GitLab

Simon Peyton Jones pushed to branch wip/T23559 at Glasgow Haskell Compiler / GHC

Commits:

f7dc61d5

by Simon Peyton Jones at 2025-11-26T23:26:35+00:00

Switch -fpolymorphic-specialisation on by default

This patch addresses #23559.

Now that !10479 has landed and #26329 is fixed, we can switch on
polymorphic specialisation by default, addressing a bunch of other
tickets listed in #23559.

Metric changes:
  * CoOpt_Singleton: +4% compiler allocations: we just get more
    specialisations

  * info_table_map_perf: -20% decrease in compiler allocations.
    This is caused by using -fno-specialise in ExactPrint.hs
    Without that change we get a 4x blow-up in compile time;
    see !15058 for details

Metric Decrease:
    info_table_map_perf
Metric Increase:
    CoOpt_Singletons

4 changed files:

compiler/GHC/Driver/DynFlags.hs
compiler/GHC/Driver/Flags.hs
docs/users_guide/using-optimisation.rst
testsuite/tests/simplCore/should_compile/T8331.stderr

Changes:

compiler/GHC/Driver/DynFlags.hs

@@ -1268,6 +1268,7 @@ optLevelFlags -- see Note [Documenting optimisation flags]
      , ([1,2],   Opt_CfgBlocklayout)      -- Experimental
      , ([1,2],   Opt_Specialise)
 +    , ([1,2],   Opt_PolymorphicSpecialisation)  -- Now on by default (#23559)
      , ([1,2],   Opt_CrossModuleSpecialise)
      , ([1,2],   Opt_InlineGenerics)
      , ([1,2],   Opt_Strictness)

compiler/GHC/Driver/Flags.hs

@@ -909,6 +909,7 @@ optimisationFlags = EnumSet.fromList
     , Opt_SpecialiseAggressively
     , Opt_CrossModuleSpecialise
     , Opt_StaticArgumentTransformation
 +   , Opt_PolymorphicSpecialisation
     , Opt_CSE
     , Opt_StgCSE
     , Opt_StgLiftLams

docs/users_guide/using-optimisation.rst

@@ -1325,10 +1325,7 @@ as such you shouldn't need to set any of them explicitly. A flag
      :reverse: -fno-polymorphic-specialisation
      :category:
 -    :default: off
+-
 -    Warning, this feature is highly experimental and may lead to incorrect runtime
 -    results. Use at your own risk (:ghc-ticket:`23469`, :ghc-ticket:`23109`, :ghc-ticket:`21229`, :ghc-ticket:`23445`).
 +    :default: on
      Enable specialisation of function calls to known dictionaries with free type variables.
      The created specialisation will abstract over the type variables free in the dictionary.

testsuite/tests/simplCore/should_compile/T8331.stderr

  ==================== Tidy Core rules ====================
 +"SPEC $c*> @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT_$c*> @(ST s) @r $dApplicative
 +      = ($fApplicativeReaderT2 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <ReaderT r (ST s) a>_R
 +                ->_R <ReaderT r (ST s) b>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <b>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <b>_N)
 +                :: Coercible
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> ReaderT r (ST s) b -> r -> STRep s b)
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> ReaderT r (ST s) b -> ReaderT r (ST s) b))
 +"SPEC $c<$ @(ST s) @_"
 +    forall (@s) (@r) ($dFunctor :: Functor (ST s)).
 +      $fFunctorReaderT_$c<$ @(ST s) @r $dFunctor
 +      = ($fApplicativeReaderT6 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <a>_R
 +                ->_R <ReaderT r (ST s) b>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <a>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <a>_N)
 +                :: Coercible
 +                     (forall a b. a -> ReaderT r (ST s) b -> r -> STRep s a)
 +                     (forall a b. a -> ReaderT r (ST s) b -> ReaderT r (ST s) a))
 +"SPEC $c<* @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT_$c<* @(ST s) @r $dApplicative
 +      = ($fApplicativeReaderT1 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <ReaderT r (ST s) a>_R
 +                ->_R <ReaderT r (ST s) b>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <a>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <a>_N)
 +                :: Coercible
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> ReaderT r (ST s) b -> r -> STRep s a)
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> ReaderT r (ST s) b -> ReaderT r (ST s) a))
 +"SPEC $c<*> @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT9 @(ST s) @r $dApplicative
 +      = ($fApplicativeReaderT4 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <ReaderT r (ST s) (a -> b)>_R
 +                ->_R <ReaderT r (ST s) a>_R
 +                ->_R <r>_R
 +                ->_R Sym (N:ST <s>_N <b>_R)
 +                :: Coercible
 +                     (forall a b.
 +                      ReaderT r (ST s) (a -> b) -> ReaderT r (ST s) a -> r -> STRep s b)
 +                     (forall a b.
 +                      ReaderT r (ST s) (a -> b) -> ReaderT r (ST s) a -> r -> ST s b))
 +"SPEC $c>> @(ST s) @_"
 +    forall (@s) (@r) ($dMonad :: Monad (ST s)).
 +      $fMonadReaderT1 @(ST s) @r $dMonad
 +      = $fMonadAbstractIOSTReaderT_$s$c>> @s @r
 +"SPEC $c>>= @(ST s) @_"
 +    forall (@s) (@r) ($dMonad :: Monad (ST s)).
 +      $fMonadReaderT2 @(ST s) @r $dMonad
 +      = ($fMonadAbstractIOSTReaderT2 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <ReaderT r (ST s) a>_R
 +                ->_R <a -> ReaderT r (ST s) b>_R
 +                ->_R <r>_R
 +                ->_R Sym (N:ST <s>_N <b>_R)
 +                :: Coercible
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> (a -> ReaderT r (ST s) b) -> r -> STRep s b)
 +                     (forall a b.
 +                      ReaderT r (ST s) a -> (a -> ReaderT r (ST s) b) -> r -> ST s b))
 +"SPEC $cfmap @(ST s) @_"
 +    forall (@s) (@r) ($dFunctor :: Functor (ST s)).
 +      $fFunctorReaderT_$cfmap @(ST s) @r $dFunctor
 +      = ($fApplicativeReaderT7 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N).
 +                <a -> b>_R
 +                ->_R <ReaderT r (ST s) a>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <b>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <b>_N)
 +                :: Coercible
 +                     (forall a b. (a -> b) -> ReaderT r (ST s) a -> r -> STRep s b)
 +                     (forall a b. (a -> b) -> ReaderT r (ST s) a -> ReaderT r (ST s) b))
 +"SPEC $cliftA2 @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT_$cliftA2 @(ST s) @r $dApplicative
 +      = ($fApplicativeReaderT3 @s @r)
 +        `cast` (forall (a ::~ <*>_N) (b ::~ <*>_N) (c ::~ <*>_N).
 +                <a -> b -> c>_R
 +                ->_R <ReaderT r (ST s) a>_R
 +                ->_R <ReaderT r (ST s) b>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <c>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <c>_N)
 +                :: Coercible
 +                     (forall a b c.
 +                      (a -> b -> c)
 +                      -> ReaderT r (ST s) a -> ReaderT r (ST s) b -> r -> STRep s c)
 +                     (forall a b c.
 +                      (a -> b -> c)
 +                      -> ReaderT r (ST s) a -> ReaderT r (ST s) b -> ReaderT r (ST s) c))
 +"SPEC $cp1Applicative @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT_$cp1Applicative @(ST s) @r $dApplicative
 +      = $fApplicativeReaderT_$s$fFunctorReaderT @s @r
 +"SPEC $cp1Monad @(ST s) @_"
 +    forall (@s) (@r) ($dMonad :: Monad (ST s)).
 +      $fMonadReaderT_$cp1Monad @(ST s) @r $dMonad
 +      = $fApplicativeReaderT_$s$fApplicativeReaderT @s @r
 +"SPEC $cpure @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT_$cpure @(ST s) @r $dApplicative
 +      = ($fApplicativeReaderT5 @s @r)
 +        `cast` (forall (a ::~ <*>_N).
 +                <a>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <a>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <a>_N)
 +                :: Coercible
 +                     (forall a. a -> r -> STRep s a)
 +                     (forall a. a -> ReaderT r (ST s) a))
 +"SPEC $creturn @(ST s) @_"
 +    forall (@s) (@r) ($dMonad :: Monad (ST s)).
 +      $fMonadReaderT_$creturn @(ST s) @r $dMonad
 +      = ($fApplicativeReaderT5 @s @r)
 +        `cast` (forall (a ::~ <*>_N).
 +                <a>_R
 +                ->_R <r>_R ->_R Sym (N:ST <s>_N <a>_R)
 +                     ; Sym (N:ReaderT <*>_N <r>_R <ST s>_R <a>_N)
 +                :: Coercible
 +                     (forall a. a -> r -> STRep s a)
 +                     (forall a. a -> ReaderT r (ST s) a))
 +"SPEC $fApplicativeReaderT @(ST s) @_"
 +    forall (@s) (@r) ($dApplicative :: Applicative (ST s)).
 +      $fApplicativeReaderT @(ST s) @r $dApplicative
 +      = $fApplicativeReaderT_$s$fApplicativeReaderT @s @r
 +"SPEC $fFunctorReaderT @(ST s) @_"
 +    forall (@s) (@r) ($dFunctor :: Functor (ST s)).
 +      $fFunctorReaderT @(ST s) @r $dFunctor
 +      = $fApplicativeReaderT_$s$fFunctorReaderT @s @r
 +"SPEC $fMonadReaderT @(ST s) @_"
 +    forall (@s) (@r) ($dMonad :: Monad (ST s)).
 +      $fMonadReaderT @(ST s) @r $dMonad
 +      = $fMonadAbstractIOSTReaderT_$s$fMonadReaderT @s @r
  "USPEC useAbstractMonad @(ReaderT Int (ST s))"
      forall (@s)
             ($dMonadAbstractIOST :: MonadAbstractIOST (ReaderT Int (ST s))).