1 files changed, 8 insertions, 2 deletions
diff --git a/gcc/fold-const.c b/gcc/fold-const.c
index 55f4ce4..0e301a7 100644
--- a/gcc/fold-const.c
+++ b/gcc/fold-const.c
@@ -7436,11 +7436,17 @@ tree_expr_nonnegative_p (t)
     {
     case ABS_EXPR:
     case FFS_EXPR:
-    case CLZ_EXPR:
-    case CTZ_EXPR:
     case POPCOUNT_EXPR:
     case PARITY_EXPR:
       return 1;
+
+    case CLZ_EXPR:
+    case CTZ_EXPR:
+      /* These are undefined at zero.  This is true even if
+	 C[LT]Z_DEFINED_VALUE_AT_ZERO is set, since what we're
+	 computing here is a user-visible property.  */
+      return 0;
+      
     case INTEGER_CST:
       return tree_int_cst_sgn (t) >= 0;
     case TRUNC_DIV_EXPR: