[PATCH v18 22/26] libstdc++: Optimize std::rank compilation performance

[Ken Matsui]

This patch optimizes the compilation performance of std::rank
by dispatching to the new __array_rank built-in trait.

libstdc++-v3/ChangeLog:

        * include/std/type_traits (rank): Use __array_rank built-in
        trait.
        (rank_v): Likewise.

Signed-off-by: Ken Matsui <kmat...@gcc.gnu.org>
---
 libstdc++-v3/include/std/type_traits | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/libstdc++-v3/include/std/type_traits 
b/libstdc++-v3/include/std/type_traits
index 4cc587d4e08..e9313205550 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1473,6 +1473,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     };
 
   /// rank
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__array_rank)
+  template<typename _Tp>
+    struct rank
+    : public integral_constant<std::size_t, __array_rank(_Tp)> { };
+#else
   template<typename>
     struct rank
     : public integral_constant<std::size_t, 0> { };
@@ -1484,6 +1489,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<typename _Tp>
     struct rank<_Tp[]>
     : public integral_constant<std::size_t, 1 + rank<_Tp>::value> { };
+#endif
 
   /// extent
   template<typename, unsigned _Uint = 0>
@@ -3583,12 +3589,17 @@ template <typename _Tp>
 template <typename _Tp>
   inline constexpr size_t alignment_of_v = alignment_of<_Tp>::value;
 
+#if _GLIBCXX_USE_BUILTIN_TRAIT(__array_rank)
+template <typename _Tp>
+  inline constexpr size_t rank_v = __array_rank(_Tp);
+#else
 template <typename _Tp>
   inline constexpr size_t rank_v = 0;
 template <typename _Tp, size_t _Size>
   inline constexpr size_t rank_v<_Tp[_Size]> = 1 + rank_v<_Tp>;
 template <typename _Tp>
   inline constexpr size_t rank_v<_Tp[]> = 1 + rank_v<_Tp>;
+#endif
 
 template <typename _Tp, unsigned _Idx = 0>
   inline constexpr size_t extent_v = 0;
-- 
2.44.0