[PATCH] Fix constexpr evaluation of comparisons involving pointer-to-members

[Patrick Palka]

We are currently failing to fold equality comparisons involving
PTRMEM_CSTs since (I think) r229018 thus making this a GCC 6 regression.
This regression shows up in the boost testsuite.

Fixed in a straightforward way.  OK to commit after bootstrap + regtest?

gcc/cp/ChangeLog:

	* constexpr.c (cxx_eval_binary_expression): Expand
	the PTRMEM_CST operands of an equality comparison.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/constexpr-ptrmem5.C: New test.
---
 gcc/cp/constexpr.c                             |  9 +++++++++
 gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem5.C | 14 ++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem5.C

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 208f43b..1ad87aa 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -1630,6 +1630,15 @@ cxx_eval_binary_expression (const constexpr_ctx *ctx, tree t,
   location_t loc = EXPR_LOCATION (t);
   enum tree_code code = TREE_CODE (t);
   tree type = TREE_TYPE (t);
+
+  if (code == EQ_EXPR || code == NE_EXPR)
+    {
+      if (TREE_CODE (lhs) == PTRMEM_CST && CONSTANT_CLASS_P (rhs))
+	lhs = cplus_expand_constant (lhs);
+      if (TREE_CODE (rhs) == PTRMEM_CST && CONSTANT_CLASS_P (lhs))
+	rhs = cplus_expand_constant (rhs);
+    }
+
   r = fold_binary_loc (loc, code, type, lhs, rhs);
   if (r == NULL_TREE)
     {
diff --git a/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem5.C b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem5.C
new file mode 100644
index 0000000..e28c917
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/constexpr-ptrmem5.C
@@ -0,0 +1,14 @@
+// { dg-do compile { target c++11 } }
+
+#define SA(x) static_assert ((x), #x)
+
+struct X { int a, b; };
+
+void
+foo ()
+{
+  SA (&X::a);
+  SA (&X::a == &X::a);
+  SA (&X::a != &X::b);
+  SA ((!&X::b) == 0);
+}
-- 
2.7.0.rc0.50.g1470d8f.dirty