Duncan Coutts pushed to branch wip/dcoutts/io-manager-feature-bitset at Glasgow Haskell Compiler / GHC Commits: 4e9297ea by Simon Jakobi at 2026-09-11T08:32:45-04:00 ci: Actually pass --ignore-perf-failures to the testsuite driver 684c0018d9 changed the IGNORE_PERF_FAILURES handling to append to RUNTEST_ARGS with bash array syntax, but the three use sites still expand RUNTEST_ARGS as a scalar, which yields only the first array element. The appended flag was therefore dropped in every job, so perf improvements kept failing Marge Bot batches and master pipelines, contrary to #19562. Append as a string instead, matching the existing --force-colors append in test_hadrian. Fixes #27563. Assisted-by: Claude Fable 5.1 - - - - - 4f78dfdf by Simon Jakobi at 2026-09-11T08:33:24-04:00 testsuite: Give T26537 a 1.5x compile timeout Its -fregs-graph compile step tends to time out in unoptimized builds (#27188, #27776). Assisted-by: Claude Fable 5.1 - - - - - 130286e3 by Alan Zimmerman at 2026-09-11T08:34:08-04:00 EPA: Remove ListBanana / ListParens from AnnListBrackets This is a step towards making AnnList only represent lists of items which can have either braces or layout. - - - - - a9827d13 by Simon Jakobi at 2026-09-11T18:53:32-04:00 Reject ~, UNPACK and multiplicity annotations on type data fields Only `!` was rejected so far. `~`, UNPACK and multiplicity annotations were silently accepted. None of them make sense at the type level, so restriction (R3) of Note [Type data declarations] now covers all of them. Fixes #27732. Assisted-by: Claude Fable 5.1 - - - - - c71d5e23 by Alan Zimmerman at 2026-09-11T18:54:11-04:00 EPA: Add a Note for the exact print main loop - - - - - 7a108e43 by Simon Jakobi at 2026-09-12T18:35:59-04:00 FastString: Drop mkFastStringWith's constructor callback All three callers passed the same callback, a partial application of mkNewFastStringShortByteString to the string being interned. That partial application is allocated as a closure before the table lookup, on the common hit path too, although the callback is needed only after a miss. Drop the parameter and call mkNewFastStringShortByteString directly after a miss. Since nothing is passed "with" anymore, rename the function to internSB. Suggested by Simon PJ in #27528: https://gitlab.haskell.org/ghc/ghc/-/work_items/27528#note_687031 Assisted-by: Claude Fable 5 - - - - - 82c73b22 by Alan Zimmerman at 2026-09-12T18:36:38-04:00 EPA: More targeted HsDo exact print annotation HsDo is multi-purpose, as encoded in its HsDoFlavour field. Some of these are in a layout context (DoExpr, MDoExpr), others are not (ListComp, MonadComp). We are moving towards using AnnList only in layout contexts, so we switch the HsDo TTG annotation from holding an AnnList for this, to holding Either (EpToken "[", EpToken "]") AnnList This also allows us to trim down AnnListBrackets to only have braces or None, thereby opening the door for unification with the existing layout context data type EpLayout. - - - - - 749d2448 by Luite Stegeman at 2026-09-15T14:07:01-04:00 rts: handle large CONSTR 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 1 Closure type 1 is CONSTR. This patch adds cases for CONSTR and CONSTR_NOCAF. This is the same problem as #27434 (large AP closures, fixed by cca0d58963), which missed this case. Fixes #27649 - - - - - 177d6155 by Luite Stegeman at 2026-09-15T14:07:02-04:00 testsuite: fix T27434 test with compacting GC Ensure that the interpreter is actually run with the compacting GC - - - - - 5796aa63 by Luite Stegeman at 2026-09-15T14:07:49-04:00 rts: initialise the stack frame header for mask_frame and apply_mask_frame We must leave the stack in consistent state before jumping to mask_frame or apply_mask_frame because they may result. Failing to do so could lead to a crash if there were waiting exceptions. Fixes #27651 - - - - - 2486cc92 by Simon Peyton Jones at 2026-09-15T14:08:36-04:00 Re-introduce the "weird SpecDict" case In this commit commit f80375dd4945350a1d784e436975b48b9c736eaf Author: Simon Peyton Jones <simon.peytonjones@gmail.com> Date: Sun Jun 29 15:26:58 2025 +0100 Refactor of Specialise.hs I removed a test for a dictionary with unbound type variables. This turned out to be wrong; see #27629. So this MR re-introduces it. - - - - - 8e09a46f by Duncan Coutts at 2026-09-15T20:11:35-04:00 Refactor (and rename) removeFromQueues, to simplify I/O managers Rename it to unblockAndAppendToRunQueue which better reflects what it is intended to do. The post-condition for unblockAndAppendToRunQueue is that the TSO is on the run queue or it is in the process of migrating to another cap. Previously it achieved that by always directly adding the TSO to the run queue itself. But this actually made things more complicated for the I/O managers, because it meant they needed a separate code path for notifying for cancellation compared to notifying for completion. The general notification code would always add the TSO to the run queue itself. So the improvement is to allow different cases in unblockAndAppendToRunQueue to achieve the same outcome in different ways: either directly adding to the run queue or calling helper functions that do so themselves. This then allows the new I/O managers to share code between the sync and async cancellation, and to reuse their notifyIOCompletion helpers for cancellation. This avoids a source of bugs where the completion path may be updated but the cancellation path may be forgotten, or similarly in future for sync/async operations. Update all the existing in-RTS I/O managers, and the posix timeout code. - - - - - d668782c by Duncan Coutts at 2026-09-15T20:11:35-04:00 Document that awaitCompletedTimeoutsOrIO expects an empty run queue This was true before but implicit and not relied on much. It's better to be explicit, and allow things to depend on it. - - - - - 11d938bb by Duncan Coutts at 2026-09-15T20:11:35-04:00 Store the I/O opcode and fd in the StgAsyncIOOp This will be useful in several I/O managers and it is handy for logging and debugging. It also doesn't increase the size of the StgAsyncIOOp structure. There was enough spare padding space already. Update the poll I/O manager to set the new fields. Add a helper function to convert the enum IOReadOrWrite into the enum IOOpCode. Also change IOReadOrWrite to be an enum without a typedef, for consistency with other enumerations in IOManager.h - - - - - bfa87882 by Duncan Coutts at 2026-09-15T20:11:36-04:00 Add a new I/O manager based on select() Yes, this is the second such I/O manager, but it is a modern re-implementation based on the new in-RTS I/O manager infrastructure. So it is cleaner and faster than the old select I/O manager. Why do we need another I/O manager based on select? Why isn't the poll() one good enough as a baseline portable unix I/O manager? Because macOS. Apple Inc. is why we cannot have nice things. The man page for poll on macOS documents the fact that it does not work. At least, it does not work for all files. Specifically, it does not work for device files. Whereas macOS select() does work for device files. Aaaaarg! We _do_ want to deprecate and remove the old select I/O manager, but due to macOS we cannot do that until we have a replacement. This is that replacement. Until of course a nice new k-queue I/O manager arrives, which could become the new default for macOS and FreeBSD. Interestingly, this select I/O manager is actually faster than the poll one, on Linix, in some circumstances: specifically when many Haskell threads are waiting on the same fd. The poll I/O manager does O(n) work for n threads waiting on I/O, whereas the select one does O(fds) work for the number of fds that threads are waiting on. Usually this is 1:1, so it's not noticable, but one can concoct extreme benchmarks to show the difference. - - - - - 8e9de15a by Duncan Coutts at 2026-09-15T20:11:36-04:00 Minor updates in the poll I/O manager to keep in sync with select This keeps it in sync with select one. The changes are based on code review while implementing the new select I/O manager. The two I/O managers are so similar in structure that it makes sense to try to minimise the diff between them. This should aid understanding, and fixes to both in future. - - - - - 222668bb by Duncan Coutts at 2026-09-15T20:11:36-04:00 Document the new select I/O manager in the user guide in the RTS section about I/O managers. And add a changelog entry. - - - - - 0f48735b by Cheng Shao at 2026-09-15T20:12:23-04:00 Revert "wasm: workaround WebKit bug in dyld" This reverts commit c9b8465c2c338176fcab9d197e9d31f4aee11f68. The underlying webkit bug has been fixed in https://commits.webkit.org/314219@main. Closes #27564. - - - - - 809294f1 by Luite Stegeman at 2026-09-15T20:13:08-04:00 rts: make stg_threadLabelzh return a valid pointer for unlabeled threads. This fixes a segfault in the GC caused by stg_threadLabelzh returning a 0 pointer in a GC pointer field. stg_threadLabelzh returns a tuple of type (# Int#, ByteArray# #). If a thread has no label, the second field is unused. We must still return a valid heap object pointer. Instead of returning 0, we now return stg_DEAD_SLOT_closure. fixes #27618 - - - - - e2d57026 by Luite Stegeman at 2026-09-15T20:13:54-04:00 JS: fix selector thunk handling fix a bug where entering a selector thunk could lead to a crash if the selected field was still a thunk. fixes #27788 - - - - - f8a7e988 by Duncan Coutts at 2026-09-16T13:38:38+01:00 Fix a couple comments in the new selectbis I/O manager Noticed late in the review process. - - - - - 8272e000 by Duncan Coutts at 2026-09-16T13:38:38+01:00 New rts_IOManagerFeatures bitset for I/O manager features The idea is that code in the RTS and ghc-internal can use this feature bitset to do things that have to be conditional. But instead of basing it on threaded/non-threaded, win32 etc it can be based on features of the current I/O manager. In particular this will allow us to have in-RTS I/O managers when using the threaded RTS way, by changing code to use the feature test rather than testing for threaded/non-threaded. There are also numerous conditions in existing RTS and library code that could benefit from being clearly based on I/O manager features rather than on (historically) correlated aspects of the platform. For example, a major difference between WinIO and the win32-legacy I/O manager is whether it uses C lib fds or Win32 API HANDLEs. This distinction is not necessarily unique forever to these I/O managers. Future Windows I/O managers may want to take advantage of the same distinction. For example, we could have a feature to say if the I/O manager supports readiness notifications threadWaitRead# etc (win32-legacy does not support these for example), so I/O code in ghc-internal can use appropriate workarounds. Similarly, if/when we add support for async I/O, or I/O to files at given offsets (without affecting or being affected by the file pointer) then library code can consult the feature bits and either use emulated fallbacks or throw appropriate exceptions. - - - - - 6f859ae2 by Duncan Coutts at 2026-09-16T13:38:38+01:00 Use rts_IOManagerFeatures bitset in GHC.Internal.IO.SubSystem Establish a pattern for exposing the features. We will start using them in subsequent commits. - - - - - 7c8a4f79 by Duncan Coutts at 2026-09-16T13:38:38+01:00 Turn rts_IOManagerIsWin32Native into a feature bit of rts_IOManagerFeatures And update where it is used in ghc-internal - - - - - 02d23436 by Duncan Coutts at 2026-09-16T13:38:38+01:00 Remove is_io_mng_native_p helper, replacing with iomgr_type The comment said: Temporary compat helper function used in the Win32 I/O managers. TODO: replace by consulting the iomgr_type global instead. - - - - - 89 changed files: - .gitlab/ci.sh - + changelog.d/27732 - + changelog.d/T27629 - + changelog.d/T27788-js-selector - + changelog.d/fix-compacting-gc-constr-27649 - + changelog.d/fix-control0-mask-trampoline - + changelog.d/fix-threadlabel-segfault-27618 - + changelog.d/select-io-manager - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Data/FastString.hs - compiler/GHC/Hs/Expr.hs - compiler/GHC/Hs/Pat.hs - compiler/GHC/Hs/Utils.hs - compiler/GHC/Parser.y - compiler/GHC/Parser/Annotation.hs - compiler/GHC/Parser/PostProcess.hs - compiler/GHC/Rename/Module.hs - compiler/GHC/StgToJS/Apply.hs - compiler/GHC/StgToJS/Symbols.hs - compiler/GHC/Tc/Errors/Types.hs - docs/users_guide/exts/type_data.rst - docs/users_guide/runtime_control.rst - libraries/base/src/GHC/RTS/Flags.hs - libraries/ghc-internal/src/GHC/Internal/IO/SubSystem.hs - libraries/ghc-internal/src/GHC/Internal/RTS/Flags.hsc - rts/ContinuationOps.cmm - rts/IOManager.c - rts/IOManager.h - rts/IOManagerInternals.h - rts/PrimOps.cmm - rts/RaiseAsync.c - rts/RtsStartup.c - rts/RtsSymbols.c - rts/StgMiscClosures.cmm - rts/configure.ac - rts/include/rts/Flags.h - rts/include/rts/storage/Closures.h - rts/include/stg/MiscClosures.h - rts/posix/Poll.c - rts/posix/Poll.h - + rts/posix/SelectBis.c - + rts/posix/SelectBis.h - rts/posix/Timeout.c - rts/posix/Timeout.h - rts/rts.cabal - rts/sm/Compact.c - rts/win32/AwaitEvent.c - rts/win32/ThrIOManager.c - testsuite/tests/codeGen/should_run/all.T - testsuite/tests/ghc-api/T25121_status.stdout - testsuite/tests/interface-stability/ghc-experimental-exports.stdout - testsuite/tests/interface-stability/ghc-experimental-exports.stdout-mingw32 - + testsuite/tests/javascript/T27788.hs - + testsuite/tests/javascript/T27788.stdout - testsuite/tests/javascript/all.T - testsuite/tests/parser/should_compile/DumpParsedAstComments.stderr - testsuite/tests/parser/should_compile/DumpSemis.stderr - testsuite/tests/printer/Test20297.stdout - + testsuite/tests/rts/T27618.hs - + testsuite/tests/rts/T27618.stdout - + testsuite/tests/rts/T27649.hs - + testsuite/tests/rts/T27649.stdout - testsuite/tests/rts/all.T - + testsuite/tests/rts/continuations/T27651.hs - + testsuite/tests/rts/continuations/T27651.stdout - testsuite/tests/rts/continuations/all.T - testsuite/tests/simplCore/should_compile/Makefile - + testsuite/tests/simplCore/should_compile/T27629.hs - + testsuite/tests/simplCore/should_compile/T27629.stderr - + testsuite/tests/simplCore/should_compile/T27629Plugin.hs - testsuite/tests/simplCore/should_compile/all.T - + testsuite/tests/type-data/should_fail/T27732a.hs - + testsuite/tests/type-data/should_fail/T27732a.stderr - + testsuite/tests/type-data/should_fail/T27732b.hs - + testsuite/tests/type-data/should_fail/T27732b.stderr - + testsuite/tests/type-data/should_fail/T27732c.hs - + testsuite/tests/type-data/should_fail/T27732c.stderr - + testsuite/tests/type-data/should_fail/T27732d.hs - + testsuite/tests/type-data/should_fail/T27732d.stderr - + testsuite/tests/type-data/should_fail/T27732e.hs - + testsuite/tests/type-data/should_fail/T27732e.stderr - + testsuite/tests/type-data/should_fail/T27732f.hs - + testsuite/tests/type-data/should_fail/T27732f.stderr - testsuite/tests/type-data/should_fail/TDStrictnessGADT.stderr - testsuite/tests/type-data/should_fail/TDStrictnessH98.stderr - testsuite/tests/type-data/should_fail/all.T - utils/check-exact/ExactPrint.hs - utils/check-exact/Utils.hs - utils/jsffi/dyld.mjs The diff was not included because it is too large. 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