diff options
Diffstat (limited to 'compiler/GHC/Core/Type.hs')
| -rw-r--r-- | compiler/GHC/Core/Type.hs | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/compiler/GHC/Core/Type.hs b/compiler/GHC/Core/Type.hs index 17519d8dd5..8d41466d30 100644 --- a/compiler/GHC/Core/Type.hs +++ b/compiler/GHC/Core/Type.hs @@ -4,6 +4,7 @@ -- Type - public interface {-# LANGUAGE FlexibleContexts, PatternSynonyms, ViewPatterns #-} +{-# LANGUAGE MagicHash #-} {-# OPTIONS_GHC -fno-warn-orphans #-} {-# OPTIONS_GHC -Wno-incomplete-record-updates #-} @@ -294,10 +295,10 @@ import GHC.Data.Pair import GHC.Data.List.SetOps import GHC.Types.Unique ( nonDetCmpUnique ) +import GHC.Base (reallyUnsafePtrEquality#) import GHC.Data.Maybe ( orElse, expectJust, isJust ) import Control.Monad ( guard ) import qualified Data.Semigroup as S --- import GHC.Utils.Trace -- $type_classification -- #type_classification# @@ -556,7 +557,7 @@ expandTypeSynonyms ty in_scope = mkInScopeSet (tyCoVarsOfType ty) go subst (TyConApp tc tys) - | Just (tenv, rhs, tys') <- expandSynTyCon_maybe tc expanded_tys + | ExpandsSyn tenv rhs tys' <- expandSynTyCon_maybe tc expanded_tys = let subst' = mkTvSubst in_scope (mkVarEnv tenv) -- Make a fresh substitution; rhs has nothing to -- do with anything that has happened so far @@ -2787,6 +2788,16 @@ comparing type variables is nondeterministic, note the call to nonDetCmpVar in nonDetCmpTypeX. See Note [Unique Determinism] for more details. +Note [Type comparisons using object pointer comparisons] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Quite often we substitute the type from a definition site into +occurances without a change. This means for code like: + \x -> (x,x,x) +The type of every `x` will often be represented by a single object +in the heap. We can take advantage of this by shortcutting the equality +check if two types are represented by the same pointer under the hood. +In some cases this reduces compiler allocations by ~2%. + Note [Computing equality on types] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ There are several places within GHC that depend on the precise choice of @@ -2800,11 +2811,15 @@ See also Note [Non-trivial definitional equality] in GHC.Core.TyCo.Rep. -} nonDetCmpType :: Type -> Type -> Ordering +nonDetCmpType !t1 !t2 + -- See Note [Type comparisons using object pointer comparisons] + | 1# <- reallyUnsafePtrEquality# t1 t2 + = EQ nonDetCmpType (TyConApp tc1 []) (TyConApp tc2 []) | tc1 == tc2 = EQ -nonDetCmpType t1 t2 +nonDetCmpType t1 t2 = -- we know k1 and k2 have the same kind, because they both have kind *. - = nonDetCmpTypeX rn_env t1 t2 + nonDetCmpTypeX rn_env t1 t2 where rn_env = mkRnEnv2 (mkInScopeSet (tyCoVarsOfTypes [t1, t2])) {-# INLINE nonDetCmpType #-} |