[libcxx-commits] [PATCH] D115986: [libc++] Allow __move_constexpr to work with unrelated pointers

[Nikolas Klauser via Phabricator via libcxx-commits]

philnik created this revision.
philnik added reviewers: Quuxplusone, ldionne.
philnik requested review of this revision.
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Herald added a reviewer: libc++.

Allow `__move_constexpr` to work with unrelated pointers and `_LIBCPP_ASSERT` that `__copy_constexpr`, `__move_constexpr` and `__assign_constexpr` are only run during constant evaluation


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D115986

Files:
  libcxx/include/__string


Index: libcxx/include/__string
===================================================================
--- libcxx/include/__string
+++ libcxx/include/__string
@@ -290,31 +290,34 @@
 
 template <class _CharT>
 static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
-_CharT* __move_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
+_CharT* __copy_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 {
-    if (__n == 0) return __s1;
-    if (__s1 < __s2) {
-      _VSTD::copy(__s2, __s2 + __n, __s1);
-    } else if (__s2 < __s1) {
-      _VSTD::copy_backward(__s2, __s2 + __n, __s1 + __n);
-    }
-    return __s1;
+  _LIBCPP_ASSERT(__libcpp_is_constant_evaluated(), "__copy_constexpr() should always be constant evaluated");
+  _VSTD::copy_n(__s2, __n, __s1);
+  return __s1;
 }
 
 template <class _CharT>
 static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
-_CharT* __copy_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
+_CharT* __move_constexpr(_CharT* __s1, const _CharT* __s2, size_t __n) _NOEXCEPT
 {
-    _VSTD::copy_n(__s2, __n, __s1);
+  _LIBCPP_ASSERT(__libcpp_is_constant_evaluated(), "__move_constexpr() should always be constant evaluated");
+  if (__n == 0)
     return __s1;
+  _CharT* __allocation = new _CharT[__n];
+  _VSTD::__copy_constexpr(__allocation, __s2, __n);
+  _VSTD::__copy_constexpr(__s1, static_cast<const _CharT*>(__allocation), __n);
+  delete[] __allocation;
+  return __s1;
 }
 
 template <class _CharT>
 static inline _LIBCPP_CONSTEXPR_AFTER_CXX17
 _CharT* __assign_constexpr(_CharT* __s, size_t __n, _CharT __a) _NOEXCEPT
 {
-     _VSTD::fill_n(__s, __n, __a);
-     return __s;
+  _LIBCPP_ASSERT(__libcpp_is_constant_evaluated(), "__assign_constexpr() should always be constant evaluated");
+  _VSTD::fill_n(__s, __n, __a);
+  return __s;
 }
 
 // char_traits<char>


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