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| author | Ben Gamari <ben@smart-cactus.org> | 2020-03-24 13:13:43 -0400 |
|---|---|---|
| committer | Ben Gamari <ben@smart-cactus.org> | 2020-12-14 15:22:29 -0500 |
| commit | dad87210efffce9cfc2d17dc088a71d9dea14535 (patch) | |
| tree | 42e1c3cb031775598afce272e7caca4c578a20f2 /compiler/GHC/Core/Unify.hs | |
| parent | af855ac1d37359df3db8c48dc6c9dd2f3fe24e77 (diff) | |
| download | haskell-wip/tyconapp-opts.tar.gz | |
Optimise nullary type constructor usagewip/tyconapp-opts
During the compilation of programs GHC very frequently deals with
the `Type` type, which is a synonym of `TYPE 'LiftedRep`. This patch
teaches GHC to avoid expanding the `Type` synonym (and other nullary
type synonyms) during type comparisons, saving a good amount of work.
This optimisation is described in `Note [Comparing nullary type
synonyms]`.
To maximize the impact of this optimisation, we introduce a few
special-cases to reduce `TYPE 'LiftedRep` to `Type`. See
`Note [Prefer Type over TYPE 'LiftedPtrRep]`.
Closes #17958.
Metric Decrease:
T18698b
T1969
T12227
T12545
T12707
T14683
T3064
T5631
T5642
T9020
T9630
T9872a
T13035
haddock.Cabal
haddock.base
Diffstat (limited to 'compiler/GHC/Core/Unify.hs')
| -rw-r--r-- | compiler/GHC/Core/Unify.hs | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/compiler/GHC/Core/Unify.hs b/compiler/GHC/Core/Unify.hs index 709ccf10b4..29d2ae975c 100644 --- a/compiler/GHC/Core/Unify.hs +++ b/compiler/GHC/Core/Unify.hs @@ -957,7 +957,12 @@ unify_ty :: UMEnv -- Respects newtypes, PredTypes unify_ty env ty1 ty2 kco - -- Use tcView, not coreView. See Note [coreView vs tcView] in GHC.Core.Type. + -- See Note [Comparing nullary type synonyms] in GHC.Core.Type. + | TyConApp tc1 [] <- ty1 + , TyConApp tc2 [] <- ty2 + , tc1 == tc2 = return () + + -- TODO: More commentary needed here | Just ty1' <- tcView ty1 = unify_ty env ty1' ty2 kco | Just ty2' <- tcView ty2 = unify_ty env ty1 ty2' kco | CastTy ty1' co <- ty1 = if um_unif env |