Index: builtins.c
===================================================================
--- builtins.c	(revision 241743)
+++ builtins.c	(working copy)
@@ -3929,61 +3929,85 @@
     unsigned int arg1_align = get_pointer_alignment (arg1) / BITS_PER_UNIT;
     unsigned int arg2_align = get_pointer_alignment (arg2) / BITS_PER_UNIT;
 
+    /* If we don't have POINTER_TYPE, call the function.  */
+    if (arg1_align == 0 || arg2_align == 0)
+      return NULL_RTX;
+
     len1 = c_strlen (arg1, 1);
     len2 = c_strlen (arg2, 1);
 
-    if (len1)
-      len1 = size_binop_loc (loc, PLUS_EXPR, ssize_int (1), len1);
-    if (len2)
-      len2 = size_binop_loc (loc, PLUS_EXPR, ssize_int (1), len2);
+    if (!len1 && !len2)
+      {
+	/* If neither arg1 nor arg2 are constant strings.  */
+	/* Stabilize the arguments in case gen_cmpstrnsi fails.  */
+	arg1 = builtin_save_expr (arg1);
+	arg2 = builtin_save_expr (arg2);
+	/* Use save_expr here because cmpstrnsi may modify arg3
+	   and builtin_save_expr() doesn't force the save to happen.  */
+	len = save_expr (arg3);
+	len = fold_convert_loc (loc, sizetype, len);
+      }
+    else
+      {
+	if (len1)
+	  len1 = size_binop_loc (loc, PLUS_EXPR, ssize_int (1), len1);
+	if (len2)
+	  len2 = size_binop_loc (loc, PLUS_EXPR, ssize_int (1), len2);
 
-    /* If we don't have a constant length for the first, use the length
-       of the second, if we know it.  We don't require a constant for
-       this case; some cost analysis could be done if both are available
-       but neither is constant.  For now, assume they're equally cheap,
-       unless one has side effects.  If both strings have constant lengths,
-       use the smaller.  */
+	/* If we don't have a constant length for the first, use the length
+	   of the second, if we know it.  We don't require a constant for
+	   this case; some cost analysis could be done if both are available
+	   but neither is constant.  For now, assume they're equally cheap,
+	   unless one has side effects.  If both strings have constant lengths,
+	   use the smaller.  */
 
-    if (!len1)
-      len = len2;
-    else if (!len2)
-      len = len1;
-    else if (TREE_SIDE_EFFECTS (len1))
-      len = len2;
-    else if (TREE_SIDE_EFFECTS (len2))
-      len = len1;
-    else if (TREE_CODE (len1) != INTEGER_CST)
-      len = len2;
-    else if (TREE_CODE (len2) != INTEGER_CST)
-      len = len1;
-    else if (tree_int_cst_lt (len1, len2))
-      len = len1;
-    else
-      len = len2;
+	if (!len1)
+	  len = len2;
+	else if (!len2)
+	  len = len1;
+	else if (TREE_SIDE_EFFECTS (len1))
+	  len = len2;
+	else if (TREE_SIDE_EFFECTS (len2))
+	  len = len1;
+	else if (TREE_CODE (len1) != INTEGER_CST)
+	  len = len2;
+	else if (TREE_CODE (len2) != INTEGER_CST)
+	  len = len1;
+	else if (tree_int_cst_lt (len1, len2))
+	  len = len1;
+	else
+	  len = len2;
 
-    /* If both arguments have side effects, we cannot optimize.  */
-    if (!len || TREE_SIDE_EFFECTS (len))
-      return NULL_RTX;
+	/* If both arguments have side effects, we cannot optimize.  */
+	if (TREE_SIDE_EFFECTS (len))
+	  return NULL_RTX;
 
-    /* The actual new length parameter is MIN(len,arg3).  */
-    len = fold_build2_loc (loc, MIN_EXPR, TREE_TYPE (len), len,
-		       fold_convert_loc (loc, TREE_TYPE (len), arg3));
+	/* The actual new length parameter is MIN(len,arg3).  */
+	len = fold_build2_loc (loc, MIN_EXPR, TREE_TYPE (len), len,
+			       fold_convert_loc (loc, TREE_TYPE (len), arg3));
 
-    /* If we don't have POINTER_TYPE, call the function.  */
-    if (arg1_align == 0 || arg2_align == 0)
-      return NULL_RTX;
+	/* Stabilize the arguments in case gen_cmpstrnsi fails.  */
+	arg1 = builtin_save_expr (arg1);
+	arg2 = builtin_save_expr (arg2);
+	len = builtin_save_expr (len);
+      }
 
-    /* Stabilize the arguments in case gen_cmpstrnsi fails.  */
-    arg1 = builtin_save_expr (arg1);
-    arg2 = builtin_save_expr (arg2);
-    len = builtin_save_expr (len);
-
     arg1_rtx = get_memory_rtx (arg1, len);
     arg2_rtx = get_memory_rtx (arg2, len);
     arg3_rtx = expand_normal (len);
+    
+    /* Set MEM_SIZE as appropriate.  This will only happen in 
+       the case where incoming arg3 is constant and arg1/arg2 are not.  */
+    if (CONST_INT_P (arg3_rtx))
+      {
+	set_mem_size (arg1_rtx, INTVAL (arg3_rtx));
+	set_mem_size (arg2_rtx, INTVAL (arg3_rtx));
+      }
+    
     result = expand_cmpstrn_or_cmpmem (cmpstrn_icode, target, arg1_rtx,
 				       arg2_rtx, TREE_TYPE (len), arg3_rtx,
 				       MIN (arg1_align, arg2_align));
+
     if (result)
       {
 	/* Return the value in the proper mode for this function.  */
