[libcxx-commits] [libcxx] [libc+] Applied `[[nodiscard]]` to Allocators (PR #172131)
via libcxx-commits
libcxx-commits at lists.llvm.org
Sun Dec 14 07:58:19 PST 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Hristo Hristov (H-G-Hristov)
<details>
<summary>Changes</summary>
Towards #<!-- -->172124
---
Full diff: https://github.com/llvm/llvm-project/pull/172131.diff
5 Files Affected:
- (modified) libcxx/include/__memory/addressof.h (+7-5)
- (modified) libcxx/include/__memory/allocator.h (+4-3)
- (modified) libcxx/include/__memory/is_sufficiently_aligned.h (+1-1)
- (modified) libcxx/include/__memory/raw_storage_iterator.h (+1-1)
- (modified) libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp (+28-5)
``````````diff
diff --git a/libcxx/include/__memory/addressof.h b/libcxx/include/__memory/addressof.h
index 667071dfc6635..52ec94a5299fa 100644
--- a/libcxx/include/__memory/addressof.h
+++ b/libcxx/include/__memory/addressof.h
@@ -19,7 +19,8 @@
_LIBCPP_BEGIN_NAMESPACE_STD
template <class _Tp>
-inline _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_NO_CFI _LIBCPP_HIDE_FROM_ABI _Tp* addressof(_Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_NO_CFI _LIBCPP_HIDE_FROM_ABI _Tp*
+addressof(_Tp& __x) _NOEXCEPT {
return __builtin_addressof(__x);
}
@@ -27,24 +28,25 @@ inline _LIBCPP_CONSTEXPR_SINCE_CXX17 _LIBCPP_NO_CFI _LIBCPP_HIDE_FROM_ABI _Tp* a
// Objective-C++ Automatic Reference Counting uses qualified pointers
// that require special addressof() signatures.
template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __strong _Tp* addressof(__strong _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __strong _Tp* addressof(__strong _Tp& __x) _NOEXCEPT {
return &__x;
}
# if __has_feature(objc_arc_weak)
template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __weak _Tp* addressof(__weak _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __weak _Tp* addressof(__weak _Tp& __x) _NOEXCEPT {
return &__x;
}
# endif
template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __autoreleasing _Tp* addressof(__autoreleasing _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __autoreleasing _Tp* addressof(__autoreleasing _Tp& __x) _NOEXCEPT {
return &__x;
}
template <class _Tp>
-inline _LIBCPP_HIDE_FROM_ABI __unsafe_unretained _Tp* addressof(__unsafe_unretained _Tp& __x) _NOEXCEPT {
+[[__nodiscard__]] inline _LIBCPP_HIDE_FROM_ABI __unsafe_unretained _Tp*
+addressof(__unsafe_unretained _Tp& __x) _NOEXCEPT {
return &__x;
}
#endif
diff --git a/libcxx/include/__memory/allocator.h b/libcxx/include/__memory/allocator.h
index 1c96a2ab64578..609b305a1250f 100644
--- a/libcxx/include/__memory/allocator.h
+++ b/libcxx/include/__memory/allocator.h
@@ -120,10 +120,11 @@ class allocator
typedef allocator<_Up> other;
};
- _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI pointer address(reference __x) const _NOEXCEPT {
+ [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI pointer address(reference __x) const _NOEXCEPT {
return std::addressof(__x);
}
- _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI const_pointer address(const_reference __x) const _NOEXCEPT {
+ [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI const_pointer
+ address(const_reference __x) const _NOEXCEPT {
return std::addressof(__x);
}
@@ -131,7 +132,7 @@ class allocator
return allocate(__n);
}
- _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
+ [[__nodiscard__]] _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
return size_type(~0) / sizeof(_Tp);
}
diff --git a/libcxx/include/__memory/is_sufficiently_aligned.h b/libcxx/include/__memory/is_sufficiently_aligned.h
index 4280920cabb4b..93d24aaf78f0b 100644
--- a/libcxx/include/__memory/is_sufficiently_aligned.h
+++ b/libcxx/include/__memory/is_sufficiently_aligned.h
@@ -23,7 +23,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
#if _LIBCPP_STD_VER >= 26
template <size_t _Alignment, class _Tp>
-_LIBCPP_HIDE_FROM_ABI bool is_sufficiently_aligned(_Tp* __ptr) {
+[[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool is_sufficiently_aligned(_Tp* __ptr) {
return reinterpret_cast<uintptr_t>(__ptr) % _Alignment == 0;
}
diff --git a/libcxx/include/__memory/raw_storage_iterator.h b/libcxx/include/__memory/raw_storage_iterator.h
index d98b3faf48468..7c9b34076de46 100644
--- a/libcxx/include/__memory/raw_storage_iterator.h
+++ b/libcxx/include/__memory/raw_storage_iterator.h
@@ -67,7 +67,7 @@ class _LIBCPP_DEPRECATED_IN_CXX17 raw_storage_iterator
return __t;
}
# if _LIBCPP_STD_VER >= 14
- _LIBCPP_HIDE_FROM_ABI _OutputIterator base() const { return __x_; }
+ [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _OutputIterator base() const { return __x_; }
# endif
};
diff --git a/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp b/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp
index 6410c84e926aa..732e5e82ed508 100644
--- a/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp
+++ b/libcxx/test/libcxx/diagnostics/memory.nodiscard.verify.cpp
@@ -10,6 +10,7 @@
// check that <memory> functions are marked [[nodiscard]]
+// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_RAW_STORAGE_ITERATOR
// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ENABLE_CXX20_REMOVED_TEMPORARY_BUFFER
// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_DISABLE_DEPRECATION_WARNINGS
@@ -20,7 +21,13 @@
#include "test_macros.h"
void test() {
+ int i = 0;
+
+ std::addressof(i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
std::get_temporary_buffer<int>(0); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#if _LIBCPP_STD_VER >= 26
+ std::is_sufficiently_aligned<2>(&i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
}
void test_allocator_traits() {
@@ -31,12 +38,28 @@ void test_allocator_traits() {
}
void test_allocator() {
- std::allocator<int> allocator;
- allocator.allocate(1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-#if TEST_STD_VER <= 17
- allocator.allocate(1, nullptr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
-#endif
+ [[maybe_unused]] std::allocator<int> allocator;
+
#if TEST_STD_VER >= 23
allocator.allocate_at_least(1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
#endif
+
+#if TEST_STD_VER <= 17
+ int i = 0;
+ const int ci = 0;
+
+ allocator.address(i); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ allocator.address(ci); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ allocator.allocate(1); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ allocator.allocate(1, nullptr); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+ allocator.max_size(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+#endif
}
+
+#if TEST_STD_VER >= 14
+void test_raw_storage_iterator() {
+ std::raw_storage_iterator<int*, int> it(nullptr);
+
+ it.base(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+}
+#endif
``````````
</details>
https://github.com/llvm/llvm-project/pull/172131
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