X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fspecialise%2FSpecConstr.lhs;fp=compiler%2Fspecialise%2FSpecConstr.lhs;h=0b61a57c0d1fb45cd246ebea5240534d00ebb61f;hp=cbe1c0b76aa47f3eda59ba84ce570bbc70c3c034;hb=45a61df30f95b22d4818b6e3e3622707911bde03;hpb=8d022fe21d265d3ab982ae2826d9d9e1438c3b68

diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs
index cbe1c0b..0b61a57 100644
--- 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