C++ PATCH for c++/70386 (constexpr ICE with -Wall and PMF)

[Jason Merrill]

The compiler passes around PMF temporaries as bare CONSTRUCTORs, so we 
need to be prepared for that.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit ebbe164ea708e318be4aa911cc9e98fa333dcd02
Author: Jason Merrill <ja...@redhat.com>
Date:   Thu Mar 24 14:52:25 2016 -0400

    	PR c++/70386
    	* constexpr.c (cxx_eval_bare_aggregate): Handle PMFs.

diff --git a/gcc/cp/constexpr.c b/gcc/cp/constexpr.c
index 2d30a84..8ea7111 100644
--- a/gcc/cp/constexpr.c
+++ b/gcc/cp/constexpr.c
@@ -2268,8 +2268,19 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t,
   vec<constructor_elt, va_gc> *v = CONSTRUCTOR_ELTS (t);
   bool changed = false;
   gcc_assert (!BRACE_ENCLOSED_INITIALIZER_P (t));
+  tree type = TREE_TYPE (t);
 
-  verify_ctor_sanity (ctx, TREE_TYPE (t));
+  constexpr_ctx new_ctx;
+  if (TYPE_PTRMEMFUNC_P (type))
+    {
+      /* We don't really need the ctx->ctor business for a PMF, but it's
+	 simpler to use the same code.  */
+      new_ctx = *ctx;
+      new_ctx.ctor = build_constructor (type, NULL);
+      new_ctx.object = NULL_TREE;
+      ctx = &new_ctx;
+    };
+  verify_ctor_sanity (ctx, type);
   vec<constructor_elt, va_gc> **p = &CONSTRUCTOR_ELTS (ctx->ctor);
   vec_alloc (*p, vec_safe_length (v));
 
@@ -2280,7 +2291,6 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t,
   FOR_EACH_CONSTRUCTOR_ELT (v, i, index, value)
     {
       tree orig_value = value;
-      constexpr_ctx new_ctx;
       init_subob_ctx (ctx, new_ctx, index, value);
       if (new_ctx.ctor != ctx->ctor)
 	/* If we built a new CONSTRUCTOR, attach it now so that other
@@ -2334,7 +2344,7 @@ cxx_eval_bare_aggregate (const constexpr_ctx *ctx, tree t,
   CONSTRUCTOR_NO_IMPLICIT_ZERO (t) = false;
   TREE_CONSTANT (t) = constant_p;
   TREE_SIDE_EFFECTS (t) = side_effects_p;
-  if (VECTOR_TYPE_P (TREE_TYPE (t)))
+  if (VECTOR_TYPE_P (type))
     t = fold (t);
   return t;
 }
diff --git a/gcc/testsuite/g++.dg/expr/pmf-2.C b/gcc/testsuite/g++.dg/expr/pmf-2.C
new file mode 100644
index 0000000..79e36cf
--- /dev/null
+++ b/gcc/testsuite/g++.dg/expr/pmf-2.C
@@ -0,0 +1,18 @@
+// PR c++/70386
+// { dg-options "-Wall" }
+
+struct A { void f () {} };
+struct B : public A {};
+struct C : public A {};
+struct D : public B, public C {};
+
+typedef void (C::*cp) ();
+typedef void (D::*dp) ();
+
+int
+main ()
+{
+  cp c = &A::f;
+  dp d = c;
+  return (cp () == d);
+}