Rodrigo Mesquita pushed to branch wip/romes/27461 at Glasgow Haskell Compiler / GHC Commits: ed261a7e by Cheng Shao at 2026-07-14T17:59:38-04:00 hadrian: fix HLS support This patch fixes hadrian's HLS support so one can rely on HLS when working on the hadrian codebase. Fixes #27480. Not building/linking shared libraries for hadrian is a severely premature optimization; this top-level setting in `cabal.project` only affects home packages while the dependencies in the cabal store are built with vanilla/dynamic anyway, and even adding dynamic builds to home packages would not be costly due to cabal's usage of `-dynamic-too`. - - - - - eee8ec5b by Cheng Shao at 2026-07-14T18:00:20-04:00 compiler: fix miscompiled %load_relaxed, add missing %store_relaxed This patch fixes the %load_relaxed cmm primop compilation logic to correctly use relaxed memory ordering, and adds the missing %store_relaxed primop. Parsing logic of %load/%store with explicit ordering is covered in the AtomicFetch test case. Fixes #27483. Co-authored-by: Codex <codex@openai.com> - - - - - 1718230f by Alan Zimmerman at 2026-07-14T18:01:06-04:00 EPA: Keep binds and sigs together in HsValBindsLR We combine them into a single list for GhcPs, wrapped in the ValBind data type, which is the bind equivalent of ValD, having constructors for binds and sigs. This simplifies exact print processing, especially when using it to update the contents of local binds, as we no longer need AnnSortKey BindTag - - - - - 6bd1ad2a by Andreas Klebinger at 2026-07-14T18:01:49-04:00 Bump nofib submodule to account for MonoLocalBinds. New versions of GHC enable MonoLocalBinds by default. This breaks some of the benchmarks. I've fixed this and this bump pulls in that fix. - - - - - 7eb0f1c9 by Cheng Shao at 2026-07-14T18:02:31-04:00 testsuite: fix bytecodeIPE test under +ipe flavours This patch fixes the bytecodeIPE test under +ipe flavours. It used to fail under +ipe because the RTS is built with IPE info, then stg_AP_info in RTS carries IPE info, so whereFrom wouldn't return Nothing. Now the test checks IPE info of a datacon in the ghci-loaded module which is not affected by whether the RTS is built with IPE info or not. Fixes #27498. Co-authored-by: Codex <codex@openai.com> - - - - - ef038aae by cydparser at 2026-07-15T04:35:41-04:00 Reduce bytes allocated for `capabilities` in RTS (fixes #27487) In rts/Capability.c, `capabilities` is an array of pointers, but it was allocated as if it were an array of Capability's. - - - - - d377e83e by Cheng Shao at 2026-07-15T04:36:27-04:00 rts: fix missing UNTAG in stg_readTVarIOzh This patch fixes missing UNTAG on the current value closure read from StgTVar. UNTAG is a no-op when it's stg_TREC_HEADER_info which is word aligned; it may be a tagged closure, and reading info table from the tagged address is an unaligned load which may cause issues on platforms with strict alignment requirements. Co-authored-by: Codex <codex@openai.com> - - - - - 8ed03842 by Cheng Shao at 2026-07-15T04:36:27-04:00 rts: fix missing UNTAG in stg_control0zh_ll This patch fixes missing UNTAG on the cont closure returned by captureContinuationAndAbort. In case it's not NULL, captureContinuationAndAbort returns a tagged StgContinuation closure, in which case it must be untagged before accessing the apply_mask_frame field. In the past it worked out of luck: when apply_mask_frame was NULL then mask_frame_offset is also 0 so the control flow didn't diverge to a wrong path. Still, this is horribly wrong and will crash once StgContinuation struct is refactored and fields are shuffled around. Co-authored-by: Codex <codex@openai.com> - - - - - 5aa7000a by Cheng Shao at 2026-07-15T04:37:08-04:00 compiler: fix redundant AP thunk codegen when not using -ticky-ap-thunk This patch fixes a double negation confusion in !7525 that results in some redundant AP thunk code generation when not using -ticky-ap-thunk. Now, we use `stgToCmmUseStdApThunk` to indicate whether precomputed AP thunks in the RTS should be used, which defaults to `True`, unless `-ticky-ap-thunk` is passed. `-finfo-table-map` now also implies `-ticky-ap-thunk`, since when doing IPE profiling we want the generated AP thunks to be unique. Fixes #27502. ------------------------- Metric Decrease: T3064 ------------------------- Co-authored-by: Codex <codex@openai.com> - - - - - d43a7b7a by Brian McKenna at 2026-07-15T20:10:04+02:00 Strip ticks when desugaring bool guards The special `considerAccessible` pattern was broken when compiling with debug info. Compiling with debug info wraps expressions with `SourceNote` ticks, which broke the internals of the `desugarBoolGuard` function. Ticks are now ignored within this function. Fixes #27360 - - - - - ede4b17b by Ben Gamari at 2026-07-15T22:59:53-04:00 base: Display ExceptionContext in WhileHandling's textual description As originally-implemented the implementation for `WhileHandling(displayExceptionAnnotation)` would display the `ExceptionContext` of the exception which it carries (as this was the behavior of `displayException`, in terms of which `displayExceptionAnnotation` was implemented). However, in 284ffab3 the definition of `SomeException(displayException)` was changed to exclude the `ExceptionContext`. This means that `WhileHandling(displayExceptionAnnotation)` fails to describe the provenance of the exception which it captures, greatly limiting its utility. Return the implementation to its originally-specified behavior by implementing `WhileHandling(displayExceptionAnnotation)` in terms of `displayExceptionWithInfo`. Fixes #27456. - - - - - 0f64f348 by Cheng Shao at 2026-07-16T15:41:08+00:00 ci: add missing docker permission workaround in abi-test job - - - - - 660cb239 by Cheng Shao at 2026-07-16T19:37:48+00:00 bindist: Fix make install -j race condition on macos/freebsd This patch fixes make install -j race condition on macos/freebsd. BSD install fails with EEXIST when multiple install processes concurrently create the same prefix directory. So we add an `install_dirs` prerequisite job that sequentially creates the directories for subsequent jobs to work with. Fixes #27499. Co-authored-by: Codex <codex@openai.com> - - - - - 08130257 by Cheng Shao at 2026-07-16T19:37:48+00:00 ci: run bindist make install with -j This patch makes the ci scripts run `make install` with `-j` to reduce wall clock time when installing the bindist, see related issue for benchmark numbers. This only affects ghc ci logic, the user-facing default is up to distributors and is still `-j1`. Closes #27029. - - - - - d5ae6906 by Adam Gundry at 2026-07-17T04:57:43-04:00 Mark various language extension flags as deprecated (see #27329) The following language extensions are now deprecated: - AlternativeLayoutRule - AlternativeLayoutRuleTransitional - ParallelArrays - PolymorphicComponents - Rank2Types In addition, the warning `-Walternative-layout-rule-transitional` has been marked as deprecated, as it is emitted only under the deprecated extension `XAlternativeLayoutRuleTransitional`. - - - - - fe3b059c by Andrew Lelechenko at 2026-07-17T04:58:26-04:00 base: re-export GHC.Environment.getFullArgs from System.Environment CLC proposal https://github.com/haskell/core-libraries-committee/issues/431 - - - - - 722236dd by sheaf at 2026-07-18T08:48:31-04:00 Coercion optimisation: avoid double-Sym for InstCo Ticket #27374 pointed out an issue with GHC.Core.Coercion.Opt.optCoercion's handling of InstCo: it contravened (LC2) in Note [The LiftingContext in optCoercion] because it applied the ambient 'sym' to a coercion that was then added to the lifting context substitution. Fixes #27374 Co-authored-by: Simon Jakobi <simon.jakobi@gmail.com> - - - - - ff70fc75 by sheaf at 2026-07-18T08:48:31-04:00 Coercion optimisation: avoid exponential behaviour The change to coercion optimisation of 'InstCo' in the previous commit introduces exponential behaviour to the coercion optimiser. To avoid this, this commit provides a way to push in 'Sym' of an already-optimised coercion: GHC.Core.Coercion.Opt.mkDeepSymCo. See Note [Pushing Sym without re-optimising] in GHC.Core.Coercion.Opt. - - - - - dfef27f0 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Move THREADED_RTS-conditional struct members to end of Capability Accessing members of the Capability struct from CMM code rely on accessor macros. (The macros are generated by deriveConstants). These macros have a single definition. This means that the offsets of all struct members must *not* vary based on THREADED_RTS vs !THREADED_RTS. This requires that any struct members that are conditional on THREADED_RTS must occur after the unconditional struct members. Hence we move all the ones that are conditional on THREADED_RTS to the end. Add a deriveConstants entry for the iomgr member of the Capability struct, which was the motivation for this change. Add warning messages to help our future selves. Debugging this took me a couple hours in gdb! - - - - - c254e022 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Make the IOManager API use CapIOManager rather than Capability This makes the API somewhat more self-contained and more consistent. Now the IOManager API and each of the backends takes just the I/O manager structure. Previously we had a bit of a mixture, depending on whether the function needed access to the Capability or just the CapIOManager. We still need access to the cap, so we introduce a back reference to reach the capability, via iomgr->cap. Convert all uses in select and poll backends, but not win32 ones. Convert callers in the scheduler and elsewhere. Also convert the three CMM primops that call IOManager APIs. They just need to use Capability_iomgr(MyCapability()). - - - - - 4f3d8f31 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Split posix/MIO.c out of posix/Signals.c The MIO I/O manager was secretly living inside the Signals file. Now it gets its own file, like any other self-respecting I/O manager. - - - - - 52ce04a9 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Rationalise some scheduler run queue utilities Move them all to the same place in the file. Make some static that were used only internally. Also remove a redundant assignment after calling truncateRunQueue that is already done within truncateRunQueue. - - - - - 75bbdebc by Duncan Coutts at 2026-07-18T08:49:12-04:00 Rename initIOManager{AfterFork} to {re}startIOManager These are more accurate names, since these actions happen after initialisation and are really about starting (or restarting) background threads. - - - - - 724c0517 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Free per-cap I/O managers during shutdown and forkProcess Historically this was not strictly necessary. The select and win32 legacy I/O managers did not maintain any dynamically allocated resources. The new poll one does (an auxillary table), and so this should be freed. After forkProcess, all threads get deleted. This includes threads waiting on I/O or timers. So as of this patch, resetting the I/O manager is just about tidying things up. For example, for the poll I/O manager this will reset the size of the AIOP table (which otherwise grows but never shrinks). In future however the re-initialising will become neeecessary for functionality, since some I/O managers will need to re-initialise wakeup fds that are set CLOEXEC. - - - - - c007d122 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Add a TODO to the MIO I/O manager The direction of travel is to make I/O managers per-capability and have all their state live in the struct CapIOManager. The MIO I/O manager however still has a number of global variables. It's not obvious how handle these globals however. - - - - - b65ab7b3 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Add a FIXME note in the Poll I/O manager - - - - - daf2bd6f by Duncan Coutts at 2026-07-18T08:49:12-04:00 Add missing updateRemembSetPushClosure in poll I/O manager For the non-moving GC. - - - - - e33ca830 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Minor doc improvement to struct StgAsyncIOOp member outcome Mention the enumeration names, as well as their numeric values. The rest of the code uses the enum names. - - - - - 4edd2579 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Minor doc improvements for StgTSOBlockInfo Clarify that certain union members are used only by certain legacy I/O managers. Hopefully we will be able to remove these at some point. - - - - - 536bedbb by Duncan Coutts at 2026-07-18T08:49:12-04:00 Avoid exporting various win32-specific rts symbols The BeginPrivate.h / EndPrivate.h scheme works perfectly well on Windows, but all of the rts/win32/*.h files were not using it. - - - - - 8139b5ac by Duncan Coutts at 2026-07-18T08:49:12-04:00 Remove wakeupIOManager, ioManagerWakeup and setIOManagerWakeupFd We no longer need wakeupIOManager for the threaded RTS case, so we can remove it and the bits only needed to support it. This includes the pipe/eventfd fd shared between the RTS and the in-library I/O manager used for waking up the I/O manager thread. The pipe/eventfd still exists, but it no longer has to be communicated to the RTS, since the RTS no longer needs to use it. So we remove the RTS API export setIOManagerWakeupFd, and remove uses of it within the I/O managers in ghc-internal. - - - - - 74fe7c66 by Duncan Coutts at 2026-07-18T08:49:12-04:00 Add a new interruptIOManager API for the I/O managers It will be used to interrupt awaitCompletedTimeoutsOrIO. Also update the return type and docs for awaitCompletedTimeoutsOrIO to have it return false when it gets interrupted, and have no useful post condition in that case. - - - - - 38792843 by Duncan Coutts at 2026-07-18T08:49:13-04:00 Add interruptIOManager support for select I/O manager Uses the FdWakup mechanism. - - - - - 2f3b00aa by Duncan Coutts at 2026-07-18T08:49:13-04:00 Add interruptIOManager support for poll I/O manager Uses the FdWakup mechanism. A quirk we have to cope with is that we now need to poll one more fd -- the wakeup_fd_r -- but this fd has no corresponding entry in the aiop_table. This is awkward since we have set up our aiop_poll_table to be an auxilliary table with matching indicies. The solution this patch uses (and described in the comments) is to have two tables: struct pollfd *aiop_poll_table, *full_poll_table; and to have the aiop_poll_table alias the tail of the full_poll_table. The head entry in the full_poll_table is the extra fd. So we poll the full_poll_table, while the aiop_poll_table still has matching indicies with the aiop_table. Hurrah for C aliasing rules. - - - - - cee50131 by Duncan Coutts at 2026-07-18T08:49:13-04:00 Add interruptIOManager support for win32 legacy I/O manager And remove unused related helper resetAbandonRequestWait. It is not called because the event is created in auto-reset mode, so never needs to be reset manually. - - - - - cf453143 by Duncan Coutts at 2026-07-18T08:49:13-04:00 Note lack of interruptIOManager support for WinIO I/O manager Though there's a plausible design, we can't sanely test it at the moment due to related WinIO bugs. Filed as issue #27403. - - - - - 1b74a0ad by Duncan Coutts at 2026-07-18T08:49:13-04:00 Be more explicit about enum IOReadOrWrite values, and type within cmm Belt and braces. - - - - - b388d093 by Brian McKenna at 2026-07-18T17:51:50-04:00 Ignore ticks in the pattern-match term oracle The term-oracle in the pattern-match checker is keyed by a canonical form of the scrutinee, computed by `makeDictsCoherent`. That canonical form was tick-sensitive: two occurrences of an otherwise identical expression that happened to carry different ticks were treated as distinct values, breaking long-distance information. This shows up in practice under `-finfo-table-map`, because the desugarer wraps every record-selector use site in a `SourceNote` carrying that site's span. For example: data Box = Box { unBox :: Maybe Int } f b = case unBox b of Nothing -> 0 Just _ -> let Just x = unBox b in x The two `unBox b` expressionss carry different SourceNote spans, the pattern-match checker sees them as different, the long-distance information from the outer `Just _` branch never reaches the let-pattern, and `Just x = unBox b` is wrongly reported as non-exhaustive. We now strip all ticks in `makeDictsCoherent`. This is documented as Wrinkle (UD1) of Note [Unique dictionaries in the TmOracle CoreMap]. Fixes #27314 - - - - - c23e1acb by Mrjtjmn at 2026-07-18T17:52:45-04:00 Add explanations for unsolved Typeable constraints This commit adds explanations for unsolved 'Typeable' constraints. GHC will now provide additional explanations for an unsolved constraint of the form 'Typeable ty', explain why GHC did not solve Typeable constraint. e.g.: - 'ty' is a polymorphic type (e.g. forall a. a -> a) - 'ty' is a qualified type (e.g. Eq Int => Int) - 'ty' is an unboxed sum type - 'ty' is an unreduced type family application - 'ty' whose kind is not typeable Fixes #26532 - - - - - cbef021e by Artem Pelenitsyn at 2026-07-19T07:49:55-04:00 ghc-internal: Lock.hs: fix typo and indentation - - - - - 42918646 by Duncan Coutts at 2026-07-19T07:50:36-04:00 Fix failing test GcStaticPointers for non-moving GC Minor mistake in asserting something before checking for that same thing. Specifically, Bdescr asserts HEAP_ALLOCED_GC, but Bdescr was being used prior to a guard that checks HEAP_ALLOCED_GC. The solution is just to move the use of Bdescr after the guard. Thanks to Simon Jakobi for identifying the problem. - - - - - c2f6dcd4 by Sasha Bogicevic at 2026-07-20T10:31:56+02:00 Improve error messages for invalid record wildcards Record wildcard hints are now shown in more contexts and include constructor arity; matching with `..` on a fieldless constructor now produces a dedicated error message. Fixes #21101 - - - - - 4c02e76b by Duncan Coutts at 2026-07-21T10:37:21-04:00 Mark test T27105 as fragile, citing issue #27522 Scheduler fairness is fine, except when it isn't. And it isn't on CI machines surprisingly often! See the issue for details. - - - - - 43dd2b15 by Recursion Ninja at 2026-07-21T17:09:53-04:00 Resolving many TTG related orphan type-class instances This is part a technical debt removal effort made possible now that separating out the AST via TTG has come to a close. As the AST in 'L.H.S' has been incrementally separated from the GHC internals, there are many accumulated orphan instance of 'Binary', 'NFData', 'Outputable', and 'Uniquable'. The orphan instance of data-types from within 'L.H.S' have had their orphan instances moved to either: 1. The module which defines the data-type 2. The module which defines the type-class; i.e. moving an orphan 'Binary' instance to 'GHC.Utils.Binary' Orphan instances resolved (37): | Data-type | Resolved instance(s) | Former orphan module(s) | | -------------------- | -------------------------- | ------------------------- | | Role | Binary, NFData, Outputable | GHC.Core.Coercion.Axiom | | SrcStrictness | Binary, NFData, Outputable | GHC.Core.DataCon | | SrcUnpackedness | Binary, NFData, Outputable | GHC.Core.DataCon | | Fixity | Binary, Outputable | GHC.Hs.Basic | | FixityDirection | Binary, Outputable | GHC.Hs.Basic | | LexicalFixity | Outputable | GHC.Hs.Basic | | CCallTarget | NFData | GHC.Hs.Decls.Foreign | | CType | NFData | GHC.Hs.Decls.Foreign | | Header | NFData | GHC.Hs.Decls.Foreign | | OverlapMode | Binary, NFData | GHC.Hs.Decls.Overlap | | WithHsDocIdentifiers | NFData, Outputable | GHC.Hs.Doc | | HsDocString | NFData | GHC.Hs.DocString | | HsDocStringChunk | Binary, Outputable | GHC.Hs.DocString | | HsDocStringDecorator | Binary, Outputable | GHC.Hs.DocString | | NamespaceSpecifier | Outputable | GHC.Hs.ImpExp | | ForAllTyFlag | Binary, NFData, Outputable | GHC.Hs.Specificity | | Specificity | Binary, NFData | GHC.Hs.Specificity | | PromotionFlag | Binary, Outputable | GHC.Types.Basic | | FieldLabelString | Outputable, Uniquable | GHC.Types.FieldLabel | | InlinePragma | Binary | GHC.Types.InlinePragma | ------------------------- Metric Decrease: hard_hole_fits ------------------------- Closes #21262, #27469 - - - - - ab9ab895 by Cheng Shao at 2026-07-21T17:10:53-04:00 rts: always use StgInt to represent cost center id Currently cost center id is modeled as `Int` and it should be `StgInt` uniformly in the RTS, hence this patch. Fixes #27524. - - - - - 94d8f83b by Cheng Shao at 2026-07-22T11:30:40-04:00 hadrian: clean up stale cabal package flags in the tree This patch cleans up stale cabal package flags in the tree and related hadrian/autoconf logic. Closes #27474. Co-authored-by: Codex <codex@openai.com> - - - - - 0bf1d8c9 by Sasha Bogicevic at 2026-07-22T11:31:21-04:00 parser: don't suggest ImportQualifiedPost when it is already enabled -Wprepositive-qualified-module unconditionally attached a hint to enable ImportQualifiedPost, even when the extension was already on (as it is by default under GHC2021). Record the extension's state in the PsWarnImportPreQualified diagnostic and drop the hint when it is already enabled. Fixes #27380 - - - - - 700a1dd1 by Simon Jakobi at 2026-07-23T11:21:20-04:00 ci: Reduce lint job setup costs Avoid fetching unnecessary history and submodules for lightweight lint jobs. Run changelog validation without Hadrian. Because the lint-author job is now based on the .lint template directly, we enhance it to allow Git to read from the runner-owned checkouts, In the previously used .lint-params template, this permissions issue was addressed via `chown`. Closes #27521. Assisted-by: gpt-5.6-sol via Codex CLI - - - - - 26a44fb0 by ARATA Mizuki at 2026-07-23T11:22:10-04:00 testsuite: Fix memory issues of doublex2_* and simd010 doublex2_* had reads from uninitialized memory. simd010 had out-of-bounds array access. Fixes #27544 - - - - - 455525b3 by Rodrigo Mesquita at 2026-07-23T18:26:17+01:00 loopImports: Don't dup ms_uid in summary imports We were writing the ms_unitid of the mod summary with every single import of that module That complicated the code (as though the UnitId in that list could ever be something else) and also allocates unnecessarily per every mod import. Very slight allocation decrease measured locally in a few tests: (MultiComponentModulesRecomp: -0.06%; MultiComponentModulesRecomp100: -0.05%) Purely a clean up. - - - - - 6f7f0dd2 by Rodrigo Mesquita at 2026-07-23T18:26:17+01:00 downsweep: make control flow simpler and cache correct This refactor extracts the control flow of downsweep into a single function `dfsBuild`, which takes care of iteratively expanding and traversing all nodes of the in-construction module graph necessary to build a full `ModuleGraph`. There are three levels of caching going on, all of which are necessary to make sure we don't do repeated work (notably, NEVER summarise the same module twice). 1. `dfsBuild` accumulates the final module graph and never revisits the same node of the module graph. Cache is keyed by the final `ModuleGraph`s `NodeKey`s. 2. For Module A in home-unit u1, each import in the list of imports needs to be *found* (call to `findImportedModuleWithIsBoot`): at this point, we only have the `ModuleName` of the import, not the `Module`. This *finding* is somewhat expensive, so we cache it as well (`ImportsCache`). The cache key is the home-unit to which the module belongs~[1], the import package qualifier, and the ModuleName. [1] Different home-units will have different package flags, which means potentially different `Module` resolution for the same `ModuleName`. 3. The most expensive operation we want to avoid is summarising a `Module` into a `ModSummary`, which notably involves parsing the module header from scratch. The third cache, in essence, maps a `Module` to its `ModSummary` (named `ModSummaryCache`). This cache upholds the invariant: we NEVER summarise the same module twice. In practice, the cache key is the Module's UnitId and the Source path; the reason is we need to distinguish between `.hs` and `.hs-boot` files, as their summaries will differ. Note that (2) can't guarantee this alone: Two ModuleName imports in separate units can (and likely do) map to the same `Module`. Note that the previous implementation failed to achieve the no-duplicate-work summarisation invariant, and we ended up doing a quadratic amount of processing in scenarios like test `MultiComponentModules100`. See also Note [Downsweep Control Flow and Caching] Fixes #27461 Perf changes: MultiComponentModules(normal) ghc/alloc 2,097,389,264 1,992,186,736 -5.0% GOOD MultiComponentModules100(normal) ghc/alloc 24,310,173,770 21,293,867,360 -12.4% GOOD MultiComponentModulesRecomp(normal) ghc/alloc 602,761,394 498,543,984 -17.3% GOOD MultiComponentModulesRecomp100(normal) ghc/alloc 11,885,968,240 8,895,404,864 -25.2% GOOD ------------------------- Metric Decrease: MultiComponentModules MultiComponentModules100 MultiComponentModulesRecomp MultiComponentModulesRecomp100 ------------------------- - - - - - 1e697cf8 by Rodrigo Mesquita at 2026-07-23T18:26:17+01:00 implicitRequirementsShallow can never reach HoleUnit findImportedModule will never return `HoleUnit` for a `ModuleName` (a `HoleUnit` can only be found as a signature instantiation, never as a directly *imported* thing) Therefore, we can drop `[ModuleName]` returned by `implicitRequirementsShallow`, which makes many things dead code. Namely, the call to `implicitRequirementsShallow` from GHC.Driver.Downsweep which was a performance bottleneck (for doing lots of duplicate work in findImportedModule) is now entirely gone. Fixes #27053 In an MR with this patch and the downsweep refactor (previous commit), CI says: MultiComponentModules(normal) ghc/alloc 2,097,396,728 1,943,662,304 -7.3% GOOD MultiComponentModules100(normal) ghc/alloc 24,310,182,136 17,227,574,440 -29.1% GOOD MultiComponentModulesRecomp(normal) ghc/alloc 602,769,518 449,973,656 -25.3% GOOD MultiComponentModulesRecomp100(normal) ghc/alloc 11,885,976,408 4,828,894,160 -59.4% GOOD and the Cabal test (building Cabal with ghc --make) improves in the total time reported by +RTS -s from 54s to 40s reliably on my machine with default+profiled_ghc flavour. That's a 25% reduction in total run time! ------------------------- Metric Decrease: MultiComponentModules MultiComponentModules100 MultiComponentModulesRecomp MultiComponentModulesRecomp100 ------------------------- - - - - - a0d9d66c by Rodrigo Mesquita at 2026-07-23T18:26:17+01:00 downsweep: Cache negative results When traversing a module graph structure, a uniquely identified node should always expand to the same thing. I don't see how visiting the same node which failed to be expanded a first time would ever successfully expand the second time we try to expand it (eg. when coming from a different edge to it -- it is still the same node!). The node expansion is local, based just based on the node itself, not on the path to get there. Therefore, this patch removes the weird behavior and commentary of `dfsBuild` wrt to `Nothing` not being cached and being potentially expanded a second time around to something different, which was misleading and, ultimately, incorrect. Now, we have a `MGRes`, which is more explicit about a node being Skipped just being a node that is ignored whenever it is found (and that skip is cached) -- and we may want to do this due to failures or due to just trying nodes which might not work on purpose, like hs-boots. We uniformly cache positive and negative results and remove the assumption that there might be an ordering in which the same node visited at a later time might be expanded differently. This makes it possible to traverse the module nodes in parallel without a change in behavior, since there's no longer a hidden ordering requirement. - - - - - c501cdea by Rodrigo Mesquita at 2026-07-23T18:26:17+01:00 Organize and clean-up GHC.Driver.Downsweep Simply some cosmetic changes, moving definitions around to structure the module better into its relevant sections (In go (ns ++ ss), it's not a problem to use ++ because it's a good producer and we won't have to append fully before processing the next item in go) - - - - - 9a28992c by Rodrigo Mesquita at 2026-07-23T18:26:57+01:00 fixup! Organize and clean-up GHC.Driver.Downsweep - - - - - 244 changed files: - .gitlab-ci.yml - .gitlab/ci.sh - + changelog.d/21101 - + changelog.d/27380 - + changelog.d/T26532 - + changelog.d/T27314.md - + changelog.d/T27329 - + changelog.d/T27360 - + changelog.d/T27374 - + changelog.d/T27456 - + changelog.d/downsweep-refactor - + changelog.d/fix-cmm-atomic-load-store - + changelog.d/fix-make-install-j - + changelog.d/fix-use-std-ap-thunk - compiler/GHC/Cmm/Parser.y - compiler/GHC/Core/Coercion/Axiom.hs - compiler/GHC/Core/Coercion/Opt.hs - compiler/GHC/Core/DataCon.hs - compiler/GHC/Driver/Backpack.hs - compiler/GHC/Driver/Config/StgToCmm.hs - compiler/GHC/Driver/Downsweep.hs - compiler/GHC/Driver/Flags.hs - compiler/GHC/Driver/Session.hs - compiler/GHC/Hs/Basic.hs - compiler/GHC/Hs/Binds.hs - compiler/GHC/Hs/Decls/Overlap.hs - compiler/GHC/Hs/Doc.hs - compiler/GHC/Hs/DocString.hs - compiler/GHC/Hs/ImpExp.hs - compiler/GHC/Hs/Instances.hs - − compiler/GHC/Hs/Specificity.hs - compiler/GHC/Hs/Utils.hs - compiler/GHC/HsToCore/Pmc/Desugar.hs - compiler/GHC/HsToCore/Pmc/Solver.hs - compiler/GHC/HsToCore/Quote.hs - compiler/GHC/HsToCore/Ticks.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Parser/Annotation.hs - compiler/GHC/Parser/Errors/Ppr.hs - compiler/GHC/Parser/Errors/Types.hs - compiler/GHC/Parser/PostProcess.hs - compiler/GHC/Rename/Bind.hs - compiler/GHC/Rename/Env.hs - compiler/GHC/Rename/Expr.hs - compiler/GHC/Rename/Module.hs - compiler/GHC/Rename/Names.hs - compiler/GHC/Rename/Pat.hs - compiler/GHC/Rename/Utils.hs - compiler/GHC/Runtime/Eval.hs - compiler/GHC/StgToCmm/Bind.hs - compiler/GHC/StgToCmm/Config.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Ppr.hs - compiler/GHC/Tc/Errors/Types.hs - compiler/GHC/Tc/Instance/Typeable.hs - compiler/GHC/Tc/Types/Rank.hs - compiler/GHC/Tc/Utils/Backpack.hs - compiler/GHC/ThToHs.hs - compiler/GHC/Types/Basic.hs - compiler/GHC/Types/FieldLabel.hs - compiler/GHC/Types/Fixity.hs - compiler/GHC/Types/ForeignCall.hs - compiler/GHC/Types/GREInfo.hs - compiler/GHC/Types/Hint.hs - compiler/GHC/Types/Hint/Ppr.hs - compiler/GHC/Types/InlinePragma.hs - compiler/GHC/Types/Unique.hs - compiler/GHC/Types/Var.hs - compiler/GHC/Utils/Binary.hs - compiler/GHC/Utils/Outputable.hs - compiler/Language/Haskell/Syntax/Basic.hs - compiler/Language/Haskell/Syntax/Binds.hs - compiler/Language/Haskell/Syntax/Decls/Foreign.hs - compiler/Language/Haskell/Syntax/Doc.hs - compiler/Language/Haskell/Syntax/Extension.hs - compiler/Language/Haskell/Syntax/ImpExp.hs - compiler/Language/Haskell/Syntax/Specificity.hs - compiler/ghc.cabal.in - configure.ac - distrib/configure.ac.in - docs/users_guide/expected-undocumented-flags.txt - docs/users_guide/exts/rank_polymorphism.rst - docs/users_guide/exts/static_pointers.rst - ghc/GHCi/UI.hs - hadrian/bindist/Makefile - hadrian/cabal.project - hadrian/cfg/system.config.host.in - hadrian/cfg/system.config.target.in - hadrian/src/Oracles/Flag.hs - hadrian/src/Rules/Generate.hs - hadrian/src/Rules/Test.hs - hadrian/src/Settings/Packages.hs - libraries/base/changelog.md - libraries/base/src/System/Environment.hs - libraries/base/tests/T15349.stderr - libraries/ghc-internal/ghc-internal.cabal.in - libraries/ghc-internal/src/GHC/Internal/Event/Control.hs - libraries/ghc-internal/src/GHC/Internal/Event/Manager.hs - libraries/ghc-internal/src/GHC/Internal/Event/TimerManager.hs - libraries/ghc-internal/src/GHC/Internal/Exception/Type.hs - libraries/ghc-internal/src/GHC/Internal/IO/Handle/Lock.hs - libraries/ghc-internal/tests/backtraces/T14532b.stdout - m4/fp_check_pthreads.m4 - nofib - rts/Capability.c - rts/Capability.h - rts/ContinuationOps.cmm - rts/IOManager.c - rts/IOManager.h - rts/IOManagerInternals.h - rts/PrimOps.cmm - rts/Profiling.c - rts/RaiseAsync.c - rts/RtsStartup.c - rts/RtsSymbols.c - rts/Schedule.c - rts/Schedule.h - rts/Trace.c - rts/Trace.h - rts/eventlog/EventLog.c - rts/eventlog/EventLog.h - rts/include/rts/IOInterface.h - rts/include/rts/storage/Closures.h - rts/include/rts/storage/TSO.h - rts/posix/FdWakeup.h - + rts/posix/MIO.c - + rts/posix/MIO.h - rts/posix/Poll.c - rts/posix/Poll.h - rts/posix/Select.c - rts/posix/Select.h - rts/posix/Signals.c - rts/posix/Signals.h - rts/posix/Timeout.c - rts/posix/Timeout.h - rts/rts.cabal - rts/sm/NonMovingMark.c - rts/win32/AsyncMIO.c - rts/win32/AsyncMIO.h - rts/win32/AsyncWinIO.h - rts/win32/AwaitEvent.c - rts/win32/AwaitEvent.h - rts/win32/ConsoleHandler.h - rts/win32/MIOManager.h - rts/win32/ThrIOManager.h - rts/win32/WorkQueue.h - rts/win32/veh_excn.h - testsuite/tests/backpack/should_compile/T13149.bkp - testsuite/tests/cmm/should_run/AtomicFetch.hs - testsuite/tests/cmm/should_run/AtomicFetch_cmm.cmm - testsuite/tests/codeGen/should_run/cgrun025.stderr - testsuite/tests/concurrent/should_run/T27105.hs - testsuite/tests/concurrent/should_run/all.T - + testsuite/tests/corelint/T27374.hs - testsuite/tests/corelint/all.T - testsuite/tests/count-deps/CountDepsParser.stdout - testsuite/tests/determinism/determ017/A.hs - testsuite/tests/exceptions/T26759.stderr - testsuite/tests/ghc-api/fixed-nodes/FixedNodes.hs - testsuite/tests/ghc-api/fixed-nodes/InterfaceModuleGraph.hs - testsuite/tests/ghc-api/fixed-nodes/ModuleGraphInvariants.hs - testsuite/tests/ghc-e/should_fail/T18441fail7.stderr - testsuite/tests/ghci/scripts/T12005.script - testsuite/tests/ghci/scripts/bytecodeIPE.hs - testsuite/tests/haddock/perf/Fold.hs - testsuite/tests/indexed-types/should_fail/T7354.hs - testsuite/tests/interface-stability/base-exports.stdout - testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs - testsuite/tests/interface-stability/base-exports.stdout-mingw32 - testsuite/tests/layout/layout001.stdout - testsuite/tests/layout/layout002.stdout - testsuite/tests/layout/layout003.stdout - testsuite/tests/layout/layout004.stdout - testsuite/tests/layout/layout005.stdout - testsuite/tests/layout/layout006.stdout - testsuite/tests/layout/layout007.stdout - testsuite/tests/layout/layout008.stdout - testsuite/tests/layout/layout009.stdout - testsuite/tests/linear/should_compile/T1735Min.hs - testsuite/tests/mdo/should_fail/mdofail006.stderr - + testsuite/tests/module/T27380.hs - + testsuite/tests/module/T27380.stderr - testsuite/tests/module/all.T - testsuite/tests/module/mod184.stderr - testsuite/tests/parser/should_compile/DumpSemis.stderr - + testsuite/tests/parser/should_compile/T13087.stderr - testsuite/tests/parser/should_fail/T8431.stderr - testsuite/tests/parser/should_fail/readFail038.stderr - testsuite/tests/perf/compiler/T3064.hs - + testsuite/tests/pmcheck/should_compile/T27314.hs - + testsuite/tests/pmcheck/should_compile/T27360.hs - testsuite/tests/pmcheck/should_compile/all.T - testsuite/tests/polykinds/T7594.hs - testsuite/tests/printer/Test20297.stdout - testsuite/tests/programs/thurston-modular-arith/Main.hs - + testsuite/tests/rename/should_fail/T21101.hs - + testsuite/tests/rename/should_fail/T21101.stderr - testsuite/tests/rename/should_fail/T9815.stderr - testsuite/tests/rename/should_fail/T9815b.stderr - testsuite/tests/rename/should_fail/T9815bghci.stderr - testsuite/tests/rename/should_fail/T9815ghci.stderr - testsuite/tests/rename/should_fail/all.T - testsuite/tests/rts/ipe/IpeStats/Fold.hs - testsuite/tests/runghc/T7859.stderr-mingw32 - testsuite/tests/simd/should_run/doublex2_arith.hs - testsuite/tests/simd/should_run/doublex2_arith.stdout - testsuite/tests/simd/should_run/doublex2_arith_baseline.hs - testsuite/tests/simd/should_run/doublex2_arith_baseline.stdout - testsuite/tests/simd/should_run/doublex2_fma.hs - testsuite/tests/simd/should_run/doublex2_fma.stdout - testsuite/tests/simd/should_run/simd010.hs - testsuite/tests/simplCore/should_compile/T11562.hs - testsuite/tests/simplCore/should_run/T3591.hs - testsuite/tests/splice-imports/SI35.hs - testsuite/tests/typecheck/should_compile/DeepSubsumption02.hs - testsuite/tests/typecheck/should_compile/T12507.hs - testsuite/tests/typecheck/should_compile/T13951.hs - testsuite/tests/typecheck/should_compile/T18920.hs - testsuite/tests/typecheck/should_compile/T2595.hs - testsuite/tests/typecheck/should_compile/T7541.hs - testsuite/tests/typecheck/should_fail/T15067.stderr - + testsuite/tests/typecheck/should_fail/T26532.hs - + testsuite/tests/typecheck/should_fail/T26532.stderr - testsuite/tests/typecheck/should_fail/T6069.stderr - testsuite/tests/typecheck/should_fail/T7368a.hs - testsuite/tests/typecheck/should_fail/T9858b.stderr - testsuite/tests/typecheck/should_fail/TcStaticPointersFail02.stderr - testsuite/tests/typecheck/should_fail/all.T - testsuite/tests/typecheck/should_run/T1735_Help/Basics.hs - testsuite/tests/typecheck/should_run/T3731-short.hs - testsuite/tests/typecheck/should_run/T3731.hs - testsuite/tests/typecheck/should_run/church.hs - testsuite/tests/typecheck/should_run/tcrun008.hs - testsuite/tests/typecheck/should_run/tcrun017.hs - testsuite/tests/typecheck/should_run/tcrun026.hs - testsuite/tests/typecheck/should_run/tcrun035.hs - testsuite/tests/typecheck/should_run/tcrun036.hs - utils/check-exact/ExactPrint.hs - utils/check-exact/Main.hs - utils/check-exact/Transform.hs - utils/check-exact/Utils.hs - utils/check-ppr/Main.hs - utils/deriveConstants/Main.hs The diff was not included because it is too large. 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