C++ PATCH for c++/62659 (rejects-valid with pointer to member function in template)

C++ PATCH for c++/62659 (rejects-valid with pointer to member function in template)

[Jason Merrill]

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potential_constant_expression was getting confused by the (non-constant) 
object argument of the OFFSET_REF, but it isn't really involved in 
calculating the value of the PMF.

Tested x86_64-pc-linux-gnu, applying to trunk and 4.9.

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commit cbf61fb5d2ae5db8ff4986e2124105cb899c0037
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Sep 5 11:36:34 2014 -0400

    	PR c++/62659
    	* semantics.c (potential_constant_expression_1): Handle un-folded
    	pointer to member constants.

diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 01748da..776fa26 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -10348,6 +10348,11 @@ potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
             designates an object with thread or automatic storage
             duration;  */
       t = TREE_OPERAND (t, 0);
+
+      if (TREE_CODE (t) == OFFSET_REF && PTRMEM_OK_P (t))
+	/* A pointer-to-member constant.  */
+	return true;
+
 #if 0
       /* FIXME adjust when issue 1197 is fully resolved.  For now don't do
          any checking here, as we might dereference the pointer later.  If
diff --git a/gcc/testsuite/g++.dg/template/ptrmem29.C b/gcc/testsuite/g++.dg/template/ptrmem29.C
new file mode 100644
index 0000000..7700c0b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ptrmem29.C
@@ -0,0 +1,10 @@
+// PR c++/62659
+
+struct D {
+  typedef int (D::*cont_func)();
+  template <cont_func> struct B;
+  template <cont_func cont_f> void wait(B<cont_f> ***);
+
+  int done();
+  template <bool> void fix() { wait<&D::done>(0); }
+};