re PR tree-optimization/21541 (gcc.c-torture/execute/20031215-1.c compilation fails)

        PR 21541
        * ifcvt.c (noce_process_if_block): Avoid conversion when the
        memory destination is readonly.

From-SVN: r99951

gcc/ChangeLog

 2005-05-18  Richard Henderson  <rth@redhat.com>
 
 	PR 21541
+	* ifcvt.c (noce_process_if_block): Avoid conversion when the
+	memory destination is readonly.
+
+2005-05-18  Richard Henderson  <rth@redhat.com>
+
+	PR 21541
 	* tree-ssa-operands.c (opf_non_specific): New.
 	(get_asm_expr_operands): Set it.
 	(add_call_clobber_ops, add_call_read_ops): Likewise.

gcc/ifcvt.c

@@ -1981,6 +1981,14 @@ noce_process_if_block (struct ce_if_block * ce_info)
   if (side_effects_p (x))
     return FALSE;
 
+  /* If x is a read-only memory, then the program is valid only if we
+     avoid the store into it.  If there are stores on both the THEN and
+     ELSE arms, then we can go ahead with the conversion; either the 
+     program is broken, or the condition is always false such that the
+     other memory is selected.  */
+  if (!set_b && MEM_P (x) && MEM_READONLY_P (x))
+    return FALSE;
+
   b = (set_b ? SET_SRC (set_b) : x);
 
   /* Only operate on register destinations, and even then avoid extending