On Mon, 19 Jan 2026 at 14:31, Soumya AR <[email protected]> wrote: > > Hi Jonathan, > > I removed the changes from stdatomic.h. > Putting an updated patch up. > Should be OK to commit without the builtins for now?
Yes, this libstdc++ patch is OK for trunk now, thanks. > > > > On 16 Jan 2026, at 6:51 PM, Jonathan Wakely <[email protected]> wrote: > > > > External email: Use caution opening links or attachments > > > > > > On Fri, 16 Jan 2026 at 08:28, Soumya AR <[email protected]> wrote: > >>>> +// This file is part of the GNU ISO C++ Library. This library is free > >>>> +// software; you can redistribute it and/or modify it under the > >>>> +// terms of the GNU General Public License as published by the > >>>> +// Free Software Foundation; either version 3, or (at your option) > >>>> +// any later version. > >>>> + > >>>> +// This library is distributed in the hope that it will be useful, > >>>> +// but WITHOUT ANY WARRANTY; without even the implied warranty of > >>>> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > >>>> +// GNU General Public License for more details. > >>>> + > >>>> +// Under Section 7 of GPL version 3, you are granted additional > >>>> +// permissions described in the GCC Runtime Library Exception, version > >>>> +// 3.1, as published by the Free Software Foundation. > >>>> + > >>>> +// You should have received a copy of the GNU General Public License and > >>>> +// a copy of the GCC Runtime Library Exception along with this program; > >>>> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see > >>>> +// <http://www.gnu.org/licenses/>. > >>>> + > >>>> +// { dg-do run { target c++26 } } > >>> > >>> Do these new tests need { dg-add-options libatomic } ? I think they > >>> probably do. > >>> > >>> What about { dg-require-atomic-cmpxchg-word "" } ? > >> > >> Yes, you're right, ideally should have both directives. > >> > >> However, on re-working this patch, I don't think these tests are needed in > >> libstdc++ at all. I already have correctness tests for the builtins in the > >> GCC testsuite. > >> > >> To test the API, I've created a C++26 version of nonmembers.cc for > >> fetch_min/max. > >> And another fetch_min/max version for the correctness tests for atomic_ref. > > > > I missed this part, sorry. > > > > I think the new tests make sense in libstdc++. The builtins might be > > thouroughly tested in the compiler tests, but having library tests > > ensures we don't make a silly mistake like calling __atomic_fetch_min > > from the fetch_max function (an easy copy*paste error to make when > > refactoring). > > > > The tests in the new patch are adequate for that purpose: each > > function is called at least once and the expected result is verified. > > > >> Or for both of these, should we just update the existing tests to C++26? > > > > I think it's better to have separate tests for the new members, > > because the existing tests are typically only run for the default -std > > mode (currently gnu++20) and so would not test any parts of the file > > guarded by #if __cpp_lib_atomic_min_max. Having a separate test with { > > target c++26 } means that everybody who runs the testsuite will run > > that test. > > > > And we don't want to add { target c++26 } to the existing tests, > > because then we would not test that the C++11 features still work in > > C++11. > > > > Oh right, that makes more sense. I was not sure why we don't add > { target c++26 } to the existing tests earlier. Thanks for answering > this. > > >> What about c_compat.cc? > > > > No changes to that file, because there should be no changes to <stdatomic.h> > > > > > >> > >> Thanks, > >> Soumya > >> > >>>> +#include <atomic> > >>>> +#include <limits> > >>>> +#include <testsuite_hooks.h> > >>>> + > >>>> +template<typename T> > >>>> +void test_signed() > >>>> +{ > >>>> + std::atomic<T> a; > >>>> + const std::memory_order mo = std::memory_order_relaxed; > >>>> + T expected = 0; > >>>> + T value = 0; > >>>> + > >>>> + a.store(100); > >>>> + value = a.fetch_min(50); > >>>> + VERIFY( value == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_min(75, mo); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_min(25); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 25 ); > >>>> + > >>>> + a.store(-10); > >>>> + value = a.fetch_min(-20); > >>>> + VERIFY( value == -10 ); > >>>> + VERIFY( a.load() == -20 ); > >>>> + > >>>> + value = a.fetch_min(-5, mo); > >>>> + VERIFY( value == -20 ); > >>>> + VERIFY( a.load() == -20 ); > >>>> + > >>>> + a.store(10); > >>>> + value = a.fetch_min(-5); > >>>> + VERIFY( value == 10 ); > >>>> + VERIFY( a.load() == -5 ); > >>>> + > >>>> + a.store(20); > >>>> + value = a.fetch_max(50); > >>>> + VERIFY( value == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_max(30, mo); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_max(100); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 100 ); > >>>> + > >>>> + a.store(-50); > >>>> + value = a.fetch_max(-20); > >>>> + VERIFY( value == -50 ); > >>>> + VERIFY( a.load() == -20 ); > >>>> + > >>>> + value = a.fetch_max(-10, mo); > >>>> + VERIFY( value == -20 ); > >>>> + VERIFY( a.load() == -10 ); > >>>> + > >>>> + a.store(-10); > >>>> + value = a.fetch_max(5); > >>>> + VERIFY( value == -10 ); > >>>> + VERIFY( a.load() == 5 ); > >>>> + > >>>> + T min_val = std::numeric_limits<T>::min(); > >>>> + T max_val = std::numeric_limits<T>::max(); > >>>> + > >>>> + a.store(0); > >>>> + value = a.fetch_min(min_val); > >>>> + VERIFY( value == 0 ); > >>>> + VERIFY( a.load() == min_val ); > >>>> + > >>>> + a.store(0); > >>>> + value = a.fetch_max(max_val); > >>>> + VERIFY( value == 0 ); > >>>> + VERIFY( a.load() == max_val ); > >>>> +} > >>>> + > >>>> +template<typename T> > >>>> +void test_unsigned() > >>>> +{ > >>>> + std::atomic<T> a; > >>>> + const std::memory_order mo = std::memory_order_relaxed; > >>>> + T expected = 0; > >>>> + T value = 0; > >>>> + > >>>> + a.store(100); > >>>> + value = a.fetch_min(50); > >>>> + VERIFY( value == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_min(75, mo); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_min(25); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 25 ); > >>>> + > >>>> + a.store(20); > >>>> + value = a.fetch_max(50); > >>>> + VERIFY( value == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_max(30, mo); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + value = a.fetch_max(100); > >>>> + VERIFY( value == 50 ); > >>>> + VERIFY( a.load() == 100 ); > >>>> + > >>>> + T min_val = std::numeric_limits<T>::min(); > >>>> + T max_val = std::numeric_limits<T>::max(); > >>>> + > >>>> + a.store(10); > >>>> + value = a.fetch_min(min_val); > >>>> + VERIFY( value == 10 ); > >>>> + VERIFY( a.load() == min_val ); > >>>> + > >>>> + a.store(10); > >>>> + value = a.fetch_max(max_val); > >>>> + VERIFY( value == 10 ); > >>>> + VERIFY( a.load() == max_val ); > >>>> +} > >>>> + > >>>> +int main() > >>>> +{ > >>>> + test_signed<signed char>(); > >>>> + test_signed<short>(); > >>>> + test_signed<int>(); > >>>> + test_signed<long>(); > >>>> + test_signed<long long>(); > >>>> + > >>>> + test_unsigned<unsigned char>(); > >>>> + test_unsigned<unsigned short>(); > >>>> + test_unsigned<unsigned int>(); > >>>> + test_unsigned<unsigned long>(); > >>>> + test_unsigned<unsigned long long>(); > >>>> + > >>>> + return 0; > >>>> +} > >>>> \ No newline at end of file > >>>> diff --git > >>>> a/libstdc++-v3/testsuite/29_atomics/atomic_integral/fetch_minmax_order.cc > >>>> > >>>> b/libstdc++-v3/testsuite/29_atomics/atomic_integral/fetch_minmax_order.cc > >>>> new file mode 100644 > >>>> index 00000000000..3ed6f2e2e6f > >>>> --- /dev/null > >>>> +++ > >>>> b/libstdc++-v3/testsuite/29_atomics/atomic_integral/fetch_minmax_order.cc > >>>> @@ -0,0 +1,116 @@ > >>>> +// Copyright The GNU Toolchain Authors. > >>>> +// > >>>> +// This file is part of the GNU ISO C++ Library. This library is free > >>>> +// software; you can redistribute it and/or modify it under the > >>>> +// terms of the GNU General Public License as published by the > >>>> +// Free Software Foundation; either version 3, or (at your option) > >>>> +// any later version. > >>>> + > >>>> +// This library is distributed in the hope that it will be useful, > >>>> +// but WITHOUT ANY WARRANTY; without even the implied warranty of > >>>> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > >>>> +// GNU General Public License for more details. > >>>> + > >>>> +// Under Section 7 of GPL version 3, you are granted additional > >>>> +// permissions described in the GCC Runtime Library Exception, version > >>>> +// 3.1, as published by the Free Software Foundation. > >>>> + > >>>> +// You should have received a copy of the GNU General Public License and > >>>> +// a copy of the GCC Runtime Library Exception along with this program; > >>>> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see > >>>> +// <http://www.gnu.org/licenses/>. > >>>> + > >>>> +// { dg-do run { target c++26 } } > >>>> + > >>>> +#include <atomic> > >>>> +#include <testsuite_hooks.h> > >>>> + > >>>> +void test_memory_orderings() > >>>> +{ > >>>> + std::atomic<int> a; > >>>> + int v; > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_relaxed); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load(std::memory_order_relaxed) == 50 ); > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_consume); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_acquire); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_release); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_acq_rel); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(100); > >>>> + v = a.fetch_min(50, std::memory_order_seq_cst); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_relaxed); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load(std::memory_order_relaxed) == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_consume); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_acquire); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_release); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_acq_rel); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> + > >>>> + a.store(20); > >>>> + v = a.fetch_max(50, std::memory_order_seq_cst); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a.load() == 50 ); > >>>> +} > >>>> + > >>>> +// Test volatile atomic operations > >>>> +void test_volatile() > >>>> +{ > >>>> + volatile std::atomic<int> va; > >>>> + int v; > >>>> + > >>>> + va.store(100); > >>>> + v = va.fetch_min(50); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( va.load() == 50 ); > >>>> + > >>>> + va.store(20); > >>>> + v = va.fetch_max(50, std::memory_order_relaxed); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( va.load() == 50 ); > >>>> +} > >>>> + > >>>> +int main() > >>>> +{ > >>>> + test_memory_orderings(); > >>>> + test_volatile(); > >>>> + return 0; > >>>> +} > >>>> \ No newline at end of file > >>>> diff --git > >>>> a/libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers.cc > >>>> b/libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers.cc > >>>> index a07d9700ff4..3fb86db65b1 100644 > >>>> --- a/libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers.cc > >>>> +++ b/libstdc++-v3/testsuite/29_atomics/atomic_integral/nonmembers.cc > >>>> @@ -111,6 +111,22 @@ test01() > >>>> static_assert( std::is_same<decltype(r37), int>::value, "" ); > >>>> auto r38 = atomic_fetch_xor_explicit(&a, l, mo); > >>>> static_assert( std::is_same<decltype(r38), long>::value, "" ); > >>>> + auto r39 = atomic_fetch_min(&v, i); > >>>> + static_assert( std::is_same<decltype(r39), int>::value, "" ); > >>>> + auto r40 = atomic_fetch_min(&a, l); > >>>> + static_assert( std::is_same<decltype(r40), long>::value, "" ); > >>>> + auto r41 = atomic_fetch_min_explicit(&v, i, mo); > >>>> + static_assert( std::is_same<decltype(r41), int>::value, "" ); > >>>> + auto r42 = atomic_fetch_min_explicit(&a, l, mo); > >>>> + static_assert( std::is_same<decltype(r42), long>::value, "" ); > >>>> + auto r43 = atomic_fetch_max(&v, i); > >>>> + static_assert( std::is_same<decltype(r43), int>::value, "" ); > >>>> + auto r44 = atomic_fetch_max(&a, l); > >>>> + static_assert( std::is_same<decltype(r44), long>::value, "" ); > >>>> + auto r45 = atomic_fetch_max_explicit(&v, i, mo); > >>>> + static_assert( std::is_same<decltype(r45), int>::value, "" ); > >>>> + auto r46 = atomic_fetch_max_explicit(&a, l, mo); > >>>> + static_assert( std::is_same<decltype(r46), long>::value, "" ); > >>>> } > >>>> > >>>> void > >>>> @@ -160,4 +176,12 @@ test02() > >>>> atomic_fetch_xor(&a, i); > >>>> atomic_fetch_xor_explicit(&v, i, mo); > >>>> atomic_fetch_xor_explicit(&a, i, mo); > >>>> + atomic_fetch_min(&v, i); > >>>> + atomic_fetch_min(&a, i); > >>>> + atomic_fetch_min_explicit(&v, i, mo); > >>>> + atomic_fetch_min_explicit(&a, i, mo); > >>>> + atomic_fetch_max(&v, i); > >>>> + atomic_fetch_max(&a, i); > >>>> + atomic_fetch_max_explicit(&v, i, mo); > >>>> + atomic_fetch_max_explicit(&a, i, mo); > >>>> } > >>>> diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_ref/integral.cc > >>>> b/libstdc++-v3/testsuite/29_atomics/atomic_ref/integral.cc > >>>> index 310434cefb5..5a282320bd7 100644 > >>>> --- a/libstdc++-v3/testsuite/29_atomics/atomic_ref/integral.cc > >>>> +++ b/libstdc++-v3/testsuite/29_atomics/atomic_ref/integral.cc > >>>> @@ -155,9 +155,38 @@ test01() > >>>> v = a ^= 0x121; > >>>> VERIFY( v == 0x022 ); > >>>> VERIFY( a == 0x022 ); > >>>> + > >>>> + > >>>> + a = 100; > >>>> + v = a.fetch_min(50); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + v = a.fetch_min(75, mo); > >>>> + VERIFY( v == 50 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + a = -10; > >>>> + v = a.fetch_min(-20); > >>>> + VERIFY( v == -10 ); > >>>> + VERIFY( a == -20 ); > >>>> + > >>>> + a = 20; > >>>> + v = a.fetch_max(50); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + v = a.fetch_max(30, mo); > >>>> + VERIFY( v == 50 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + a = -50; > >>>> + v = a.fetch_max(-20); > >>>> + VERIFY( v == -50 ); > >>>> + VERIFY( a == -20 ); > >>>> } > >>>> > >>>> - VERIFY( value == 0x022 ); > >>>> + VERIFY( value == -20 ); > >>>> } > >>>> > >>>> void > >>>> @@ -292,9 +321,27 @@ test02() > >>>> v = a ^= 0x12; > >>>> VERIFY( v == 0x24 ); > >>>> VERIFY( a == 0x24 ); > >>>> + > >>>> + a = 100; > >>>> + v = a.fetch_min(50); > >>>> + VERIFY( v == 100 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + v = a.fetch_min(75, mo); > >>>> + VERIFY( v == 50 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + a = 20; > >>>> + v = a.fetch_max(50); > >>>> + VERIFY( v == 20 ); > >>>> + VERIFY( a == 50 ); > >>>> + > >>>> + v = a.fetch_max(30, mo); > >>>> + VERIFY( v == 50 ); > >>>> + VERIFY( a == 50 ); > >>>> } > >>>> > >>>> - VERIFY( value == 0x24 ); > >>>> + VERIFY( value == 50 ); > >>>> } > >>>> void > >>>> test03() > >>>> diff --git > >>>> a/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/c_compat.cc > >>>> b/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/c_compat.cc > >>>> index bcdb969b0c0..2e4c73c456c 100644 > >>>> --- a/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/c_compat.cc > >>>> +++ b/libstdc++-v3/testsuite/29_atomics/headers/stdatomic.h/c_compat.cc > >>>> @@ -131,6 +131,10 @@ static_assert( requires (::atomic_int* i, int* e) { > >>>> ::atomic_fetch_or_explicit(i, 1, memory_order_relaxed); > >>>> ::atomic_fetch_xor(i, 1); > >>>> ::atomic_fetch_xor_explicit(i, 1, memory_order_relaxed); > >>>> + ::atomic_fetch_min(i, 1); > >>>> + ::atomic_fetch_min_explicit(i, 1, memory_order_relaxed); > >>>> + ::atomic_fetch_max(i, 1); > >>>> + ::atomic_fetch_max_explicit(i, 1, memory_order_relaxed); > >>>> } ); > >>>> > >>>> static_assert( requires (::atomic_flag* f) { > >>>> -- > >>>> 2.44.0 > >
