re PR c++/79639 (ICE with -O and constexpr)

	PR c++/79639
	* constexpr.c (cxx_eval_store_expression): If *valp is a PTRMEM_CST,
	call cplus_expand_constant on it first.

	* g++.dg/cpp1y/constexpr-79639.C: New test.

From-SVN: r245635

gcc/cp/ChangeLog

+2017-02-21  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/79639
+	* constexpr.c (cxx_eval_store_expression): If *valp is a PTRMEM_CST,
+	call cplus_expand_constant on it first.
+
 2017-02-19  Jason Merrill  <jason@redhat.com>
 
 	PR c++/78139 - destructor needed by new-expression

gcc/cp/constexpr.c

@@ -3517,10 +3517,11 @@ cxx_eval_store_expression (const constexpr_ctx *ctx, tree t,
 	 wants to modify it.  */
       if (*valp == NULL_TREE)
 	{
-	  *valp = new_ctx.ctor = build_constructor (type, NULL);
-	  CONSTRUCTOR_NO_IMPLICIT_ZERO (new_ctx.ctor) = no_zero_init;
+	  *valp = build_constructor (type, NULL);
+	  CONSTRUCTOR_NO_IMPLICIT_ZERO (*valp) = no_zero_init;
 	}
-      else
+      else if (TREE_CODE (*valp) == PTRMEM_CST)
+	*valp = cplus_expand_constant (*valp);
       new_ctx.ctor = *valp;
       new_ctx.object = target;
     }

gcc/testsuite/ChangeLog

 2017-02-21  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/79639
+	* g++.dg/cpp1y/constexpr-79639.C: New test. 
+
 	PR target/79633
 	* gcc.target/i386/mpx/pr79633.c: New test.
 

gcc/testsuite/g++.dg/cpp1y/constexpr-79639.C

+// PR c++/79639
+// { dg-do compile { target c++14 } }
+
+struct A
+{
+  void foo () {}
+  void bar () {}
+};
+typedef void (A::*T) ();
+
+constexpr T
+foo (T f)
+{
+  f = 0;
+  return f;
+}
+
+constexpr T
+bar (T f)
+{
+  f = &A::bar;
+  return f;
+}
+
+constexpr T a = foo (&A::foo);
+constexpr T b = foo (&A::foo);
+static_assert (a == nullptr, "");