diff options
Diffstat (limited to 'compiler/GHC/Core/Opt/Simplify.hs')
| -rw-r--r-- | compiler/GHC/Core/Opt/Simplify.hs | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/compiler/GHC/Core/Opt/Simplify.hs b/compiler/GHC/Core/Opt/Simplify.hs index f052bae942..c44fd1d62a 100644 --- a/compiler/GHC/Core/Opt/Simplify.hs +++ b/compiler/GHC/Core/Opt/Simplify.hs @@ -2904,8 +2904,14 @@ doCaseToLet scrut case_bndr | isTyCoVar case_bndr -- Respect GHC.Core = isTyCoArg scrut -- Note [Core type and coercion invariant] - | isUnliftedType (idType case_bndr) - -- OK to call isUnliftedType: scrutinees always have a fixed RuntimeRep (see FRRCase) + | isUnliftedType (exprType scrut) + -- We can call isUnliftedType here: scrutinees always have a fixed RuntimeRep (see FRRCase). + -- Note however that we must check 'scrut' (which is an 'OutExpr') and not 'case_bndr' + -- (which is an 'InId'): see Note [Dark corner with representation polymorphism]. + -- Using `exprType` is typically cheap becuase `scrut` is typically a variable. + -- We could instead use mightBeUnliftedType (idType case_bndr), but that hurts + -- the brain more. Consider that if this test ever turns out to be a perf + -- problem (which seems unlikely). = exprOkForSpeculation scrut | otherwise -- Scrut has a lifted type |