[llvm-branch-commits] [libcxx] release/20.x: [libc++] Also provide an alignment assumption for vector in C++03 mode (#124839) (PR #125860)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libcxx

Author: None (llvmbot)

<details>
<summary>Changes</summary>

Backport ccb08b9

Requested by: @<!-- -->ldionne

---
Full diff: https://github.com/llvm/llvm-project/pull/125860.diff


1 Files Affected:

- (modified) libcxx/include/__vector/vector.h (+11-7) 


``````````diff
diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 66cb622e2096330..bad676a56a8e643 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -783,14 +783,18 @@ class _LIBCPP_TEMPLATE_VIS vector {
 
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __move_assign_alloc(vector&, false_type) _NOEXCEPT {}
 
-  static _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI pointer __add_alignment_assumption(pointer __p) _NOEXCEPT {
-#ifndef _LIBCPP_CXX03_LANG
-    if constexpr (is_pointer<pointer>::value) {
-      if (!__libcpp_is_constant_evaluated()) {
-        return static_cast<pointer>(__builtin_assume_aligned(__p, alignof(decltype(*__p))));
-      }
+  template <class _Ptr = pointer, __enable_if_t<is_pointer<_Ptr>::value, int> = 0>
+  static _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI pointer
+  __add_alignment_assumption(_Ptr __p) _NOEXCEPT {
+    if (!__libcpp_is_constant_evaluated()) {
+      return static_cast<pointer>(__builtin_assume_aligned(__p, _LIBCPP_ALIGNOF(decltype(*__p))));
     }
-#endif
+    return __p;
+  }
+
+  template <class _Ptr = pointer, __enable_if_t<!is_pointer<_Ptr>::value, int> = 0>
+  static _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI pointer
+  __add_alignment_assumption(_Ptr __p) _NOEXCEPT {
     return __p;
   }
 };

``````````

</details>


https://github.com/llvm/llvm-project/pull/125860