Use the new __has_feature(cxx_constexpr_string_builtins) for detection of the C-string intrinsics for constexpr support in std::char_traits. Thanks to Richard for the intrisic support.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@293154 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -411,15 +411,6 @@ namespace std {
 #define _LIBCPP_DISABLE_UBSAN_UNSIGNED_INTEGER_CHECK __attribute__((__no_sanitize__("unsigned-integer-overflow")))
 #endif 
 
-// A constexpr version of __builtin_memcmp was added in clang 4.0
-#if __has_builtin(__builtin_memcmp)
-# ifdef __apple_build_version__
-// No shipping version of Apple's clang has constexpr __builtin_memcmp
-# elif __clang_major__ > 3
-#  define _LIBCPP_BUILTIN_MEMCMP_ISCONSTEXPR
-# endif
-#endif
-
 #elif defined(_LIBCPP_COMPILER_GCC)
 
 #define _ALIGNAS(x) __attribute__((__aligned__(x)))

include/__string

@@ -243,7 +243,7 @@ char_traits<char>::compare(const char_type* __s1, const char_type* __s2, size_t
 {
     if (__n == 0)
         return 0;
-#ifdef _LIBCPP_BUILTIN_MEMCMP_ISCONSTEXPR
+#if __has_feature(cxx_constexpr_string_builtins)
     return __builtin_memcmp(__s1, __s2, __n);
 #elif _LIBCPP_STD_VER <= 14
     return memcmp(__s1, __s2, __n);
@@ -265,7 +265,9 @@ char_traits<char>::find(const char_type* __s, size_t __n, const char_type& __a)
 {
     if (__n == 0)
         return NULL;
-#if _LIBCPP_STD_VER <= 14
+#if __has_feature(cxx_constexpr_string_builtins)
+    return __builtin_char_memchr(__s, to_int_type(__a), __n);
+#elif _LIBCPP_STD_VER <= 14
     return (const char_type*) memchr(__s, to_int_type(__a), __n);
 #else
     for (; __n; --__n)
@@ -331,7 +333,7 @@ char_traits<wchar_t>::compare(const char_type* __s1, const char_type* __s2, size
 {
     if (__n == 0)
         return 0;
-#if __has_builtin(__builtin_wmemcmp)
+#if __has_feature(cxx_constexpr_string_builtins)
     return __builtin_wmemcmp(__s1, __s2, __n);
 #elif _LIBCPP_STD_VER <= 14
     return wmemcmp(__s1, __s2, __n);
@@ -351,7 +353,7 @@ inline _LIBCPP_CONSTEXPR_AFTER_CXX14
 size_t
 char_traits<wchar_t>::length(const char_type* __s) _NOEXCEPT
 {
-#if __has_builtin(__builtin_wcslen)
+#if __has_feature(cxx_constexpr_string_builtins)
     return __builtin_wcslen(__s);
 #elif _LIBCPP_STD_VER <= 14
     return wcslen(__s);
@@ -369,7 +371,7 @@ char_traits<wchar_t>::find(const char_type* __s, size_t __n, const char_type& __
 {
     if (__n == 0)
         return NULL;
-#if __has_builtin(__builtin_wmemchr)
+#if __has_feature(cxx_constexpr_string_builtins)
         return __builtin_wmemchr(__s, __a, __n);
 #elif _LIBCPP_STD_VER <= 14
     return wmemchr(__s, __a, __n);