[Git][ghc/ghc][wip/io-manager-deadlock-detection] 179 commits: Add type family performance test for #26426

Duncan Coutts pushed to branch wip/io-manager-deadlock-detection at Glasgow Haskell Compiler / GHC Commits: 40764930 by sheaf at 2026-06-12T14:54:43-04:00 Add type family performance test for #26426 Some GHC versions produced large numbers of coercions after typechecking and desugaring when compiling the program in #26426: Version | Typechecker time | Typechecker allocations | Coercions -------:|-----------------:|------------------------:|---------: 9.6 | 47 ms | 48 MB | 110k 9.8 | 1000 ms | 486 MB | 10,437k 9.10 | 922 ms | 489 MB | 10,436k 9.12 | 906 ms | 482 MB | 10,437k 9.14 | 63 ms | 55 MB | 333k 10.0 | 47 ms | 64 MB | 35k The improvement 9.12 -> 9.14 was due to commit 22d11fa818fae2c95c494fc0fac1f8cb4c6e7cb6, while the improvement 9.14 -> 10.0 was due to commit 0b7df6db9e46df40e86fbff1a66dc10440b99db5. As the behaviour of GHC seems better than it's ever been on this program, we declare victory, adding this performance test to ensure we don't regress on this program. On the way, we update Note [Combining equalities] in GHC.Tc.SolveR.Equality with the explanation of the 9.12 -> 9.14 improvement (getting rid of an exponential blowup in coercion sizes), and we update Note [Exploiting closed type families] in GHC.Tc.Solver.FunDeps with the explanation of the 9.14 -> 10.0 improvement (bringing down coercion size growth from cubic to quadratic). - - - - - 0f3d0a71 by Zubin Duggal at 2026-06-12T14:55:30-04:00 compiler: mark tool messages as errors/warnings depending on the exit code Fixes #27370 - - - - - d9ea2d76 by mangoiv at 2026-06-13T04:41:51-04:00 libraries/process: bump submodule to v1.6.30.0 - bump the submodule to the appropriate tag - suppress benign warning resulting from the change - - - - - 6ebaaba3 by David Eichmann at 2026-06-13T04:42:37-04:00 ghc-toolchain: don't throw when candidate executables are not found Fixes #27369 - - - - - 6c65e1e1 by David Eichmann at 2026-06-13T04:43:23-04:00 CI: lint-changelog checks for no-changelog label in script instead of rules - - - - - bab37cc6 by konsumlamm at 2026-06-13T19:10:21+02:00 Implement CLC proposal #378 Add `Data.Double` and `Data.Float` modules Document that GHC uses IEEE 754 - - - - - fb5246ad by fendor at 2026-06-15T18:07:23-04:00 Drop `preloadClosure` from `UnitState` It is always hard-coded to the same value. Backpack Unit instantiation isn't using it any more. Allows us to simplify the API and get rid of `improveUnit`. - - - - - 291ce3aa by ARATA Mizuki at 2026-06-15T18:08:26-04:00 RISC-V NCG: Zero-extend the result of castFloatToWord32 According to the ISA manual, FMV.X.W sign-extends the result. We need to truncate the result to avoid creating an exotic Word32 value. Fixes #27300 - - - - - 011be91f by ARATA Mizuki at 2026-06-15T18:08:26-04:00 RISC-V NCG: Treat d28-d31 (ft8-ft11) as caller-saved According to the calling convention, the registers d28-d31 (ft8-ft11) are caller-saved. Fixes #27306 - - - - - e8a54713 by ARATA Mizuki at 2026-06-15T18:08:26-04:00 RISC-V NCG: Set rounding mode when emitting `truncate` If we omit the rounding mode for `fcvt`, `dyn` will be used. We do not want that for `truncate`, so we set `rtz`. In other places, we set `rne` because we do not use the dynamic rounding mode. Fixes #27303 - - - - - 9438bec7 by Zubin Duggal at 2026-06-15T18:09:11-04:00 rts: fix validate build with gcc 16. `__attribute__((regparm(1)))` is ignored on x86_64 and now gcc warns that it is ignored: rts/sm/Evac.h:35:1: error: error: ‘regparm’ attribute ignored [-Werror=attributes] See https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=ccead81bbc39668376eb5cf47066ac... Fixes #27366 - - - - - 893e6133 by Andrew Lelechenko at 2026-06-15T23:55:36+01:00 base: more NonEmpty zips CLC proposal: https://github.com/haskell/core-libraries-committee/issues/409 - - - - - 1314f2fd by David Eichmann at 2026-06-16T05:46:52-04:00 Hadrian: fix ghc-internal .def file name - - - - - 7f72bcb3 by mangoiv at 2026-06-16T05:47:39-04:00 compiler: ignore camelCase and Eta reduce hlint hints These do not cohere with the style used in GHC. After disabling them, hlint lints are much less noisy again. - - - - - 842bef9f by Alan Zimmerman at 2026-06-16T05:48:25-04:00 EPA: Use standard type family declaration for Anno - - - - - f6d30767 by Wolfgang Jeltsch at 2026-06-16T15:32:34-04:00 Fix two issues in the documentation of pipeline interruption One issue is a typo (“interreuptible”), the other one the lack of an end of a sentence, which has been reconstructed from the message of 633bbc1fd4762a2bb73ba1c5b9e0c279f1dd3c40, the commit that introduced said documentation. - - - - - a3fa10e0 by Christian Georgii at 2026-06-16T15:33:26-04:00 Find plugins in sibling home units in multiple-home-unit sessions In a multiple-home-unit session (e.g. `cabal repl --enable-multi-repl` or HLS), enabling a plugin with -fplugin that is defined in (or reexported by) another home unit failed with a "hidden package" error. The plugin module finder only searched the current home unit and the registered external packages, never the sibling home units. findPluginModuleNoHsc now searches the home units that the current home unit depends on, following module reexports and respecting hidden modules, exactly as ordinary import resolution does in findImportedModuleNoHsc. To avoid two divergent copies of this logic, the shared home-unit search (the current home unit first, then its dependencies in priority order, with the accompanying ordering invariant) is extracted into findHomeModuleAmongDeps, which both findImportedModuleNoHsc and findPluginModuleNoHsc now call. Add testsuite/tests/driver/multipleHomeUnits/plugin01, which loads a plugin as byte-code from a sibling home unit, and plugin02, in which the consumer enables a plugin reexported by a sibling home unit without depending on the plugin's own home unit directly. Fixes #27349 - - - - - d216412b by Ian-Woo Kim at 2026-06-16T20:25:57-04:00 Make the order of usages deterministic It has been observed that the ordering of usages can be non-determinstic in parallel builds. Therefore, this contribution introduces sorting of usages based on a platform- and race-independent sorting criterion. Resolves #26877. Co-authored-by: Wolfgang Jeltsch <wolfgang@well-typed.com> - - - - - 8e1cc105 by Wolfgang Jeltsch at 2026-06-16T20:25:57-04:00 Change the descriptions of two existing changelog entries The descriptions now describe the changes in a user-friendly manner, as opposed to describing the contributions that led to these changes in a developer-friendly manner. - - - - - 636c1c7a by Ian Duncan at 2026-06-16T20:26:50-04:00 AArch64: use SXTH, not SXTW, for W32 signExtendReg signExtendReg was using SXTH (sign-extend halfword, 16-bit) for W32-to-W64 sign extension. This should be SXTW (sign-extend word, 32-bit). SXTH only sign-extends the lower 16 bits, producing wrong results for 32-bit values whose bit 15 differs from bit 31. Other fixes: - At sub-W64, code gen for MO_S_Mul2 should use W32 registers for SMULL source operands as per the ARM spec (SMULL Xd, Wn, Wm), and not W64. - Ensure signExtendReg uses the source width for the source operand in SXTW/SXTH/SXTB instructions. GNU as requires sxtw Xd,Wn (not sxtw Xd,Xn), while LLVM's integrated assembler on macOS is lenient. - Fix overflow flag computation for `MO_S_Mul2`. The overflow bit was exactly inverted for sub-W64 operands. Fixes #26978 and #27047 - - - - - b734c75d by Igor Ranieri at 2026-06-16T20:27:32-04:00 haddock: Update CONTRIBUTING with missing step, add missing test dependency - - - - - 7fe4f2ec by Luite Stegeman at 2026-06-17T05:35:09-04:00 tag inference: don't confuse functions with their return values inferTagRhs was mixing up taggedness for closures and return values for function closures. We really shouldn't assign TagTuple to a properly tagged function returning a tuple. We fix this by keeping track of functions (TagFun) separately from values (TagVal) and keeping track of their return value. TagFun is also used for join points. fixes #27005 - - - - - 4671c126 by Sebastian Graf at 2026-06-17T05:35:55-04:00 Seed the simplifier's in-scope set for open expressions simplifyExpr simplifies expressions typed at the GHCi prompt and the results of Template Haskell splices. Such an expression may be open: at a GHCi debugger breakpoint its free variables include RuntimeUnk skolems standing for as-yet-unknown types. The simplifier began with an in-scope set holding only the wildcard binder, so when it instantiated the unsafeCoerce# wrapper that GHCi builds around a result, it formed a substitution whose range mentioned a free skolem that was not in scope. That breaks the substitution invariant and, in a compiler built with assertions, trips substTy's sanity check. Seed the initial in-scope set with the free variables of the expression. For a closed expression this adds nothing. See Note [Seed the in-scope set for open expressions]. Fixes #17833 and its duplicate #21118. - - - - - 67d41299 by Sebastian Graf at 2026-06-18T05:18:24-04:00 Desugar a `case` scrutinee only once (#27383, #20251) In `dsExpr` for `HsCase` we desugared the scrutinee /twice/: once to build the Core `case` itself, and again inside `matchWrapper`, which re-desugared the source scrutinee (via `addHsScrutTmCs`) purely to record long-distance information for the pattern-match checker. For a single `case` that is merely wasteful. But for nested cases it is catastrophic. Consider case (case (case e of ... ) of ... ) of ... Desugaring the outer scrutinee desugars the middle `case` twice, each of which desugars the inner `case` twice, and so on. The work doubles at every level, so desugaring takes O(2^n) time in the nesting depth. That is the blowup reported in #27383; it is also what makes the machine-generated program in #20251 take an age to compile. The fix is simple. `matchWrapper` is handed the scrutinee anyway, so we give it the Core expression we have /already/ desugared, and record the long-distance term constraint with `addCoreScrutTmCs` instead of re-desugaring from source. This is just what `matchSinglePatVar` already does for single-pattern matches. So: * `matchWrapper` now takes `Maybe [CoreExpr]` rather than `Maybe [LHsExpr GhcTc]`. * The `HsCase` equation of `dsExpr` passes the already-desugared `core_discrim`; the arrow desugarer passes its match variables. * `addHsScrutTmCs` had no other use, so it is gone. Desugaring is now linear in the nesting depth. (The coverage checker still runs `simpleOptExpr` over each scrutinee, which leaves the total at O(n^2); that is ample.) The long-distance information itself is unchanged: the checker sees precisely the Core that backs the generated code. Test: deSugar/should_compile/T27383 - - - - - fa5defde by Rodrigo Mesquita at 2026-06-18T05:19:11-04:00 fix: Save FastStrings in the PMC There is no point in adding the unique to the occurrence FastString we create, since it is part of the Id anyway. Adding it to the FastString, meant each FastString was unique unnecessarily! In a separate branch, running the compiler on test `InstanceMatching` observed 30000 `FastString`s created by this code path. Plus, `fsLit "pm"` follows the existing pattern in `mkPmId`. - - - - - 4efb4a66 by Alan Zimmerman at 2026-06-18T14:41:14-04:00 TTG: Add extension points to HsConDetails Extend HsConDetails as data HsConDetails p arg rec = PrefixCon !(XPrefixCon p) [arg] -- C @t1 @t2 p1 p2 p3 | RecCon !(XRecCon p) rec -- C { x = p1, y = p2 } | InfixCon !(XInfixCon p) arg arg -- p1 `C` p2 | XHsConDetails !(XXHsConDetails p) type family XPrefixCon p type family XRecCon p type family XInfixCon p type family XXHsConDetails p - - - - - c8d27dd4 by Simon Jakobi at 2026-06-18T14:41:59-04:00 CI: quiet submodule clean output in after_script and setup The clean and cleanup_submodules functions ran 'git submodule foreach git clean -xdf', flooding the job log with 'Entering ...' and 'Removing ...' lines. Pass --quiet to 'git submodule' and -q to 'git clean' to drop the success output; errors are still reported. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> - - - - - 09326ca6 by Matthew Pickering at 2026-06-20T23:41:12+02:00 Add missing req_interp modifier to T18441fail3 and T18441fail19 These tests require the interpreter but they were failing in a different way with the javascript backend because the interpreter was disabled and stderr is ignored by the test. - - - - - 521e55bf by Matthew Pickering at 2026-06-20T23:41:13+02:00 hadrian: Fill in more of the default.host toolchain file When you are building a cross compiler this file will be used to build stage1 and it's libraries, so we need enough information here to work accurately. There is still more work to be done (see for example, word size is still fixed). - - - - - 23c9b6c3 by Matthew Pickering at 2026-06-20T23:42:52+02:00 hadrian: Build stage 2 cross compilers * Most of hadrian is abstracted over the stage in order to remove the assumption that the target of all stages is the same platform. This allows the RTS to be built for two different targets for example. * Abstracts the bindist creation logic to allow building either normal or cross bindists. Normal bindists use stage 1 libraries and a stage 2 compiler. Cross bindists use stage 2 libararies and a stage 2 compiler. * hadrian: Make binary-dist-dir the default build target. This allows us to have the logic in one place about which libraries/stages to build with cross compilers. Fixes #24192 New hadrian target: * `binary-dist-dir-cross`: Build a cross compiler bindist (compiler = stage 1, libraries = stage 2) This commit also contains various changes to make stage2 compilers feasible. ------------------------- Metric Decrease: LinkableUsage02 ManyAlternatives ManyConstructors MultiComponentModulesRecomp MultiLayerModulesRecomp RecordUpdPerf T10421 T12150 T12227 T12425 T12707 T13035 T13379 T13820 T15703 T16577 T18140 T18282 T18698a T18698b T18923 T1969 T20049 T21839c T3294 T4801 T5030 T5321FD T5321Fun T5631 T5642 T6048 T783 T9020 T9198 T9233 T9630 T9872d T9961 parsing001 T3064 Metric Increase: T26989 hard_hole_fits ------------------------- Co-authored-by: Sven Tennie <sven.tennie@gmail.com> - - - - - 26fed8ab by Matthew Pickering at 2026-06-20T23:42:52+02:00 ci: Test cross bindists We remove the special logic for testing in-tree cross compilers and instead test cross compiler bindists, like we do for all other platforms. - - - - - 80c8910e by Matthew Pickering at 2026-06-20T23:42:52+02:00 ci: Introduce CROSS_STAGE variable In preparation for building and testing stage3 bindists we introduce the CROSS_STAGE variable which is used by a CI job to determine what kind of bindist the CI job should produce. At the moment we are only using CROSS_STAGE=2 but in the future we will have some jobs which set CROSS_STAGE=3 to produce native bindists for a target, but produced by a cross compiler, which can be tested on by another CI job on the native platform. CROSS_STAGE=2: Build a normal cross compiler bindist CROSS_STAGE=3: Build a stage 3 bindist, one which is a native compiler and library for the target - - - - - 8215573d by Sven Tennie at 2026-06-20T23:42:52+02:00 ci: Increase timeout for emulators Test runs with emulators naturally take longer than on native machines. Generate jobs.yml - - - - - 5acb7dbc by Matthew Pickering at 2026-06-20T23:42:52+02:00 ci: Javascript don't set CROSS_EMULATOR There is no CROSS_EMULATOR needed to run javascript binaries, so we don't set the CROSS_EMULATOR to some dummy value. - - - - - 48345343 by Sven Tennie at 2026-06-20T23:42:52+02:00 Javascript skip T23697 See #22355 about how HSC2HS and the Javascript target don't play well together. - - - - - 5e44fd05 by Sven Tennie at 2026-06-20T23:42:52+02:00 Mark T24602 as fragile It was skipped before (due to CROSS_EMULATOR being set, which changed for JS), so we don't make things worse by marking it as fragile. - - - - - ab349ec2 by Sven Tennie at 2026-06-20T23:42:52+02:00 Fix T22744 for GHCJS In fact, this test needs Template Haskell, not necessarily an interpreter. - - - - - c73352d8 by Sven Tennie at 2026-06-20T23:42:52+02:00 haddock-test: fix GHCJS haddock test failures Add --ghc-pkg-path flag support so haddock test runner can find cross-prefixed ghc-pkg (e.g. javascript-unknown-ghcjs-ghc-pkg) which is not on $PATH in cross install directories. Skip haddockHtmlTest on GHCJS: Threaded.hs uses forkOS in a TH splice, which GHCJS RTS doesn't support. Mark with js_skip in all.T. - - - - - 5e814e76 by Andreas Klebinger at 2026-06-22T23:00:24-04:00 compiler: Deduplicate hscTidy This function was accidentally duplicated during a refactor. Fixes #27351 - - - - - 473b97eb by sheaf at 2026-06-22T23:01:22-04:00 Avoid mkTick in Core Prep breaking ANF (part II) Hotfix for 2f9579765f55b3920ceb2e04995ff41a9d0e2d4e fixing a small oversight in the call to tickTickedExpr from mkTick, in which we improperly recursively called mkTick without passing on the preserve_anf flag. Fixes #27386 - - - - - 9284a1f7 by Simon Hengel at 2026-06-23T05:55:33-04:00 Don't use global variables to address concurrency bugs! (fixes #27234) This was originally introduce with 88f38b03025386f0f1e8f5861eed67d80495168a to address #17922. In this specific case a better fix would have been to synchronize on stderr: withHandle_ "stderrSupportsAnsiColors" stderr $ \ _ -> do ... But apparently the dependency on `terminfo` was removed in 32ab07bf3d6ce45e8ea5b55e8095174a6b42a7f0, preventing #17922 in the first place. - - - - - 44309cd3 by Alan Zimmerman at 2026-06-23T05:56:20-04:00 EPA: remove LocatedL / SrcSpanAnnL and LocatedLI / SrcSpanAnnLI This is part of a refactor towards only having LocatedA / SrcSpanAnnA It removes the stated items, but has to add back one for BooleanFormula, LocatedBF / SrcSpanAnnBF This commit also use the HsConDetails RecCon extension point to capture the braces in a record constructor - - - - - 2f6a5534 by Simon Jakobi at 2026-06-23T15:46:20+02:00 Add -dstable-core-dump-order for stable Core dump ordering (#27296) The order of top-level bindings in Core dumps (-ddump-simpl etc.) is the compiler's Unique-sensitive internal processing order, so an unrelated upstream change can reorder them and defeat a textual diff of two dumps. This adds an opt-in flag -dstable-core-dump-order that reorders the top-level bindings of dumps routed through dumpPassResult into a stable, Unique-independent order, so two dumps line up across rebuilds. See Note [Stable Core dump order] in GHC.Core.Ppr for the sort key and its rationale. Adds tests T27296 (binders GHC emits in non-source order by default, asserted to come out stably ordered under the flag) and T27296b (an untidied -ddump-float-out dump pinning the ordering of the anonymous lvl floats by literal value). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> - - - - - 141986e3 by mangoiv at 2026-06-24T15:51:14-04:00 compiler: refactor error reporting code for ExplicitLevelImports Refactors error reporting code for ExplicitLevelImports to pass in a RdrName and a GlobalReaderElt to be able to report errors that are faithful to the source and to more precisely distinguish between names that are in scope from different qualifications. Fixes #27385 and #26616 - - - - - aa7df6b6 by Simon Hengel at 2026-06-24T15:52:18-04:00 Set GHC_VERSION when calling custom pre-processors (see #25952) (so that pre-processors can emit backwards compatible code) - - - - - a9e494f2 by Simon Hengel at 2026-06-24T15:54:08-04:00 Add a flag to control GHCi specific error hints (close #27409) - - - - - a805b2a2 by Simon Hengel at 2026-06-24T15:55:20-04:00 Reference correct package in error messages for reexported modules (fixes #27417) - - - - - f235d183 by Simon Jakobi at 2026-06-25T05:51:18-04:00 Add explicit setBit/clearBit/complementBit for instance Bits Integer (#21176) The default setBit, clearBit, and complementBit methods allocate intermediate Integers per call. Define them explicitly via the new integerSetBit[#], integerClearBit[#] and integerComplementBit[#], built on the BigNat# primitives, which avoid those allocations. Allocation is not eliminated entirely -- the negative (IN) cases would need in-place mutation, which is left as future work. The default methods constant-folded on literal arguments via the integerOr/integerAnd/integerXor rules, which fold literal Integers of any size. The explicit functions have no such rule, so they (their Word-argument wrappers, and the Bits Integer methods) are marked INLINE to expose the underlying primops to the simplifier; see Note [INLINE for constant folding of bit operations]. This restores folding only on the small-int (IS) path -- large literal Integers (IP/IN) are no longer constant-folded, a minor regression for that case. T8832 covers the IS-path folding. The new golden-output test T21176 checks all three operations against the default implementations across the sign/size boundaries, recording each result plus its integerCheck validity. The base and ghc-bignum interface- stability export goldens gain the new functions. The main changelog entry lives in changelog.d under a new ghc-internal section (renamed from ghc-prim). CLC proposal: https://github.com/haskell/core-libraries-committee/issues/423 Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com> - - - - - 202ed264 by Marc Scholten at 2026-06-25T05:52:21-04:00 haddock: use Text in documentation pipeline This patch moves Haddock's documentation pipeline from String to Text where the data is already textual. It avoids repeated conversions while keeping the existing decoding behavior for invalid UTF-8 docstring chunks. The main changes are: * Render and carry docstrings as Text in Haddock-facing paths. * Use the Binary Text instance from GHC.Utils.Binary for Haddock interface files, and bump the Haddock binary interface version. * Add a FastString HTML instance so XHTML rendering avoids intermediate String allocation. * Keep HsDocStringChunk decoding lenient, matching the previous unpackHDSC behavior on invalid UTF-8 input. * Update the xhtml submodule to 3000.4.1.0, which contains the apostrophe escaping fix used by the Haddock test output. Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com> Assisted-by: Codex <codex@openai.com> - - - - - a72ff58f by mangoiv at 2026-06-25T05:53:07-04:00 compiler: rename ZonkAny to UnusedType and add pretty printing logic ZonkAny is a hard to understand name for users who do not know how the compiler works internally. Additionally, it is confusing that ZonkAny, while being a concrete type *represents* a meta variable, espeically in the compiler output. This patch changes the name of ZonkAny to UnusedType which is closer to its intended semantics and adds special pretty printing logic to display this type in the same fashion the compiler displays meta variables in other places, whenever they leak from the implementation to the user. It also exports the type from ghc-internal:GHC.Internal.Types in order to expose documentation. Fixes #27390 Co-Authored-By: Sam Derbyshire <sam.derbyshire@gmail.com> - - - - - 6813f002 by Simon Jakobi at 2026-06-26T04:51:47-04:00 Reg.Linear: drop Platform argument from most FR (FreeRegs) methods The FR class has one instance per CPU architecture, so any architecture-constant information its methods derived from the Platform argument can instead be baked into the instance. This removes the now needless Platform argument from frAllocateReg, frGetFreeRegs and frReleaseReg. frInitFreeRegs keeps its Platform argument: the initial allocatable set is genuinely platform-dependent, see Note [Aarch64 Register x18 at Darwin and Windows]. Fixes #26665 Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> - - - - - 3b2a9409 by Zubin Duggal at 2026-06-26T04:52:39-04:00 testsuite: Report fragile failures as skipped in JUnit output - - - - - 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. - - - - - ed09895d by Andreas Klebinger at 2026-07-08T16:53:27-04:00 Fix a profiling race condition resulting in segfaults. StgToCmm: Don't assume tagged FUN closures in closureCodeBody. When entering a closure the self/node pointer might not be tagged in some situations when a thunk is evaluated by multiple threads. So we most AND away the tag bits rather than subtracting an expected tag. Apply.cmm: Fix a race condition occuring when a thunk is mutated during GC. In stg_ap_0_fast when might need to run GC before entering a thunk. If this happens another thread or the GC itself might mutate the closure making entering it no longer valid. We now check for this. Add test and changelog for #27123 fixes. - - - - - 67c03eb2 by Cheng Shao at 2026-07-08T16:54:09-04:00 ghc-heap: fix invalid srtlen returned by peekItbl when no-TNTC This patch fixes the no-TNTC code path of `peekItbl` so that it looks at the right memory address when reading the `srt` field from the `StgInfoTable_` struct. Also adds a `T27465` regression test that reproduces the bug on no-TNTC builds before the fix. Fixes #27465. Co-authored-by: Codex <codex@openai.com> - - - - - 2ecabb4f by Zubin Duggal at 2026-07-09T09:23:25-04:00 hadrian: binary-dist-dir should not be the default target Revert behaviour to pre 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2 In 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2, we applied the following behaviour change: ``` hadrian: Build stage 2 cross compilers ... * hadrian: Make binary-dist-dir the default build target. This allows us to have the logic in one place about which libraries/stages to build with cross compilers. Fixes #24192 ``` This is a major regression to development experience, a plain hadrian/build --freeze1 now takes ages because we rebuild all docs (which need to go in the binary dist dir). `binary-dist-dir` is the wrong default target for regular GHC development work Fixes #27445 - - - - - e16388e3 by Zubin Duggal at 2026-07-09T09:23:25-04:00 .gitignore: Add the hadrian system.config introduced by commit 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2 Since commit 23c9b6c392f52ec9d7a8618b204ff6b885f5fba2 Author: Matthew Pickering <matthewtpickering@gmail.com> Date: Thu Dec 21 16:17:41 2023 +0000 hadrian: Build stage 2 cross compilers ./configure produces /hadrian/cfg/system.config.{host,target} Add these to .gitignore - - - - - 7e8abf41 by Alan Zimmerman at 2026-07-09T09:24:12-04:00 EPA: Replace AnnListItem with simply [TrailingAnn] Remove the unnecessary wrapper around a single field. - - - - - 29032f17 by Zubin Duggal at 2026-07-09T09:24:58-04:00 testsuite: Keep real reason for fragile test failures - - - - - c34e03a7 by Zubin Duggal at 2026-07-09T09:24:58-04:00 testsuite: Fall back to the failure reason for empty JUnit bodies - - - - - 409d40f0 by Zubin Duggal at 2026-07-09T09:24:58-04:00 testsuite: Show output diffs in JUnit output Also refactor compare_outputs to return essentially a `Maybe Diff` (`CompareOutput`) instead of a bool, but more pythonic. This allows us to pass the diff through nice. - - - - - 06fee1ab by Zubin Duggal at 2026-07-09T09:24:58-04:00 perf notes: include stat deviation and acceptance window in notes so they show up in gitlab - - - - - 57c0f32c by mangoiv at 2026-07-10T11:08:38-04:00 driver: enable -finter-module-far-jumps by default this fixes a compatibility bug with certain binutils/gcc versions where we were seeing jump offset overflow errors. This commit can probably reverted if we stop supporting the problematic binutils/gcc verions (2.44 and 14.2, respectively) Reolves #26994 - - - - - 4396a6f2 by Andrea Vezzosi at 2026-07-10T11:09:25-04:00 [Fix #27287] preserve ModBreaks in ModIface - - - - - 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. - - - - - 4f54bcc1 by Duncan Coutts at 2026-07-16T09:14:38+01:00 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! - - - - - 74adf094 by Duncan Coutts at 2026-07-16T09:14:38+01:00 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()). - - - - - 7ef31daf by Duncan Coutts at 2026-07-16T09:14:38+01:00 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. - - - - - 12382f85 by Duncan Coutts at 2026-07-16T09:14:38+01:00 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. - - - - - 87367a1d by Duncan Coutts at 2026-07-16T09:14:38+01:00 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. - - - - - e7326bb0 by Duncan Coutts at 2026-07-16T09:14:38+01:00 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. - - - - - 76125f45 by Duncan Coutts at 2026-07-16T09:14:38+01:00 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. - - - - - 73ddbe67 by Duncan Coutts at 2026-07-16T09:14:38+01:00 Add a FIXME note in the Poll I/O manager - - - - - 3feb9efe by Duncan Coutts at 2026-07-16T09:14:39+01:00 Add missing updateRemembSetPushClosure in poll I/O manager For the non-moving GC. - - - - - d4932eb6 by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - a9bff207 by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - 06e132fd by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - bc110400 by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - d41446b8 by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - 991324b1 by Duncan Coutts at 2026-07-16T09:14:39+01:00 Add interruptIOManager support for select I/O manager Uses the FdWakup mechanism. - - - - - ba470b5a by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - 6197fecf by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - c0393a7c by Duncan Coutts at 2026-07-16T09:14:39+01:00 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. - - - - - e6ee1c89 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Make signal handling be a respondibility of the I/O manager(s) Previously it was scattered between I/O managers and the scheduler, and especially the scheduler's deadlock detection. Previously the scheduler would poll for pending signals each iteration of the scheduler loop. The scheduler also had some hairy signal functionality in the deadlock detection: in the non-threaded RTS (only) if there were still no threads running after deadlock detection then it would block waiting for signals. But signals can and (in my opinion) should be thought of as just a funny kind of I/O, and thus should be a responsibility of the I/O manager. So now we have the I/O managers poll for signals when they are polling for I/O completion (and removing the separate poll in the scheduler). And when I/O managers block waiting for I/O then they now also start signal handlers if they get interrupted by a signal. Crucially, if there is no pending I/O or timers, the awaitCompletedTimeoutsOrIO will still block waiting for signals. This patch puts us into an intermediate state: it temporarily breaks deadlock detection in the non-threaded RTS. The waiting on I/O currently happens before deadlock detection. This means we'll now wait forever on signals before doing deadlock detection. We need to move waiting after deadlock detection. We'll do that in a later patch. - - - - - 68a22a05 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Clean up the RTS internal signal handling API Now that the I/O manager is responsible for signals, we can simplify the API we present for signal handling. We now just need startPendingSignalHandlers, which is called from the I/O managers. We can get rid of awaitUserSignals. We also don't need RtsSignals.h to re-export the platform-specific posix/Signals.h or win32/ConsoleHandler.h We can also hide more of the implementation of signals. Less has to be exposed in posix/Signals.h or win32/ConsoleHandler.h. Indeed, posix/Signals.h becomes empty and we remove it. Partly this is because we don't need inline functions (or macros) in the interface. Also remove signal_handlers from RTS ABI exported symbols list. It does not appear to have any users in the core libs, and its really an internal implementation detail. It should not be exposed unless it's really necessary. - - - - - f566aac9 by Duncan Coutts at 2026-07-16T09:36:44+01:00 In the scheduler, move I/O blocking after deadlock detection To make deadlock detection effective in the non-threaded RTS when there are deadlocked threads and other unrelated threads waiting on I/O, we need to arrange to do deadlock detection before we block in scheduler to wait on I/O. The solution is to: 1. adjust scheduleFindWork, which runs before deadlock detection, to only poll for I/O and not block; and 2. add a step after deadlock detection to wait on I/O if there are still no threads to run (and there's any I/O or timeouts outstanding) The scheduleCheckBlockedThreads is now so simple that it made more sense to inline it into scheduleFindWork. - - - - - fe408939 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Remove bogus anyPendingTimeoutsOrIO guard from scheduleDetectDeadlock The deadlock detection was only invoked if both of these conditions hold: 1. the run queue is empty 2. there is no pending I/O or timeouts The second condition is unnecessary. The deadlock detection mechanism can find deadlocks even if there are other threads waiting on I/O or timers. Having this extra condition means that we fail to detect blocked threads if there are any threads waiting on I/O or timers. Part of fixing issue #26408 - - - - - ec5706a0 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Don't consider pending I/O for early context switch optimisation Context switches are normally initiated by the timer signal. If however the user specifies "context switch as often as possible", with +RTS -C0 then the scheduler arranges for an early context switch (when it's just about to run a Haskell thread). Context switching very often is expensive, so as an optimisation there cases where we do not arrange an early context switch: 1. if there's no other threads to run 2. if there is no pending I/O or timers This patch eliminates case 2, leaving only case 1. The rationale is as follows. The use of this was inconsistent across platforms and threaded/non-threaded RTS ways. It only worked on the non-threaded RTS and on Windows only worked for the win32-legacy I/O manager. On all other combinations anyPendingTimeoutsOrIO would always return false. The fact that nobody noticed and complained about this inconsistency suggests that the feature is not relied upon. If however it turns out that applications do rely on this, then the proper thing to do is not to restore this check, but to add a new I/O manager hint function that returns if there is any pending events that are likely to happen *soon*: for example timeouts expiring within one timeslice, or I/O waits on things likely to complete soon like disk I/O, but not for example socket/pipe I/O. The motivation to avoid this use of anyPendingTimeoutsOrIO is to allow us to eliminate anyPendingTimeoutsOrIO entirely. All other uses of this are just guards on {await,poll}CompletedTimeoutsOrIO and the guards can safely be folded into those functions. This will better cope with some I/O managers having no proper implementation of anyPendingTimeoutsOrIO. Ultimately this will let us simplify the scheduler which currently has to have special #ifdef mingw32_HOST_OS cases to cope with the lack of a working anyPendingTimeoutsOrIO for some Windows I/O managers - - - - - df340a0f by Duncan Coutts at 2026-07-16T09:36:44+01:00 Remove anyPendingTimeoutsOrIO guarding {poll,await}CompletedTimeoutsOrIO Previously the API of the I/O manager used a two step process: check anyPendingTimeoutsOrIO and then call {poll,await}CompletedTimeoutsOrIO. This was primarily there as a performance thing, to cheaply check if we need to do anything. And then because anyPendingTimeoutsOrIO existed, it was used for other things too. We have now eliminated the other uses, and are just left with the performance pattern. But this was problematic because not all I/O managers correctly implement anyPendingTimeoutsOrIO (specifically the win32 ones), and now that we also make I/O managers responsible for signals then we need to poll/await even if there is no pending I/O or timeouts. If there is no pending I/O or timeouts then poll/await needs to degenerate to just waiting forever for any signals. - - - - - 11dde2c6 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Remove anyPendingTimeoutsOrIO, it is no longer used And this avoids the problems arising from the win32 I/O managers having had a bogus implementation. - - - - - 99037204 by Duncan Coutts at 2026-07-16T09:36:44+01:00 Remove second scheduler call to awaitCompletedTimeoutsOrIO Previously awaitCompletedTimeoutsOrIO was called both before and after deadlock detection in the scheduler. The reason for that was that the win32 I/O managers had a bogus implementation of anyPendingTimeoutsOrIO and this was used to guard the call of awaitCompletedTimeoutsOrIO prior to deadlock detection. This meant the first call site was never actually called when using the win32 I/O managers. This was the reason for the second call: the first one was never used. What a mess. So now we have a simple design in the scheduler: 1. poll for completed I/O, timers or signals 2. if no runnable threads: do deadlock detection 3. if still no runnable threads: block waiting for I/O, timers or signals. - - - - - ccbe220a by Duncan Coutts at 2026-07-16T09:36:45+01:00 Lift emptyRunQueue guard out of scheduleDetectDeadlock this improved the clarity of the logic when reading the scheduler code. - - - - - 748bf4d9 by Duncan Coutts at 2026-07-16T09:36:45+01:00 Make non-threaded deadlock detection also rely on idle GC Only do deadlock detection GC when idle GC kicks in. This also relies on using wakeUpRts, so now do this unconditionally. Previously wakeUpRts was for the threaded rts only. - - - - - 490d8fe3 by Duncan Coutts at 2026-07-16T09:36:45+01:00 Enable idle GC by default on non-threaded RTS. The behaviour is now uniform between threaded and non-threaded. The deadlock detection now relies on idle GC for both threaded and non-threaded ways. Previously deadlock detection did not rely on idle GC for the non-threaded way. - - - - - e08746e0 by Duncan Coutts at 2026-07-16T09:36:45+01:00 Add a long Note [Deadlock detection] It describes the historical and modern designs and their trade-offs. The point is we've now unified the code for deadlock detection between the threaded and non-threaded ways, by changing the non-threaded to follow the same design as the threaded. - - - - - dee3a735 by Duncan Coutts at 2026-07-16T09:36:45+01:00 Add a test for deadlock detection, issue #26408 - - - - - 1120a867 by Duncan Coutts at 2026-07-16T09:36:45+01:00 Update the user guide with the revised idle GC behaviour i.e. it's now not just for the threaded RTS, but general. Also document the fact that disabling idle GC also disables deadlock detection. And add a changelog entry. - - - - - 750 changed files: - .gitignore - .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/26616 - + changelog.d/AbstractQ - + changelog.d/T17833 - + changelog.d/T21176 - + changelog.d/T21628 - + changelog.d/T26978 - + changelog.d/T27047 - + changelog.d/T27123.md - + changelog.d/T27308 - + changelog.d/T27360 - + changelog.d/T27386 - + changelog.d/T27456 - + changelog.d/add_can_drop_to_occurence_analyser - changelog.d/config - + changelog.d/deterministic-usage-order - + changelog.d/fix-absent-dict-projection - + changelog.d/fix-cmm-atomic-load-store - + changelog.d/fix-compacting-gc-ap-27434 - + changelog.d/fix-exponential-case-desugar-27383 - + changelog.d/fix-layout-stack-fcall - + changelog.d/fix-peekitbl-no-tntc - + changelog.d/fix-plugin-finder-multi-home-unit.md - + changelog.d/fix-unreg - 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