CWG 2096 - constraints on literal unions.

	* class.c (check_field_decls): Initialize booleans directly.  A union
	is literal if at least one of its non-static data members is of
	non-volatile literal type.

	* g++.dg/cpp0x/literal-type1.C: New test.

From-SVN: r271267

4 files changed, 88 insertions, 10 deletions

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 7a22c5e..3119c03 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2019-05-15  Marek Polacek  <polacek@redhat.com>
+
+	CWG 2096 - constraints on literal unions.
+	* class.c (check_field_decls): Initialize booleans directly.  A union
+	is literal if at least one of its non-static data members is of
+	non-volatile literal type.
+
 2019-05-15  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* cp-tree.h (REFERENCE_VLA_OK): Remove.
diff --git a/gcc/cp/class.c b/gcc/cp/class.c
index a47777c..ed885a5 100644
--- a/gcc/cp/class.c
+++ b/gcc/cp/class.c
@@ -3403,18 +3403,19 @@ check_field_decls (tree t, tree *access_decls,
 {
   tree *field;
   tree *next;
-  bool has_pointers;
-  bool any_default_members;
   int cant_pack = 0;
   int field_access = -1;
 
   /* Assume there are no access declarations.  */
   *access_decls = NULL_TREE;
   /* Assume this class has no pointer members.  */
-  has_pointers = false;
+  bool has_pointers = false;
   /* Assume none of the members of this class have default
      initializations.  */
-  any_default_members = false;
+  bool any_default_members = false;
+  /* Assume none of the non-static data members are of non-volatile literal
+     type.  */
+  bool found_nv_literal_p = false;
 
   for (field = &TYPE_FIELDS (t); *field; field = next)
     {
@@ -3498,13 +3499,19 @@ check_field_decls (tree t, tree *access_decls,
       if (TREE_PRIVATE (x) || TREE_PROTECTED (x))
 	CLASSTYPE_NON_AGGREGATE (t) = 1;
 
-      /* If at least one non-static data member is non-literal, the whole
-         class becomes non-literal.  Per Core/1453, volatile non-static
-	 data members and base classes are also not allowed.
+      /* If it is not a union and at least one non-static data member is
+	 non-literal, the whole class becomes non-literal.  Per Core/1453,
+	 volatile non-static data members and base classes are also not allowed.
+	 If it is a union, we might set CLASSTYPE_LITERAL_P after we've seen all
+	 members.
 	 Note: if the type is incomplete we will complain later on.  */
-      if (COMPLETE_TYPE_P (type)
-	  && (!literal_type_p (type) || CP_TYPE_VOLATILE_P (type))) 
-        CLASSTYPE_LITERAL_P (t) = false;
+      if (COMPLETE_TYPE_P (type))
+	{
+	  if (!literal_type_p (type) || CP_TYPE_VOLATILE_P (type))
+	    CLASSTYPE_LITERAL_P (t) = false;
+	  else
+	    found_nv_literal_p = true;
+	}
 
       /* A standard-layout class is a class that:
 	 ...
@@ -3677,6 +3684,11 @@ check_field_decls (tree t, tree *access_decls,
 		   "field %q#D with same name as class", x);
     }
 
+  /* Per CWG 2096, a type is a literal type if it is a union, and at least
+     one of its non-static data members is of non-volatile literal type.  */
+  if (TREE_CODE (t) == UNION_TYPE && found_nv_literal_p)
+    CLASSTYPE_LITERAL_P (t) = true;
+
   /* Effective C++ rule 11: if a class has dynamic memory held by pointers,
      it should also define a copy constructor and an assignment operator to
      implement the correct copy semantic (deep vs shallow, etc.). As it is
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index ffba7ba..8eb8b25 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2019-05-15  Marek Polacek  <polacek@redhat.com>
+
+	CWG 2096 - constraints on literal unions.
+	* g++.dg/cpp0x/literal-type1.C: New test.
+
 2019-05-15  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	PR fortran/90461
diff --git a/gcc/testsuite/g++.dg/cpp0x/literal-type1.C b/gcc/testsuite/g++.dg/cpp0x/literal-type1.C
new file mode 100644
index 0000000..7b5d428
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/literal-type1.C
@@ -0,0 +1,54 @@
+// CWG 2096 - constraints on literal unions.
+// { dg-do compile { target c++11 } }
+
+struct literal { };
+typedef volatile int nonliteral_v;
+struct nonliteral {
+  nonliteral() {}
+};
+
+union U {
+  literal l;
+  nonliteral n;
+
+  constexpr U() : l{} {}
+};
+
+constexpr U u{};
+
+union U2 {
+  nonliteral n;
+  literal l;
+
+  constexpr U2() : l{} {}
+};
+
+constexpr U2 u2{};
+
+union U3 { // { dg-message "not literal" }
+  nonliteral_v n; // { dg-message "volatile type" }
+
+  constexpr U3() : n{} {}
+};
+
+constexpr U3 u3{}; // { dg-error "not literal" }
+
+union U4 {
+  nonliteral n;
+  nonliteral_v n2;
+  literal l;
+  nonliteral n3;
+
+  constexpr U4() : l{} {}
+};
+
+constexpr U4 u4{};
+
+union U5 {
+  nonliteral_v n;
+  literal l;
+
+  constexpr U5() : n{} {}
+};
+
+constexpr U5 u5{};