Support copying local_specializations.

	* cp-tree.h (enum lss_policy): New.
	(local_specialization_stack): Add policy parameter to default ctor.
	* pt.c (local_specialization_stack): Copy local_specializations if
	lss_copy.

From-SVN: r251424

gcc/cp/ChangeLog

 2017-08-29  Jason Merrill  <jason@redhat.com>
 
+	Support copying local_specializations.
+	* cp-tree.h (enum lss_policy): New.
+	(local_specialization_stack): Add policy parameter to default ctor.
+	* pt.c (local_specialization_stack): Copy local_specializations if
+	lss_copy.
+
 	* constexpr.c (potential_constant_expression_1): Add "now" parm.
 	(is_constant_expression, require_constant_expression): New.
 	(is_static_init_expression, is_nondependent_constant_expression)

gcc/cp/cp-tree.h

@@ -5117,9 +5117,10 @@ enum unification_kind_t {
 // An RAII class used to create a new pointer map for local
 // specializations. When the stack goes out of scope, the
 // previous pointer map is restored.
+enum lss_policy { lss_blank, lss_copy };
 struct local_specialization_stack
 {
-  local_specialization_stack ();
+  local_specialization_stack (lss_policy = lss_blank);
   ~local_specialization_stack ();
 
   hash_map<tree, tree> *saved;

gcc/cp/pt.c

@@ -77,10 +77,13 @@ static tree cur_stmt_expr;
 //
 // Implementation of the RAII helper for creating new local
 // specializations.
-local_specialization_stack::local_specialization_stack ()
+local_specialization_stack::local_specialization_stack (lss_policy policy)
   : saved (local_specializations)
 {
+  if (policy == lss_blank || !saved)
     local_specializations = new hash_map<tree, tree>;
+  else
+    local_specializations = new hash_map<tree, tree>(*saved);
 }
 
 local_specialization_stack::~local_specialization_stack ()