re PR c++/52796 ([C++11] Initialization of primitive object with 0-length…

re PR c++/52796 ([C++11] Initialization of primitive object with 0-length parameter pack fails to value-initialize)

	PR c++/52796
	* pt.c (tsubst_initializer_list): A pack expansion with no elements
	means value-initialization.

From-SVN: r186122

gcc/cp/ChangeLog

+2012-04-03  Jason Merrill  <jason@redhat.com>
+
+	PR c++/52796
+	* pt.c (tsubst_initializer_list): A pack expansion with no elements
+	means value-initialization.
+
 2012-04-01  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/50043

gcc/cp/pt.c

@@ -18925,6 +18925,7 @@ tsubst_initializer_list (tree t, tree argvec)
             }
           else
             {
+	      tree tmp;
               decl = tsubst_copy (TREE_PURPOSE (t), argvec, 
                                   tf_warning_or_error, NULL_TREE);
 
@@ -18933,10 +18934,17 @@ tsubst_initializer_list (tree t, tree argvec)
                 in_base_initializer = 1;
 
 	      init = TREE_VALUE (t);
+	      tmp = init;
 	      if (init != void_type_node)
 		init = tsubst_expr (init, argvec,
 				    tf_warning_or_error, NULL_TREE,
 				    /*integral_constant_expression_p=*/false);
+	      if (init == NULL_TREE && tmp != NULL_TREE)
+		/* If we had an initializer but it instantiated to nothing,
+		   value-initialize the object.  This will only occur when
+		   the initializer was a pack expansion where the parameter
+		   packs used in that expansion were of length zero.  */
+		init = void_type_node;
               in_base_initializer = 0;
             }
 

gcc/testsuite/ChangeLog

+2012-04-03  Jason Merrill  <jason@redhat.com>
+
+	PR c++/52796
+	* g++.dg/cpp0x/variadic-value1.C: New.
+
 2012-04-03  Eric Botcazou  <ebotcazou@adacore.com>
 
 	* gnat.dg/pack18.adb: New test.

gcc/testsuite/g++.dg/cpp0x/variadic-value1.C

+// PR c++/52796
+// { dg-do run { target c++11 } }
+
+inline void *operator new(__SIZE_TYPE__ s, void *p) { return p; }
+
+struct A
+{
+  int i;
+  template<class... Ts>
+  A(Ts&&... ts): i(ts...) { }
+};
+
+static union {
+  unsigned char c[sizeof(A)];
+  int i;
+};
+
+int main()
+{
+  i = 0xdeadbeef;
+  new(c) A;
+  if (i != 0)
+    __builtin_abort();
+}