_rules env) f + , Just (rule, expr) <- specLookupRule env f args activeInInitialPhase rules , let rest_args = drop (ruleArity rule) args -- See Note [Extra args in the target] zapped_subst = Core.zapSubst (se_subst env) expr' = simpleOptExprWith defaultSimpleOpts zapped_subst expr -- simplOptExpr needed because lookupRule returns -- (\x y. rhs) arg1 arg2 - , (fun, args) <- collectArgs expr' - = fireRewriteRules env fun (args++rest_args) + , (fun', args') <- collectArgs expr' + = fireRewriteRules env fun' (args'++rest_args) fireRewriteRules _ fun args = (fun, args) -------------- @@ -1620,7 +1621,7 @@ specCalls :: Bool -- True => specialising imported fn -- This function checks existing rules, and does not create -- duplicate ones. So the caller does not need to do this filtering. --- See 'already_covered' +-- See `alreadyCovered` type SpecInfo = ( [CoreRule] -- Specialisation rules , [(Id,CoreExpr)] -- Specialised definition @@ -1644,15 +1645,13 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs = -- pprTrace "specCalls: some" (vcat -- [ text "function" <+> ppr fn - -- , text "calls:" <+> ppr calls_for_me - -- , text "subst" <+> ppr (se_subst env) ]) $ + -- , text "calls:" <+> ppr calls_for_me + -- , text "subst" <+> ppr (se_subst env) ]) $ foldlM spec_call ([], [], emptyUDs) calls_for_me | otherwise -- No calls or RHS doesn't fit our preconceptions - = warnPprTrace (not (exprIsTrivial rhs) && notNull calls_for_me && not (isClassOpId fn)) + = warnPprTrace (not (exprIsTrivial rhs) && notNull calls_for_me) "Missed specialisation opportunity for" (ppr fn $$ trace_doc) $ - -- isClassOpId: class-op Ids never inline; we specialise them - -- through fireRewriteRules. So don't complain about missed opportunities -- Note [Specialisation shape] -- pprTrace "specCalls: none" (ppr fn <+> ppr calls_for_me) $ return ([], [], emptyUDs) @@ -1664,6 +1663,10 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs fn_unf = realIdUnfolding fn -- Ignore loop-breaker-ness here inl_prag = idInlinePragma fn inl_act = inlinePragmaActivation inl_prag + is_active = isActive (beginPhase inl_act) :: Activation -> Bool + -- is_active: inl_act is the activation we are going to put in the new + -- SPEC rule; so we want to see if it is covered by another rule with + -- that same activation. is_local = isLocalId fn is_dfun = isDFunId fn dflags = se_dflags env @@ -1674,16 +1677,6 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs (rhs_bndrs, rhs_body) = collectBindersPushingCo rhs -- See Note [Account for casts in binding] - already_covered :: SpecEnv -> [CoreRule] -> [CoreExpr] -> Bool - already_covered env new_rules args -- Note [Specialisations already covered] - = isJust (specLookupRule env fn args (beginPhase inl_act) - (new_rules ++ existing_rules)) - -- Rules: we look both in the new_rules (generated by this invocation - -- of specCalls), and in existing_rules (passed in to specCalls) - -- inl_act: is the activation we are going to put in the new SPEC - -- rule; so we want to see if it is covered by another rule with - -- that same activation. - ---------------------------------------------------------- -- Specialise to one particular call pattern spec_call :: SpecInfo -- Accumulating parameter @@ -1717,8 +1710,12 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs -- , ppr dx_binds ]) $ -- return () + ; let all_rules = rules_acc ++ existing_rules + -- all_rules: we look both in the rules_acc (generated by this invocation + -- of specCalls), and in existing_rules (passed in to specCalls) ; if not useful -- No useful specialisation - || already_covered rhs_env2 rules_acc rule_lhs_args + || alreadyCovered rhs_env2 rule_bndrs fn rule_lhs_args is_active all_rules + -- See (SC1) in Note [Specialisations already covered] then return spec_acc else do { -- Run the specialiser on the specialised RHS @@ -1780,7 +1777,7 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs spec_fn_details = case idDetails fn of JoinId join_arity _ -> JoinId (join_arity - join_arity_decr) Nothing - DFunId is_nt -> DFunId is_nt + DFunId unary -> DFunId unary _ -> VanillaId ; spec_fn <- newSpecIdSM (idName fn) spec_fn_ty spec_fn_details spec_fn_info @@ -1804,6 +1801,8 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs , ppr spec_fn <+> dcolon <+> ppr spec_fn_ty , ppr rhs_bndrs, ppr call_args , ppr spec_rule + , text "acc" <+> ppr rules_acc + , text "existing" <+> ppr existing_rules ] ; -- pprTrace "spec_call: rule" _rule_trace_doc @@ -1812,19 +1811,35 @@ specCalls spec_imp env existing_rules calls_for_me fn rhs , spec_uds `thenUDs` uds_acc ) } } +alreadyCovered :: SpecEnv + -> [Var] -> Id -> [CoreExpr] -- LHS of possible new rule + -> (Activation -> Bool) -- Which rules are active + -> [CoreRule] -> Bool +-- Note [Specialisations already covered] esp (SC2) +alreadyCovered env bndrs fn args is_active rules + = case specLookupRule env fn args is_active rules of + Nothing -> False + Just (rule, _) + | isAutoRule rule -> -- Discard identical rules + -- We know that (fn args) is an instance of RULE + -- Check if RULE is an instance of (fn args) + ruleLhsIsMoreSpecific in_scope bndrs args rule + | otherwise -> True -- User rules dominate + where + in_scope = substInScopeSet (se_subst env) + -- Convenience function for invoking lookupRule from Specialise -- The SpecEnv's InScopeSet should include all the Vars in the [CoreExpr] specLookupRule :: SpecEnv -> Id -> [CoreExpr] - -> CompilerPhase -- Look up rules as if we were in this phase + -> (Activation -> Bool) -- Which rules are active -> [CoreRule] -> Maybe (CoreRule, CoreExpr) -specLookupRule env fn args phase rules +specLookupRule env fn args is_active rules = lookupRule ropts in_scope_env is_active fn args rules where dflags = se_dflags env in_scope = substInScopeSet (se_subst env) in_scope_env = ISE in_scope (whenActiveUnfoldingFun is_active) ropts = initRuleOpts dflags - is_active = isActive phase {- Note [Specialising DFuns] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -2323,21 +2338,24 @@ This plan is implemented in the Rec case of specBindItself. Note [Specialisations already covered] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We obviously don't want to generate two specialisations for the same -argument pattern. There are two wrinkles - -1. We do the already-covered test in specDefn, not when we generate -the CallInfo in mkCallUDs. We used to test in the latter place, but -we now iterate the specialiser somewhat, and the Id at the call site -might therefore not have all the RULES that we can see in specDefn - -2. What about two specialisations where the second is an *instance* -of the first? If the more specific one shows up first, we'll generate -specialisations for both. If the *less* specific one shows up first, -we *don't* currently generate a specialisation for the more specific -one. (See the call to lookupRule in already_covered.) Reasons: - (a) lookupRule doesn't say which matches are exact (bad reason) - (b) if the earlier specialisation is user-provided, it's - far from clear that we should auto-specialise further +argument pattern. Wrinkles + +(SC1) We do the already-covered test in specDefn, not when we generate + the CallInfo in mkCallUDs. We used to test in the latter place, but + we now iterate the specialiser somewhat, and the Id at the call site + might therefore not have all the RULES that we can see in specDefn + +(SC2) What about two specialisations where the second is an *instance* + of the first? It's a bit arbitrary, but here's what we do: + * If the existing one is user-specified, via a SPECIALISE pragma, we + suppress the further specialisation. + * If the existing one is auto-generated, we generate a second RULE + for the more specialised version. + The latter is important because we don't want the accidental order + of calls to determine what specialisations we generate. + +(SC3) Annoyingly, we /also/ eliminate duplicates in `filterCalls`. + See (MP3) in Note [Specialising polymorphic dictionaries] Note [Auto-specialisation and RULES] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -2800,12 +2818,10 @@ non-dictionary bindings too. Note [Specialising polymorphic dictionaries] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - Note June 2023: This has proved to be quite a tricky optimisation to get right see (#23469, #23109, #21229, #23445) so it is now guarded by a flag `-fpolymorphic-specialisation`. - Consider class M a where { foo :: a -> Int } @@ -2845,11 +2861,26 @@ Here are the moving parts: function. (MP3) If we have f :: forall m. Monoid m => blah, and two calls - (f @(Endo b) (d :: Monoid (Endo b)) - (f @(Endo (c->c)) (d :: Monoid (Endo (c->c))) + (f @(Endo b) (d1 :: Monoid (Endo b)) + (f @(Endo (c->c)) (d2 :: Monoid (Endo (c->c))) we want to generate a specialisation only for the first. The second is just a substitution instance of the first, with no greater specialisation. - Hence the call to `remove_dups` in `filterCalls`. + Hence the use of `removeDupCalls` in `filterCalls`. + + You might wonder if `d2` might be more specialised than `d1`; but no. + This `removeDupCalls` thing is at the definition site of `f`, and both `d1` + and `d2` are in scope. So `d1` is simply more polymorphic than `d2`, but + is just as specialised. + + This distinction is sadly lost once we build a RULE, so `alreadyCovered` + can't be so clever. E.g if we have an existing RULE + forall @a (d1:Ord Int) (d2: Eq a). f @a @Int d1 d2 = ... + and a putative new rule + forall (d1:Ord Int) (d2: Eq Int). f @Int @Int d1 d2 = ... + we /don't/ want the existing rule to subsume the new one. + + So we sadly put up with having two rather different places where we + eliminate duplicates: `alreadyCovered` and `removeDupCalls`. All this arose in #13873, in the unexpected form that a SPECIALISE pragma made the program slower! The reason was that the specialised @@ -2947,16 +2978,29 @@ data CallInfoSet = CIS Id (Bag CallInfo) -- The list of types and dictionaries is guaranteed to -- match the type of f -- The Bag may contain duplicate calls (i.e. f @T and another f @T) - -- These dups are eliminated by already_covered in specCalls + -- These dups are eliminated by alreadyCovered in specCalls data CallInfo - = CI { ci_key :: [SpecArg] -- All arguments + = CI { ci_key :: [SpecArg] -- Arguments of the call + -- See Note [The (CI-KEY) invariant] + , ci_fvs :: IdSet -- Free Ids of the ci_key call -- /not/ including the main id itself, of course -- NB: excluding tyvars: -- See Note [Specialising polymorphic dictionaries] } +{- Note [The (CI-KEY) invariant] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Invariant (CI-KEY): + In the `ci_key :: [SpecArg]` field of `CallInfo`, + * The list is non-empty + * The least element is always a `SpecDict` + +In this way the RULE has as few args as possible, which broadens its +applicability, since rules only fire when saturated. +-} + type DictExpr = CoreExpr ciSetFilter :: (CallInfo -> Bool) -> CallInfoSet -> CallInfoSet @@ -3045,10 +3089,7 @@ mkCallUDs' env f args ci_key :: [SpecArg] ci_key = dropWhileEndLE (not . isSpecDict) $ zipWith mk_spec_arg args pis - -- Drop trailing args until we get to a SpecDict - -- In this way the RULE has as few args as possible, - -- which broadens its applicability, since rules only - -- fire when saturated + -- Establish (CI-KEY): drop trailing args until we get to a SpecDict mk_spec_arg :: OutExpr -> PiTyBinder -> SpecArg mk_spec_arg arg (Named bndr) @@ -3086,34 +3127,76 @@ site, so we only look through ticks that RULE matching looks through -} wantCallsFor :: SpecEnv -> Id -> Bool -wantCallsFor _env _f = True - -- We could reduce the size of the UsageDetails by being less eager - -- about collecting calls for LocalIds: there is no point for - -- ones that are lambda-bound. We can't decide this by looking at - -- the (absence of an) unfolding, because unfoldings for local - -- functions are discarded by cloneBindSM, so no local binder will - -- have an unfolding at this stage. We'd have to keep a candidate - -- set of let-binders. - -- - -- Not many lambda-bound variables have dictionary arguments, so - -- this would make little difference anyway. - -- - -- For imported Ids we could check for an unfolding, but we have to - -- do so anyway in canSpecImport, and it seems better to have it - -- all in one place. So we simply collect usage info for imported - -- overloaded functions. - -{- Note [Interesting dictionary arguments] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Consider this - \a.\d:Eq a. let f = ... in ...(f d)... -There really is not much point in specialising f wrt the dictionary d, -because the code for the specialised f is not improved at all, because -d is lambda-bound. We simply get junk specialisations. - -What is "interesting"? Just that it has *some* structure. But what about -variables? We look in the variable's /unfolding/. And that means -that we must be careful to ensure that dictionaries have unfoldings, +-- See Note [wantCallsFor] +wantCallsFor _env f + = case idDetails f of + RecSelId {} -> False + DataConWorkId {} -> False + DataConWrapId {} -> False + ClassOpId {} -> False + PrimOpId {} -> False + FCallId {} -> False + TickBoxOpId {} -> False + CoVarId {} -> False + + DFunId {} -> True + VanillaId {} -> True + JoinId {} -> True + WorkerLikeId {} -> True + RepPolyId {} -> True + +{- Note [wantCallsFor] +~~~~~~~~~~~~~~~~~~~~~~ +`wantCallsFor env f` says whether the Specialiser should collect calls for +function `f`; other thing being equal, the fewer calls we collect the better. It +is False for things we can't specialise: + +* ClassOpId: never inline and we don't have a defn to specialise; we specialise + them through fireRewriteRules. +* PrimOpId: are never overloaded +* Data constructors: we never specialise them + +We could reduce the size of the UsageDetails by being less eager about +collecting calls for some LocalIds: there is no point for ones that are +lambda-bound. We can't decide this by looking at the (absence of an) unfolding, +because unfoldings for local functions are discarded by cloneBindSM, so no local +binder will have an unfolding at this stage. We'd have to keep a candidate set +of let-binders. + +Not many lambda-bound variables have dictionary arguments, so this would make +little difference anyway. + +For imported Ids we could check for an unfolding, but we have to do so anyway in +canSpecImport, and it seems better to have it all in one place. So we simply +collect usage info for imported overloaded functions. + +Note [Interesting dictionary arguments] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In `mkCallUDs` we only use `SpecDict` for dictionaries of which +`interestingDict` holds. Otherwise we use `UnspecArg`. Two reasons: + +* Consider this + \a.\d:Eq a. let f = ... in ...(f d)... + There really is not much point in specialising f wrt the dictionary d, + because the code for the specialised f is not improved at all, because + d is lambda-bound. We simply get junk specialisations. + +* Consider this (#25703): + f :: (Eq a, Show b) => a -> b -> INt + goo :: forall x. (Eq x) => x -> blah + goo @x (d:Eq x) (arg:x) = ...(f @x @Int d $fShowInt)... + If we built a `ci_key` with a (SpecDict d) for `d`, we would end up + discarding the call at the `\d`. But if we use `UnspecArg` for that + uninteresting `d`, we'll get a `ci_key` of + f @x @Int UnspecArg (SpecDict $fShowInt) + and /that/ can float out to f's definition and specialise nicely. + Hooray. (NB: the call can float only if `-fpolymorphic-specialisation` + is on; otherwise it'll be trapped by the `\@x -> ...`.)( + +What is "interesting"? (See `interestingDict`.) Just that it has *some* +structure. But what about variables? We look in the variable's /unfolding/. +And that means that we must be careful to ensure that dictionaries /have/ +unfoldings, * cloneBndrSM discards non-Stable unfoldings * specBind updates the unfolding after specialisation @@ -3159,7 +3242,7 @@ Now `f` turns into: meth @a dc .... When we specialise `f`, at a=Int say, that superclass selection can -nfire (via rewiteClassOps), but that info (that 'dc' is now a +fire (via rewiteClassOps), but that info (that 'dc' is now a particular dictionary `C`, of type `C Int`) must be available to the call `meth @a dc`, so that we can fire the `meth` class-op, and thence specialise `wombat`. @@ -3286,7 +3369,11 @@ dumpUDs :: [CoreBndr] -> UsageDetails -> (UsageDetails, OrdList DictBind) -- Used at a lambda or case binder; just dump anything mentioning the binder dumpUDs bndrs uds@(MkUD { ud_binds = orig_dbs, ud_calls = orig_calls }) | null bndrs = (uds, nilOL) -- Common in case alternatives - | otherwise = -- pprTrace "dumpUDs" (ppr bndrs $$ ppr free_uds $$ ppr dump_dbs) $ + | otherwise = -- pprTrace "dumpUDs" (vcat + -- [ text "bndrs" <+> ppr bndrs + -- , text "uds" <+> ppr uds + -- , text "free_uds" <+> ppr free_uds + -- , text "dump-dbs" <+> ppr dump_dbs ]) $ (free_uds, dump_dbs) where free_uds = uds { ud_binds = free_dbs, ud_calls = free_calls } @@ -3325,20 +3412,17 @@ callsForMe fn uds@MkUD { ud_binds = orig_dbs, ud_calls = orig_calls } calls_for_me = case lookupDVarEnv orig_calls fn of Nothing -> [] Just cis -> filterCalls cis orig_dbs - -- filterCalls: drop calls that (directly or indirectly) - -- refer to fn. See Note [Avoiding loops (DFuns)] ---------------------- filterCalls :: CallInfoSet -> FloatedDictBinds -> [CallInfo] --- Remove dominated calls (Note [Specialising polymorphic dictionaries]) --- and loopy DFuns (Note [Avoiding loops (DFuns)]) +-- Remove +-- (a) dominated calls: (MP3) in Note [Specialising polymorphic dictionaries] +-- (b) loopy DFuns: Note [Avoiding loops (DFuns)] filterCalls (CIS fn call_bag) (FDB { fdb_binds = dbs }) - | isDFunId fn -- Note [Avoiding loops (DFuns)] applies only to DFuns - = filter ok_call de_dupd_calls - | otherwise -- Do not apply it to non-DFuns - = de_dupd_calls -- See Note [Avoiding loops (non-DFuns)] + | isDFunId fn = filter ok_call de_dupd_calls -- Deals with (b) + | otherwise = de_dupd_calls where - de_dupd_calls = remove_dups call_bag + de_dupd_calls = removeDupCalls call_bag -- Deals with (a) dump_set = foldl' go (unitVarSet fn) dbs -- This dump-set could also be computed by splitDictBinds @@ -3352,10 +3436,10 @@ filterCalls (CIS fn call_bag) (FDB { fdb_binds = dbs }) ok_call (CI { ci_fvs = fvs }) = fvs `disjointVarSet` dump_set -remove_dups :: Bag CallInfo -> [CallInfo] +removeDupCalls :: Bag CallInfo -> [CallInfo] -- Calls involving more generic instances beat more specific ones. -- See (MP3) in Note [Specialising polymorphic dictionaries] -remove_dups calls = foldr add [] calls +removeDupCalls calls = foldr add [] calls where add :: CallInfo -> [CallInfo] -> [CallInfo] add ci [] = [ci] @@ -3364,12 +3448,20 @@ remove_dups calls = foldr add [] calls | otherwise = ci2 : add ci1 cis beats_or_same :: CallInfo -> CallInfo -> Bool +-- (beats_or_same ci1 ci2) is True if specialising on ci1 subsumes ci2 +-- That is: ci1's types are less specialised than ci2 +-- ci1 specialises on the same dict args as ci2 beats_or_same (CI { ci_key = args1 }) (CI { ci_key = args2 }) = go args1 args2 where - go [] _ = True + go [] [] = True go (arg1:args1) (arg2:args2) = go_arg arg1 arg2 && go args1 args2 - go (_:_) [] = False + + -- If one or the other runs dry, the other must still have a SpecDict + -- because of the (CI-KEY) invariant. So neither subsumes the other; + -- one is more specialised (faster code) but the other is more generally + -- applicable. + go _ _ = False go_arg (SpecType ty1) (SpecType ty2) = isJust (tcMatchTy ty1 ty2) go_arg UnspecType UnspecType = True ===================================== compiler/GHC/Core/Rules.hs ===================================== @@ -9,7 +9,7 @@ -- The 'CoreRule' datatype itself is declared elsewhere. module GHC.Core.Rules ( -- ** Looking up rules - lookupRule, matchExprs, + lookupRule, matchExprs, ruleLhsIsMoreSpecific, -- ** RuleBase, RuleEnv RuleBase, RuleEnv(..), mkRuleEnv, emptyRuleEnv, @@ -587,8 +587,8 @@ findBest :: InScopeSet -> (Id, [CoreExpr]) findBest _ _ (rule,ans) [] = (rule,ans) findBest in_scope target (rule1,ans1) ((rule2,ans2):prs) - | isMoreSpecific in_scope rule1 rule2 = findBest in_scope target (rule1,ans1) prs - | isMoreSpecific in_scope rule2 rule1 = findBest in_scope target (rule2,ans2) prs + | ruleIsMoreSpecific in_scope rule1 rule2 = findBest in_scope target (rule1,ans1) prs + | ruleIsMoreSpecific in_scope rule2 rule1 = findBest in_scope target (rule2,ans2) prs | debugIsOn = let pp_rule rule = ifPprDebug (ppr rule) (doubleQuotes (ftext (ruleName rule))) @@ -603,15 +603,25 @@ findBest in_scope target (rule1,ans1) ((rule2,ans2):prs) where (fn,args) = target -isMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool --- The call (rule1 `isMoreSpecific` rule2) +ruleIsMoreSpecific :: InScopeSet -> CoreRule -> CoreRule -> Bool +-- The call (rule1 `ruleIsMoreSpecific` rule2) -- sees if rule2 can be instantiated to look like rule1 --- See Note [isMoreSpecific] -isMoreSpecific _ (BuiltinRule {}) _ = False -isMoreSpecific _ (Rule {}) (BuiltinRule {}) = True -isMoreSpecific in_scope (Rule { ru_bndrs = bndrs1, ru_args = args1 }) - (Rule { ru_bndrs = bndrs2, ru_args = args2 }) - = isJust (matchExprs in_scope_env bndrs2 args2 args1) +-- See Note [ruleIsMoreSpecific] +ruleIsMoreSpecific in_scope rule1 rule2 + = case rule1 of + BuiltinRule {} -> False + Rule { ru_bndrs = bndrs1, ru_args = args1 } + -> ruleLhsIsMoreSpecific in_scope bndrs1 args1 rule2 + +ruleLhsIsMoreSpecific :: InScopeSet + -> [Var] -> [CoreExpr] -- LHS of a possible new rule + -> CoreRule -- An existing rule + -> Bool -- New one is more specific +ruleLhsIsMoreSpecific in_scope bndrs1 args1 rule2 + = case rule2 of + BuiltinRule {} -> True + Rule { ru_bndrs = bndrs2, ru_args = args2 } + -> isJust (matchExprs in_scope_env bndrs2 args2 args1) where full_in_scope = in_scope `extendInScopeSetList` bndrs1 in_scope_env = ISE full_in_scope noUnfoldingFun @@ -620,9 +630,9 @@ isMoreSpecific in_scope (Rule { ru_bndrs = bndrs1, ru_args = args1 }) noBlackList :: Activation -> Bool noBlackList _ = False -- Nothing is black listed -{- Note [isMoreSpecific] +{- Note [ruleIsMoreSpecific] ~~~~~~~~~~~~~~~~~~~~~~~~ -The call (rule1 `isMoreSpecific` rule2) +The call (rule1 `ruleIsMoreSpecific` rule2) sees if rule2 can be instantiated to look like rule1. Wrinkle: @@ -825,7 +835,7 @@ bound on the LHS: The rule looks like forall (a::*) (d::Eq Char) (x :: Foo a Char). - f (Foo a Char) d x = True + f @(Foo a Char) d x = True Matching the rule won't bind 'a', and legitimately so. We fudge by pretending that 'a' is bound to (Any :: *). ===================================== compiler/GHC/Core/Unify.hs ===================================== @@ -331,35 +331,57 @@ Wrinkles `DontBindMe`, the unifier must return `SurelyApart`, not `MaybeApart`. See `go_fam` in `uVarOrFam` -(ATF6) You might think that when /matching/ the um_fam_env will always be empty, - because type-class-instance and type-family-instance heads can't include type - families. E.g. instance C (F a) where ... -- Illegal - - But you'd be wrong: when "improving" type family constraint we may have a - type family on the LHS of a match. Consider +(ATF6) When /matching/ can we ever have a type-family application on the LHS, in + the template? You might think not, because type-class-instance and + type-family-instance heads can't include type families. E.g. + instance C (F a) where ... -- Illegal + + But you'd be wrong: even when matching, we can see type families in the LHS template: + * In `checkValidClass`, in `check_dm` we check that the default method has the + right type, using matching, both ways. And that type may have type-family + applications in it. Example in test CoOpt_Singletons. + + * In the specialiser: see the call to `tcMatchTy` in + `GHC.Core.Opt.Specialise.beats_or_same` + + * With -fpolymorphic-specialsation, we might get a specialiation rule like + RULE forall a (d :: Eq (Maybe (F a))) . + f @(Maybe (F a)) d = ... + See #25965. + + * A user-written RULE could conceivably have a type-family application + in the template. It might not be a good rule, but I don't think we currently + check for this. + + In all these cases we are only interested in finding a substitution /for + type variables/ that makes the match work. So we simply want to recurse into + the arguments of the type family. E.g. + Template: forall a. Maybe (F a) + Target: Mabybe (F Int) + We want to succeed with substitution [a :-> Int]. See (ATF9). + + Conclusion: where we enter via `tcMatchTy`, `tcMatchTys`, `tc_match_tys`, + etc, we always end up in `tc_match_tys_x`. There we invoke the unifier + but we do not distinguish between `SurelyApart` and `MaybeApart`. So in + these cases we can set `um_bind_fam_fun` to `neverBindFam`. + +(ATF7) There is one other, very special case of matching where we /do/ want to + bind type families in `um_fam_env`, namely in GHC.Tc.Solver.Equality, the call + to `tcUnifyTyForInjectivity False` in `improve_injective_wanted_top`. + Consider + of a match. Consider type family G6 a = r | r -> a type instance G6 [a] = [G a] type instance G6 Bool = Int - and the Wanted constraint [W] G6 alpha ~ [Int]. We /match/ each type instance - RHS against [Int]! So we try - [G a] ~ [Int] + and suppose we haev a Wanted constraint + [W] G6 alpha ~ [Int] +. According to Section 5.2 of "Injective type families for Haskell", we /match/ + the RHS each type instance [Int]. So we try + Template: [G a] Target: [Int] and we want to succeed with MaybeApart, so that we can generate the improvement - constraint [W] alpha ~ [beta] where beta is fresh. - See Section 5.2 of "Injective type families for Haskell". - - A second place that we match with type-fams on the LHS is in `checkValidClass`. - In `check_dm` we check that the default method has the right type, using matching, - both ways. And that type may have type-family applications in it. Example in - test CoOpt_Singletons. - -(ATF7) You might think that (ATF6) is a very special case, and in /other/ uses of - matching, where we enter via `tc_match_tys_x` we will never see a type-family - in the template. But actually we do see that case in the specialiser: see - the call to `tcMatchTy` in `GHC.Core.Opt.Specialise.beats_or_same` - - Also: a user-written RULE could conceivably have a type-family application - in the template. It might not be a good rule, but I don't think we currently - check for this. + constraint + [W] alpha ~ [beta] + where beta is fresh. We do this by binding [G a :-> Int] (ATF8) The treatment of type families is governed by um_bind_fam_fun :: BindFamFun @@ -399,6 +421,8 @@ Wrinkles Key point: when decomposing (F tys1 ~ F tys2), we should /also/ extend the type-family substitution. + (ATF11-1) All this cleverness only matters when unifying, not when matching + (ATF12) There is a horrid exception for the injectivity check. See (UR1) in in Note [Specification of unification]. @@ -595,7 +619,7 @@ tc_match_tys_x :: HasDebugCallStack -> [Type] -> Maybe Subst tc_match_tys_x bind_tv match_kis (Subst in_scope id_env tv_env cv_env) tys1 tys2 - = case tc_unify_tys alwaysBindFam -- (ATF7) in Note [Apartness and type families] + = case tc_unify_tys neverBindFam -- (ATF7) in Note [Apartness and type families] bind_tv False -- Matching, not unifying False -- Not an injectivity check @@ -1857,6 +1881,7 @@ uVarOrFam env ty1 ty2 kco = go_fam_fam tc1 tys1 tys2 kco -- Now check if we can bind the (F tys) to the RHS + -- This can happen even when matching: see (ATF7) | BindMe <- um_bind_fam_fun env tc1 tys1 rhs = -- ToDo: do we need an occurs check here? do { extendFamEnv tc1 tys1 rhs @@ -1881,11 +1906,6 @@ uVarOrFam env ty1 ty2 kco -- go_fam_fam: LHS and RHS are both saturated type-family applications, -- for the same type-family F go_fam_fam tc tys1 tys2 kco - | tcEqTyConAppArgs tys1 tys2 - -- Detect (F tys ~ F tys); otherwise we'd build an infinite substitution - = return () - - | otherwise -- Decompose (F tys1 ~ F tys2): (ATF9) -- Use injectivity information of F: (ATF10) -- But first bind the type-fam if poss: (ATF11) @@ -1902,13 +1922,19 @@ uVarOrFam env ty1 ty2 kco (inj_tys1, noninj_tys1) = partitionByList inj tys1 (inj_tys2, noninj_tys2) = partitionByList inj tys2 - bind_fam_if_poss | BindMe <- um_bind_fam_fun env tc tys1 rhs1 - = extendFamEnv tc tys1 rhs1 - | um_unif env - , BindMe <- um_bind_fam_fun env tc tys2 rhs2 - = extendFamEnv tc tys2 rhs2 - | otherwise - = return () + bind_fam_if_poss + | not (um_unif env) -- Not when matching (ATF11-1) + = return () + | tcEqTyConAppArgs tys1 tys2 -- Detect (F tys ~ F tys); + = return () -- otherwise we'd build an infinite substitution + | BindMe <- um_bind_fam_fun env tc tys1 rhs1 + = extendFamEnv tc tys1 rhs1 + | um_unif env + , BindMe <- um_bind_fam_fun env tc tys2 rhs2 + = extendFamEnv tc tys2 rhs2 + | otherwise + = return () + rhs1 = mkTyConApp tc tys2 `mkCastTy` mkSymCo kco rhs2 = mkTyConApp tc tys1 `mkCastTy` kco @@ -1993,7 +2019,7 @@ data UMState = UMState -- in um_foralls; i.e. variables bound by foralls inside the types being unified -- When /matching/ um_fam_env is usually empty; but not quite always. - -- See (ATF6) and (ATF7) of Note [Apartness and type families] + -- See (ATF7) of Note [Apartness and type families] newtype UM a = UM' { unUM :: UMState -> UnifyResultM (UMState, a) } ===================================== compiler/GHC/Tc/Solver/Equality.hs ===================================== @@ -3017,6 +3017,7 @@ improve_wanted_top_fun_eqs fam_tc lhs_tys rhs_ty improve_injective_wanted_top :: FamInstEnvs -> [Bool] -> TyCon -> [TcType] -> Xi -> TcS [TypeEqn] -- Interact with top-level instance declarations +-- See Section 5.2 in the Injective Type Families paper improve_injective_wanted_top fam_envs inj_args fam_tc lhs_tys rhs_ty = concatMapM do_one branches where @@ -3035,6 +3036,7 @@ improve_injective_wanted_top fam_envs inj_args fam_tc lhs_tys rhs_ty do_one branch@(CoAxBranch { cab_tvs = branch_tvs, cab_lhs = branch_lhs_tys, cab_rhs = branch_rhs }) | let in_scope1 = in_scope `extendInScopeSetList` branch_tvs , Just subst <- tcUnifyTyForInjectivity False in_scope1 branch_rhs rhs_ty + -- False: matching, not unifying = do { let inSubst tv = tv `elemVarEnv` getTvSubstEnv subst unsubstTvs = filterOut inSubst branch_tvs -- The order of unsubstTvs is important; it must be ===================================== compiler/GHC/Types/Basic.hs ===================================== @@ -87,7 +87,7 @@ module GHC.Types.Basic ( CompilerPhase(..), PhaseNum, beginPhase, nextPhase, laterPhase, Activation(..), isActive, competesWith, - isNeverActive, isAlwaysActive, activeInFinalPhase, + isNeverActive, isAlwaysActive, activeInFinalPhase, activeInInitialPhase, activateAfterInitial, activateDuringFinal, activeAfter, RuleMatchInfo(..), isConLike, isFunLike, ===================================== testsuite/tests/simplCore/should_compile/T25703.hs ===================================== @@ -0,0 +1,7 @@ +module T25703 where + +f :: (Eq a, Show b) => a -> b -> Int +f x y = f x y + +goo :: forall x. (Eq x) => x -> Int +goo arg = f arg (3::Int) ===================================== testsuite/tests/simplCore/should_compile/T25703.stderr ===================================== @@ -0,0 +1,2 @@ +Rule fired: SPEC f @_ @Int (T25703) +Rule fired: SPEC f @_ @Int (T25703) ===================================== testsuite/tests/simplCore/should_compile/T25703a.hs ===================================== @@ -0,0 +1,69 @@ +{-# LANGUAGE DataKinds #-} +{-# LANGUAGE GADTs #-} + +{-# OPTIONS_GHC -O2 -fspecialise-aggressively #-} + +-- This pragma is just here to pretend that the function body of 'foo' is huge +-- and should never be inlined. +{-# OPTIONS_GHC -funfolding-use-threshold=-200 #-} + +module T25703a where + +import Data.Kind +import Data.Type.Equality +import Data.Proxy +import GHC.TypeNats + +-- Pretend this is some big dictionary that absolutely must get +-- specialised away for performance reasons. +type C :: Nat -> Constraint +class C i where + meth :: Proxy i -> Double +instance C 0 where + meth _ = 0.1 +instance C 1 where + meth _ = 1.1 +instance C 2 where + meth _ = 2.1 + +{-# INLINEABLE foo #-} +foo :: forall a (n :: Nat) (m :: Nat) + . ( Eq a, C n, C m ) + => a -> ( Proxy n, Proxy m ) -> Int -> Double +-- Pretend this is a big complicated function, too big to inline, +-- for which we absolutely must specialise away the 'C n', 'C m' +-- dictionaries for performance reasons. +foo a b c + = if a == a + then meth @n Proxy + fromIntegral c + else 2 * meth @m Proxy + +-- Runtime dispatch to a specialisation of 'foo' +foo_spec :: forall a (n :: Nat) (m :: Nat) + . ( Eq a, KnownNat n, KnownNat m ) + => a -> ( Proxy n, Proxy m ) -> Int -> Double +foo_spec a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @0 Proxy Proxy + = foo @a @0 @0 a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @1 Proxy Proxy + = foo @a @0 @1 a b c + | Just Refl <- sameNat @n @1 Proxy Proxy + , Just Refl <- sameNat @m @1 Proxy Proxy + = foo @a @1 @1 a b c + | Just Refl <- sameNat @n @0 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @0 @2 a b c + | Just Refl <- sameNat @n @1 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @1 @2 a b c + | Just Refl <- sameNat @n @2 Proxy Proxy + , Just Refl <- sameNat @m @2 Proxy Proxy + = foo @a @2 @2 a b c + | otherwise + = error $ unlines + [ "f: no specialisation" + , "n: " ++ show (natVal @n Proxy) + , "m: " ++ show (natVal @m Proxy) + ] ===================================== testsuite/tests/simplCore/should_compile/T25703a.stderr ===================================== @@ -0,0 +1,6 @@ +Rule fired: SPEC foo @_ @2 @2 (T25703a) +Rule fired: SPEC foo @_ @1 @2 (T25703a) +Rule fired: SPEC foo @_ @0 @2 (T25703a) +Rule fired: SPEC foo @_ @1 @1 (T25703a) +Rule fired: SPEC foo @_ @0 @1 (T25703a) +Rule fired: SPEC foo @_ @0 @0 (T25703a) ===================================== testsuite/tests/simplCore/should_compile/T25965.hs ===================================== @@ -0,0 +1,18 @@ +{-# LANGUAGE TypeFamilies #-} +{-# OPTIONS_GHC -O -fpolymorphic-specialisation #-} + +module Foo where + +type family F a + +data T a = T1 + +instance Eq (T a) where { (==) x y = False } + +foo :: Eq a => a -> Bool +foo x | x==x = True + | otherwise = foo x + +bar :: forall b. b -> T (F b) -> Bool +bar y x = foo x + ===================================== testsuite/tests/simplCore/should_compile/all.T ===================================== @@ -543,3 +543,8 @@ test('T25883c', normal, compile_grep_core, ['']) test('T25883d', [extra_files(['T25883d_import.hs'])], multimod_compile_filter, ['T25883d', '-O -ddump-simpl -dno-typeable-binds -dsuppress-all -dsuppress-uniques', r'grep -e "y ="']) test('T25976', [grep_errmsg('Dead Code')], compile, ['-O -ddump-simpl -dsuppress-uniques -dno-typeable-binds']) + +test('T25965', normal, compile, ['-O']) +test('T25703', [grep_errmsg(r'SPEC')], compile, ['-O -fpolymorphic-specialisation -ddump-rule-firings']) +test('T25703a', [grep_errmsg(r'SPEC')], compile, ['-O -fpolymorphic-specialisation -ddump-rule-firings']) + View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/ce616f4976b6bdf9093372eb454787d… -- View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/ce616f4976b6bdf9093372eb454787d… You're receiving this email because of your account on gitlab.haskell.org.

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