Re: [C++ Patch] PR 63265

[Paolo Carlini]

Hi,

On 11/10/2014 06:16 PM, Jason Merrill wrote:

I don't think we want to suppress this warning in general. The problem in this PR is that the warning code is failing to recognize that the first operand is constant false.

Thanks. Then, shall we do something like the below? Passes testing.

Thanks,
Paolo.

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

/cp
2014-11-11  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/63265
        * pt.c (tsubst_copy_and_build, case COND_EXPR): Maybe fold to
        const the condition.

/testsuite
2014-11-11  Paolo Carlini  <paolo.carl...@oracle.com>

        PR c++/63265
        * g++.dg/cpp0x/constexpr-63265.C: New.

Index: cp/pt.c
===================================================================
--- cp/pt.c     (revision 217342)
+++ cp/pt.c     (working copy)
@@ -15137,7 +15137,9 @@ tsubst_copy_and_build (tree t,
 
     case COND_EXPR:
       {
-       tree cond = RECUR (TREE_OPERAND (t, 0));
+       tree cond
+         = maybe_constant_value (fold_non_dependent_expr_sfinae
+                                 (RECUR (TREE_OPERAND (t, 0)), tf_none));
        tree exp1, exp2;
 
        if (TREE_CODE (cond) == INTEGER_CST)
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");