sheaf pushed to branch wip/romes/27514 at Glasgow Haskell Compiler / GHC Commits: 1a5108eb by sheaf at 2026-08-25T18:53:54+02:00 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. - - - - - efe55b84 by sheaf at 2026-08-25T19:17:22+02:00 Driver: structured concurrent worker abstraction This commits introduces a structured concurrency framework in the style of the 'ki' library: a collection of threads within a scope. We implement two kind 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. - - - - - d4a8eecc by sheaf at 2026-08-25T19:25:12+02:00 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. To achieve this, the finder cache was slightly restructured in order to account for modules whose source files are directly specified as targets; see the new Note [Known home modules] in GHC.Unit.Finder.Types. This allowed us to remove 'addModuleToFinder', 'addHomeModuleToFinder' and a few brittle hacks (e.g. in Backpack). Fixes #27514 - - - - - 58 changed files: - + changelog.d/parallel-downsweep - compiler/GHC.hs - compiler/GHC/Builtin.hs - + compiler/GHC/Data/Dependent.hs - compiler/GHC/Driver/Backpack.hs - + compiler/GHC/Driver/Concurrency.hs - + compiler/GHC/Driver/Config/Concurrency.hs - compiler/GHC/Driver/Downsweep.hs - compiler/GHC/Driver/Env.hs - compiler/GHC/Driver/Errors/Ppr.hs - compiler/GHC/Driver/Errors/Types.hs - compiler/GHC/Driver/Main/Passes.hs - compiler/GHC/Driver/Make.hs - compiler/GHC/Driver/MakeAction.hs - compiler/GHC/Driver/MakeFile.hs - compiler/GHC/Driver/MakeSem.hs - compiler/GHC/Driver/Pipeline/Execute.hs - compiler/GHC/Driver/Pipeline/LogQueue.hs - compiler/GHC/Iface/Load.hs - compiler/GHC/Iface/Recomp.hs - compiler/GHC/Linker/Deps.hs - compiler/GHC/Parser/Header.hs - compiler/GHC/Runtime/Interpreter/JS.hs - compiler/GHC/Runtime/Loader.hs - compiler/GHC/StgToJS/Linker/Linker.hs - compiler/GHC/Tc/Gen/Splice.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Tc/Plugin.hs - compiler/GHC/Tc/Utils/Backpack.hs - compiler/GHC/Types/Error/Codes.hs - compiler/GHC/Types/UnresolvedImport.hs - compiler/GHC/Unit/Finder.hs - compiler/GHC/Unit/Finder/Types.hs - compiler/GHC/Unit/Module/Graph.hs - compiler/GHC/Unit/Module/ModSummary.hs - compiler/GHC/Unit/State.hs - compiler/GHC/Unit/Types.hs - + compiler/GHC/Utils/Concurrent/Scope.hs - compiler/GHC/Utils/TmpFs.hs - compiler/ghc.cabal.in - ghc/GHCi/UI.hs - ghc/Main.hs - linters/lint-codes/LintCodes/Static.hs - testsuite/tests/diagnostic-codes/codes.stdout - testsuite/tests/driver/T27461/Makefile - + testsuite/tests/driver/T27461/T27461c.stderr - testsuite/tests/driver/T27461/all.T - + testsuite/tests/driver/T27461/src/Wrong.hs - testsuite/tests/ghc-api/downsweep/IncrementalDownsweep.hs - testsuite/tests/ghc-api/downsweep/OldModLocation.hs - testsuite/tests/ghc-api/downsweep/PartialDownsweep.hs - testsuite/tests/ghc-api/fixed-nodes/FixedNodes.hs - testsuite/tests/ghc-api/fixed-nodes/InterfaceModuleGraph.hs - testsuite/tests/ghc-api/fixed-nodes/ModuleGraphInvariants.hs - testsuite/tests/plugins/defaulting-plugin/DefaultLifted.hs - testsuite/tests/splice-imports/SI35.hs - utils/check-ppr/Main.hs - utils/haddock/haddock-api/src/Haddock/Interface.hs The diff was not included because it is too large. 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