[libc++] Remove _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED.

Zoe Carver says: "We decided that libc++ only supports C++20 constexpr algorithms
when `is_constant_evaluated` is also supported. Here's a link to the discussion."
https://reviews.llvm.org/D65721#inline-735682

Remove _LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED from tests, too.
See Louis's 5911e6a885 if needed to fix bots.
I've applied `UNSUPPORTED: clang-8` preemptively to the altered tests;
I don't know for sure that this was needed, because no clang-8 buildbots
are triggered on pull requests.

libcxx/include/__config

@@ -1029,14 +1029,6 @@ typedef unsigned int   char32_t;
 #  define _LIBCPP_CONSTEXPR_AFTER_CXX17
 #endif
 
-#if _LIBCPP_STD_VER > 17 && \
-    !defined(_LIBCPP_HAS_NO_CXX14_CONSTEXPR) && \
-    !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
-#  define _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED constexpr
-#else
-#  define _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
-#endif
-
 // The _LIBCPP_NODISCARD_ATTRIBUTE should only be used to define other
 // NODISCARD macros to the correct attribute.
 #if __has_cpp_attribute(nodiscard) || defined(_LIBCPP_COMPILER_MSVC)

libcxx/include/__string

@@ -318,7 +318,7 @@ char_traits<_CharT>::assign(char_type* __s, size_t __n, char_type __a)
 // constexpr versions of move/copy/assign.
 
 template <class _CharT>
-static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
 _CharT* __move_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 {
     if (__n == 0) return __s1;
@@ -331,7 +331,7 @@ _CharT* __move_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 }
 
 template <class _CharT>
-static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
 _CharT* __copy_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 {
     _VSTD::copy_n(__s2, __n, __s1);
@@ -339,7 +339,7 @@ _CharT* __copy_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 }
 
 template <class _CharT>
-static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
 _CharT* __assign_constexpr(_CharT* __s, size_t __n, _CharT __a) _NOEXCEPT
 {
      _VSTD::fill_n(__s, __n, __a);
@@ -370,14 +370,14 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char>
     length(const char_type* __s)  _NOEXCEPT {return __builtin_strlen(__s);}
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()
                        ? __move_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : (char_type*)memmove(__s1, __s2, __n);
         }
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
             _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
@@ -385,7 +385,7 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char>
                        ? __copy_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : (char_type*)memcpy(__s1, __s2, __n);
         }
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* assign(char_type* __s, size_t __n, char_type __a) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()
@@ -473,14 +473,14 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<wchar_t>
     size_t length(const char_type* __s) _NOEXCEPT;
     static _LIBCPP_CONSTEXPR_AFTER_CXX14
     const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()
                        ? __move_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : wmemmove(__s1, __s2, __n);
         }
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
             _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
@@ -488,7 +488,7 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<wchar_t>
                        ? __copy_constexpr(__s1, __s2, __n)
                        : __n == 0 ? __s1 : wmemcpy(__s1, __s2, __n);
         }
-    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type* assign(char_type* __s, size_t __n, char_type __a) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()
@@ -606,7 +606,7 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char8_t>
     _LIBCPP_INLINE_VISIBILITY static constexpr
     const char_type* find(const char_type* __s, size_t __n, const char_type& __a) _NOEXCEPT;
 
-    static _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type*       move(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()
@@ -614,7 +614,7 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char8_t>
                        : __n == 0 ? __s1 : (char_type*)memmove(__s1, __s2, __n);
         }
 
-    static _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type*       copy(char_type* __s1, const char_type* __s2, size_t __n) _NOEXCEPT
        {
             _LIBCPP_ASSERT(__s2 < __s1 || __s2 >= __s1+__n, "char_traits::copy overlapped range");
@@ -623,7 +623,7 @@ struct _LIBCPP_TEMPLATE_VIS char_traits<char8_t>
                        : __n == 0 ? __s1 : (char_type*)memcpy(__s1, __s2, __n);
         }
 
-    static _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+    static _LIBCPP_CONSTEXPR_AFTER_CXX17
     char_type*       assign(char_type* __s, size_t __n, char_type __a) _NOEXCEPT
         {
             return __libcpp_is_constant_evaluated()

libcxx/include/algorithm

@@ -1727,7 +1727,7 @@ __copy(_Tp* __first, _Tp* __last, _Up* __result)
 }
 
 template <class _InputIterator, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 _OutputIterator
 copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result)
 {
@@ -1780,7 +1780,7 @@ __copy_backward(_Tp* __first, _Tp* __last, _Up* __result)
 }
 
 template <class _BidirectionalIterator1, class _BidirectionalIterator2>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 _BidirectionalIterator2
 copy_backward(_BidirectionalIterator1 __first, _BidirectionalIterator1 __last,
               _BidirectionalIterator2 __result)
@@ -1818,7 +1818,7 @@ copy_if(_InputIterator __first, _InputIterator __last,
 // copy_n
 
 template<class _InputIterator, class _Size, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 typename enable_if
 <
     __is_cpp17_input_iterator<_InputIterator>::value &&
@@ -1844,7 +1844,7 @@ copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)
 }
 
 template<class _InputIterator, class _Size, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 typename enable_if
 <
     __is_cpp17_random_access_iterator<_InputIterator>::value,

libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/copy.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <algorithm>
 
 // template<InputIterator InIter, OutputIterator<auto, InIter::reference> OutIter>
@@ -79,7 +81,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/copy_backward.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <algorithm>
 
 // template<BidirectionalIterator InIter, BidirectionalIterator OutIter>
@@ -58,7 +60,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/algorithms/alg.modifying.operations/alg.copy/copy_n.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <algorithm>
 
 // template<InputIterator InIter, OutputIterator<auto, InIter::reference> OutIter>
@@ -82,7 +84,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/assign3.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<char>
@@ -33,7 +35,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/copy.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<char>
@@ -35,7 +37,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char/move.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<char>
@@ -39,7 +41,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/assign3.pass.cpp

@@ -5,7 +5,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: clang-8
 
 // <string>
 
@@ -36,7 +38,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/copy.pass.cpp

@@ -5,7 +5,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: clang-8
 
 // <string>
 
@@ -38,7 +40,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.char8_t/move.pass.cpp

@@ -5,7 +5,9 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
+
 // UNSUPPORTED: c++03, c++11, c++14, c++17
+// UNSUPPORTED: clang-8
 
 // <string>
 
@@ -42,7 +44,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/assign3.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<wchar_t>
@@ -33,7 +35,7 @@ int main(int, char**)
 {
   test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
     static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/copy.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<wchar_t>
@@ -35,7 +37,7 @@ int main(int, char**)
 {
   test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
   static_assert(test());
 #endif
 

libcxx/test/std/strings/char.traits/char.traits.specializations/char.traits.specializations.wchar.t/move.pass.cpp

@@ -6,6 +6,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: clang-8
+
 // <string>
 
 // template<> struct char_traits<wchar_t>
@@ -39,7 +41,7 @@ int main(int, char**)
 {
   test();
 
-#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
+#if TEST_STD_VER > 17
   static_assert(test());
 #endif