PR c++/82764 - C++17 ICE with empty base

	* class.c (build_base_field_1): Set DECL_SIZE to zero for empty
	base.

From-SVN: r257745

gcc/cp/ChangeLog

 2018-02-16  Jason Merrill  <jason@redhat.com>
 
+	PR c++/82764 - C++17 ICE with empty base
+	* class.c (build_base_field_1): Set DECL_SIZE to zero for empty base.
+
+2018-02-16  Jason Merrill  <jason@redhat.com>
+
 	PR c++/84421 - type-dependent if constexpr
 	* semantics.c (finish_if_stmt_cond): Check type_dependent_expression_p.
 

gcc/cp/class.c

@@ -4216,8 +4216,14 @@ build_base_field_1 (tree t, tree basetype, tree *&next_field)
   DECL_ARTIFICIAL (decl) = 1;
   DECL_IGNORED_P (decl) = 1;
   DECL_FIELD_CONTEXT (decl) = t;
-  DECL_SIZE (decl) = CLASSTYPE_SIZE (basetype);
-  DECL_SIZE_UNIT (decl) = CLASSTYPE_SIZE_UNIT (basetype);
+  if (is_empty_class (basetype))
+    /* CLASSTYPE_SIZE is one byte, but the field needs to have size zero.  */
+    DECL_SIZE (decl) = DECL_SIZE_UNIT (decl) = size_zero_node;
+  else
+    {
+      DECL_SIZE (decl) = CLASSTYPE_SIZE (basetype);
+      DECL_SIZE_UNIT (decl) = CLASSTYPE_SIZE_UNIT (basetype);
+    }
   SET_DECL_ALIGN (decl, CLASSTYPE_ALIGN (basetype));
   DECL_USER_ALIGN (decl) = CLASSTYPE_USER_ALIGN (basetype);
   SET_DECL_MODE (decl, TYPE_MODE (basetype));

gcc/testsuite/g++.dg/cpp0x/nsdmi-empty1.C

+// PR c++/82764
+// { dg-do compile { target c++11 } }
+
+struct Empty {};
+struct Empty2 : Empty {};
+
+struct A : Empty2
+{
+  int x {1};
+  int y {2};
+};
+
+struct B
+{
+  A a {};
+};
+
+B b;