re PR target/14478 ([3.3 only] rs6000 geu/ltu patterns generate incorrect code)

	PR target/14478
	* config/rs6000/rs6000.c (reg_or_neg_short_operand): Don't allow zero.

From-SVN: r82315

gcc/ChangeLog

+2004-05-27  Alan Modra  <amodra@bigpond.net.au>
+
+	PR target/14478
+	* config/rs6000/rs6000.c (reg_or_neg_short_operand): Don't allow zero.
+
 2004-05-27  Josef Zlomek  <zlomekj@suse.cz>
 
 	PR middle-end/14084

gcc/config/rs6000/rs6000.c

@@ -1407,13 +1407,16 @@ reg_or_short_operand (rtx op, enum machine_mode mode)
 }
 
 /* Similar, except check if the negation of the constant would be
-   valid for a D-field.  */
+   valid for a D-field.  Don't allow a constant zero, since all the
+   patterns that call this predicate use "addic r1,r2,-constant" on
+   a constant value to set a carry when r2 is greater or equal to
+   "constant".  That doesn't work for zero.  */
 
 int
 reg_or_neg_short_operand (rtx op, enum machine_mode mode)
 {
   if (GET_CODE (op) == CONST_INT)
-    return CONST_OK_FOR_LETTER_P (INTVAL (op), 'P');
+    return CONST_OK_FOR_LETTER_P (INTVAL (op), 'P') && INTVAL (op) != 0;
 
   return gpc_reg_operand (op, mode);
 }