Simon Peyton Jones pushed to branch wip/T27557 at Glasgow Haskell Compiler / GHC

Commits:

• 3ec9e2b9
  by Mike Pilgrem at 2026-07-31T08:21:33-04:00

  GHC Guide: Improve docs on response files
  

• e5b2a1f7
  by sheaf at 2026-07-31T08:22:23-04:00

  Disable Core Lint for TcPlugin_RewritePerf
  
  This is a compiler performance test, but the test source hard-coded
  -dcore-lint, defeating the measurement.
  
  -------------------------
  Metric Decrease:
      TcPlugin_RewritePerf
  -------------------------
  

• 85b10c00
  by Alan Zimmerman at 2026-07-31T22:09:47+01:00

  EPA: Remove LocatedP from OverlapMode
  
  We have
  
    type LocatedP = GenLocated SrcSpanAnnP
    type SrcSpanAnnP = EpAnn AnnPragma
  
  As the first step in removing this in favour of LocatedA which only
  captures location, comments and trailing annotations, we remove it
  from OverlapMode
  
  We do this by moving the AnnPragma into the TTG extension point
  instead.
  

• c9a34a00
  by Viktor Dukhovni at 2026-08-02T04:34:17-04:00

  Fix note typo
  

• 40a8449c
  by Simon Peyton Jones at 2026-08-02T16:19:25+01:00

  Fix three bugs related to required type args and INLINE pragmas
  
  * `GHC.Core.Opt.Arity.mkEtaForAllMCo` got the visibility flags back to front,
    leading to a Lint error (#27557)
  
  * The arity in an InlineSaturation is the VisArity not the Arity; the
    two can differ when we have "required" type arguments.  This made the
    INLINE pragma argument counting go wrong in `makeCorePair` (#27590).
  
  * When a simple binding has a type signature, we take special path in `tcPolyCheck`,
    leading to an outer `AbsBinds` that has no dictionaries, even when the binding
    is in fact overloaded.  That confused the inline-arity computation in
    `makeCorePair` (#27589).
  
  The latter two are fixed using the new function `GHC.HsToCore.Binds.findSatArity`.
  That actually simplifies the API of `makeCorePair`, which is nice.
  
  The first bug is fixed by swapping the visiblity flags in
  `GHC.Core.Opt.Arity.mkEtaForAllMCo`
  
  Getting the INLINE behaviour right led to some perf changes:
    * Runtime /halved/ on T7954 due to better specialisation
    * Compile time increased by 6% in T21839c because a bit more inlining
      happened, as it always should have done.
  
  Geometric mean effect on our compile time benchmarks is +0.1%.
  
  Metric Decrease:
      T7954
  Metric Increase:
      T21839c
  

32 changed files:

• + changelog.d/T27557
• compiler/GHC/Core/Opt/Arity.hs
• compiler/GHC/Hs/Decls.hs
• compiler/GHC/Hs/Decls/Overlap.hs
• compiler/GHC/Hs/Expr.hs
• compiler/GHC/HsToCore/Binds.hs
• compiler/GHC/HsToCore/Match.hs
• compiler/GHC/HsToCore/Ticks.hs
• compiler/GHC/Iface/Ext/Ast.hs
• compiler/GHC/Parser.y
• compiler/GHC/Tc/Deriv.hs
• compiler/GHC/Tc/Gen/Bind.hs
• compiler/GHC/Tc/Gen/Sig.hs
• compiler/GHC/Tc/TyCl/Instance.hs
• compiler/GHC/Tc/Utils/Instantiate.hs
• compiler/GHC/ThToHs.hs
• compiler/GHC/Types/Arity.hs
• compiler/GHC/Types/InlinePragma.hs
• compiler/GHC/Types/Var.hs
• docs/users_guide/using.rst
• libraries/ghc-internal/src/GHC/Internal/Ix.hs
• + testsuite/tests/simplCore/should_compile/T27589.hs
• + testsuite/tests/simplCore/should_compile/T27589.stderr
• + testsuite/tests/simplCore/should_compile/T27590.hs
• + testsuite/tests/simplCore/should_compile/T27590.stderr
• testsuite/tests/simplCore/should_compile/all.T
• testsuite/tests/tcplugins/TcPlugin_RewritePerf.hs
• testsuite/tests/tcplugins/TcPlugin_RewritePerf.stderr
• + testsuite/tests/typecheck/should_compile/T27557.hs
• testsuite/tests/typecheck/should_compile/all.T
• utils/check-exact/ExactPrint.hs
• utils/haddock/haddock-api/src/Haddock/Types.hs

The diff was not included because it is too large.