[libcxx-commits] [libcxx] 7255747 - [libc++] Consistency on _LIBCPP_CLANG_VER tests in <type_traits>.

[Arthur O'Dwyer via libcxx-commits]

Author: Arthur O'Dwyer
Date: 2021-03-19T10:49:00-04:00
New Revision: 72557476d459969dbee95252e73f6ff1dfcc46c5

URL: https://github.com/llvm/llvm-project/commit/72557476d459969dbee95252e73f6ff1dfcc46c5
DIFF: https://github.com/llvm/llvm-project/commit/72557476d459969dbee95252e73f6ff1dfcc46c5.diff

LOG: [libc++] Consistency on _LIBCPP_CLANG_VER tests in <type_traits>.

This came out of my review comments on D97283.

This patch re-enables the use of `__is_fundamental`, `__is_signed`, etc.
on non-Clang compilers. Previously, when we found that a builtin didn't
work on old Clangs, we had been reacting by limiting its use to new Clangs
(i.e., we'd also stop using it on new GCCs and new MSVCs, just because of
the old Clang bug). I claim that this was unintentional.

Notice that on Apple Clang, `_LIBCPP_COMPILER_CLANG` is defined and
`_LIBCPP_CLANG_VER` is not defined (therefore `0` in arithmetic expressions).
We assume that Apple Clang has all the bugs of all the Clangs.

Differential Revision: https://reviews.llvm.org/D98720

Added: 
    

Modified: 
    libcxx/include/type_traits

Removed: 
    


################################################################################
diff  --git a/libcxx/include/type_traits b/libcxx/include/type_traits
index 7477e6d143de..d028ca22fac0 100644
--- a/libcxx/include/type_traits
+++ b/libcxx/include/type_traits
@@ -834,8 +834,8 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_array_v
 
 // is_pointer
 
-// In clang 10.0.0 and earlier __is_pointer didn't work with Objective-C types.
-#if __has_keyword(__is_pointer) && _LIBCPP_CLANG_VER > 1000
+// Before Clang 11, __is_pointer didn't work for Objective-C types.
+#if __has_keyword(__is_pointer) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1100)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_pointer : _BoolConstant<__is_pointer(_Tp)> { };
@@ -1129,9 +1129,9 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_arithmetic_v
 
 // is_fundamental
 
-// In clang 9 and lower, this builtin did not work for nullptr_t. Additionally, in C++03 mode,
-// nullptr isn't defined by the compiler so, this builtin won't work.
-#if __has_keyword(__is_fundamental) && _LIBCPP_CLANG_VER > 900 && !defined(_LIBCPP_CXX03_LANG)
+// Before Clang 10, __is_fundamental didn't work for nullptr_t.
+// In C++03 nullptr_t is library-provided but must still count as "fundamental."
+#if __has_keyword(__is_fundamental) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1000) && !defined(_LIBCPP_CXX03_LANG)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_fundamental : _BoolConstant<__is_fundamental(_Tp)> { };
@@ -1158,7 +1158,7 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_fundamental_v
 
 // is_scalar
 
-// >= 11 because in C++03 nullptr isn't actually nullptr
+// In C++03 nullptr_t is library-provided but must still count as "scalar."
 #if __has_keyword(__is_scalar) && !defined(_LIBCPP_CXX03_LANG)
 
 template<class _Tp>
@@ -1415,8 +1415,8 @@ template<class _Tp> using type_identity_t = typename type_identity<_Tp>::type;
 
 // is_signed
 
-// In clang 9 and earlier, this builtin did not work for floating points or enums
-#if __has_keyword(__is_signed) && _LIBCPP_CLANG_VER > 900
+// Before Clang 10, __is_signed didn't work for floating-point types or enums.
+#if __has_keyword(__is_signed) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1000)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_signed : _BoolConstant<__is_signed(_Tp)> { };
@@ -1451,8 +1451,8 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_signed_v
 
 // is_unsigned
 
-// Before clang 13, __is_unsigned returned true for enums with signed underlying type
-#if __has_keyword(__is_unsigned) && _LIBCPP_CLANG_VER >= 1300
+// Before Clang 13, __is_unsigned returned true for enums with signed underlying type.
+#if __has_keyword(__is_unsigned) && !(defined(_LIBCPP_COMPILER_CLANG) && _LIBCPP_CLANG_VER < 1300)
 
 template<class _Tp>
 struct _LIBCPP_TEMPLATE_VIS is_unsigned : _BoolConstant<__is_unsigned(_Tp)> { };
@@ -1462,7 +1462,7 @@ template <class _Tp>
 _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_unsigned_v = __is_unsigned(_Tp);
 #endif
 
-#else // __has_keyword(__is_unsigned) && _LIBCPP_CLANG_VER >= 1300
+#else // __has_keyword(__is_unsigned)
 
 template <class _Tp, bool = is_integral<_Tp>::value>
 struct __libcpp_is_unsigned_impl : public _LIBCPP_BOOL_CONSTANT(_Tp(0) < _Tp(-1)) {};
@@ -1483,7 +1483,7 @@ _LIBCPP_INLINE_VAR _LIBCPP_CONSTEXPR bool is_unsigned_v
     = is_unsigned<_Tp>::value;
 #endif
 
-#endif // __has_keyword(__is_unsigned) && _LIBCPP_CLANG_VER >= 1300
+#endif // __has_keyword(__is_unsigned)
 
 // rank