(fold): Avoid exponential work when simplifying conditional

expressions; don't recurse twice if ARG1 is constant.

From-SVN: r7010

gcc/fold-const.c

@@ -3420,7 +3420,8 @@ fold (expr)
 	      tree lhs = fold (build (code, type, true_value, arg1));
 	      tree rhs = fold (build (code, type, false_value, arg1));
 
-	      if (TREE_CONSTANT (lhs) || TREE_CONSTANT (rhs))
+	      if (TREE_CONSTANT (lhs) || TREE_CONSTANT (rhs)
+		  || TREE_CONSTANT (arg1))
 		return fold (build (COND_EXPR, type, test, lhs, rhs));
 
 	      arg1 = save_expr (arg1);