[PATCH 2/2] libstdc++: Optimize is_reference

[Patrick Palka <ppalka@redhat.com>]

Instead of defining is_reference in terms of is_lvalue_reference
and is_rvalue_reference, just define it directly.

Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
This reduces memory usage of join.cc by 1%.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_reference): Make the primary
	template derive from false_type.  Define two partial
	specializations that derive from true_type.
---
 libstdc++-v3/include/std/type_traits | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index b83e7257a9f..94e73eafd2f 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -611,8 +611,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// is_reference
   template<typename _Tp>
     struct is_reference
-    : public __or_<is_lvalue_reference<_Tp>,
-                   is_rvalue_reference<_Tp>>::type
+    : public false_type
+    { };
+
+  template<typename _Tp>
+    struct is_reference<_Tp&>
+    : public true_type
+    { };
+
+  template<typename _Tp>
+    struct is_reference<_Tp&&>
+    : public true_type
     { };
 
   /// is_arithmetic
-- 
2.37.3.518.g79f2338b37