[libcxx-commits] [libcxx] [libc++] Fix behavior for `get_temporary_buffer` with non-positive size (PR #206871)
A. Jiang via libcxx-commits
libcxx-commits at lists.llvm.org
Wed Jul 1 01:46:09 PDT 2026
https://github.com/frederick-vs-ja updated https://github.com/llvm/llvm-project/pull/206871
>From 92bae65367bbcc5caa6601e70e37715d1bec9e5b Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Wed, 1 Jul 2026 10:12:44 +0800
Subject: [PATCH 1/4] [libc++] Fix behavior for `get_temporary_buffer` with
non-positive size
Per C++17 [depr.temporary.buffer]/4, `get_temporary_buffer` is required
to return `{nullptr, 0}` when the size argument is zero or negative.
libc++ used to correctly handle this, but the refactoring in
94e7c0b051c79fd56205f115771980f2e7812306 got this wrong.
---
libcxx/include/__memory/temporary_buffer.h | 3 +++
.../memory/temporary.buffer/overaligned.pass.cpp | 14 ++++++++++++++
.../temporary.buffer/temporary_buffer.pass.cpp | 14 ++++++++++++++
3 files changed, 31 insertions(+)
diff --git a/libcxx/include/__memory/temporary_buffer.h b/libcxx/include/__memory/temporary_buffer.h
index d18717f52d1cd..3c572e43db641 100644
--- a/libcxx/include/__memory/temporary_buffer.h
+++ b/libcxx/include/__memory/temporary_buffer.h
@@ -26,6 +26,9 @@ _LIBCPP_BEGIN_NAMESPACE_STD
template <class _Tp>
[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI _LIBCPP_DEPRECATED_IN_CXX17 pair<_Tp*, ptrdiff_t>
get_temporary_buffer(ptrdiff_t __n) _NOEXCEPT {
+ if (__n <= 0)
+ return pair<_Tp*, ptrdiff_t>();
+
__unique_temporary_buffer<_Tp> __unique_buf = std::__allocate_unique_temporary_buffer<_Tp>(__n);
pair<_Tp*, ptrdiff_t> __result(__unique_buf.get(), __unique_buf.get_deleter().__count_);
__unique_buf.release();
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
index 3fa9355270866..678e4e3d342fb 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
@@ -38,5 +38,19 @@ int main(int, char**)
assert(reinterpret_cast<std::uintptr_t>(ip.first) % alignof(A) == 0);
std::return_temporary_buffer(ip.first);
+ // C++17 [depr.temporary.buffer]/4
+ // Returns: If n <= 0 or if no storage could be obtained,
+ // returns a pair P such that P.first is a null pointer value and P.second == 0;
+ {
+ std::pair<A*, std::ptrdiff_t> ret = std::get_temporary_buffer<A>(0);
+ assert(ret.first == NULL);
+ assert(ret.second == 0);
+ }
+ {
+ std::pair<A*, std::ptrdiff_t> ret = std::get_temporary_buffer<A>(-5);
+ assert(ret.first == NULL);
+ assert(ret.second == 0);
+ }
+
return 0;
}
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
index 39a4767d874e3..50ca6b21ae46c 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
@@ -31,5 +31,19 @@ int main(int, char**)
assert(ip.second == 5);
std::return_temporary_buffer(ip.first);
+ // C++17 [depr.temporary.buffer]/4
+ // Returns: If n <= 0 or if no storage could be obtained,
+ // returns a pair P such that P.first is a null pointer value and P.second == 0;
+ {
+ std::pair<int*, std::ptrdiff_t> ret = std::get_temporary_buffer<int>(0);
+ assert(ret.first == NULL);
+ assert(ret.second == 0);
+ }
+ {
+ std::pair<int*, std::ptrdiff_t> ret = std::get_temporary_buffer<int>(-5);
+ assert(ret.first == NULL);
+ assert(ret.second == 0);
+ }
+
return 0;
}
>From 90d750fbdc0f9a9fcb01c7b5cfa3ed36d99cd163 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Wed, 1 Jul 2026 13:35:25 +0800
Subject: [PATCH 2/4] `-Wno-alloc-size-larger-than`
---
.../utilities/memory/temporary.buffer/overaligned.pass.cpp | 5 +++++
.../memory/temporary.buffer/temporary_buffer.pass.cpp | 5 +++++
2 files changed, 10 insertions(+)
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
index 678e4e3d342fb..0f119ae90b82e 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
@@ -27,6 +27,11 @@
#include <memory>
#include <utility>
+#include "test_macros.h"
+
+// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
+TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
+
struct alignas(32) A {
int field;
};
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
index 50ca6b21ae46c..729cb14b9c5e9 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
@@ -24,6 +24,11 @@
#include <memory>
#include <utility>
+#include "test_macros.h"
+
+// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
+TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
+
int main(int, char**)
{
std::pair<int*, std::ptrdiff_t> ip = std::get_temporary_buffer<int>(5);
>From 3590c72e1e0cb065b9297b2060c73344869f6f41 Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Wed, 1 Jul 2026 15:40:16 +0800
Subject: [PATCH 3/4] Locally suppress the warning
---
.../utilities/memory/temporary.buffer/overaligned.pass.cpp | 7 ++++---
.../memory/temporary.buffer/temporary_buffer.pass.cpp | 7 ++++---
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
index 0f119ae90b82e..2b4b6586f5563 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
@@ -29,9 +29,6 @@
#include "test_macros.h"
-// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
-TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
-
struct alignas(32) A {
int field;
};
@@ -52,7 +49,11 @@ int main(int, char**)
assert(ret.second == 0);
}
{
+ TEST_DIAGNOSTIC_PUSH
+ // This warning is coupled with completeness of control flow analysis which is affected by optimizations.
+ TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
std::pair<A*, std::ptrdiff_t> ret = std::get_temporary_buffer<A>(-5);
+ TEST_DIAGNOSTIC_POP
assert(ret.first == NULL);
assert(ret.second == 0);
}
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
index 729cb14b9c5e9..6935e8a9d83d5 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
@@ -26,9 +26,6 @@
#include "test_macros.h"
-// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
-TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
-
int main(int, char**)
{
std::pair<int*, std::ptrdiff_t> ip = std::get_temporary_buffer<int>(5);
@@ -45,7 +42,11 @@ int main(int, char**)
assert(ret.second == 0);
}
{
+ TEST_DIAGNOSTIC_PUSH
+ // This warning is coupled with completeness of control flow analysis which is affected by optimizations.
+ TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
std::pair<int*, std::ptrdiff_t> ret = std::get_temporary_buffer<int>(-5);
+ TEST_DIAGNOSTIC_POP
assert(ret.first == NULL);
assert(ret.second == 0);
}
>From c95c07613f6cebd619601ad85fc4d209cb8bfe4e Mon Sep 17 00:00:00 2001
From: "A. Jiang" <de34 at live.cn>
Date: Wed, 1 Jul 2026 16:45:46 +0800
Subject: [PATCH 4/4] Tweak the suppressing style and add test cases
---
.../memory/temporary.buffer/overaligned.pass.cpp | 5 +++--
.../temporary.buffer/temporary_buffer.pass.cpp | 12 +++++++++++-
2 files changed, 14 insertions(+), 3 deletions(-)
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
index 2b4b6586f5563..c55e488af53b1 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/overaligned.pass.cpp
@@ -24,6 +24,7 @@
#include <cassert>
#include <cstddef>
#include <cstdint>
+#include <limits>
#include <memory>
#include <utility>
@@ -51,8 +52,8 @@ int main(int, char**)
{
TEST_DIAGNOSTIC_PUSH
// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
- TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
- std::pair<A*, std::ptrdiff_t> ret = std::get_temporary_buffer<A>(-5);
+ TEST_GCC_DIAGNOSTIC_IGNORED("-Walloc-size-larger-than=")
+ std::pair<A*, std::ptrdiff_t> ret = std::get_temporary_buffer<A>(std::numeric_limits<std::ptrdiff_t>::min());
TEST_DIAGNOSTIC_POP
assert(ret.first == NULL);
assert(ret.second == 0);
diff --git a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
index 6935e8a9d83d5..9bd49edbb0d02 100644
--- a/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
+++ b/libcxx/test/std/utilities/memory/temporary.buffer/temporary_buffer.pass.cpp
@@ -21,6 +21,7 @@
#include <cassert>
#include <cstddef>
+#include <limits>
#include <memory>
#include <utility>
@@ -44,12 +45,21 @@ int main(int, char**)
{
TEST_DIAGNOSTIC_PUSH
// This warning is coupled with completeness of control flow analysis which is affected by optimizations.
- TEST_GCC_DIAGNOSTIC_IGNORED("-Wno-alloc-size-larger-than")
+ TEST_GCC_DIAGNOSTIC_IGNORED("-Walloc-size-larger-than=")
std::pair<int*, std::ptrdiff_t> ret = std::get_temporary_buffer<int>(-5);
TEST_DIAGNOSTIC_POP
assert(ret.first == NULL);
assert(ret.second == 0);
}
+ {
+ TEST_DIAGNOSTIC_PUSH
+ // This warning is coupled with completeness of control flow analysis which is affected by optimizations.
+ TEST_GCC_DIAGNOSTIC_IGNORED("-Walloc-size-larger-than=")
+ std::pair<int*, std::ptrdiff_t> ret = std::get_temporary_buffer<int>(std::numeric_limits<std::ptrdiff_t>::min());
+ TEST_DIAGNOSTIC_POP
+ assert(ret.first == NULL);
+ assert(ret.second == 0);
+ }
return 0;
}
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