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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2021-04-15 15:20:26 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2021-04-26 23:56:53 -0400 |
| commit | 6c7fff0b6f9514d6572cbe6bbfa4aafc259caebe (patch) | |
| tree | befd67e0d63bef6c6aee6b318e4ef6e287a62797 /compiler/GHC/Core/Subst.hs | |
| parent | 06654a6e0e4c1f9eb58947439092ae27b00d8c10 (diff) | |
| download | haskell-6c7fff0b6f9514d6572cbe6bbfa4aafc259caebe.tar.gz | |
Eliminate unsafeEqualityProof in CorePrep
The main idea here is to avoid treating
* case e of {}
* case unsafeEqualityProof of UnsafeRefl co -> blah
specially in CoreToStg. Instead, nail them in CorePrep,
by converting
case e of {}
==> e |> unsafe-co
case unsafeEqualityProof of UnsafeRefl cv -> blah
==> blah[unsafe-co/cv]
in GHC.Core.Prep. Now expressions that we want to treat as trivial
really are trivial. We can get rid of cpExprIsTrivial.
And we fix #19700.
A downside is that, at least under unsafeEqualityProof, we substitute
in types and coercions, which is more work. But a big advantage is
that it's all very simple and principled: CorePrep really gets rid of
the unsafeCoerce stuff, as it does empty case, runRW#, lazyId etc.
I've updated the overview in GHC.Core.Prep, and added
Note [Unsafe coercions] in GHC.Core.Prep
Note [Implementing unsafeCoerce] in base:Unsafe.Coerce
We get 3% fewer bytes allocated when compiling perf/compiler/T5631,
which uses a lot of unsafeCoerces. (It's a happy-generated parser.)
Metric Decrease:
T5631
Diffstat (limited to 'compiler/GHC/Core/Subst.hs')
| -rw-r--r-- | compiler/GHC/Core/Subst.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/Core/Subst.hs b/compiler/GHC/Core/Subst.hs index e0f153287f..f60b60b02b 100644 --- a/compiler/GHC/Core/Subst.hs +++ b/compiler/GHC/Core/Subst.hs @@ -579,7 +579,7 @@ cloneTyVarBndr (Subst in_scope id_env tv_env cv_env) tv uniq (TCvSubst in_scope' tv_env' cv_env', tv') -> (Subst in_scope' id_env tv_env' cv_env', tv') -substCoVarBndr :: Subst -> TyVar -> (Subst, TyVar) +substCoVarBndr :: Subst -> CoVar -> (Subst, CoVar) substCoVarBndr (Subst in_scope id_env tv_env cv_env) cv = case Coercion.substCoVarBndr (TCvSubst in_scope tv_env cv_env) cv of (TCvSubst in_scope' tv_env' cv_env', cv') |