[Git][ghc/ghc][wip/T24359] 4 commits: Specialising expressions -- at last

sheaf (@sheaf) gitlab at gitlab.haskell.org
Wed Feb 19 12:05:30 UTC 2025 


sheaf pushed to branch wip/T24359 at Glasgow Haskell Compiler / GHC


Commits:
ca397cb7 by Simon Peyton Jones at 2025-02-19T13:04:47+01:00
Specialising expressions -- at last

This MR addresses #24359, which implements the GHC proposal 493 on SPECIALISE pragmas.

* The old code path (using SpecSig and SpecPrag) still exists.
* The new code path (using SpecSigE and SpecPragE) runs alongside it.
* All SPECIALISE pragmas are routed through the new code path, except
  if you give multiple type sigs, when the old code path is still used.
* Main documentation: Note [Handling new-form SPECIALISE pragmas] in
  GHC.Tc.Gen.Sig`

Thanks to @sheaf for helping with this MR.

The Big Thing is to introduce

  {-# SPECIALISE forall x.  f @Int x True #-}

where you can give type arguments and value argument to specialise; and
you can quantify them with forall, just as in Rules.

I thought it was going to be pretty simple, but it was a Long, Long Saga.

Highlights

* Overview Note [Handling new-form SPECIALISE pragmas] in GHC.Tc.Gen.Sig
  - New data constructor `SpecSigE` in data type `L.H.S.Binds.Sig`
  - New data construtor `SpecPragE` in data type `GHC.Hs.Binds.TcSpecPrag`
  - Renamer: uses `checkSpecESigShape` to decide which function to assocate the
             SPECIALISE pragma with
  - Some of the action is in `GHC.Tc.Gen.Sig.tcSpecPrag`
  - The rest is in `GHC.HsToCore.Binds.dsSpec`

* All of GHC.Tc.Gen.Rule is moved into GHC.Tc.Gen.Sig, because the code is
  very closely related.

* The forall'd binders for SPECIALISE are the same as those for a RULE, so I
  refactored, introducing data type `L.H.S.Binds.RuleBndrs`, with functions
  to rename, zonk, typecheck it.  I refactored this data type a bit; nicer now.

* On the LHS of RULES, or SPECIALISE, we want to disable the tricky mechanims
  described in Note [Desugaring non-canonical evidence] in GHC.HsToCore.Expr.
  Previously it wasn't fully disabled (just set to the empty set), and that
  didn't quite work in the new regime.

* There are knock-on changes to Template Haskell.

* For the LHS of a RULE and a SPECIALISE expression, I wanted to simplify
  it /without/ inlining the let-bindings for evidence variables.  I added
  a flag `so_inline` to the SimpleOpt optimiser to support this.  The
  entry point is `GHC.Core.SimpleOpt.simpleOptExprNoInline`

* Since forever we have had a hack for type variables on the LHS of
  RULES. I took the opportunity to tidy this up.  The main action is
  in the zonker.  See GHC.Tc.Zonk.Type Note [Free tyvars on rule LHS],
  and especially data construtor `SkolemiseFlexi`
  in data type `GHC.Tc.Zonk.Env.ZonkFlexi`

* Move `scopedSort` from GHC.Core.TyCo.FVs to GHC.Core.Predicate
  Reason: it now works for Ids as well, and I wanted to use isEvVar,
          which is defined in GHC.Core.Predicate
  Avoiding module loops meant that instead of exporting GHC.Core.TyCo.Tidy
  from GHC.Core.Type, modules now import the former directly.

  I also took the opportunity to remove unused exports
  from GHC.Core.Type.hs-boot

* Flag stuff:
  - Add flag `-Wdeprecated-pragmas` and use it to control the warning when
    using old-style SPECIALISE pragmas with multiple type ascriptions,

  - Add flag `-Wuseless-specialisations` and use it to control the warning emitted
    when GHC determines that a SPECIALISE pragma would have no effect. Don't
    want if the SPECIALISE is SPECIALISE INLINE (#4444)

    In response to #25389, we continue to generate these seemingly code for these
    seemingly useless SPECIALISE pragmas

  - Adds deprecations to Template Haskell `pragSpecD` and `pracSpecInlD`,

* Split up old-style SPECIALISE pragmas in GHC.Internal.Float,
  GHC.Internal.Numeric, GHC.Internal.Real

* Remove useless SPECIALISE pragmas in Data.Array (updating the array submodule)

Smaller things:

- Update the Users Guide

- Add mention of the changes to the 9.14 release notes as well as
  the Template Haskell changelog,

- - - - -
4c03d320 by Simon Peyton Jones at 2025-02-19T13:04:47+01:00
Warn about rules that previously quantified over equalities

- - - - -
1caac6b4 by sheaf at 2025-02-19T13:04:48+01:00
Add -Wrule-lhs-equalities warning

This commit adds a new warning flag, -Wrule-lhs-equalities, which
controls the warning message that is emitted when the LHS of a RULE
gives rise to equality constraints that previous GHC versions would
have quantified over.

GHC instead discards such RULES, as GHC was never able to generate
a rule template that would ever fire; it's better to be explicit about
the fact that the RULE doesn't work.

- - - - -
c4c2a7f0 by sheaf at 2025-02-19T13:04:48+01:00
New plan from Feb 10

- - - - -


151 changed files:

- compiler/GHC/Builtin/Names/TH.hs
- compiler/GHC/Builtin/PrimOps/Ids.hs
- compiler/GHC/Core/FamInstEnv.hs
- compiler/GHC/Core/InstEnv.hs
- compiler/GHC/Core/Make.hs
- compiler/GHC/Core/Opt/CSE.hs
- compiler/GHC/Core/Opt/Simplify/Iteration.hs
- compiler/GHC/Core/Opt/Simplify/Utils.hs
- compiler/GHC/Core/Opt/SpecConstr.hs
- compiler/GHC/Core/Predicate.hs
- compiler/GHC/Core/Rules.hs
- compiler/GHC/Core/SimpleOpt.hs
- compiler/GHC/Core/Tidy.hs
- compiler/GHC/Core/TyCo/FVs.hs
- compiler/GHC/Core/TyCo/Ppr.hs
- compiler/GHC/Core/TyCo/Tidy.hs
- compiler/GHC/Core/Type.hs
- compiler/GHC/Core/Type.hs-boot
- compiler/GHC/Core/Unify.hs
- compiler/GHC/CoreToIface.hs
- compiler/GHC/Driver/Config.hs
- compiler/GHC/Driver/Flags.hs
- compiler/GHC/Driver/Session.hs
- compiler/GHC/Hs/Binds.hs
- compiler/GHC/Hs/Decls.hs
- compiler/GHC/Hs/Instances.hs
- compiler/GHC/Hs/Stats.hs
- compiler/GHC/HsToCore.hs
- compiler/GHC/HsToCore/Binds.hs
- compiler/GHC/HsToCore/Errors/Ppr.hs
- compiler/GHC/HsToCore/Errors/Types.hs
- compiler/GHC/HsToCore/Expr.hs
- compiler/GHC/HsToCore/Foreign/Call.hs
- compiler/GHC/HsToCore/Monad.hs
- compiler/GHC/HsToCore/Quote.hs
- compiler/GHC/HsToCore/Types.hs
- compiler/GHC/Iface/Decl.hs
- compiler/GHC/Iface/Ext/Ast.hs
- compiler/GHC/Iface/Tidy.hs
- compiler/GHC/Parser.y
- compiler/GHC/Parser/Errors/Ppr.hs
- compiler/GHC/Parser/Errors/Types.hs
- compiler/GHC/Parser/PostProcess.hs
- compiler/GHC/Rename/Bind.hs
- compiler/GHC/Rename/HsType.hs
- compiler/GHC/Rename/Module.hs
- compiler/GHC/Rename/Names.hs
- compiler/GHC/Runtime/Debugger.hs
- compiler/GHC/Runtime/Eval.hs
- compiler/GHC/Runtime/Heap/Inspect.hs
- compiler/GHC/StgToByteCode.hs
- compiler/GHC/Tc/Deriv.hs
- compiler/GHC/Tc/Errors.hs
- compiler/GHC/Tc/Errors/Ppr.hs
- compiler/GHC/Tc/Errors/Types.hs
- compiler/GHC/Tc/Gen/Bind.hs
- compiler/GHC/Tc/Gen/HsType.hs
- − compiler/GHC/Tc/Gen/Rule.hs
- compiler/GHC/Tc/Gen/Sig.hs
- compiler/GHC/Tc/Module.hs
- compiler/GHC/Tc/Solver.hs
- compiler/GHC/Tc/Solver/Default.hs
- compiler/GHC/Tc/Solver/Monad.hs
- compiler/GHC/Tc/Solver/Solve.hs
- compiler/GHC/Tc/TyCl.hs
- compiler/GHC/Tc/TyCl/Instance.hs
- compiler/GHC/Tc/TyCl/PatSyn.hs
- compiler/GHC/Tc/Types/Constraint.hs
- compiler/GHC/Tc/Types/Evidence.hs
- compiler/GHC/Tc/Types/Origin.hs
- compiler/GHC/Tc/Utils/Instantiate.hs
- compiler/GHC/Tc/Utils/TcMType.hs
- compiler/GHC/Tc/Validity.hs
- compiler/GHC/Tc/Zonk/Env.hs
- compiler/GHC/Tc/Zonk/TcType.hs
- compiler/GHC/Tc/Zonk/Type.hs
- compiler/GHC/ThToHs.hs
- compiler/GHC/Types/Basic.hs
- compiler/GHC/Types/Error/Codes.hs
- compiler/GHC/Types/Hint.hs
- compiler/GHC/Types/Hint/Ppr.hs
- compiler/GHC/Types/Var.hs
- compiler/Language/Haskell/Syntax/Binds.hs
- compiler/Language/Haskell/Syntax/Decls.hs
- compiler/Language/Haskell/Syntax/Extension.hs
- compiler/ghc.cabal.in
- docs/users_guide/9.14.1-notes.rst
- docs/users_guide/exts/pragmas.rst
- docs/users_guide/using-warnings.rst
- libraries/array
- libraries/ghc-boot-th/GHC/Internal/TH/Ppr.hs
- libraries/ghc-internal/src/GHC/Internal/Float.hs
- libraries/ghc-internal/src/GHC/Internal/Numeric.hs
- libraries/ghc-internal/src/GHC/Internal/Real.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Lib.hs
- libraries/ghc-internal/src/GHC/Internal/TH/Syntax.hs
- libraries/template-haskell/Language/Haskell/TH/Lib.hs
- libraries/template-haskell/changelog.md
- + testsuite/tests/deSugar/should_compile/T10251.stderr
- testsuite/tests/diagnostic-codes/codes.stdout
- testsuite/tests/ghc-api/T18522-dbg-ppr.hs
- testsuite/tests/interface-stability/template-haskell-exports.stdout
- testsuite/tests/parser/should_compile/OpaqueParseWarn1.stderr
- testsuite/tests/parser/should_fail/T7848.stderr
- + testsuite/tests/simplCore/should_compile/DsSpecPragmas.hs
- + testsuite/tests/simplCore/should_compile/DsSpecPragmas.stderr
- testsuite/tests/simplCore/should_compile/T12603.stdout
- testsuite/tests/simplCore/should_compile/T15445.stderr
- + testsuite/tests/simplCore/should_compile/T24359a.hs
- + testsuite/tests/simplCore/should_compile/T24359a.stderr
- + testsuite/tests/simplCore/should_compile/T25389.hs
- + testsuite/tests/simplCore/should_compile/T25389.stderr
- testsuite/tests/simplCore/should_compile/T4398.stderr
- testsuite/tests/simplCore/should_compile/T5821.hs
- testsuite/tests/simplCore/should_compile/T8537.stderr
- + testsuite/tests/simplCore/should_compile/T9578b.hs
- testsuite/tests/simplCore/should_compile/all.T
- − testsuite/tests/simplCore/should_compile/simpl016.stderr
- + testsuite/tests/simplCore/should_fail/T25117a.hs
- + testsuite/tests/simplCore/should_fail/T25117a.stderr
- + testsuite/tests/simplCore/should_fail/T25117b.hs
- + testsuite/tests/simplCore/should_fail/T25117b.stderr
- testsuite/tests/simplCore/should_fail/all.T
- + testsuite/tests/simplCore/should_run/T24359b.hs
- + testsuite/tests/simplCore/should_run/T24359b.stdout
- testsuite/tests/simplCore/should_run/all.T
- + testsuite/tests/th/T13123.stderr
- testsuite/tests/th/T19363.stdout
- testsuite/tests/th/T7064.stdout
- testsuite/tests/th/TH_pragma.hs
- testsuite/tests/th/TH_pragma.stderr
- + testsuite/tests/typecheck/should_compile/RuleEqs.hs
- + testsuite/tests/typecheck/should_compile/RuleEqs.stderr
- testsuite/tests/typecheck/should_compile/T10504.stderr
- testsuite/tests/typecheck/should_compile/T2494.stderr
- + testsuite/tests/typecheck/should_compile/TcSpecPragmas.hs
- + testsuite/tests/typecheck/should_compile/TcSpecPragmas.stderr
- testsuite/tests/typecheck/should_compile/all.T
- testsuite/tests/typecheck/should_compile/tc186.hs
- testsuite/tests/typecheck/should_compile/tc212.hs
- + testsuite/tests/typecheck/should_fail/SpecPragmasFail.hs
- + testsuite/tests/typecheck/should_fail/SpecPragmasFail.stderr
- testsuite/tests/typecheck/should_fail/T5853.stderr
- + testsuite/tests/warnings/should_compile/SpecMultipleTys.hs
- + testsuite/tests/warnings/should_compile/SpecMultipleTys.stderr
- testsuite/tests/warnings/should_compile/T19296.stderr
- testsuite/tests/warnings/should_compile/all.T
- + testsuite/tests/warnings/should_fail/SpecEMultipleTys.hs
- + testsuite/tests/warnings/should_fail/SpecEMultipleTys.stderr
- testsuite/tests/warnings/should_fail/all.T
- utils/check-exact/ExactPrint.hs


The diff was not included because it is too large.


View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/29320b3074cff6ba0e5c8615cc38243507efe1e5...c4c2a7f040a3b0f9f255c4df1d670150cc135c75

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/compare/29320b3074cff6ba0e5c8615cc38243507efe1e5...c4c2a7f040a3b0f9f255c4df1d670150cc135c75
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