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| author | Sebastian Graf <sebastian.graf@kit.edu> | 2022-04-07 17:21:08 +0200 |
|---|---|---|
| committer | Sebastian Graf <sebastian.graf@kit.edu> | 2022-04-12 17:54:57 +0200 |
| commit | 4d2ee313f23a4454d12c9f94ff132f078dd64d31 (patch) | |
| tree | e7bd7b66f35660864f19feb998ab1d9ca96665fa /compiler/GHC/Core/SimpleOpt.hs | |
| parent | 0090ad7b8b436961fe1e225aae214d0ea1381c07 (diff) | |
| download | haskell-4d2ee313f23a4454d12c9f94ff132f078dd64d31.tar.gz | |
Specialising through specialised method calls (#19644)
In #19644, we discovered that the ClassOp/DFun rules from
Note [ClassOp/DFun selection] inhibit transitive specialisation in a scenario
like
```
class C a where m :: Show b => a -> b -> ...; n :: ...
instance C Int where m = ... -- $cm :: Show b => Int -> b -> ...
f :: forall a b. (C a, Show b) => ...
f $dC $dShow = ... m @a $dC @b $dShow ...
main = ... f @Int @Bool ...
```
After we specialise `f` for `Int`, we'll see `m @a $dC @b $dShow` in the body of
`$sf`. But before this patch, Specialise doesn't apply the ClassOp/DFun rule to
rewrite to a call of the instance method for `C Int`, e.g., `$cm @Bool $dShow`.
As a result, Specialise couldn't further specialise `$cm` for `Bool`.
There's a better example in `Note [Specialisation modulo dictionary selectors]`.
This patch enables proper Specialisation, as follows:
1. In the App case of `specExpr`, try to apply the CalssOp/DictSel rule on the
head of the application
2. Attach an unfolding to freshly-bound dictionary ids such as `$dC` and
`$dShow` in `bindAuxiliaryDict`
NB: Without (2), (1) would be pointless, because `lookupRule` wouldn't be able
to look into the RHS of `$dC` to see the DFun.
(2) triggered #21332, because the Specialiser floats around dictionaries without
accounting for them in the `SpecEnv`'s `InScopeSet`, triggering a panic when
rewriting dictionary unfoldings.
Fixes #19644 and #21332.
Diffstat (limited to 'compiler/GHC/Core/SimpleOpt.hs')
| -rw-r--r-- | compiler/GHC/Core/SimpleOpt.hs | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/compiler/GHC/Core/SimpleOpt.hs b/compiler/GHC/Core/SimpleOpt.hs index 925eaf5841..360c868738 100644 --- a/compiler/GHC/Core/SimpleOpt.hs +++ b/compiler/GHC/Core/SimpleOpt.hs @@ -22,7 +22,7 @@ import GHC.Prelude import GHC.Core import GHC.Core.Opt.Arity -import GHC.Core.Subst +import GHC.Core.Subst hiding ( extendInScopeSet ) import GHC.Core.Utils import GHC.Core.FVs import GHC.Core.Unfold |