PR c++/82336 - link error with list-init default argument.

	* decl.c (check_default_argument): Unshare an initializer list.

Co-Authored-By: Jason Merrill <jason@redhat.com>

From-SVN: r258512

gcc/cp/ChangeLog

+2018-03-13  Paolo Carlini  <paolo.carlini@oracle.com>
+	    Jason Merrill  <jason@redhat.com>
+
+	PR c++/82336 - link error with list-init default argument.
+	* decl.c (check_default_argument): Unshare an initializer list.
+
 2018-03-13  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/84843

gcc/cp/decl.c

@@ -12668,7 +12668,9 @@ check_default_argument (tree decl, tree arg, tsubst_flags_t complain)
      A default argument expression is implicitly converted to the
      parameter type.  */
   ++cp_unevaluated_operand;
-  perform_implicit_conversion_flags (decl_type, arg, complain,
+  /* Avoid digest_init clobbering the initializer.  */
+  tree carg = BRACE_ENCLOSED_INITIALIZER_P (arg) ? unshare_expr (arg): arg;
+  perform_implicit_conversion_flags (decl_type, carg, complain,
 				     LOOKUP_IMPLICIT);
   --cp_unevaluated_operand;
 

gcc/testsuite/g++.dg/cpp0x/initlist-defarg2.C

+// PR c++/82336
+// { dg-do link { target c++11 } }
+
+struct foo { int x = 5; };
+struct bar : foo { bar() = default; };
+struct baz { bar x; };
+void qux(baz = {}){}
+int main() { qux(); }