From bb399e300fd47a0b4ee7ef075fdf22002a5d5b8b Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Wed, 31 May 2017 13:53:06 -0400
Subject: [PATCH] PR c++/80605 - __is_standard_layout and empty base

	* class.c (check_bases): Ignore empty bases.
	* class.c (check_bases): Use DECL_FIELD_IS_BASE.

From-SVN: r248753
---
 gcc/cp/ChangeLog                          |  6 ++++++
 gcc/cp/class.c                            |  4 +++-
 gcc/testsuite/g++.dg/ext/is_std_layout1.C | 12 ++++++++++++
 gcc/testsuite/g++.dg/ext/is_std_layout2.C |  6 ++++++
 4 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/ext/is_std_layout1.C
 create mode 100644 gcc/testsuite/g++.dg/ext/is_std_layout2.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index d901ad2dcb4..cad06036027 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,11 @@
 2017-05-31  Jason Merrill  <jason@redhat.com>
 
+	PR c++/80605 - __is_standard_layout and zero-length array
+	* class.c (check_bases): Use DECL_FIELD_IS_BASE.
+
+	PR c++/80605 - __is_standard_layout and empty base
+	* class.c (check_bases): Ignore empty bases.
+
 	PR c++/66297, DR 1684 - literal class and constexpr member fns
 	* constexpr.c (is_valid_constexpr_fn): Only complain about
 	non-literal enclosing class in C++11.
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index 0edf42a4c0f..c6f8f3fa41d 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -1861,7 +1861,9 @@ check_bases (tree t,
 	       members */
 	    for (basefield = TYPE_FIELDS (basetype); basefield;
 		 basefield = DECL_CHAIN (basefield))
-	      if (TREE_CODE (basefield) == FIELD_DECL)
+	      if (TREE_CODE (basefield) == FIELD_DECL
+		  && !(DECL_FIELD_IS_BASE (basefield)
+		       && integer_zerop (DECL_SIZE (basefield))))
 		{
 		  if (field)
 		    CLASSTYPE_NON_STD_LAYOUT (t) = 1;
diff --git a/gcc/testsuite/g++.dg/ext/is_std_layout1.C b/gcc/testsuite/g++.dg/ext/is_std_layout1.C
new file mode 100644
index 00000000000..007c94a453c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_std_layout1.C
@@ -0,0 +1,12 @@
+// { dg-do compile { target c++11 } }
+
+template <int> struct E { };
+
+struct E1: E<0>, E<1> { };
+struct E2: E<2>, E<3> { };
+
+struct A1x { int n; };
+struct D2: A1x, E1, E2 { };
+
+#define SA(X) static_assert((X),#X)
+SA(__is_standard_layout (D2));
diff --git a/gcc/testsuite/g++.dg/ext/is_std_layout2.C b/gcc/testsuite/g++.dg/ext/is_std_layout2.C
new file mode 100644
index 00000000000..02dc4f7ffb5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_std_layout2.C
@@ -0,0 +1,6 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S { int a[0]; };
+struct T : public S { int b[0]; int c; };
+static_assert(!__is_standard_layout (T), "");