Rodrigo Mesquita pushed to branch wip/romes/multi-threaded-debugger at Glasgow Haskell Compiler / GHC Commits: d07a5176 by Simon Peyton Jones at 2026-10-13T18:10:39-04:00 Remove the Eq and Ord instances for ForAllTyFlag In Note [Comparing visibility] in GHC.Core.TyCo.Compare we read that "we always compare ForAllTyFlags with `eqForAllVis` or `cmpForAllVis`" But alas there was an Eq and Ord instance for ForAllTyFlag, which made it impossible to check this claim. So I made these changes: * Move the definition of ForAllTyFlag and its related functions from L.H.S.Specificity (where it did not belong, since L.H.S didn't use it) into GHC.Types.Var. * Remove the Eq and Ord instances for ForAllTyFlag * Deal with the fallout, by using `eqForAllVis` or related functions. * In interface files we use IfaceType as a key for a de-deduplication map See Note [Deduplication during iface binary serialisation] in GHC.Iface.Binary. For this we need /exact/ comparison, so we use a newtype wrapper for IfaceForAllTyFlag, and give use `cmpForAllTyFlagExactly` to implement its Ord instance. Tiresome but easy. * Rename `toIfaceForAllBndrs` to `toIfaceForAllTyBndrs` - - - - - ea5c054d by Simon Peyton Jones at 2026-10-13T18:10:39-04:00 Refactor type and coercion substitution This MR refactors type and coercion substitution so that they use TyCoMapper, rather than hand-rolled code. Fundamentally it's a simple idea, but I had to do quite a bit of refactoring to make it fly. I got Claude to help me this this refactoring, but I paid careful attention to every line of code. Main changes: * New module GHC.Core.TyCo.Make which defines TyCoMapper, and a bunch of other simple "smart constructors" for types and coercions. See GHC.Core.TyCo.Rep Note [The Type-related module hierarchy], esp (TRM1) * The new TyCoMapper has new fields `tcm_tcapp_ty` and `tcm_tcapp_co` to handle type-constructor applications. These replace `tcm_tycon`. * Rewrite GHC.Core.TyCo.Subst to use TyCoMapper * Rewrite GHC.Core.Type.expandTypeSynonyms to use TyCoMapper. * Implement `seqType` and `seqCo` with TyCoFolder. To to this I had to add a `tcf_lit` field to TyCoFolder. * A new module GHC.Utils.StrictIdentity to define a strict identity monad, which itself is used for substTyCoMapper :: TyCoMapper Subst StrictIdentity * I removed an apparently-unused instance for Binary Levity Refactoring `seq` functions * In GHC.Core.Seq, redefine `seqOneShot`, `seqRuleInfo`, and friends to return `SeqResult`, a new type defined in GHC.Types.Baseic, rather than `()`. We can define a Monoid instance for `SeqResult` that does the right thing. * This has knock-on effects across the compiler. - - - - - 34165e23 by Simon Peyton Jones at 2026-10-13T18:10:39-04:00 Refactor TyCoMapper to take a single monad; add StrictReaderT TyCoMapper used to be parameterised over both an environment and a monad, with fields like tcm_tyvar :: env -> TyVar -> m Type Now it is parameterised over just the monad: tcm_tyvar :: TyVar -> m Type If the mapping needs an environment, `m` is a reader monad over that environment. Many uses (e.g. zonkTcTypeMapper, swizzleMapper) need no environment at all, and used to pass a dummy (). The binder field becomes tcm_tycobinder :: forall r. TyCoVar -> ForAllTyFlag -> (TyCoVar -> m r) -> m r and runs the continuation in the extended environment. mapTyCoX is gone; only mapTyCo remains. To make this efficient, the reader monad must use the one-shot trick and be strict in the environment. So: * New module GHC.Utils.Monad.StrictReader defines newtype StrictReaderT r m a with hand-written instances. The builder of the pattern synonym `StrictReaderT` is a smart constructor that adds both `oneShot` and a bang on the environment, so every StrictReaderT computation is strict in the environment. See Note [Instances for StrictReaderT]. * ZonkT becomes type ZonkT = StrictReaderT ZonkEnv ZonkM becomes type ZonkM = StrictReaderT ZonkGblEnv IO replacing their own hand-written instances. * Substitution uses type SubstM = StrictReaderT Subst StrictIdentity substTyCoMapper :: TyCoMapper SubstM and similarly expandTypeSynonymMapper. * zonk_tycomapper :: TyCoMapper (ZonkT TcM) is now much simpler. * swizzleMapper uses StrictIdentity rather than Identity. * Module renaming, so that the strict monads are all peers in GHC.Utils.Monad: GHC.Utils.StrictIdentity ==> GHC.Utils.Monad.StrictIdentity GHC.Utils.Monad.State.Strict ==> GHC.Utils.Monad.StrictState alongside the new GHC.Utils.Monad.StrictReader. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> - - - - - c0299e15 by Simon Jakobi at 2026-10-13T18:11:23-04:00 testsuite: Line-buffer the driver's stdout Python block-buffers stdout when it is a pipe. This is the case for example in CI. As a result there is often no indication of progress at all until the run ends. To fix this, we configure it explicitly to use line buffering instead. stderr is reconfigured too, for consistency: Python line-buffers it by default since 3.9. The type-ignores are for mypy, which types these handles as TextIO — an interface without reconfigure. Fixes #12934. Assisted-by: Claude Fable 5 - - - - - 9b5beaa2 by Florian Ragwitz at 2026-10-13T18:12:05-04:00 hpc: Improve coverage semantics for instance methods and instances Users care about which of their explicitly written methods are or aren't covered, not whether all of the inherited methods are covered as well. Those should be covered where they are implemented. We therefore skip generating top-level boxes for inherited methods which will appear as uncovered with no clear indication as to why, and no way to fix other than exercising code the user has not written. Previously, top-level boxes for those inherited methods would use the instance head as their source span. Now that those boxes are gone, we can use that source span for another purpose: We introduce a new top-level box for each class instance with its instance head as the source span, and use that to indicate whether or not an instance has been covered at all. We do this by making any method of the instance, inherited/generated or otherwise, tick the box for the instance head. Excluded from this are methodless classes, which could never be covered using the current mechanism. This could be improved upon further. These changes apply to ticking for program coverage only, and don't affect source notes. Additionally, we update the scope of record selector ticking to be limited to program coverage as well, as the oversight to also extend it to source notes has previously caused bugs and because record selector ticking is coverage-specific. Fixes #17155, #15932. - - - - - 836ec50a by Simon Peyton Jones at 2026-10-13T18:12:54-04:00 Refactor fundeps again This MR fixes #27828; there was a bad scoping error in `trim_qtvs`. The main changes are * Refactor `trim_qtvs` completely to eliminate the bug. * Remove a redundant `apartnessCheck` from `mkTopOpenFamEqFDs`. * Lots of improvements to the Notes in FunDeps.hs I also did a couple of pure refactors: * I realised that we were carefully caching `cab_incomps` in each `CoAxBranch`, to make it more efficient to reduce a type family application, but we were not doing the same thing when computing relevance for functional dependencies; see Note [Relevance] in GHC.Tc.Solver.FunDeps. So I added `cab_overlaps`, which is now used in `noEarlierMatch`. * Use a proper data types, `AmIUnifying` and `OuterKindsFlag`, for two previously-Boolean arguments to `tc_unify_tys`. This is a pure refactor. - - - - - 889ef371 by Simon Peyton Jones at 2026-10-13T18:13:36-04:00 Refactor and simplify solver's unification code Ticket #27844 showed that GHC's constraint solver could miss an occurs check, and thereby build an infinite type. This patch significantly simplifes the code in GHC.Tc.Solver.Equality.canEqCanLHSFinish_try_unification GHC.Tc.Solver.Equality.canEqCanLHSFinish_no_unification It is now significantly simpler, and requires much less subtle reasoning to understand. Main changes * If `canEqCanLHSFinish_try_unification` fails to unify, it now /always/ calls `canEqCanLHSFinish_no_unification` rather than trying to finish the job itself. * `GHC.Tc.Solver.Monad.checkTypeEq` is moved from Monad into Equality, and renamed to `GHC.Tc.Solver.Equality.checkTypeEqNoUnification`. * `canEqCanLHSFinish_no_unification` calls `checkTypeEqNoUnification` to test the invariants for an inert equality. Before this MR there was a special case for `do_not_prevent_rewriting`, but that has gone; instead it's just a consequence of the flags passed to `checkTyEqRhs`, documented in the `PuOK` case of `canEqCanLHSFinish_no_unification`. * There is only one bit of "swap back" code, in `finish_no_unify` in `canEqCanLHSFinish_try_unification. Previously this code was duplicated. * `kickOutAfterFillingCoercionHole` should account for equalities with a TyFamLHS. See (KOC5) in Note [Kick out after filling a coercion hole] * No need to gather coercion holes in the `PuOK` case of `canEqCanLHSFinish_no_unification`. See documentation with that code. - - - - - f9193e53 by Simon Peyton Jones at 2026-10-13T18:13:37-04:00 One line fix to fallout from ...#27731, !16564, simplifying Tc.Errors machinery There was an over-eager assert! - - - - - cdd56b7a by Florian Ragwitz at 2026-10-13T18:14:19-04:00 Fix several sphinx errors and warnings from rendering the release notes The extension references which are removed here are for extension which were already previously undocumented, so just removing them seems fine for now. - - - - - 4f00da25 by Florian Ragwitz at 2026-10-13T18:14:19-04:00 Link to QualifiedStrings documentation - - - - - 97adaf89 by Simon Peyton Jones at 2026-10-14T00:07:27+01:00 Line up simpleUnifyCheck and check_ty_eq_rhs Even after #26543 was allegedly fixed, the original repo case in the Description continued to fail. The reason was that the QuickLook unifier, `qlUnify`, used `simpleUnifyCheck` for checking unification invariants; and `simpleUnifyCheck` conservatively rejected any RHS with a coercion hole in it. The upshot was that QuickLook was not as clever as it should be, wrongly failing to do an impredicative instantiation. Interestingly `check_ty_eq_rhs`, which does the same job during constraint solving, was more liberal: it just looked at the free vars of the coercion, and allowed coercion holes. This MR lines them up, adding some careful notes. See Note [simpleUnifyCheck] Note [Occurs check and coercions] Note [Unification preconditions] esp (COERCIONS) Things are better than before, but I am still uncomfortable about the possibilty that a hole might be filled with a coercion that mentions the LHS type variable; for now I have left this discomfort documented in Note [Occurs check and coercions]. Main changes * `qlUnify` now only unifies /instantiation variables/ not regular unification variables. This makes QuickLook more predictable. See (UQL6) in Note [QuickLook unification]. * `qlUnify` no longer needs to call `simpleUnifyCheck`, so we can get rid of `UC_QuickLook` and its code in `simpleUnifyCheck`. * I found I could get rid of `mkOccFolders` in favour of `anyFreeVarsOfType`. Hooray. * Improve documentation of CycleBreakerTv, and rename it to GivenCycleBreakerTv because they are only uesd for Givens! * I accepted a 9% worsening in compile time allocation on T5030 because the newly-consistent story triggered #27934. Other changes * I refactored `atvFolder` so that it pairs the "interesting-var" function with the in-scope set, to avoid building a closure with a free variable. Now we get nice tight loops for `anyFreeVarsOfType` and friends. See Note [Any-free-var folder]. Metric Increase: T5030 - - - - - 5f7b3047 by Simon Peyton Jones at 2026-10-14T00:07:27+01:00 Fix order-dependence in QuickLook Ticket #27917 pointed out that QuickLook was order-dependent -- very bad! The solution is in `qlUnify`: spot when we are unifying a type with a definite monotype, and then monomorphise any free instantiation variables of that type. See (UQL8) and (UQL9) in Note [QuickLook unification]. - - - - - c391c70c by Simon Peyton Jones at 2026-10-14T00:07:28+01:00 Add some comments about RuntimeUnk This commit just adds comments explaining why we don't need to worry about RuntimeUnkTv in the constraint solver. It also tightens up docmentation of earlier (overlapping) commits in this MR. - - - - - 7df3ba2f by Andrea Vezzosi at 2026-10-14T06:15:48-04:00 add runGhcWithSignalHandlers and remove handling from runGhc[T] it only ever makes sense to call `withSignalHandlers` from `main`, otherwise signals can be too easily swallowed without notification to the rest of your process. This commit takes withSignalHandlers out of `runGhc/runGhcT` and provides `runGhcWithSignalHandlers` for the old behaviour. - - - - - 3a72b8a2 by Hannes Siebenhandl at 2026-10-14T13:48:32-04:00 Fix #27836, normalise unit database path in ExternalUnitDatabases Add a regression test, proofing that all variations: - local-unit-db/my-test.conf - ./local-unit-db/my-test.conf - ./local-unit-db/my-test.conf/ are parsed only once. - - - - - 8ddbc6f9 by Florian Ragwitz at 2026-10-14T13:49:28-04:00 Remove obsolete HPC types Fixes #27946. - - - - - f34c79ee by Alan Zimmerman at 2026-10-15T04:54:47-04:00 EPA: Start using vocurly as basis for AnnListLayout For the existing cases that populate AnnList. This uses AnnListBraces when braces are explicitly supplied, and AnnListLayout when vocurly is used The change also shows up AnnList usages that can never capture layout, these are cleared up later. - - - - - 033ba59c by sheaf at 2026-10-15T04:55:44-04:00 Make exprFreeVars deep exprFreeVars used to be a shallow free-variable finder (it didn't look into kinds), but most callers wanted it to be deep. In particular, 'exprFreeVars' is often used to seed an 'InScopeSet', and that must contain the /deep/ free variables. This commit makes it deep, which allows us to get rid of calls to 'closeOverKinds' or other workarounds for shallowness in: - 'GHC.Core.Opt.Simplify.Utils.abstractFloats' - 'GHC.HsToCore.Binds.dsSpec_help' - 'GHC.Core.Opt.Arity.etaBodyForJoinPoint' - 'GHC.Core.FVs.freeVars' - 'GHC.Core.Lint.lintCoreRule' We also remove 'deepExprsFreeVarsDSet' and 'closeOverKindsDSet'. Other places needed a little bit more care, in particular to properly handle coercion variables free in kinds: - 'GHC.Core.Opt.Specialise.specHeader' quantifies over the binder of an unspecialised argument directly, instead of computing the free Ids of the argument. - 'GHC.HsToCore.dsWarnRuleShadowing' filters out 'CoVar's. - 'GHC.Core.Opt.SpecConstr.callToPat' had some ad-hoc logic to compute argument pattern types and a workaround with 'expandTypeSynonyms'. That logic is removed in favour of a new 'argsToPats' function which directly computes the argument pattern types by instantiating the type of the head of the call pattern. Fixes #27936 - - - - - f93d523c by Luite Stegeman at 2026-10-15T04:56:34-04:00 testsuite: Use mkWeakMVar in memo001/memo002 mkWeakPtr in the memo001/memo001 tests created weak pointers with the MVar box as the key, which is fragile in the presence of optimization. The fix is using mkWeakMVar, keying on the primitive MVar# instead. Fixes #27924 and #27396 - - - - - 8c947573 by Simon Peyton Jones at 2026-10-16T13:11:53+01:00 Improve exprOkForSpeculation Fixes #27910, which exposed an infelicity in exprOkForSpeculation The new story is carefully described in new Note [exprOkForSpeculation], esp (a-c) and (EOKS1). - - - - - 7dedcf13 by Alan Zimmerman at 2026-10-16T19:03:17-04:00 EPA: Add TTG fields to FamilyInfo This commit is a simple add, with unused extension fields. It lays the groundwork for using them for exact print annotations - - - - - 26b9a8a0 by Arkissa at 2026-10-17T16:04:10+00:00 ghci: Prefer exact source spans in :type-at Prefer expression types for identical source spans. Fixes #27412. - - - - - 70dc4e61 by sheaf at 2026-10-18T18:15:15-04:00 Carefully implement coercion zapping This commit implements coercion zapping in the rewriter, controlled by the -fzap-coercions flag (on by default). This significantly reduces the size of coercions produced when rewriting type family applications, resulting in much faster compilation. See Note [Coercion zapping] in GHC.Tc.Solver.Rewrite for an explanation and further details. The rewriter now keeps track of the `CoVar`s and `CoercionHole`s it uses when rewriting, which allows computing the dependencies of a zapped coercion without traversing the coercion the rewriter produced, as explained in Note [Computing coercion dependencies] in GHC.Tc.Solver.Rewrite. Accompanying changes: - Rework how dependencies of 'UnivCo's are tracked, purely for performance reasons. We now use the 'UnivCoDeps' datatype instead of '[Coercion]', and we now insist that 'uco_deps' also contains the CoVars that appear in the LHS and RHS types of the UnivCo (as a caching mechanism). - Several performance improvements to the rewriter (e.g. increased strictness). - Improvements to the family application cache, including: - Better documentation. - Only cache a whole chain of reduction steps. - Don't put coercion holes in the cache, fixing #27518. - Allow Core Lint to be called from within the typechecker (and from within the coercion optimiser). - Move out "annotation linting" from Core Lint into the general Core pipeline, to avoid the dependency GHC.Core.Coercion.Opt->GHC.Core.Lint causing a regression in CountDepsParser due to transitive dependencies of GHC.Core.Opt.Monad and GHC.Unit.Module.ModGuts. Fixes #8095 #27336 #27518 Summary of performance numbers Compile-time byte allocated in GHC's testsuite (0 regressions) CoOpt_Singletons(normal) ghc/alloc 634,040,332 595,448,728 -6.1% GOOD FamAppCachePerf(normal) ghc/alloc 495,629,812 191,612,920 -61.3% GOOD LargeRecord(normal) ghc/alloc 1,226,806,434 966,260,976 -21.2% GOOD SimplCastPerf(normal) ghc/alloc 160,505,678 148,112,688 -7.7% GOOD T12227(normal) ghc/alloc 244,668,982 233,037,216 -4.8% GOOD T12545(normal) ghc/alloc 697,804,842 424,705,152 -39.1% GOOD T13386(normal) ghc/alloc 422,871,076 35,213,656 -91.7% GOOD T15703(normal) ghc/alloc 288,402,364 273,692,560 -5.1% GOOD T26426(normal) ghc/alloc 86,002,052 78,152,104 -9.1% GOOD T27336(normal) ghc/alloc 498,932,268 35,886,016 -92.8% GOOD T5030(normal) ghc/alloc 117,057,706 88,785,648 -24.2% GOOD T5321Fun(normal) ghc/alloc 252,552,628 243,820,176 -3.5% GOOD T8095(normal) ghc/alloc 768,198,564 127,779,520 -83.4% GOOD T9872a(normal) ghc/alloc 1,655,675,020 1,406,017,008 -15.1% GOOD T9872b(normal) ghc/alloc 1,864,180,628 1,644,706,696 -11.8% GOOD T9872b_defer(normal) ghc/alloc 2,834,585,468 1,657,729,760 -41.5% GOOD T9872c(normal) ghc/alloc 1,572,573,116 1,354,055,424 -13.9% GOOD T9872d(normal) ghc/alloc 351,516,004 331,071,424 -5.8% GOOD TcPlugin_RewritePerf(normal) ghc/alloc 2,063,065,680 1,847,464,272 -10.5% GOOD Chesskell (github.com/Proxymoron461/chesskell/issues) Typechecking that the first N plies of kholmovVsBronsteinShort are a valid chess game: Plies | GHC 9.14 time/alloc | This commit time/alloc | -----:|---------------------|------------------------| 2 | 41s/20GB | 0.2s/19MB | 4 | 95s/49GB | 0.3s/25MB | 6 | timed out | 0.6s/522MB | 8 | timed out | 7s/673MB | 10 | timed out | timed out | Compilation of singletons-base: compile time -28%, allocations -25% ------------------------- Metric Decrease: CoOpt_Singletons FamAppCachePerf LargeRecord SimplCastPerf T12227 T12545 T13386 T15703 T24984 T26426 T27336 T5030 T5321Fun T8095 T9872a T9872b T9872b_defer T9872c T9872d TcPlugin_RewritePerf ------------------------- Co-Authored-By: Sylvain Henry <sylvain@haskus.fr> - - - - - 3d326d7d by Sylvain Henry at 2026-10-18T18:16:09-04:00 JS: fix stack corruption in h$ap_gen_fast's pushAllRegs (#27624) The loop added in 9e46990976 ("JS: support more than 128 registers (#26558)") pushed register N to stack[sp - N - 2] while the switch it falls through into, and every reader of the h$ap_gen frame, uses stack[sp - (N - 2)]. Registers >= R32 were therefore written 4 slots too low: the slots the readers consult were left stale and the frame below was silently corrupted. Fix the loop to use the same slot formula as the switch, and add a regression test: an unknown call to a thunk with 35 argument register slots, which goes through the generic apply. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> - - - - - 6bbca569 by Andreas Klebinger at 2026-10-21T10:01:10+00:00 Fix a few tag inference bugs. * Treat bottoming functions and nullary join points as functions. * When generating bytecode don't rely on imported tag sigs. Fixes #27831, #27841 and #27842. - - - - - 71808e29 by Sylvain Henry at 2026-10-22T04:50:24-04:00 Add GHC.Internal.Unboxed.Do: do-notation for unboxed values (#27944) QualifiedDo operators can be representation-polymorphic: a do-block is expanded into ordinary applications before typechecking, and the only check on a bound variable is the deferred fixed-runtime-rep check. A representation-polymorphic (>>=) cannot be defined directly, though, because its body would bind a variable of unknown representation. The new module provides such operators for State#-passing code as methods of a class indexed by RuntimeRep, with one instance per representation. With optimisation the dictionaries disappear and a block compiles to the usual nested case expressions: Ubx.do { x <- readWordArray# mba 0# -- x :: Word# ; writeWordArray# mba 1# x -- unit actions are statements ; Ubx.pure x } Also add users guide documentation and tests. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> - - - - - 33247780 by Sylvain Henry at 2026-10-22T04:50:24-04:00 Bignum: use Ubx.do for State#-passing code (#27944) Rewrite the State#-passing code of the GHC.Internal.Bignum modules (Primitives, WordArray, BigNat, Natural, Integer, Backend.Native, Backend.GMP) with the qualified do-notation of GHC.Internal.Unboxed.Do. Nested case chains such as case newWordArray# sz s of { (# s, mwa #) -> case act mwa s of { s -> unsafeFreezeByteArray# mwa s }} become Ubx.do mwa <- newWordArray# sz act mwa unsafeFreezeByteArray# mwa The optimised Core is unchanged (compared per top-level binding). BigNat now enables MonoLocalBinds: local loops written with Ubx.do must stay monomorphic in the state type, otherwise GHC does not turn them into join points. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> - - - - - 593f5f5b by Sylvain Henry at 2026-10-22T04:51:16-04:00 JS: remove archive padding after wasm objects (#25665) On Darwin hosts, emar (llvm-ar) writes archives in the Darwin format when the first member is not a known object file, which is the case for the archives of the JS backend. This format pads each member to 8 bytes with '\n' and includes the padding in the member size. Wasm objects do not accept trailing bytes: wasm-ld failed with "section too large". The JS linker now removes this padding when it extracts a wasm object from an archive. In addition, Hadrian passes --format=gnu to emar for the JS target. See Note [Wasm objects in Darwin archives]. Also document the format of Cc (wasm) objects in Note [Cc object format]. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> - - - - - 13dff5d0 by L0neGamer at 2026-10-22T21:37:31-04:00 add options for resizing bytearrays (#27244) add five mutable bytearray resizing operations for various kinds of pinnedness and aligning. - prefer unpinned when allocating new array (``resizeMutableByteArrayPreferUnpinned#``; the ``resizeMutableByteArray#`` default) - prefer pinned when allocating new array (``resizeMutableByteArrayPreferPinned#``) - prefer aligned and pinned when allocating new array (``resizeMutableByteArrayPreferAlignedPinned#``) - prefer same as input bytearray when allocating new array (``resizeMutableByteArrayKeepPinnedness#``) - ensure the output array is aligned and pinned after operation (``resizeMutableByteArrayMakeAlignedPinned#``) - - - - - 0c17201c by Sylvain Henry at 2026-10-22T21:38:23-04:00 JS: implement performMinorGC and performBlockingMajorGC (#28012) GHC.Internal.System.Mem imports three C entry points: performMajorGC, performGC (for performMinorGC) and performBlockingMajorGC. The JS RTS only defined h$performMajorGC, so calling performMinorGC or performBlockingMajorGC threw "ReferenceError: h$performGC is not defined" at runtime. The JS RTS has a single non-generational collector, so both missing entry points are now aliases of h$performMajorGC. Add a test that calls every GC entry point of System.Mem. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> - - - - - 7a631ff2 by L0neGamer at 2026-10-23T09:11:39-04:00 Mon(a|oi)d of No (Return|Mappend) progress (!15795) Make non-canonical definitions of return and mappend non-suppressible errors, and make canonical definitions of those methods warnings. CLC proposal: https://github.com/haskell/core-libraries-committee/issues/328 - - - - - 14656fd4 by Simon Jakobi at 2026-10-23T09:12:27-04:00 Cmm: keep the CBE substitution idempotent When blocks are merged over multiple rounds during common block elimination, a block that won a merge in an earlier round can still lose a merge in a later round. The substitution map (Subst) used to record this as a chain: the earlier loser mapped to a block that was itself eliminated. In PLT terminology, the substitution became *non-idempotent*. Applying such a substitution with a single lookup left edges to unreachable blocks in the Cmm graph, eventually leading to a setInfoTableStackMap panic (#27368). With this patch, each round's fresh substitutions are applied to the old ones as they are added (extendSubst), so every eliminated block maps directly to its final replacement and the substitution stays idempotent. Fixes #27368. Assisted-by: Claude Fable 5.1 - - - - - 92848e61 by Evgeny Malyshev at 2026-10-23T20:26:04-04:00 hadrian: Include transitive dependencies in Haddock builds Haddock needs indirect dependency interfaces to resolve references to definitions outside a package's direct dependencies. Expose Cabal's configured dependency closure through ContextData and use it alongside the direct list, preserving direct-interface precedence. Bump Shake's cache version for the serialized oracle change. Add a Hadrian selftest requiring template-haskell's indirect ghc-prim interface. Fixes #25850. Fixes #27786. Assisted-By: OpenAI Codex Metric Increase: haddock.Cabal - - - - - 5e8ae81b by Zubin Duggal at 2026-10-23T20:26:47-04:00 WinIO: Don't confuse Win32 errors and NTSTATUS codes WinIO misinterpreted NTSTATUS codes as Win32 errors, and had some ad hoc logic to deal with this. However, this logic was incomplete and resulted in the mishandling of results of certain I/O operations (see testcase). Now the `ErrCode` argument in `CompletionCallback` is always the Win32 error code, and we convert the NTSTATUS using RtlNtStatusToDosError. Also when an overlapped/async operation such as ReadFile fails immediately, with a Win32 error such as ERROR_BROKEN_PIPE, we don't get a further completion notification, so we never recorded the failure. This worked by coincidence earlier, because `STATUS_PENDING` happened to have the same numerical code as `ERROR_NO_MORE_ITEMS`, but it doesn't now that we translate `STATUS_PENDING` into the correct Win32 error code (`ERROR_IO_PENDING`). Fix this by using the Win32 error value we obtained when an operation returns `STATUS_PENDING`. Fixes #27971 - - - - - c42ed66a by Martijn Bastiaan at 2026-10-24T16:00:42+02:00 Add single-threaded test for #27526 + #27123 Issue #27526 is a duplicate of #27123, which has already been fixed in HEAD. The proposed patch in the former carries a "nicer" regression test in that it doesn't rely on multi-threading to trigger. Closes #27526 - - - - - 7f73f515 by Simon Peyton Jones at 2026-10-24T17:29:19-04:00 Refactor QuickLook a bit This MR simply refactors QuickLook a bit. In particular, it simplifies `tcApp`, and moves shared code into `finishApp`. It also adds `Note [QuickLook: arguments before result]` responding to #26599. There should be no user-visible changes, except perhaps in error messages, which improve marginally. For some reason T24984 compiles 8% faster. I'll take the win! Metric Decrease: T24984 - - - - - a4a3a964 by Alan Zimmerman at 2026-10-24T17:30:03-04:00 EPA: Use AnnList for XClosedTypeFamily We now have TTG annotations for FamilyInfo. Make use of it to store the AnnList annotations for a closed type family. - - - - - 953e4c7f by sheaf at 2026-10-26T18:19:10-04:00 Rework LogQueue to be a proper queue Now 'LogQueue' uses a 'TQueue' with a separate 'TVar' to indicate whether the log queue is finished logging, instead of the previous weird data representation using a reverse-order '[Maybe Msg]' with 'Nothing' denoting the end of the queue. - - - - - ec29c5fa by Rodrigo Mesquita at 2026-10-26T18:19:10-04:00 Refactor GHC.Driver.MakeAction Pull out of 'runParPipelines' the logic for creating a 'MakeEnv' ready to be used by multiple threads, as that will be useful for downsweep as well (which doesn't fit the 'runPipelines' flow), rather than being just for upsweep. The code is moved and re-structured to match the export list, simplify the sequentiality checks previously both in 'runPipelines' and 'runAllPipelines', which were weirdly similar and confusing; into the two part step where we need these checks: (1) to construct the MakeEnv, (2) to run the MakeActions in parallel. These two steps are separate and used to be too mixed up. Some additional little simplifications or clean ups here and there. - - - - - 3fb22073 by Rodrigo Mesquita at 2026-10-26T18:19:11-04:00 Refactor GHC.Driver.Downsweep in preparation for parallel downsweep Pure refactor to improve the code to facilitate implementing parallel downsweep in the next commit. This commit puts a MakeEnv into the DownsweepEnv, gives the fields proper names and uses RecordWildcards to simplify, rather than passing around all diagnostic wrappers, driver-message-things and using 10s of positional fields. No behavior changes here! - - - - - 52f385a7 by sheaf at 2026-10-26T18:19:11-04:00 Driver: enableCodeGenForTH in load', not downsweep enableCodeGenForTH modifies the module graph for planning, creating fresh temporary paths. So it should only be run when we are about to execute a build plan (e.g. in load'), so that consumers that want to know facts about the module graph don't go looking for files that don't exist yet (in particular 'haddock --no-compilation'). - - - - - 82402d14 by sheaf at 2026-10-26T18:19:11-04:00 2-phase Cache/Search Finder monad This commit restructures the finder abstraction by introducing the 'FinderM' monad, which splits module lookup operations into two phases: - a cache-only phase, performing no filesystem access, - from the first cache miss onwards, a search action which may access the filesystem. This allows consumers to distinguish between quick cached results versus more expensive filesystem search operations. - - - - - 5c302b40 by sheaf at 2026-10-26T18:19:11-04:00 Separate Home/External finder caches The caches for home modules and modules from external units have different lifetimes, needing to be invalidated at different points. This commit moves the cache for modules from external units into the 'UnitState' type, which keeps the cache correct whenever package flags or package databases change (setSessionDynFlags, :set -package ..., Backpack's addUnit). This also makes it easier to clear the cache of home modules, as they are now stored separately (obviating the 'isUnitEnvInstalledModule' check we used to perform). - - - - - 605fbb96 by sheaf at 2026-10-26T18:19:11-04:00 Add known home modules to the finder cache The finder looks in the file system for the on-disk source that corresponds to a Haskell module name. There are two kinds of modules where we need to bypass this search: - a file passed directly in the command line, which may not be in any search path and whose module name may differ from the file name; - Backpack signatures and modules, which do not exist as files at all. This commit handles these two situations by adding an immutable 'KnownHomeModules' in the finder cache, which is always consulted first before doing any search. This removes the ad-hoc imperative logic which relied on mutating the finder cache at careful points. 'setModuleGraph' now also takes the known home modules, so that the module graph and the known home modules are always set consistently. See Note [Known home modules] in GHC.Unit.Finder.Types. - - - - - 82718f44 by sheaf at 2026-10-26T18:19:11-04:00 Make 'UnresolvedImport' into a suitable cache key The goal of this commit is to make 'UnresolvedImport' suitable for use as a cache key. Specifically, during downsweep we want to be able to cache module resolution queries. We want to do this using some kind of map, e.g. (roughly speaking): Map UnresolvedImport ResolvedImport For this to work, 'UnresolvedImport' must contain **precisely** the input data to each resolution computation. In other words: 1. If something changes that materially affects resolution, it must be stored in the cache key. 2. If changing some input does not materially affect the outcome, then it must not be stored in the cache key. To satisfy (1), we change 'UnitNode' to also keep track of the home unit in whose unit state the unit's dependencies were looked up. For (2), 'ImportResolution' now stores a 'ModuleLookupScope' instead of an 'UnresolvedImportOrigin'. Plugin imports are expressed with a new 'LookupPlugin' scope. The source location of an import, which is immaterial to the resolution, is stored out of band outside 'UnresolvedImport', in 'ModSummary'. - - - - - d4635c7c by sheaf at 2026-10-26T18:19:11-04:00 Add GHC.Data.Dependent This commit adds a minimal implementation of dependent sums ('Some', 'DSum') and dependent maps ('DMap'). The implementation is not entirely performance optimal, as there are a few extraneous allocations compared to the full-blown implementation in the 'dependent-map' package. For our use case (caching downsweep computations), this does not matter much. See GHC.Data.Dependent. - - - - - 6759533e by sheaf at 2026-10-26T18:19:11-04:00 Driver: structured concurrent worker abstraction This commit introduces a structured concurrency framework in the style of the 'ki' library: a collection of threads within a scope. We implement two kinds of concurrent workers on top of this framework: - Independent workers cannot wait for one another at all. The only scheduling operation is to wait for quiescence. - Coordinating workers declare an STM readiness condition (waiting on other workers to complete) which gates their start. See Note [Deterministic concurrent workers] in GHC.Driver.Concurrency. This commit ports upsweep to this new framework, with downsweep being left as subsequent work. Further changes along the way: - Refactoring of how concurrency is acquired to avoid the footgun of trying to use a no-op 'AbstractSem' as a lock in the serial case. - The "re-run with -j1" logic for semaphore opening errors no longer triggers on late semaphore failures (part-way through a lengthy computation). - Logger threads are properly cleaned up on exception, with each concurrent worker's log queue and local TmpFs properly bracketed. - The 'GhcMessage -> AnyGhcDiagnostic' and 'Maybe Messager' arguments of 'depanalE', 'depanalPartial' and 'downsweep', which were all dead in practice, have been dropped. - Concurrent logging has been completely overhauled. Each worker has its own log queue. Workers whose logs are printed as we go are spawned in the order in which their logs must be printed, now using a TQueue instead of the old complicated LogQueueQueue mechanism. 'logThread' is replaced by 'withLogPrinter', which runs the thread that prints the log queues within a concurrent worker scope. These changes allow us to fix issues with the exception handling: we now always flush remaining log queues before exiting (even when the action throws an exception), and exceptions that arise while printing are properly rethrown. This fixes #28009. - - - - - 38a99006 by sheaf at 2026-10-26T18:19:11-04:00 Rule-based deterministic concurrent downsweep This commit rewrites downsweep as a single query-answering rule (see 'DownsweepRule') that can be executed by concurrent worker threads. The design allows every expensive operation (preprocessing files with CPP, parsing headers, reading interfaces) to be performed concurrently according to the -j<N>/-jsem flags. See Note [Rules-based downsweep] in GHC.Driver.Downsweep. The rules are run by "GHC.Driver.Concurrency.runRules" in a demand-driven way: each worker can demand other workers to run, but never wait on another worker. Every piece of work is done at most once. Fixes #27514 Memory usage can increase due to doing more work concurrently: ------------------------- Metric Increase: MultiComponentModulesRecomp MultiComponentModulesRecomp100 mhu-perf ------------------------- - - - - - 9fa7b7be by sheaf at 2026-10-26T18:19:11-04:00 Acquire/release semaphore tokens more readily This commit reworks GHC.Driver.MakeSem to use the scoped worker abstraction of GHC.Utils.Concurrent.Scope. This allows us to get rid of a lot of the tricky logic in GHC.Driver.MakeSem involving manual exception handling, thread spawning and lifetime management, etc. The main user-visible change is that token acquisition is no longer rate limited (due to a bug, there previously was a 1s rate limit on acquisition of semaphore tokens), with the release debounce period shortened from 1s to 10ms. Other changes: - With -jsem, the number of capabilities is now capped at the number of processors, bringing it in line with the -jN behaviour. - Pending jobs whose wait for a token is interrupted by an exception are now withdrawn from the jobserver, instead of acquiring a token that it hung onto without doing useful work. Fixes #27763 - - - - - c83c6733 by Alan Zimmerman at 2026-10-26T18:19:55-04:00 EPA: Update AnnClsInstDecl to contain AnnList It was already separately tracking the '{', '}' and leading ';' values. This aligns it with layout-introducing parser productions ('vocurly'), so the layout processing can be handled uniformly - - - - - 4c252691 by Rodrigo Mesquita at 2026-10-27T10:57:42+00:00 Asynchronous RPC with external interpreter There's a single pipe to connect the host compiler to the external interpreter. On this pipe, we have historically done synchronous request/reply communication to invoke methods on the external interpreter. However, with the advent of multi-threaded debugging, it has become necessary to do asynchronous calls on the external interpreter, where we may block on the host waiting for a reply, but the external interpreter should handle the request asynchronously and reply when ready. For instance, we want to start the evaluation of the debuggee but not block the interpreter waiting for it to finish or hit a breakpoint. Or e.g. we want to resume two threads of the debuggee simulatenously instead of blocking waiting for the resume result of each one sequentially. And it turns out, we were already doing some ad-hoc asynchronous communication to evaluate Template Haskell on the external interpreter. It used to go as an ad-hoc "send request without expecting reply", followed by handling on the host a set of 'THMessage's sent by the interpreter, followed by "expect a response to arrive now". It worked because there was still a fixed order of messages, but it fits an async model in a non-ad-hoc way. Asynchronous communication that unblocks the external interpreter main thread will also make it possible to resolve issues such as #18852 (exceptions leaving the external interpreter in an unrecoverrable state) The new design -------------- The new invariant: every single request should receive a matching reply. The pipe is bidirectional (the ext. interpreter can receive requests, but it can also send requests for TH evaluation; the host can send requests, but it can also receive TH requests from the interpreter). When a request is sent in whichever direction, it always contains a correlation-id header. The Sender places an empty MVar on a pending-reply map keyed by id and waits on it for a response. See 'remoteCall' and 'remoteTHCall'. The pipe is associated to a thread which drains the read end. Because it's bidirectional, two things may be read off the pipe: - A Reply, with a correlation-id header, which we match against the pending requests map to unblock the corresponding pending-reply MVar - A Request, which is queued to the pending-request queue. To handle a message, we take a Request from the pending-request queue and run a handler that produces a Reply. Currently, the handler is run synchronously in the thread, but it is trivial to make the handler run in a forked thread for certain ("interruptible") messages in an upcoming patch (when it is necessary for the multi-threaded debugger). See 'handleRemoteCall' and 'handleRemoteTHCall'. The old interp lock now just protect the pipe writing (reads don't lock bc they are done exclusively by drainPipe), it doesn't need nor should lock the full remote procedure call. Fixes #27960 - - - - - 23f928a6 by Rodrigo Mesquita at 2026-10-27T10:57:42+00:00 interp: Add separate mailboxes for TH async RPC When the host sends a `RunTH` command to the interpreter, it expects a few "reverse requests" from the interpreter (e.g. `NewName`) which must be run in the same context that initiated the `RunTH`. When the host is evaluating many splices at once, it will send many `RunTH` commands to the interpreter and start listening for reverse requests in the meantime. However, a received request previously had no way to be associated to the scope of a particular `RunTH` invocation, so the reverse commands could get replied to from incorrect contexts, or e.g. a `RunTHDone` from the interp. could terminate early the wrong `RunTH` computation. In this commit we add independent mailboxes to the interpreter asynchronous RPC infrastructure, allowing a RunTH to announce a particular `InboxId` that all reverse requests for that RunTH should use. On the host, we create that mailbox id and have `handleRemoteTHCall` listen on that specific mailbox rather than for requests without a specific mailbox address. - - - - - 380cd1c4 by Rodrigo Mesquita at 2026-10-27T10:57:42+00:00 refactor: Move Async RPC abstraction into GHCi.Message.Async Carves out the Async RPC over the Pipe abstraction to a new module, making the GHCi.Message more about the specific interpreter messages rather than about the IPC protocol. - - - - - 5dc6dd97 by Rodrigo Mesquita at 2026-10-27T10:57:42+00:00 interp: If we have pending reads in the queue we can deliver them We may still be able to reply even if the read end was closed. As long as we have pending messages we should try to deliver them. - - - - - 45129774 by Andrea Vezzosi at 2026-10-27T10:57:43+00:00 interp: close Handles when done with Pipe Ensures we close the pipe handles (if created using 'mkPipeFromHandles') on `closePipe`, and do `closePipe` on `Shutdown`. The thread draining the read end always `'finally'` closes the read end. And `closePipe` kills the draining thread and closes the write end. When `remoteAsyncReq`, we throw PipeReadClosedException if the pipe read is closed, since we wouldn't be able to receive the reply. It's fine for the drain thread not to close the write end, even if it dies without `closePipe` (which does close the write end), because: - requests pending a reply will get PipeClosedException (we'll not be able to read any further "real" reply) - new calls to `remoteAsyncReq` will throw PipeReadClosedException - pending pipe writes, in response to an already read request, might still succeed And the clean up code should call close pipe to ensure the write end is closed as well. So, if the drain thread dies naturally and the read end is closed, may still be attempted to be used, but it will throw accordingly. The user likely wants to catch this to close the write end as well. - - - - - 7f15068c by Zubin Duggal at 2026-10-27T10:57:43+00:00 interp: fix external interpreter shutdown deadlock on Windows On shutdown both GHC and iserv call `closePipe`, which stopped the drain thread before closing the write end. On Windows the drain thread reads with a safe foreign call to _read, which `throwTo' can't interrupt, so the two sides were stuck in the deadlock deadlock. Closing the write end first is not enough on its own. On Windows a read on a pipe only unblocks once all write handles to it are closed [1]. However, all all four pipe ends were inheritable and we didn't close the child's ends in the parent. This means a close on any one side wouldn't unblock any reads, becuase the other side had another copy open. * runWithPipes now uses System.Process.CommunicationHandle [2], which is built for passing pipes to a child process: only the child's ends are inheritable, and it simplifies our mess of CPP. Additionally, it is important to close our copy of the endpoints passed to the child so each side only keeps open copies it needs to allow a close to unblock reads. * readGhcHandle makes the handle non-inheritable so we don't have additional references floating around that stop reads from unblocking on close. * In closePipe the ordering is subtle and important. We first fail any requests still waiting for a reply, then close the write end so the other side sees EOF. We take the write lock to close it, so we never close under a concurrent write [3]. Only then do we stop the drain thread, which closes the read end itself once its read has finished. Bump bound to process >= 1.6.20 as this is the version with System.Process.CommunicationHandle [1] https://learn.microsoft.com/en-us/windows/win32/ipc/anonymous-pipe-operation... [2] https://github.com/haskell/process/pull/308 [3] https://gitlab.haskell.org/ghc/ghc/-/work_items/27801 - - - - - 3940d78f by Andrea Vezzosi at 2026-10-27T10:57:43+00:00 GHCi.Server: handle RunTH and RunModFinalizers in forked thread This commit makes the external interpreter able to many interpret template haskell splices in parallel without blocking the main server thread. Simply: fork off a thread to handle a RunTH request. The handler will issue the reverse-requests on the given RunTH mailbox, to keep each RunTH isolated from the others. `handleRemoteCall` was generalised slightly by allowing `WriteReply` to be used linearly in the handler directly, so that the caller of `handleRemoteCall` may `WriteReply` in the forked thread rather than in the main thread. The only question is how can we guarantee `WriteReply` is used linearly if we want to use it inside a forked thread? We need two guarantees: 1. `WriteReply` is used in the forked thread regardless of whether an exception is thrown to that thread. 2. The forked thread is always awaited for, so that the main program doesn't exit before the thread has a chance to actually use `WriteReply`. We introduced a small `ThreadManager` which provides a `spawnFinally` that provides these two guarantees: 1. is guaranteed by `forkFinally`, which always runs the clean up action exactly once. 2. is guaranteed by `ThreadManager` being abstract and the only exposed function that introduces `ThreadManager` being `withThreadManager`, which always awaits for all spawned threads. Co-authored-by: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com> - - - - - 3067f05a by Andrea Vezzosi at 2026-10-27T10:57:43+00:00 interp: spawn fillPipe thread, writePipe now safely interruptible Previously an async exception during a call to `writePipe` could have caused a partial write, making any further write impossible to parse from the other end. Now `writePipe` merely pushes the message onto a queue, and the actual write happens in a separate `fillPipe` thread. As a result of this and previous changes, `interpCmd` no longer needs `interruptibleMask` to preserve the state of the protocol. `writePipe` waits for the actual write to complete, and rethrows exceptions raised in the write attempt, if any. - - - - - 9c0010fe by Andrea Vezzosi at 2026-10-27T10:57:43+00:00 Follow `Note [Exceptions in TH]` in `qReport` implementation `qReport b msg` should use `seqList msg` to trigger any exceptions in the `String`, as explained in the note. Through refactors the `seqList msg` call followed the bulk of the implementation in `GHC.Tc.Gen.Splice.report`, but the call should be in `qReport` itself, so that, even with -fexternal-interpreter, `msg` gets forced right away and any exceptions get reported as a compilation error. Follow up to 'interp: spawn fillPipe thread, writePipe now safely interruptible'. - - - - - ebe700ac by Rodrigo Mesquita at 2026-10-27T10:57:43+00:00 test: make T3171 not fragile and add version for ext interp too - actually test the sleep of the user-given expression gets interrupted - the ext interp version tests two things: - Requests can be cancelled without terminating the ext interp (#18852) - The stmt being evaluated gets interrupted in the ext interp (that is, ^C gets sent to the thread running the user-given expression and doesn't affect the ext interp main thread) - testing ext interp requires sending ^C to whole process group Fixes #15383 - - - - - 33fe4002 by Andrea Vezzosi at 2026-10-27T10:57:43+00:00 interp: cancel requests if async exceptions while waiting for reply. - - - - - 61f0d8e0 by Andrea Vezzosi at 2026-10-27T11:00:15+00:00 interp: do not terminate ext. interp. process on exception `sendMessage` throwing an exception does not warrant terminating the external interpreter process anymore, because communication can keep going no matter what. `stopInterp` now resets the whole `Interp` state, so that a new ExtInterpInstance can be later created and work correctly. `withExtInterp` now calls `stopInterp` on a `PipeClosedException` and rethrows. Fixes #18852 - - - - - 34a76212 by Rodrigo Mesquita at 2026-10-27T11:06:26+00:00 Global break action which uses shared thread map the status Var must actually be global across all threads, otherwise all of them will block trying to write some Status Var no one is looking at at all have to fix these toggle untoggle things very satisfying solution with mutable state Matthew-certified big brain WIP HMmm almost there I think pretty great progressssssssss ExecOptions isolateThreadBreaks ThreadBreaksIsolationMode move to GHCi.Run.Breakpoints - - - - - 35c2e7ff by Rodrigo Mesquita at 2026-10-27T11:06:28+00:00 Refactor: we have the interactive Ids directly... clean up significantly Removes things like names <- map idName ids map (\i -> let id = find (\x -> i==idName x) names) idso and is more straightforward because there's less state going around (no more updating HscEnv as an output) It also kills `printTypeOfNames` completely, since now we just have the Ids. No longer `lookupName` names to get back the ids... ``` printTypeOfName :: GHC.GhcMonad m => Name -> m () printTypeOfName n = do maybe_tything <- GHC.lookupName n case maybe_tything of Nothing -> return () Just thing -> printTyThing thing ``` now is just `printTyThing . AnId` Also: ```diff - tythings <- catMaybes `liftM` mapM GHC.lookupName namesSorted - docs <- mapM pprTypeAndContents [i | AnId i <- tythings] + docs <- mapM pprTypeAndContents idsSorted ``` (and yes, in ExecBreaks there are only Ids, no TyThings, bc they are only constructed by the interpreter execution which can only bind ids. for TyThings use runDecls which doesn't return execBreaks.) I have a plan for the `resumes`, I'm getting there. fixes grrr UNDO the removing-hsc-env-globality part of the clean up and keep just the good parts fixes - - - - - 69e27644 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Make the ExecBreak contain a Resume Put the resume in ExecBreak - - - - - bac05ae3 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Make resumeExec receive a Resume as an argument - - - - - 86dc0230 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Build EvalOpts once per exec rather than per breakpoint stop in interpreter_steplocal the allocations increased because now we're updating `eval_opts` after constructing them in `handleRunStatus` (which is run many times since in step-local most often we don't stop, just check). So drop the update to the eval_opts, and, in fact, pull their construction out. the loop always uses the same eval_opts, so no point in constructing them inside from scratch every time. -3.6% from this branch which had the regressions in interpreter_steplocal - - - - - f4d262e2 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Look up a thread's ResumeContext without taking a lock modifyMVar is unnecessarily expensive and blocking when most often we just care about reading without modifying. optimize for default case (thread context already exists). It is called every single time a breakpoint is hit (regardless of whether we stop there, e.g. in interpreter_steplocal we do not stop there often) -3.3% improvement over original regression - - - - - 08ebbf4a by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Every thread resume-context keeps a var for its EvalStatus Kill the global mapping from thread id to EvalStatus Instead, keep the EvalStatus in the ResumeContext associated to a thread in the threadContextVar (where entries are created on breakpoints being hit and when writing an EvalComplete result) Before, every breakpoint hit meant reading the global map TVar and deleting a map entry which did a lot of allocations. Now, we have a Nothing variable which we overwrite to "take" rather than deleting from a Map and allocating the GlobalDbgMap too. Note that for every breakpoint hit we'd have to insert the ThreadId entry in the map again (because we deleted it last time we resumed), again allocating unnecessarily. Now it's only a look up on the map and an update on the variable directly. And a LOT of breakpoints were hit on interpreter_steplocal, stress testing the cost of hitting a breakpoint The isolated threads move to their own top-level TVar Set. -4.4% improvement over the regression - - - - - 01b13397 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Move whether a thread is isolated to the same global map Stops us from reconstructing the set every time this changed instead to being a per thread variable just toggled on/off, by default non-isolated like before (before it was Set.empty, Set.insert for True, Set.delete for FALSE). This is more straightforward -- there's always an isolation mode per thread and we can toggle it directly reduces slightly allocations, but the main advantage is killing a second global map and making it more uniform with just one thread map and no membership check for toggledness. - - - - - 6788c8a2 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Prefer foldl' in readAnyThreadEvalBreak txn retry 'orElse' next is just next, so we might as well use a strict fold - - - - - f79c8788 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Add inline TODO about improving efficiency of readyAnyThreadBreak It is currently O(N) in number of threads that have hit breakpoints It should be number of *live* threads that have hit breaks, bc we still need to find a way to evacuate threads from the map - - - - - c1249bc8 by Rodrigo Mesquita at 2026-10-27T11:06:29+00:00 Set global breakpoint action in sandboxIO rather than withBreakAction - - - - - 5bebf7e7 by Rodrigo Mesquita at 2026-10-27T11:06:30+00:00 TODO comment on breakOnException being global rather than per-thread - - - - - 64f77c09 by Rodrigo Mesquita at 2026-10-27T11:06:30+00:00 WIP: Asynchronous eval/resume - - - - - 7d3e9860 by Rodrigo Mesquita at 2026-10-27T11:06:30+00:00 Fix commentary - - - - - b5b99eb9 by Rodrigo Mesquita at 2026-10-27T11:07:09+00:00 clean up some comments in GHCi.Signals - - - - - 240ab622 by Rodrigo Mesquita at 2026-10-27T11:07:10+00:00 TSO_STOP_ON_EXCEPTION -- per-thread break-on-exception - - - - - 9c391269 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 unmask runIt only - - - - - b7b880ec by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 Move cmmtn - - - - - fbaecdb5 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 internal interp: redirect interrupts on waits to the thread we're waiting for - - - - - 1a769032 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 Do redirectInterrupts to ext interp too - - - - - 09f71c70 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 get rid of installSignalHandlers and discardCtrlC and uninterruptibleMask - - - - - 2959d959 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 fixes - - - - - 32740ef1 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 Manage thread status stopped vs running and allow many threads to read the same result off of a stoped thread - - - - - d6abc792 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 abstracrt resumeStoppedThread and use it in abandonStmt too. - - - - - 51dfa0c5 by Rodrigo Mesquita at 2026-10-27T11:07:32+00:00 fix redirect todo on seq/resumeseq - - - - - 524 changed files: - + changelog.d/25665 - + changelog.d/25850 - changelog.d/26616 - + changelog.d/27368 - + changelog.d/27624 - + changelog.d/27936 - + changelog.d/27971 - + changelog.d/28012 - + changelog.d/T26543 - changelog.d/T27329 - + changelog.d/T27412 - + changelog.d/T27763 - + changelog.d/T27828 - + changelog.d/T27831-bottoming-strict-field - + changelog.d/T27842-bytecode-imported-tags - + changelog.d/T27844 - + changelog.d/T27960 - + changelog.d/T4162 - changelog.d/boxing-family - + changelog.d/hpc-classinsts - + changelog.d/hpc-cleanup - + changelog.d/monad-of-no-return-canonical - 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+ testsuite/tests/typecheck/should_fail/T27844.stderr - testsuite/tests/typecheck/should_fail/T7019.hs - testsuite/tests/typecheck/should_fail/T8450.stderr - testsuite/tests/typecheck/should_fail/T8603.hs - testsuite/tests/typecheck/should_fail/all.T - + testsuite/tests/warnings/should_compile/RedundantCanonicalMethods.hs - + testsuite/tests/warnings/should_compile/RedundantCanonicalMethods.stderr - testsuite/tests/warnings/should_compile/WarnNoncanonical.hs - testsuite/tests/warnings/should_compile/WarnNoncanonical.stderr - testsuite/tests/warnings/should_compile/all.T - utils/check-exact/ExactPrint.hs - utils/check-exact/Parsers.hs - utils/check-exact/Utils.hs - utils/check-ppr/Main.hs - utils/count-deps/Main.hs - utils/dump-decls/Main.hs - utils/haddock/haddock-api/haddock-api.cabal - utils/haddock/haddock-api/src/Haddock.hs - utils/haddock/haddock-api/src/Haddock/Backends/Hoogle.hs - utils/haddock/haddock-api/src/Haddock/Backends/Hyperlinker/Utils.hs - utils/haddock/haddock-api/src/Haddock/Backends/LaTeX.hs - utils/haddock/haddock-api/src/Haddock/Backends/Xhtml/Decl.hs - utils/haddock/haddock-api/src/Haddock/Convert.hs - utils/haddock/haddock-api/src/Haddock/Interface.hs - utils/haddock/haddock-api/src/Haddock/Interface/ParseModuleHeader.hs - utils/haddock/haddock-api/src/Haddock/Interface/Rename.hs - utils/haddock/haddock-api/src/Haddock/Types.hs - utils/haddock/haddock-api/src/Haddock/Utils/Json.hs - utils/haddock/haddock-api/test/Haddock/Backends/Hyperlinker/ParserSpec.hs - utils/haddock/haddock-library/haddock-library.cabal - utils/haddock/haddock.cabal - utils/runghc/Main.hs The diff was not included because it is too large. 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