[PATCH v16 20/26] libstdc++: Optimize std::decay compilation performance

[Ken Matsui]

This patch optimizes the compilation performance of std::decay
by dispatching to the new __builtin_decay trait.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (decay): Use __builtin_decay trait.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/std/type_traits | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 36ac900605a..45c73d477d0 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2316,6 +2316,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// @cond undocumented
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__builtin_decay)
+  template<typename _Tp>
+    struct decay
+    { using type = __builtin_decay(_Tp); };
+#else
   // Decay trait for arrays and functions, used for perfect forwarding
   // in make_pair, make_tuple, etc.
   template<typename _Up>
@@ -2347,6 +2352,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct decay<_Tp&&>
     { using type = typename __decay_selector<_Tp>::type; };
+#endif
 
   /// @cond undocumented
 
-- 
2.44.0