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From: Jonathan Wakely <redi@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc r11-9926] libstdc++: Remove "no stronger" assertion in compare exchange [PR102177] Date: Thu, 21 Apr 2022 15:33:55 +0000 (GMT) [thread overview] Message-ID: <20220421153355.8C3B138485BC@sourceware.org> (raw) https://gcc.gnu.org/g:fef3d31bd35f53cbcacaec63b279d38c38b78abe commit r11-9926-gfef3d31bd35f53cbcacaec63b279d38c38b78abe Author: Jonathan Wakely <jwakely@redhat.com> Date: Thu Sep 2 15:29:22 2021 +0100 libstdc++: Remove "no stronger" assertion in compare exchange [PR102177] P0418R2 removed some preconditions from std::atomic::compare_exchange_* but we still enforce them via __glibcxx_assert. This removes those assertions. Signed-off-by: Jonathan Wakely <jwakely@redhat.com> libstdc++-v3/ChangeLog: PR c++/102177 * include/bits/atomic_base.h (__is_valid_cmpexch_failure_order): New function to check if a memory order is valid for the failure case of compare exchange operations. (__atomic_base<I>::compare_exchange_weak): Simplify assertions by using __is_valid_cmpexch_failure_order. (__atomic_base<I>::compare_exchange_strong): Likewise. (__atomic_base<P*>::compare_exchange_weak): Likewise. (__atomic_base<P*>::compare_exchange_strong): Likewise. (__atomic_impl::compare_exchange_weak): Add assertion. (__atomic_impl::compare_exchange_strong): Likewise. * include/std/atomic (atomic::compare_exchange_weak): Likewise. (atomic::compare_exchange_strong): Likewise. (cherry picked from commit dba1ab212292839572fda60df00965e094a11252) Diff: --- libstdc++-v3/include/bits/atomic_base.h | 61 +++++++++------------------------ libstdc++-v3/include/std/atomic | 8 +++++ 2 files changed, 25 insertions(+), 44 deletions(-) diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h index 60b976bf8d1..315f5a25e93 100644 --- a/libstdc++-v3/include/bits/atomic_base.h +++ b/libstdc++-v3/include/bits/atomic_base.h @@ -121,6 +121,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION | __memory_order_modifier(__m & __memory_order_modifier_mask)); } + constexpr bool + __is_valid_cmpexch_failure_order(memory_order __m) noexcept + { + return (__m & __memory_order_mask) != memory_order_release + && (__m & __memory_order_mask) != memory_order_acq_rel; + } + _GLIBCXX_ALWAYS_INLINE void atomic_thread_fence(memory_order __m) noexcept { __atomic_thread_fence(int(__m)); } @@ -511,13 +518,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_weak(__int_type& __i1, __int_type __i2, memory_order __m1, memory_order __m2) noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 1, int(__m1), int(__m2)); @@ -528,13 +529,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION memory_order __m1, memory_order __m2) volatile noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 1, int(__m1), int(__m2)); @@ -560,13 +555,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_strong(__int_type& __i1, __int_type __i2, memory_order __m1, memory_order __m2) noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 0, int(__m1), int(__m2)); @@ -577,14 +566,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION memory_order __m1, memory_order __m2) volatile noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_i, &__i1, __i2, 0, int(__m1), int(__m2)); @@ -869,13 +851,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION memory_order __m1, memory_order __m2) noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 0, int(__m1), int(__m2)); @@ -886,14 +862,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION memory_order __m1, memory_order __m2) volatile noexcept { - memory_order __b2 __attribute__ ((__unused__)) - = __m2 & __memory_order_mask; - memory_order __b1 __attribute__ ((__unused__)) - = __m1 & __memory_order_mask; - - __glibcxx_assert(__b2 != memory_order_release); - __glibcxx_assert(__b2 != memory_order_acq_rel); - __glibcxx_assert(__b2 <= __b1); + __glibcxx_assert(__is_valid_cmpexch_failure_order(__m2)); return __atomic_compare_exchange_n(&_M_p, &__p1, __p2, 0, int(__m1), int(__m2)); @@ -996,6 +965,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _Val<_Tp> __desired, memory_order __success, memory_order __failure) noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__failure)); + return __atomic_compare_exchange(__ptr, std::__addressof(__expected), std::__addressof(__desired), true, int(__success), int(__failure)); @@ -1007,6 +978,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION _Val<_Tp> __desired, memory_order __success, memory_order __failure) noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__failure)); + return __atomic_compare_exchange(__ptr, std::__addressof(__expected), std::__addressof(__desired), false, int(__success), int(__failure)); diff --git a/libstdc++-v3/include/std/atomic b/libstdc++-v3/include/std/atomic index fdffacc35df..e9d906f2485 100644 --- a/libstdc++-v3/include/std/atomic +++ b/libstdc++-v3/include/std/atomic @@ -320,6 +320,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_weak(_Tp& __e, _Tp __i, memory_order __s, memory_order __f) noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__f)); + return __atomic_compare_exchange(std::__addressof(_M_i), std::__addressof(__e), std::__addressof(__i), @@ -330,6 +332,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_weak(_Tp& __e, _Tp __i, memory_order __s, memory_order __f) volatile noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__f)); + return __atomic_compare_exchange(std::__addressof(_M_i), std::__addressof(__e), std::__addressof(__i), @@ -352,6 +356,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_strong(_Tp& __e, _Tp __i, memory_order __s, memory_order __f) noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__f)); + return __atomic_compare_exchange(std::__addressof(_M_i), std::__addressof(__e), std::__addressof(__i), @@ -362,6 +368,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION compare_exchange_strong(_Tp& __e, _Tp __i, memory_order __s, memory_order __f) volatile noexcept { + __glibcxx_assert(__is_valid_cmpexch_failure_order(__f)); + return __atomic_compare_exchange(std::__addressof(_M_i), std::__addressof(__e), std::__addressof(__i),
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