[libcxx-commits] [libcxx] [libc++] Add __new_at_least (PR #215813)
Nikolas Klauser via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Aug 12 07:46:13 PDT 2026
https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/215813
None
>From 08a0cceee65e9a2006785a8092da214072bd91e7 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Sat, 8 Aug 2026 08:13:25 +0200
Subject: [PATCH] [libc++] Add __new_at_least
---
libcxx/include/__configuration/availability.h | 10 +++
libcxx/include/__memory/allocate_at_least.h | 11 +--
libcxx/include/__memory/allocator.h | 6 +-
libcxx/include/__new/allocate.h | 15 +++++
libcxx/include/__new/new_at_least.h | 45 +++++++++++++
libcxx/src/support/new.ipp | 67 +++++++++++++++++++
6 files changed, 143 insertions(+), 11 deletions(-)
create mode 100644 libcxx/include/__new/new_at_least.h
diff --git a/libcxx/include/__configuration/availability.h b/libcxx/include/__configuration/availability.h
index 0709deff47ea6..d48e0146e138a 100644
--- a/libcxx/include/__configuration/availability.h
+++ b/libcxx/include/__configuration/availability.h
@@ -39,6 +39,9 @@
// in all versions of the library are available.
#if !_LIBCPP_HAS_VENDOR_AVAILABILITY_ANNOTATIONS
+# define _LIBCPP_INTRODUCED_IN_LLVM_24 1
+# define _LIBCPP_INTRODUCED_IN_LLVM_24_ATTRIBUTE /* nothing */
+
# define _LIBCPP_INTRODUCED_IN_LLVM_23 1
# define _LIBCPP_INTRODUCED_IN_LLVM_23_ATTRIBUTE /* nothing */
@@ -73,6 +76,11 @@
// clang-format off
+// LLVM 23
+// TODO: Fill this in
+# define _LIBCPP_INTRODUCED_IN_LLVM_24 0
+# define _LIBCPP_INTRODUCED_IN_LLVM_24_ATTRIBUTE __attribute__((unavailable))
+
// LLVM 23
// TODO: Fill this in
# define _LIBCPP_INTRODUCED_IN_LLVM_23 0
@@ -239,6 +247,8 @@
#endif
+#define _LIBCPP_AVAILABILITY_HAS_NEW_AT_LEAST _LIBCPP_INTRODUCED_IN_LLVM_24
+
// This determines whether we assume that the internal std::__bad_variant_access_with_msg class
// (which carries a message describing the cause of the failure in bad_variant_access::what())
// provides a key function in the dylib. This allows centralizing its vtable and typeinfo instead
diff --git a/libcxx/include/__memory/allocate_at_least.h b/libcxx/include/__memory/allocate_at_least.h
index 72140d0de27af..0cb406e1941ca 100644
--- a/libcxx/include/__memory/allocate_at_least.h
+++ b/libcxx/include/__memory/allocate_at_least.h
@@ -12,6 +12,7 @@
#include <__config>
#include <__cstddef/size_t.h>
#include <__memory/allocator_traits.h>
+#include <__new/allocate.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
@@ -19,16 +20,6 @@
_LIBCPP_BEGIN_NAMESPACE_STD
-template <class _Pointer, class _SizeT = size_t>
-struct __allocation_result {
- _Pointer ptr;
- _SizeT count;
-
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __allocation_result(_Pointer __ptr, _SizeT __count)
- : ptr(__ptr), count(__count) {}
-};
-_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__allocation_result);
-
#if _LIBCPP_STD_VER >= 23
template <class _Alloc>
diff --git a/libcxx/include/__memory/allocator.h b/libcxx/include/__memory/allocator.h
index dd8c8647c178a..86fabb01fb7f2 100644
--- a/libcxx/include/__memory/allocator.h
+++ b/libcxx/include/__memory/allocator.h
@@ -96,7 +96,11 @@ class allocator
#if _LIBCPP_STD_VER >= 23
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr allocation_result<_Tp*> allocate_at_least(size_t __n) {
static_assert(sizeof(_Tp) >= 0, "cannot allocate memory for an incomplete type");
- return {allocate(__n), __n};
+ if consteval {
+ return {allocate(__n), __n};
+ } else {
+ return std::__libcpp_allocate_at_least<_Tp>(__n);
+ }
}
#endif
diff --git a/libcxx/include/__new/allocate.h b/libcxx/include/__new/allocate.h
index b9bc2e1a50710..09c3fd040531e 100644
--- a/libcxx/include/__new/allocate.h
+++ b/libcxx/include/__new/allocate.h
@@ -13,6 +13,7 @@
#include <__cstddef/max_align_t.h>
#include <__cstddef/size_t.h>
#include <__new/align_val_t.h>
+#include <__new/new_at_least.h>
#include <__type_traits/type_identity.h>
#include <__utility/element_count.h>
@@ -42,6 +43,20 @@ __libcpp_allocate(__element_count __n, [[__maybe_unused__]] size_t __align = _LI
return static_cast<_Tp*>(__builtin_operator_new(__size));
}
+template <class _Tp>
+_LIBCPP_NO_CFI __allocation_result<_Tp*>
+__libcpp_allocate_at_least(__element_count __n, [[__maybe_unused__]] size_t __align = _LIBCPP_ALIGNOF(_Tp)) {
+ size_t __size = static_cast<size_t>(__n) * sizeof(_Tp);
+#if _LIBCPP_HAS_ALIGNED_ALLOCATION
+ if (__is_overaligned_for_new(__align)) {
+ auto [__ptr, __count] = std::__new_at_least(__size, static_cast<align_val_t>(__align));
+ return {static_cast<_Tp*>(__ptr), __count / sizeof(_Tp)};
+ }
+#endif
+ auto [__ptr, __count] = std::__new_at_least(__size);
+ return {static_cast<_Tp*>(__ptr), __count / sizeof(_Tp)};
+}
+
#if defined(__cpp_sized_deallocation) && __cpp_sized_deallocation >= 201309L
# define _LIBCPP_ONLY_IF_SIZED_DEALLOCATION(...) __VA_ARGS__
#else
diff --git a/libcxx/include/__new/new_at_least.h b/libcxx/include/__new/new_at_least.h
new file mode 100644
index 0000000000000..801b02be7e23d
--- /dev/null
+++ b/libcxx/include/__new/new_at_least.h
@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP___NEW_NEW_AT_LEAST_H
+#define _LIBCPP___NEW_NEW_AT_LEAST_H
+
+#include <__config>
+#include <__cstddef/size_t.h>
+#include <__new/align_val_t.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+# pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Pointer, class _SizeT = size_t>
+struct __allocation_result {
+ _Pointer ptr;
+ _SizeT count;
+
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __allocation_result(_Pointer __ptr, _SizeT __count)
+ : ptr(__ptr), count(__count) {}
+};
+_LIBCPP_CTAD_SUPPORTED_FOR_TYPE(__allocation_result);
+
+#if _LIBCPP_AVAILABILITY_HAS_NEW_AT_LEAST
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
+
+_LIBCPP_EXPORTED_FROM_ABI __allocation_result<void*> __new_at_least(size_t);
+# if _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
+_LIBCPP_EXPORTED_FROM_ABI __allocation_result<void*> __new_at_least(size_t, align_val_t);
+# endif
+
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
+#endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___NEW_NEW_AT_LEAST_H
diff --git a/libcxx/src/support/new.ipp b/libcxx/src/support/new.ipp
index 80be2d904af4c..6556d181ea928 100644
--- a/libcxx/src/support/new.ipp
+++ b/libcxx/src/support/new.ipp
@@ -6,6 +6,7 @@
//
//===----------------------------------------------------------------------===//
+#include <__memory/allocate_at_least.h>
#include <cstddef>
#include <cstdlib>
#include <new>
@@ -211,3 +212,69 @@ OVERRIDABLE_FUNCTION void* operator new[](size_t size, std::align_val_t alignmen
::operator delete[](ptr, alignment);
}
#endif // _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
+
+#ifdef __APPLE__
+# include <malloc/malloc.h>
+#elifdef __FreeBSD__
+# include <malloc_np.h>
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+_LIBCPP_BEGIN_EXPLICIT_ABI_ANNOTATIONS
+
+#if __has_cpp_attribute(gnu::ifunc)
+
+using new_at_least_t = __allocation_result<void*>(std::size_t);
+using new_at_least_aligned_t = __allocation_result<void*>(std::size_t, std::align_val_t);
+
+new_at_least_t* new_at_least_resolver() {
+ if (std::__is_function_overridden < void*(std::size_t), operator new>()) {
+ return [](std::size_t size) -> __allocation_result<void*> { return {::operator new(size), size}; };
+ } else {
+ return [](std::size_t size) -> __allocation_result<void*> {
+# ifdef __APPLE__
+ auto good_size = malloc_good_size(size);
+ return {operator_new_impl(good_size), good_size};
+#elifdef __FreeBSD__
+ auto good_size = nallocx(size, 0);
+ return {operator_new_impl(good_size), good_size};
+# else
+ return {operator_new_impl(size), size};
+# endif
+ };
+ }
+}
+
+[[gnu::weak, gnu::ifunc("new_at_least_resolver")]] new_at_least_t __new_at_least;
+
+new_at_least_t* new_at_least_aligned_resolver() {
+ if (std::__is_function_overridden < void*(std::size_t), operator new>()) {
+ return [](std::size_t size) -> __allocation_result<void*> { return {::operator new(size), size}; };
+ } else {
+ return [](std::size_t size) -> __allocation_result<void*> {
+# ifdef __APPLE__
+ auto good_size = malloc_good_size(size);
+ return {operator_new_impl(good_size), good_size};
+# else
+ return {operator_new_impl(size), size};
+# endif
+ };
+ }
+}
+
+[[gnu::weak, gnu::ifunc("new_at_least_aligned_resolver")]] new_at_least_aligned_t __new_at_least;
+
+#else
+
+std::__allocation_result<void*> __new_at_least(std::size_t size) { return {::operator new(size), size}; }
+
+# if _LIBCPP_HAS_LIBRARY_ALIGNED_ALLOCATION
+std::__allocation_result<void*> __new_at_least(std::size_t size, std::align_val_t align) {
+ return {::operator new(size, align), size};
+}
+# endif
+
+#endif
+
+_LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
+_LIBCPP_END_NAMESPACE_STD
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