Make SpecConstr "look through" identity coercions

[ghc-hetmet.git] / compiler / specialise / SpecConstr.lhs

diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs
index cbe1c0b..0b61a57 100644 (file)
--- a/compiler/specialise/SpecConstr.lhs
+++ b/compiler/specialise/SpecConstr.lhs
@@ -1549,6 +1549,9 @@ argToPat env in_scope val_env (Case scrut _ _ [(_, _, rhs)]) arg_occ
 -}
 
 argToPat env in_scope val_env (Cast arg co) arg_occ
+  | isIdentityCoercion co     -- Substitution in the SpecConstr itself
+                              -- can lead to identity coercions
+  = argToPat env in_scope val_env arg arg_occ
   | not (ignoreType env ty2)
   = do { (interesting, arg') <- argToPat env in_scope val_env arg arg_occ
        ; if not interesting then