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

[via llvm-branch-commits]

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

Backport ccb08b9

Requested by: @ldionne

>From c17d86fa59ade7b180e0de2df91a3e425b06e132 Mon Sep 17 00:00:00 2001
From: Louis Dionne <ldionne.2 at gmail.com>
Date: Wed, 5 Feb 2025 08:57:22 -0500
Subject: [PATCH] [libc++] Also provide an alignment assumption for vector in
 C++03 mode (#124839)

There's no reason not to, and it's easy enough to do using enable_if. As
a drive-by change, also add a missing _LIBCPP_NO_CFI attribute on
__add_alignment_assumption.

(cherry picked from commit ccb08b9dab7d829f8d9703d8b46b98e2d6717d0e)
---
 libcxx/include/__vector/vector.h | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 66cb622e209633..bad676a56a8e64 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;
   }
 };