For C++17 aggregate bases, we have started adding base fields for
empty bases.  The code for calculating whether a class is standard
layout needs to ignore these.

The C++17 mode diagnostic for direct-enum-init1.C was incorrect.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit 9a612cc30d4b3ef905ce45304545d8b99a3cf5b9
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue May 9 14:15:38 2017 -0400

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

diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index fc71766..085dbc3 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -1860,7 +1860,9 @@ 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_SIZE (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 0000000..007c94a
--- /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));

commit 90bdd7df4aa641d53edacd20414d724babfe4af8
Author: Jason Merrill <ja...@redhat.com>
Date:   Tue May 9 13:51:07 2017 -0400

            * g++.dg/cpp1z/direct-enum-init1.C: Correct error message.

diff --git a/gcc/testsuite/g++.dg/cpp1z/direct-enum-init1.C 
b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init1.C
index a17473f..11269cc 100644
--- a/gcc/testsuite/g++.dg/cpp1z/direct-enum-init1.C
+++ b/gcc/testsuite/g++.dg/cpp1z/direct-enum-init1.C
@@ -22,7 +22,7 @@ foo ()
   C c1 { s };
   D d1 { D(t) };       // { dg-error "invalid cast from type 'T' to type 'D 
{enum}'" }
   D d2 { t };          // { dg-error "cannot convert 'T' to 'D {enum}' in 
initialization" "" { target c++14_down } }
-                       // { dg-error "invalid cast from type 'T' to type 'D'" 
"" { target c++1z } .-1 }
+                       // { dg-error "invalid cast from type 'T' to type 'D 
{enum}'" "" { target c++1z } .-1 }
   D d3 { 9 };          // { dg-error "cannot convert 'int' to 'D {enum}' in 
initialization" "" { target c++14_down } }
   D d4 { l };          // { dg-error "cannot convert 'long int' to 'D {enum}' 
in initialization" "" { target c++14_down } }
   D d5 { D(l) };
@@ -89,7 +89,7 @@ foo2 ()
   C c1 { s };
   D d1 { D(t) };       // { dg-error "invalid cast from type 'T' to type 'D 
{enum}'" }
   D d2 { t };          // { dg-error "cannot convert 'T' to 'D {enum}' in 
initialization" "" { target c++14_down } }
-                       // { dg-error "invalid cast from type 'T' to type 'D'" 
"" { target c++1z } .-1 }
+                       // { dg-error "invalid cast from type 'T' to type 'D 
{enum}'" "" { target c++1z } .-1 }
   D d3 { 9 };          // { dg-error "cannot convert 'int' to 'D {enum}' in 
initialization" "" { target c++14_down } }
   D d4 { l };          // { dg-error "cannot convert 'long int' to 'D {enum}' 
in initialization" "" { target c++14_down } }
   D d5 { D(l) };

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