[Git][ghc/ghc][wip/T26868] 12 commits: Refactor eta-expansion in Prep

Simon Peyton Jones pushed to branch wip/T26868 at Glasgow Haskell Compiler / GHC Commits: c1fc1c44 by Simon Peyton Jones at 2026-04-03T19:56:07-04:00 Refactor eta-expansion in Prep The Prep pass does eta-expansion but I found cases where it was doing bad things. So I refactored and simplified it quite a bit. In the new design * There is no distinction between `rhs` and `body`; in particular, lambdas can now appear anywhere, rather than just as the RHS of a let-binding. * This change led to a significant simplification of Prep, and a more straightforward explanation of eta-expansion. See the new Note [Eta expansion] * The consequences is that CoreToStg needs to handle naked lambdas. This is very easy; but it does need a unique supply, which forces some simple refactoring. Having a unique supply to hand is probably a good thing anyway. - - - - - 21beda2c by Simon Peyton Jones at 2026-04-03T19:56:07-04:00 Clarify Note [Interesting dictionary arguments] Ticket #26831 ended up concluding that the code for GHC.Core.Opt.Specialise.interestingDict was good, but the commments were a bit inadequate. This commit improves the comments slightly. - - - - - 3eaac1f2 by Simon Peyton Jones at 2026-04-03T19:56:07-04:00 Make inlining a bit more eager for overloaded functions If we have f d = ... (class-op d x y) ... we should be eager to inline `f`, because that may change the higher order call (class-op d x y) into a call to a statically known function. See the discussion on #26831. Even though this does a bit /more/ inlining, compile times decrease by an average of 0.4%. Compile time changes: DsIncompleteRecSel3(normal) 431,786,104 -2.2% ManyAlternatives(normal) 670,883,768 -1.6% ManyConstructors(normal) 3,758,493,832 -2.6% GOOD MultilineStringsPerf(normal) 29,900,576 -2.8% T14052Type(ghci) 1,047,600,848 -1.2% T17836(normal) 392,852,328 -5.2% T18478(normal) 442,785,768 -1.4% T21839c(normal) 341,536,992 -14.1% GOOD T3064(normal) 174,086,152 +5.3% BAD T5631(normal) 506,867,800 +1.0% hard_hole_fits(normal) 209,530,736 -1.3% info_table_map_perf(normal) 19,523,093,184 -1.2% parsing001(normal) 377,810,528 -1.1% pmcOrPats(normal) 60,075,264 -0.5% geo. mean -0.4% minimum -14.1% maximum +5.3% Runtime changes haddock.Cabal(normal) 27,351,988,792 -0.7% haddock.base(normal) 26,997,212,560 -0.6% haddock.compiler(normal) 219,531,332,960 -1.0% Metric Decrease: LinkableUsage01 ManyConstructors T17949 T21839c T13035 TcPlugin_RewritePerf hard_hole_fits Metric Increase: T3064 - - - - - 5cbc2c82 by Matthew Pickering at 2026-04-03T19:57:02-04:00 bytecode: Add magic header/version to bytecode files In order to avoid confusing errors when using stale interface files (ie from an older compiler version), we add a simple header/version check like the one for interface files. Fixes #27068 - - - - - d95a1936 by fendor at 2026-04-03T19:57:02-04:00 Add constants for bytecode in-memory buffer size Introduce a common constant for the default size of the .gbc and .bytecodelib binary buffer. The buffer is by default set to 1 MB. - - - - - b822c30a by mangoiv at 2026-04-03T19:57:49-04:00 testsuite: filter stderr for static001 on darwin This reactivates the test on x86_64 darwin as this should have been done long ago and ignores warnings emitted by ranlib on newer version of the darwin toolchain since they are benign. (no symbols for stub libraries) Fixes #27116 - - - - - 28ce1f8a by Andreas Klebinger at 2026-04-03T19:58:44-04:00 Give the Data instance for ModuleName a non-bottom toConstr implementation. I've also taken the liberty to add Note [Data.Data instances for GHC AST Types] describing some of the uses of Data.Data I could find. Fixes #27129 - - - - - 8ca41ffe by mangoiv at 2026-04-03T19:59:30-04:00 issue template: fix add bug label - - - - - 3981db0c by Sylvain Henry at 2026-04-03T20:00:33-04:00 Add more canned GC functions for common register patterns (#27142) Based on analysis of heap-check sites across the GHC compiler and Cabal, the following patterns were not covered by existing canned GC functions but occurred frequently enough to warrant specialisation: stg_gc_ppppp -- 5 GC pointers stg_gc_ip -- unboxed word + GC pointer stg_gc_pi -- GC pointer + unboxed word stg_gc_ii -- two unboxed words stg_gc_bpp -- byte (I8) + two GC pointers Adding these reduces the fraction of heap-check sites falling back to the generic GC path from ~1.4% to ~0.4% when compiling GHC itself. Co-Authored-By: Claude Sonnet 4.6 - - - - - d17d1435 by Matthew Pickering at 2026-04-03T20:01:19-04:00 Make home unit dependencies stored as sets Co-authored-by: Wolfgang Jeltsch - - - - - 92a97015 by Simon Peyton Jones at 2026-04-05T00:58:57+01:00 Add Invariant (NoTypeShadowing) to Core This commit addresses #26868, by adding a new invariant (NoTypeShadowing) to Core. See Note [No type-shadowing in Core] in GHC.Core - - - - - 8b5a5020 by Simon Peyton Jones at 2026-04-05T00:58:57+01:00 Major refactor of free-variable functions For some time we have had two free-variable mechanims for types: * The "FV" mechanism, embodied in GHC.Utils.FV, which worked OK, but was fragile where eta-expansion was concerned. * The TyCoFolder mechanism, using a one-shot EndoOS accumulator I finally got tired of this and refactored the whole thing, thereby addressing #27080. Now we have * `GHC.Types.Var.FV`, which has a composable free-variable result type, very much in the spirit of the old `FV`, but much more robust. (It uses the "one shot trick".) * GHC.Core.TyCo.FVs now has just one technology for free variables. All this led to a lot of renaming. There are couple of error-message changes. The change in T18451 makes an already-poor error message even more mysterious. But it really needs a separate look. We also now traverse the AST in a different order leading to a different but still deterministic order for FVs and test output has been adjusted accordingly. - - - - - 124 changed files: - .gitlab/issue_templates/default.md - compiler/GHC/Builtin/PrimOps.hs - compiler/GHC/ByteCode/Serialize.hs - compiler/GHC/Core.hs - compiler/GHC/Core/Coercion.hs - compiler/GHC/Core/FVs.hs - compiler/GHC/Core/Lint.hs - compiler/GHC/Core/Opt/Arity.hs - compiler/GHC/Core/Opt/DmdAnal.hs - compiler/GHC/Core/Opt/SetLevels.hs - compiler/GHC/Core/Opt/Specialise.hs - compiler/GHC/Core/Rules.hs - compiler/GHC/Core/Subst.hs - compiler/GHC/Core/Tidy.hs - compiler/GHC/Core/TyCo/FVs.hs - compiler/GHC/Core/TyCo/Rep.hs - compiler/GHC/Core/TyCo/Subst.hs - compiler/GHC/Core/Type.hs - compiler/GHC/Core/Unfold.hs - compiler/GHC/Core/Unify.hs - compiler/GHC/CoreToStg.hs - compiler/GHC/CoreToStg/Prep.hs - compiler/GHC/Driver/Main.hs - compiler/GHC/Hs/Instances.hs - compiler/GHC/Hs/Utils.hs - compiler/GHC/HsToCore/Binds.hs - compiler/GHC/HsToCore/Ticks.hs - compiler/GHC/Iface/Ext/Ast.hs - compiler/GHC/Iface/Syntax.hs - compiler/GHC/Linker/Loader.hs - compiler/GHC/Rename/Bind.hs - compiler/GHC/Rename/Env.hs - compiler/GHC/Rename/Expr.hs - compiler/GHC/Rename/Expr.hs-boot - compiler/GHC/Rename/HsType.hs - compiler/GHC/Rename/Lit.hs - compiler/GHC/Rename/Module.hs - compiler/GHC/Rename/Names.hs - compiler/GHC/Rename/Pat.hs - compiler/GHC/Rename/Splice.hs - compiler/GHC/Rename/Splice.hs-boot - compiler/GHC/Rename/Utils.hs - compiler/GHC/Stg/Lint.hs - compiler/GHC/StgToCmm/Heap.hs - compiler/GHC/Tc/Deriv.hs - compiler/GHC/Tc/Errors.hs - compiler/GHC/Tc/Errors/Hole.hs - compiler/GHC/Tc/Gen/App.hs - compiler/GHC/Tc/Gen/HsType.hs - compiler/GHC/Tc/Instance/Family.hs - compiler/GHC/Tc/Instance/FunDeps.hs - compiler/GHC/Tc/Module.hs - compiler/GHC/Tc/Solver/Solve.hs - compiler/GHC/Tc/TyCl/Utils.hs - compiler/GHC/Tc/Types/Constraint.hs - compiler/GHC/Tc/Types/Evidence.hs - compiler/GHC/Tc/Utils/TcMType.hs - compiler/GHC/Tc/Utils/TcType.hs - compiler/GHC/Tc/Utils/Unify.hs - compiler/GHC/Tc/Validity.hs - compiler/GHC/Types/Id.hs - compiler/GHC/Types/Id/Info.hs - compiler/GHC/Types/Name/Set.hs - + compiler/GHC/Types/Var/FV.hs - compiler/GHC/Types/Var/Set.hs - compiler/GHC/Unit/Finder.hs - compiler/GHC/Unit/Home/Graph.hs - compiler/GHC/Unit/State.hs - compiler/GHC/Utils/EndoOS.hs - − compiler/GHC/Utils/FV.hs - compiler/Language/Haskell/Syntax/Module/Name.hs - compiler/ghc.cabal.in - rts/HeapStackCheck.cmm - rts/RtsSymbols.c - rts/include/stg/MiscClosures.h - testsuite/driver/testlib.py - testsuite/tests/arityanal/should_compile/Arity01.stderr - testsuite/tests/arityanal/should_compile/Arity05.stderr - testsuite/tests/arityanal/should_compile/Arity08.stderr - testsuite/tests/arityanal/should_compile/Arity11.stderr - testsuite/tests/arityanal/should_compile/Arity14.stderr - testsuite/tests/count-deps/CountDepsAst.stdout - testsuite/tests/count-deps/CountDepsParser.stdout - testsuite/tests/cpranal/should_compile/T18401.stderr - testsuite/tests/deriving/should_fail/deriving-via-fail4.stderr - testsuite/tests/driver/all.T - testsuite/tests/driver/bytecode-object/Makefile - testsuite/tests/driver/bytecode-object/all.T - testsuite/tests/indexed-types/should_fail/T2693.stderr - testsuite/tests/interface-stability/base-exports.stdout - testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs - testsuite/tests/interface-stability/base-exports.stdout-mingw32 - testsuite/tests/interface-stability/base-exports.stdout-ws-32 - testsuite/tests/partial-sigs/should_compile/T10403.stderr - testsuite/tests/partial-sigs/should_compile/T12844.stderr - testsuite/tests/partial-sigs/should_compile/T15039a.stderr - testsuite/tests/partial-sigs/should_compile/T15039b.stderr - testsuite/tests/partial-sigs/should_compile/T15039c.stderr - testsuite/tests/partial-sigs/should_compile/T15039d.stderr - testsuite/tests/partial-sigs/should_fail/T10999.stderr - testsuite/tests/partial-sigs/should_fail/T12634.stderr - testsuite/tests/polykinds/T15789.stderr - testsuite/tests/polykinds/T18451.stderr - testsuite/tests/polykinds/T7328.stderr - testsuite/tests/simplCore/should_compile/DsSpecPragmas.stderr - testsuite/tests/simplCore/should_compile/T15205.stderr - testsuite/tests/simplCore/should_compile/T24229a.stderr - testsuite/tests/simplCore/should_compile/T24229b.stderr - testsuite/tests/simplCore/should_compile/T24359a.stderr - testsuite/tests/simplCore/should_compile/T26116.stderr - testsuite/tests/simplCore/should_compile/T4908.stderr - testsuite/tests/simplCore/should_compile/spec-inline.stderr - testsuite/tests/typecheck/no_skolem_info/T20063.stderr - testsuite/tests/typecheck/should_compile/T25180.stderr - testsuite/tests/typecheck/should_compile/free_monad_hole_fits.stderr - testsuite/tests/typecheck/should_fail/T10971d.stderr - testsuite/tests/typecheck/should_fail/T12589.stderr - testsuite/tests/typecheck/should_fail/T13311.stderr - testsuite/tests/typecheck/should_fail/T17773.stderr - testsuite/tests/typecheck/should_fail/T2846b.stderr - testsuite/tests/typecheck/should_fail/T7851.stderr - testsuite/tests/typecheck/should_fail/T8603.stderr - testsuite/tests/wasm/should_run/control-flow/LoadCmmGroup.hs - utils/haddock/haddock-api/src/Haddock/GhcUtils.hs The diff was not included because it is too large. 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