Re: [C++ Patch] PR 63265

[Paolo Carlini]

Hi,

On 11/11/2014 02:19 PM, Jason Merrill wrote:

On 11/11/2014 08:04 AM, Paolo Carlini wrote:

-    tree cond = RECUR (TREE_OPERAND (t, 0));
+    tree cond
+      = maybe_constant_value (fold_non_dependent_expr_sfinae
+                  (RECUR (TREE_OPERAND (t, 0)), tf_none));

I like this approach, but if the result of maybe_constant_value doesn't turn out to be an INTEGER_CST, we want to end up with the result of RECUR rather than the result of fold_non_dependent_expr, as the latter might not be suitable for subsequent tsubsting.

I see. Something like the below, then?

Thanks,
Paolo.

/////////////////

Index: cp/pt.c
===================================================================
--- cp/pt.c     (revision 217342)
+++ cp/pt.c     (working copy)
@@ -15138,11 +15138,13 @@ tsubst_copy_and_build (tree t,
     case COND_EXPR:
       {
        tree cond = RECUR (TREE_OPERAND (t, 0));
+       tree folded_cond = (maybe_constant_value
+                           (fold_non_dependent_expr_sfinae (cond, tf_none)));
        tree exp1, exp2;
 
-       if (TREE_CODE (cond) == INTEGER_CST)
+       if (TREE_CODE (folded_cond) == INTEGER_CST)
          {
-           if (integer_zerop (cond))
+           if (integer_zerop (folded_cond))
              {
                ++c_inhibit_evaluation_warnings;
                exp1 = RECUR (TREE_OPERAND (t, 1));
@@ -15156,6 +15158,7 @@ tsubst_copy_and_build (tree t,
                exp2 = RECUR (TREE_OPERAND (t, 2));
                --c_inhibit_evaluation_warnings;
              }
+           cond = folded_cond;
          }
        else
          {
Index: testsuite/g++.dg/cpp0x/constexpr-63265.C
===================================================================
--- testsuite/g++.dg/cpp0x/constexpr-63265.C    (revision 0)
+++ testsuite/g++.dg/cpp0x/constexpr-63265.C    (working copy)
@@ -0,0 +1,19 @@
+// PR c++/63265
+// { dg-do compile { target c++11 } }
+
+#define LSHIFT (sizeof(unsigned int) * __CHAR_BIT__)
+
+template <int lshift>
+struct SpuriouslyWarns1 {
+    static constexpr unsigned int v = lshift < LSHIFT ? 1U << lshift : 0;
+};
+
+static_assert(SpuriouslyWarns1<LSHIFT>::v == 0, "Impossible occurred");
+
+template <int lshift>
+struct SpuriouslyWarns2 {
+    static constexpr bool okay = lshift < LSHIFT;
+    static constexpr unsigned int v = okay ? 1U << lshift : 0;
+};
+
+static_assert(SpuriouslyWarns2<LSHIFT>::v == 0, "Impossible occurred");