C++ PATCH for c++/65695 (pointer-to-member constants and constexpr)

[Jason Merrill]

adjust_temp_type was wrapping a PTRMEM_CST in a NOP_EXPR, which confused 
constexpr evaluation.  We can avoid this by fixing cp_fold_convert to 
properly fold away the conversion.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit a5a7219fc54d6d724a032befea810910cda01fc7
Author: Jason Merrill <ja...@redhat.com>
Date:   Sat Apr 11 10:57:07 2015 -0400
    	PR c++/65695
    	* cvt.c (cp_fold_convert): Avoid wrapping PTRMEM_CST in NOP_EXPR.

diff --git a/gcc/cp/cvt.c b/gcc/cp/cvt.c
index d0924f1..9aa9006 100644
--- a/gcc/cp/cvt.c
+++ b/gcc/cp/cvt.c
@@ -603,8 +603,20 @@ ignore_overflows (tree expr, tree orig)
 tree
 cp_fold_convert (tree type, tree expr)
 {
-  tree conv = fold_convert (type, expr);
-  conv = ignore_overflows (conv, expr);
+  tree conv;
+  if (TREE_TYPE (expr) == type)
+    conv = expr;
+  else if (TREE_CODE (expr) == PTRMEM_CST)
+    {
+      /* Avoid wrapping a PTRMEM_CST in NOP_EXPR.  */
+      conv = copy_node (expr);
+      TREE_TYPE (conv) = type;
+    }
+  else
+    {
+      conv = fold_convert (type, expr);
+      conv = ignore_overflows (conv, expr);
+    }
   return conv;
 }
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem4.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem4.C
new file mode 100644
index 0000000..68788ca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem4.C
@@ -0,0 +1,26 @@
+// PR c++/65695
+// { dg-do compile { target c++11 } }
+
+struct Foo;
+
+struct Bar
+{
+    using MemberFuncT = int (Foo::*)();
+
+    MemberFuncT h_;
+    constexpr Bar(MemberFuncT h) : h_{h}
+    {
+    }
+};
+
+struct Foo
+{
+    int test()
+    {
+        return -1;
+    }
+
+    static constexpr Bar bar {&Foo::test};
+};
+
+constexpr Bar Foo::bar;