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| author | Ben Gamari <ben@smart-cactus.org> | 2020-06-02 17:09:43 -0400 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-06-14 15:35:23 -0400 |
| commit | 9a7462fb6b8bdd6326a607bbd7b9453eb588193b (patch) | |
| tree | 8300a7c5da0b49c63b81946bf94b3f8c4efc3d59 /compiler/GHC/CoreToStg.hs | |
| parent | c0e6dee99242eff08420176a36d77b715972f1f2 (diff) | |
| download | haskell-9a7462fb6b8bdd6326a607bbd7b9453eb588193b.tar.gz | |
codeGen: Don't discard live case binders in unsafeEqualityProof logic
Previously CoreToStg would unconditionally discard cases of the form:
case unsafeEqualityProof of wild { _ -> rhs }
and rather replace the whole thing with `rhs`. However, in some cases
(see #18227) the case binder is still live, resulting in unbound
occurrences in `rhs`. Fix this by only discarding the case if the case
binder is dead.
Fixes #18227.
Diffstat (limited to 'compiler/GHC/CoreToStg.hs')
| -rw-r--r-- | compiler/GHC/CoreToStg.hs | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/compiler/GHC/CoreToStg.hs b/compiler/GHC/CoreToStg.hs index 8657b5a84c..42369fe45b 100644 --- a/compiler/GHC/CoreToStg.hs +++ b/compiler/GHC/CoreToStg.hs @@ -435,7 +435,10 @@ coreToStgExpr e0@(Case scrut bndr _ alts) = do let stg = StgCase scrut2 bndr (mkStgAltType bndr alts) alts2 -- See (U2) in Note [Implementing unsafeCoerce] in base:Unsafe.Coerce case scrut2 of - StgApp id [] | idName id == unsafeEqualityProofName -> + StgApp id [] | idName id == unsafeEqualityProofName + , isDeadBinder bndr -> + -- We can only discard the case if the case-binder is dead + -- It usually is, but see #18227 case alts2 of [(_, [_co], rhs)] -> return rhs |