[libc++] Fixed copy/copy_n/copy_backward for compilers that do not support is_constant_evaluated.

Differential Revision: https://reviews.llvm.org/D69940

Author: ldionne

libcxx/include/__config

@@ -1002,6 +1002,14 @@ 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/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
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
 _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
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
 _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
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
 typename enable_if
 <
     __is_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
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17_WITH_IS_CONSTANT_EVALUATED
 typename enable_if
 <
     __is_random_access_iterator<_InputIterator>::value,

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

@@ -79,7 +79,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17
+#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
     static_assert(test());
 #endif
 

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

@@ -58,7 +58,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17
+#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
     static_assert(test());
 #endif
 

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

@@ -82,7 +82,7 @@ int main(int, char**)
 {
     test();
 
-#if TEST_STD_VER > 17
+#if TEST_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_BUILTIN_IS_CONSTANT_EVALUATED)
     static_assert(test());
 #endif