sheaf pushed to branch wip/romes/27514 at Glasgow Haskell Compiler / GHC Commits: 448beaf1 by sheaf at 2026-10-05T18:11:35+02:00 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). - - - - - 47af3406 by sheaf at 2026-10-05T18:11:45+02:00 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. - - - - - 918b2c73 by sheaf at 2026-10-05T18:12:32+02:00 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 keeps 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'. - - - - - 73e4a93e by sheaf at 2026-10-05T18:12:33+02:00 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. - - - - - df511386 by sheaf at 2026-10-05T18:12:33+02:00 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. - - - - - d87a5d8f by sheaf at 2026-10-05T18:12:34+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. 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 ------------------------- Metric Increase: MultiComponentModulesRecomp MultiComponentModulesRecomp100 ------------------------- - - - - - bda147c2 by sheaf at 2026-10-05T18:12:43+02:00 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 - - - - - 51 changed files: - + changelog.d/T27763 - + 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/Recomp.hs - compiler/GHC/Parser/Header.hs - compiler/GHC/Runtime/Interpreter/JS.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Types/Error/Codes.hs - compiler/GHC/Types/UnresolvedImport.hs - compiler/GHC/Unit/Finder.hs - + compiler/GHC/Unit/Finder/Cache.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 - testsuite/tests/count-deps/CountDepsParser.stdout - 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/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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