Simon Jakobi pushed to branch wip/sjakobi/T27448 at Glasgow Haskell Compiler / GHC Commits: 27463426 by Rodrigo Mesquita at 2026-06-26T20:54:58-04:00 perf: Share Module in Iface Symbol Table This commit modifies the structure of the serialized `SymbolTable Name` to then re-use and share the `Module` (both on disk and in memory) across all `Name`s from the same module. The new structure looks like: <total name count> $modules.size for (mod, names) in $modules: $mod $names.size for table_ix, occ in $names $table_ix $occ i.e. we put the module just once, followed by all names in that module. When deserializing, we deserialize the module just once, and all the following `Name`s are constructed with a pointer to that same decoded `Module`. In `hoogle-test`, we must use `DNameEnv` rather than `Map Name`, otherwise the output fixities order was susceptible to changes in the uniques assigned to each Names, which is not stable. Fixes #27401 ------------------------- Metric Decrease: InstanceMatching LinkableUsage01 LinkableUsage02 hard_hole_fits ------------------------- - - - - - 412f1675 by Simon Hengel at 2026-06-26T20:55:41-04:00 Rename `MCDiagnostic` to `InternalMCDiagnostic` `MCDiagnostic` is meant to be used for compiler diagnostics. Any code that creates `MCDiagnostic` directly, without going through `GHC.Driver.Errors.printMessage`, sidesteps `-fdiagnostics-as-json` (see e.g. !14616, !14475, !14492 !14548). To avoid this in the future, this change more narrowly controls who creates `MCDiagnostic` (see #24113). - - - - - 6f212121 by Facundo Domínguez at 2026-06-26T20:56:27-04:00 Encapsulate options of occurAnalysePgm in a record - - - - - adfbb179 by Facundo Domínguez at 2026-06-26T20:56:27-04:00 Allow to configure the occurrence analyser to retain some dead bindings This is needed by plugins that are the only consumers of a binding which is otherwise unused in the program. See Note [Controlling elimination of dead bindings in occurrence analysis] added in this commit, or https://gitlab.haskell.org/ghc/ghc/-/issues/27240 for more discussion. - - - - - c745b11f by Copilot at 2026-06-26T20:56:27-04:00 Address documentation feedback - - - - - 2c2a4a2a by Copilot at 2026-06-26T20:56:27-04:00 Keep the imp_rules parameter of occurPgmAnalysePgm and add occ_opts to OccEnv - - - - - e2262b0e by Copilot at 2026-06-26T20:56:27-04:00 Strengthen T27240.hs with a binding that should be removed - - - - - 5f9d9268 by Copilot at 2026-06-26T20:56:27-04:00 Move the reference #27240 to a related paragraph - - - - - d86d2644 by Simon Hengel at 2026-06-26T20:57:10-04:00 Remove deprecated flag `-ddump-json` (see #24113) This was first deprecated in 9.10.1. - - - - - 3b15ff03 by Simon Jakobi at 2026-06-27T18:48:34+02:00 Tweak mk_mod_usage_info * Use O(log n) `elemModuleEnv` instead of O(n) `elem` to filter the direct imports. * Use `nonDetModuleEnvKeys` to avoid sorting the ent_map keys twice. * Prepend the presumably shorter list when creating all_mods with `(++)`. Actually this eliminates the `(++)` entirely, as it seems to fuse with the `filter` expression. As a result there is a tiny speed-up when generating the .hi-files for modules with many imports. None of the changes affect compilation determinism as the module list is explicitly sorted to ensure a canonical order. - - - - - 2d0fd154 by Alan Zimmerman at 2026-06-29T11:44:00-04:00 EPA: Remove LocatedC / SrcSpanAnnC This is part of a cleanup of the zoo of SrcSpanAnnXXX types for exact print annotations. This one removes SrcSpanAnnC used for storing exact print annotations for contexts. It replaces it with an explicit `HsContext` data type that carries the annotations and the context. So, replace type HsContext pass = [LHsType pass] with type HsContext pass = HsContextDetails pass (LHsType pass) data HsContextDetails pass arg = HsContext { hsc_ext :: !(XHsContext pass) , hsc_ctxt :: [arg] } | XHsContextDetails !(XXHsContextDetails pass) We need the parameterised HsContextDetails because it is used both for HsQual carrying 'LHsExpr p' and "normal" contexts carrying 'LHsType p'. - - - - - cca0d589 by Luite Stegeman at 2026-06-30T13:33:40-04:00 rts: handle large AP closures in compacting GC The function update_fwd_large in the compacting GC could run into an unexpected object with the following error: internal error: update_fwd_large: unknown/strange object 24 Closure type 24 is the AP closure, which was not handled in upd_fwd_large. This patch adds handling them. fixes #27434 - - - - - 42935858 by Luite Stegeman at 2026-06-30T13:33:40-04:00 testsuite: use compacting_gc way instead of hardcoding +RTS -c - - - - - bf7b5ce6 by Alan Zimmerman at 2026-06-30T13:34:23-04:00 EPA: Remove LocatedLW from LStmtLR HsDo already had its XDo extension point for an AnnList, which also appeared in LocatedLW. So we remove the redundant one and use the one inside HsDo as originally intended. Also delete LocatedLC/LocatedLS as they were unused - - - - - d7cfea49 by Recursion Ninja at 2026-06-30T21:37:12-04:00 Decoupling 'L.H.S' from 'GHC.Types.SourceText' * Migrated 'IntegralLit' to 'L.H.S.Lit'. * Migrated 'FractionalLit' to 'L.H.S.Lit'. * Migrated 'StringLiteral' to 'L.H.S.Lit'. * Added TTG extension points to the types above. * Added nice export list to 'GHC.Hs.Lit'. * Added 'rnOverLitVal' and 'tcOverLitVal' functions to 'GHC.Hs.Lit'. * Added instance 'Anno (StringLiteral (GhcPass p)) = SrcSpanAnnN' * Moved [Notes] about 'SourceText' from 'L.H.S.*' to 'GHC.*'. * Removed all references to 'SourceText' from 'L.H.S'. * Removed the trailing comma record field from 'StringLiteral' * Renamed exported functions for nomenclature consistency. * Deprecated the renamed functions Fixes #26953 - - - - - a1f2558b by Recursion Ninja at 2026-06-30T21:37:12-04:00 Monomorphising GHC pass parameters where appropriate - - - - - 7bf9e3c5 by Teo Camarasu at 2026-06-30T21:38:03-04:00 Make Q abstract This patch aims to clearly demarcate the internal and external interfaces of Q. In the past the `Quasi` typeclass was both part of the external, public-facing interface, and was used to give the implementation of `Q`. Now we separate out these two distinct roles. `Quasi` continues to exist in the public interface, but we introduce a new `MetaHandlers` type, which is equivalent to `Dict Quasi`. `Q a` is now defined to be `MetaHandlers -> IO a`, and, crucially, the constructor and the new `MetaHandlers` type are not exposed from the public interface. This gives us the ability to vary the interface on the GHC side without forcing a breaking change on the `template-haskell` side. Similarly `template-haskell` has more freedom to change the `Quasi` typeclass without needing any changes in `lib:ghc`. Implements https://github.com/ghc-proposals/ghc-proposals/pull/700 Resolves #27341 - - - - - 4262af36 by L0neGamer at 2026-06-30T21:38:56-04:00 generically defines mconcat in terms of internal type's Semigroup instance add changelog entry use simpler definition for mconcat `nonEmpty` isn't available yet; inline branches in case add test case fixup generically defines mconcat in terms of internal type's Semigroup instance add comment on Generically and deriving mishaps swap mconcat to foldr version add some strictness testing for mconcat add to `base` changelog entry - - - - - e22ad997 by Cheng Shao at 2026-06-30T21:39:43-04:00 hadrian/rts: fix unregisterised build for gcc 15+ This patch fixes unregisterised build for gcc 15+: - Pass -optc-Wno-error in hadrian when +werror enables -optc-Werror, see added comment for details. - For RTS functions that the codegen would emit calls, ensure their real prototype is hidden when the header is included in .hc fies (IN_STG_CODE), and the dummy prototype is provided to match the EFF_ convention. In the future we should get rid of EFF_ (#14647) and remove these hacks, but for now this patch makes unregisterised work again on newer toolchains. Fixes #27404. Co-authored-by: Codex <codex@openai.com> - - - - - 3f00f234 by Cheng Shao at 2026-06-30T21:40:32-04:00 compiler: fix missing handling of CmmUnsafeForeignCall node in LayoutStack This patch fixes missing handling of `CmmUnsafeForeignCall` middle node in the `LayoutStack` pass. Before proc-points splitting, this pass computes liveliness of local registers, and spills those alive across a Cmm native call onto the stack. It need to traverse all middle nodes in each block and check whether a local register is an assignee, if so then the previous mapping in `sm_regs` is invalidated and needs to be dropped. However, it didn't handle `CmmUnsafeForeignCall` node which may also assign to a local register. When proc-points splitting is enabled, this can produce an invalid basic block that doesn't properly backup the updated local register to the stack before doing a Cmm call, resulting in completely invalid runtime behavior. The patch also adds a `T27447` regression test. With no-TNTC or with LLVM backend, without the fix the test case would output a stale 0x1111111111111111 value, instead of the expected 0x2222222222222222 output. Fixes #27447. Co-authored-by: Codex <codex@openai.com> - - - - - 701088db by Ben Gamari at 2026-07-01T10:34:03-04:00 gitlab-ci: Drop vestigial references to make build system - - - - - 62d54a53 by Ben Gamari at 2026-07-01T10:34:03-04:00 gitlab-ci: Add support for running specifying a job's testsuite ways - - - - - 7f97ac2c by Ben Gamari at 2026-07-01T10:34:03-04:00 gitlab-ci: Run llvm testsuite ways in llvm jobs Addresses #25762. - - - - - 7ea75116 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Add normalise_ddump_deriv setup function Some tests check the result of -ddump-deriv, which may contain INLINE pragmas depending on optimization flags. With normalise_ddump_deriv setup function, INLINE pragmas are stripped off. - - - - - c7a8199f by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Use -dsuppress-idinfo to make tests more robust Previously, T18052a and T21755 were failing on 'optasm' and 'optllvm' ways because of visibility of unfoldings. - - - - - a12122e5 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Use a trick to keep large objects alive Previously, T17574 and T19381 were failing on 'optasm' and 'optllvm' ways because of compiler optimizations. Change them to use NOINLINE to prevent unwanted optimizations. - - - - - 1a95b327 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Only run T24224 in 'normal' way This test is a frontend-only one and breaks if optimizations are enabled. - - - - - 8abea737 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Ignore T18118's stderr When optimizations are enabled, the compiler emits a warning (You cannot SPECIALISE ...). The message is not important, so ignore it. - - - - - 9453a722 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Mark T816 and tc216 broken with optimizations These tests are about type checking, so we should not care too much if they are broken with optimizations. See #26952 - - - - - 0aef9ec0 by Ben Gamari at 2026-07-01T10:34:03-04:00 testsuite: ds014 is not longer broken It now appears to pass in the ways it was marked as broken in. Closes #14901. - - - - - 4692d1e4 by Ben Gamari at 2026-07-01T10:34:03-04:00 testsuite: Only run stack cloning tests in the normal way These are too dependent upon code generation specifics to pass in most other ways. - - - - - c154df26 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Update options_ghc_fbyte-code The `-fbyte-code` option used to be overriden by `-fllvm` but it is no longer true since !14872 was merged. I updated the test to accept the new behavior. Closes #27049 - - - - - 5d8bb7b5 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Only run T22744 in 'normal' way This test takes a long time on optimized ways. - - - - - d1e74c8e by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Disable tests that use -finfo-table-map on llvm ways Currently, -finfo-table-map does not work with -fllvm. See #26435 - - - - - 3bf38c84 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Don't run T24726 on optimized ways If optimizations are enabled, the rewrite rule just fires and -drule-check will report nothing. - - - - - e4eef116 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Use -fno-unoptimized-core-for-interpreter when running LinkableUsage01/02 Optimizations for the bytecode interpreter are considered experimental, and need a flag to be enabled. - - - - - 234a9872 by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Suppress unwanted optimizations on T25284 - - - - - 99a2af2f by ARATA Mizuki at 2026-07-01T10:34:03-04:00 testsuite: Don't run stack_big_ret with optimizations Stack layout may change with optimizations enabled. - - - - - 04c836df by ARATA Mizuki at 2026-07-01T10:34:04-04:00 testsuite: Mark memo001 broken on optimized ways See #27396 - - - - - 1a8a24f4 by ARATA Mizuki at 2026-07-01T10:34:04-04:00 testsuite: Mark syn-perf broken on optimized ways See #27398 - - - - - 40412093 by Duncan Coutts at 2026-07-01T10:34:50-04:00 Add a test for thread scheduler fairness It also tests that the interval timer and context switching works. We also test that fairness is lost when the context switching interval is too coarse for the duration of the test. We add this test before doing surgery on the interval timer, so we have decent coverage. - - - - - 3f34d557 by Duncan Coutts at 2026-07-01T10:34:50-04:00 Make exported stop/startTimer no-ops, and rename internal functions Specifically, internally rename: stop/startTimer to pause/unpauseTimer stop/startTicker to pause/unpauseTicker and keep stop/startTimer as exported functions, but now as no-ops. In the past the stop/startTicker actions were used incorrectly as if they were synchronous, which they are not. See issue #27105. We now document pause/unpackTicker as being async and not to be used for the purpose of concurrency safety. The existing stop/startTimer (note Timer not Ticker, the Timer calls the Ticker!) are also exported from the RTS as a public API. This was historically because the ticker used signals and it was important to suspend the timer signel over a process fork. So these functions were exported to be used by the process and unix libraries. We cannot just remove the RTS exports, but we now make them no-ops, and they can be removed from the process and unix library later. This was already documented in a changelog.d entry no-more-timer-signal but due to changes during the MR process the change to make stop/startTicker into no-ops didn't make it into the earlier MR. - - - - - 02e84e5f by Duncan Coutts at 2026-07-01T10:34:51-04:00 Make exitTicker/exitTimer unconditionally synchronous We never use them asynchronously, and we should never need to do so. And update some related comments. - - - - - 13db6a72 by Duncan Coutts at 2026-07-01T10:34:51-04:00 posix ticker: update and improve comments on (un)pause and exit Clarify what is async vs sync. - - - - - 43d9a07d by Duncan Coutts at 2026-07-01T10:34:51-04:00 posix ticker: split out ppoll/select helper functions Move the #ifdefs out of the main code body by introducing local helper functions and types, which themselves have two implementations (with a common API) based on ppoll or select. This helps improve clarity/readability. - - - - - a5491baa by Duncan Coutts at 2026-07-01T10:34:51-04:00 posix ticker: improve the implementation The existing implementation supported pausing and exiting, with the implementation of pausing reling on a mutex and condition variable. It needed to check the pause and stop shared variables on every iteration. It relies on ppoll or select, to wait on the timeout and also wait on an interrupt fd. The interrupt fd was only used for prompt exit/shutdown, and not for pausing or other notification. The pause only needed a lock and a memory operation, but the pause was not prompt. The resume used a lock, and signaling a cond var. The new implementation uses a somewhat more regular design: every notification is done by setting a shared variable and interrupting/notifying the ticker via the fd. The ticker thread does not need to check any shared variables on normal timer expiry, only when it recevies notification. This may be a micro-optimisation, but the tick occurs 100 times a second by default so any improvements in the hot path are amplified. When the ticker thread does receive notification it can check the various shared variables and update its local state. The blocking relies on using ppoll/select but without a timeout. This avoids the condition var and also allows further notifications when paused (also used for unpausing). This design can be extended with further notification types if needed by using and checking further shared vars (or making existing shared vars an enum or counter). This may be used in future for additional notifications to the ticker thread. This will likely be used to proxy wakeUpRts from a single handler context for example. And this approach, avoiding mutexes, is compatible with use from signal handlers. So overall, it's: * slightly simpler / more regular; * easier to extend with additional notifications; * probably slightly more efficient (but a micro-optimisation); * and supports calling notification from signal handlers - - - - - 5b20821e by Duncan Coutts at 2026-07-01T10:34:51-04:00 posix ticker: further minor local renaming for code clarity Improve the clarity with better choice of names for several local vars and function. - - - - - 1f3ec5e0 by Duncan Coutts at 2026-07-01T10:34:51-04:00 win32 ticker: split out local helper functions - - - - - 596e7307 by Duncan Coutts at 2026-07-01T10:34:51-04:00 win32 ticker: provide guarantee about concurrency and idempotency Use a lock to ensure pause/unpause can be used concurrently. Use a paused variable, protected by the lock, to ensure that pause and unpause are both idempotent. This is what the portable API expects. - - - - - 1870edd7 by Duncan Coutts at 2026-07-01T10:34:51-04:00 win32 ticker: make the initial tick be after one wait interval There is no need to tick immediately. This is consistent with the posix implementation. - - - - - 7c15ab5b by Duncan Coutts at 2026-07-01T10:34:51-04:00 ticker: remove now-unnecessary layer of enable/disable There was an atomic variable used to block *part* of the actions of the tick handler. This still did not make stopTimer synchronous, even for the part of the the handle_tick actions it covered. It also added a more expensive (sequentuially consistent) atomic operation in the hot path for the handle_tick action, whereas our new design requires no atomic ops at all. Now that we have eliminate the need for synchronous stop/startTicker, we don't need this not-quite-working-anyway atomic protocol. The new pause/unpauseTicker is explicitly asynchronous and idempotent. - - - - - 8585f8cb by Duncan Coutts at 2026-07-01T10:34:51-04:00 ticker: add TODOs about issue #27250: too much being done from handle_tick The handle_tick should not perform I/O, block, perform long-running operations or call arbitrary user code. Unfortunately, everything to do with the eventlog (at the moment) falls into all those categories. - - - - - 6e381626 by Duncan Coutts at 2026-07-01T22:29:55+01:00 Adjust releaseCapability_ precondition to allow cap->running_task == NULL There are two use cases for releaseCapability_: 1. The current Task (cap->running_task) releases the Capability. The Capability is marked free, and if there is any work to do, an appropriate Task is woken up. 2. There is no current task (cap->task == NULL), and thus the Capability is idle, and we want to wake up an idle Task to animate the Capability. This case uses always_wakeup. Currently, the precondition for releaseCapability_ is cap->running_task != NULL and so the 2nd use cases have to set cap->running_task (which is then immediately overwritten) just to satisfy the precondition. See the use cases in sendMessage and prodCapability. So we can relax the precondition to be: cap->running_task != NULL || always_wakeup so that in the always_wakeup case, we say it is ok for the cap->running_task to be NULL. This lets us simplify sendMessage and prodCapability. In particular it will allow prodCapability to not need a Task parameter. The ulterior motive for all this is that I want to be able to call prodCapability from an OS thread that is not itself a Task, in persuit of issue #27086: disentangle I/O managers from wakeUpRts. The most straightforward way to wake the RTS is using prodCapability, but the context in which we will need to do that are threads that are not Tasks. - - - - - 89404ebc by Duncan Coutts at 2026-07-01T22:29:55+01:00 prodCapability no longer needs to take a Task param Now that releaseCapability_ can accept cap->running_task == NULL then it is no longer necessary for prodCapability to require a Task. - - - - - 4e60c5f6 by Duncan Coutts at 2026-07-01T22:29:56+01:00 Define prodOneCapability There was an existing declaration for this in the header file, but no definition. Similarly, there is a declaration for prodAllCapabilities but no definition, and we don't need it, so remove the declaration. - - - - - 2527026f by Duncan Coutts at 2026-07-01T22:29:56+01:00 Add a wakeUpRtsViaTicker feature to the posix ticker It proxies a call to wakeUpRts, but crucially, this can be called from a signal handler context. It will be used for ctl-c handling. - - - - - aa5a03a5 by Duncan Coutts at 2026-07-01T22:29:56+01:00 Change how wakeUpRts works Previously it would call wakeupIOManager to get a capability to wake up and run. This works but it entangles the I/O managers with unrelated features: ctl-c handling and idle gc (the two features that use wakeUpRts). The reason it used wakeupIOManager is that this action is safe to use from a posix signal handler, since it just posts bytes to a pipe. Otherwise the more direct approach (used e.g. by sendMessage when the target capability is idle) is to use releaseCapability. But that uses condition variables and mutexes, which are not safe to use from within a signal handler. So instead of entangling the (multiple) I/O managers with this, we make wakeUpRts use the direct approach (using prodOneCapability). On win32 the ctl-c console handler can call wakeUpRts directly, since it is called in a proper thread. On posix, to deal with the signal handler problem, we make the signal handler ask the ticker thread to proxy the call to wakeUpRts, since the ticker thread is also a proper thread. This will allow the I/O managers to no longer be concerned with this. This is good because there are many I/O managers (and they're complicated), but there is (on posix) only one ticker implementation. So this is an overall reduction in coupling and complexity. Fixes issue #27086 - - - - - c6d53c16 by sheaf at 2026-07-02T21:35:44-04:00 Test driver: normalise line numbers into libraries When comparing the stdout of tests that print out callstacks, we can't rely on the stability of exact line:column spans pointing into libraries (e.g. ghc-internal), as any change (such as adding a comment) can change them. This commit addresses this by normalising away line:column in callstacks, but only when those point into internal libraries. We don't do this in general, as the exact span might be important to the test (e.g. for a span within the test module itself). Fixes #27387 - - - - - 81ee62e0 by Alan Zimmerman at 2026-07-02T21:36:33-04:00 EPA: Remove LocatedLW from MatchGroup This is the last usage of LocatedLW / SrcSpanAnnLW - - - - - 925959db by Recursion Ninja at 2026-07-04T04:14:12-04:00 Decoupling 'L.H.S' from 'GHC.Hs.Doc' * Migrated 'GHC.Hs.Doc' and 'GHC.Hs.DocString' AST defintions from 'GHC.*' namespace, to new 'Language.Haskell.Syntax.Doc' module in the 'L.H.S' "namespace." * Updated 'HsDocString to be TTG-parameterised as 'HsDocString pass'. * Added 'GHC.Hs.Extension.Pass': splits 'GhcPass'/'Pass' and all 'HsDocString' TTG instances out of 'GHC.Hs.Extension', which re-exports it unchanged (this is backwards compatible and prevents the introduction of a boot file). * Deleted 'GHC.Hs.Doc.hs-boot'; removed all 'L.H.S.*' imports of 'GHC.Hs.Doc'. * Updated 'GHC.Hs.DocString' to be TTG pass-parameterised throughout; moved 'mkHsDocStringChunk'/'unpackHDSC' here (require 'GHC.Utils.Encoding'). * Split 'GHC.Rename.Doc.rnHsDoc' from 'rnHsDocIdentifiersOnly'. * Updated parser, renamer, typechecker, HIE, and exact-print for new types. * Added 'HsDocString' TTG instances for 'DocNameI' to 'Haddock.Types'. * Killed the last module loop between GHC.* and LHS.*. - Only edges from LHS.* to GHC.Data.FastString now! Resolves #26971 - - - - - b7e24044 by mangoiv at 2026-07-04T04:14:56-04:00 ci: retry fetching test metrics Retry fetching test metrics to make the CI not fail if the services is temporarily unavailable - - - - - 4180af3f by Zubin Duggal at 2026-07-04T04:15:38-04:00 Bump semaphore-compat submodule to 2.0.1 This versions includes some cruicial fixes for darwin - - - - - 242d4317 by sheaf at 2026-07-04T04:16:19-04:00 Remove outdated comment in GHC.Data.ShortText There was a long comment in GHC.Data.ShortText about a workaround that was necessary when bootstrapping with GHC 9.2 and below. The actual logic has since been dropped, but the comment remained. This commit removes the vestigial comment. - - - - - 9b714c4c by Zubin Duggal at 2026-07-05T09:40:36+05:30 CorePrep: Don't speculatively evaluate bindings that we have already discovered to be absent In #25924, we segfault because speculation forces a projection out of a RUBBISH dictionary (which we generated because it absent). Solution: Don't speculate on bindings we already know are absent. Fixes 25924 - - - - - 4a59b3ee by Zubin Duggal at 2026-07-05T09:40:36+05:30 Don't make absent fillers for terminating types In #25924 we discovered that we could speculatively evaluate an absent filler for a dictionary, and project a field (a superclass selector) out of it, resulting in segfaults. Solution: Never make an absent filler or rubbish literal for a terminating type like a dictionary. mkAbsentFiller returns Nothing for isTerminatingType, so worker/wrapper and the specialiser keep the real argument instead. Some small metric decreases because we do a little less work in the simplifier now. Metric Decrease: T9872a T9872b T9872c TcPlugin_RewritePerf - - - - - 383ddcd4 by Alan Zimmerman at 2026-07-06T07:08:16-04:00 EPA: Move the 'where' annotation for PatSynBind This allows us to move it out of the MatchGroup exact print annotation too - - - - - 66d1a5d5 by fendor at 2026-07-07T16:57:56-04:00 Add 'backendInfoTableMapValidity' backend predicate Check whether the backend supports the `-finfo-table-map` flag and ignore it otherwise. Improve by-design documentation of `backendCodeOutput`. `Backend` is **abstract by design**. Make this clearer in `backendCodeOutput` which is incorrectly being used as a proxy for `Backend`. Instead, define the desired property predicates in GHC.Driver.Backend In the process, make `backendCodeOutput` total. - - - - - 74f1071d by fendor at 2026-07-07T16:57:56-04:00 Add failing test for `-finfo-table-map` and bytecode backend If you compile a module using the bytecode backend, with -finfo-table-map, then the info table map doesn't get populated for the module. This is because the -finfo-table-map code path is implemented mostly in the StgToCmm phase which isn't run when creating bytecode. Ticket #27039 - - - - - 28d63bca by mangoiv at 2026-07-07T16:59:16-04:00 ci: don't fail nightly if there have been no changes that night Fixes #27127 - - - - - 4ebfc478 by Rodrigo Mesquita at 2026-07-08T04:47:53-04:00 ttg: Using ShortText over FastString in the AST To make the AST independent of GHC, this commit replaces usages of `FastString` with `HText` in the AST, killing the last edge from Language.Haskell.* to GHC.* modules. Even though we /do/ want to use FastStrings in general -- critically in Names or Ids -- there is no particular reason for the FastStrings that occur in the AST proper to be FastStrings. Strings in the AST are typically unique and don't benefit particularly from being interned FastStrings with Uniques for fast comparison. `HText` is a type synonym for `ShortText` which uses GHC's Modified UTF-8 encoding exclusively. Modified UTF-8 must be used to represent the Haskell AST because the Haskell Report allows surrogate code points. `Data.Text.Text` functions use Standard UTF-8 which replace surrogates with a placeholder value, thus `Data.Text.Text` is unsuitable for AST strings. See the `Language.Haskell.Syntax.Text` module header for more details. Final progress towards #21592 Closes #21628 - - - - - d910b353 by Simon Peyton Jones at 2026-07-08T04:48:36-04:00 Update equality-type documenation in GHC.Builtin.Types.Prim Fix #27466 - - - - - b2530542 by Simon Peyton Jones at 2026-07-08T04:48:36-04:00 Honour -dsuppress-coercions in GHC.Core.TyCo.pprCo Fixes #27467 - - - - - 9a73179a by Facundo Domínguez at 2026-07-08T04:49:26-04:00 Add item to MR checklist asking to squash fixup commits after approval The checklist has an item that reads All commits are either individually buildable or squashed. This item could be checked immediately after sending the merge request though. If reviewers ask for amends later on, and the author amends the merge request, there was no item that would remind the contributors to squash the fixup commits before landing. This commit adds a new item After all approvals and before landing: all fixup commits are squashed with their originating commits. which should be harder to mark as done before approvals have been given. - - - - - 1e8d118c by Simon Jakobi at 2026-07-08T13:01:38+02:00 NCG: optimize loopInfo.mkDomMap Previously, mkDomMap built an intermediate association list with (++) and a recursive concatMap before handing it to mapFromList. The concatMap re-copied each node's list once per ancestor, so the work was O(n^2) in the depth of the dominator tree. The new code builds the LabelMap directly, with one mapInsert per dominator-tree node, so each node is handled once. This reduces allocation when compiling the new ManyBasicBlocks test by ~27% at -O1 and -O2. (At -O0, static control-flow prediction is disabled.) This also fixes a small inconsistency: previously a leaf of the dominator tree included itself in its dominator set, while interior nodes did not. The map is consumed only by isBackEdge, so the only observable effect was that a self-loop edge was treated as a back edge iff its block was a dominator-tree leaf. domMap now holds each block's strict dominators, excluding the entry. Closes #27448 Assisted-by: Claude Opus 4.8 - - - - - 325 changed files: - .gitlab-ci.yml - .gitlab/ci.sh - .gitlab/generate-ci/gen_ci.hs - .gitlab/jobs.yaml - .gitlab/merge_request_templates/Default.md - .gitlab/rel_eng/mk-ghcup-metadata/mk_ghcup_metadata.py - .gitlab/test-metrics.sh - + changelog.d/AbstractQ - + changelog.d/T21628 - + changelog.d/add_can_drop_to_occurence_analyser - + changelog.d/fix-absent-dict-projection - + changelog.d/fix-compacting-gc-ap-27434 - + changelog.d/fix-layout-stack-fcall - + changelog.d/fix-unreg - + changelog.d/generically-mconcat - + changelog.d/remove-ddump-json-flag - changelog.d/semaphore-v2 - compiler/GHC/Builtin/Types/Prim.hs - compiler/GHC/Builtin/Utils.hs - compiler/GHC/Cmm/CLabel.hs - compiler/GHC/Cmm/LayoutStack.hs - compiler/GHC/CmmToAsm/CFG.hs - compiler/GHC/Core/Make.hs - compiler/GHC/Core/Opt/OccurAnal.hs - compiler/GHC/Core/Opt/Simplify.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Opt/WorkWrap.hs - compiler/GHC/Core/Opt/WorkWrap/Utils.hs - 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