[PATCH] Don't fold PTR - (UN)SIGNED comparison (PR middle-end/54945)

[Marek Polacek <polacek@redhat.com>]

This patch changes folding in fold_sign_changed_comparison in a way
that when we have pointer/non-pointer comparison, we give up folding
here.  The issue is e.g. when we have (intptr_t) &MEM[(void *)&x + 4B]
== (intptr_t) &y and forwprop wants to fold this one via
fold_binary_loc--we then end up folding non-sign-changing comparison.

I don't know about the testcase though.  I had something, but I think
it is too unrealiable.  Regtested/bootstrapped on
x86_64-unknown-linux-gnu.  Ok for trunk?

2012-10-18  Marek Polacek  <polacek@redhat.com>

	* fold-const.c (fold_sign_changed_comparison):  Punt if folding
	pointer/non-pointer comparison.

--- gcc/fold-const.c.mp	2012-10-17 15:01:34.882926243 +0200
+++ gcc/fold-const.c	2012-10-18 18:02:55.482642941 +0200
@@ -6731,12 +6731,14 @@ fold_sign_changed_comparison (location_t
 	   && TREE_TYPE (TREE_OPERAND (arg1, 0)) == inner_type))
     return NULL_TREE;
 
-  if ((TYPE_UNSIGNED (inner_type) != TYPE_UNSIGNED (outer_type)
-       || POINTER_TYPE_P (inner_type) != POINTER_TYPE_P (outer_type))
+  if (TYPE_UNSIGNED (inner_type) != TYPE_UNSIGNED (outer_type)
       && code != NE_EXPR
       && code != EQ_EXPR)
     return NULL_TREE;
 
+  if (POINTER_TYPE_P (inner_type) != POINTER_TYPE_P (outer_type))
+    return NULL_TREE;
+
   if (TREE_CODE (arg1) == INTEGER_CST)
     arg1 = force_fit_type_double (inner_type, tree_to_double_int (arg1),
 				  0, TREE_OVERFLOW (arg1));

	Marek