From 45a61df30f95b22d4818b6e3e3622707911bde03 Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Thu, 25 Nov 2010 17:21:38 +0000
Subject: [PATCH] Make SpecConstr "look through" identity coercions

---
 compiler/specialise/SpecConstr.lhs |    3 +++
 1 file changed, 3 insertions(+)

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 
-- 
1.7.10.4