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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2021-04-15 15:20:26 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2021-04-22 23:29:32 +0100 |
| commit | 8d135dfb871662f86b522c6fa337d1695f6bfe1a (patch) | |
| tree | f1ac26cda512f01a680f05758fdf7b38f9f46119 /compiler/GHC/Core/Unfold.hs | |
| parent | 7bc7eea3897dcb8a87fdb0921f451b9bc77309f6 (diff) | |
| download | haskell-wip/T19700.tar.gz | |
Eliminate unsafeEqualityProof in CorePrepwip/T19700
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/Unfold.hs')
| -rw-r--r-- | compiler/GHC/Core/Unfold.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/Core/Unfold.hs b/compiler/GHC/Core/Unfold.hs index 93b41c1c3b..49a10c5a39 100644 --- a/compiler/GHC/Core/Unfold.hs +++ b/compiler/GHC/Core/Unfold.hs @@ -278,7 +278,7 @@ Moreover, if we /don't/ inline it, we may be left with which will build a thunk -- bad, bad, bad. Conclusion: we really want inlineBoringOk to be True of the RHS of -unsafeCoerce. This is (U4a) in Note [Implementing unsafeCoerce]. +unsafeCoerce. This is (U4) in Note [Implementing unsafeCoerce]. Note [Computing the size of an expression] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |