diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index fb7cc49a018..10657a44a90 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+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
diff --git a/gcc/ifcvt.c b/gcc/ifcvt.c
index 8367316847f..be02aaa7d24 100644
--- a/gcc/ifcvt.c
+++ b/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