[project @ 2002-09-02 16:38:24 by simonpj]

Fix an obscure bug in an optimisation for 'coerce' which
wasn't taking account of the possiblity of type arguments.

		MERGE TO STABLE

diff --git a/ghc/compiler/simplCore/Simplify.lhs b/ghc/compiler/simplCore/Simplify.lhs
index 0a30390..303fd65 100644 (file)
--- a/ghc/compiler/simplCore/Simplify.lhs
+++ b/ghc/compiler/simplCore/Simplify.lhs
@@ -795,12 +795,14 @@ simplNote env (Coerce to from) body cont
                                                -- the inner one is redundant
 
        addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
-         | Just (s1, s2) <- splitFunTy_maybe s1s2
+         | not (isTypeArg arg),        -- This whole case only works for value args
+                                       -- Could upgrade to have equiv thing for type apps too  
+           Just (s1, s2) <- splitFunTy_maybe s1s2
                --      (coerce (T1->T2) (S1->S2) F) E
                -- ===> 
                --      coerce T2 S2 (F (coerce S1 T1 E))
                --
-               -- t1t2 must be a function type, T1->T2
+               -- t1t2 must be a function type, T1->T2, because it's applied to something
                -- but s1s2 might conceivably not be
                --
                -- When we build the ApplyTo we can't mix the out-types