* [committed] libstdc++: Remove "no stronger" assertion in compare exchange [PR102177]
@ 2021-09-02 17:53 Jonathan Wakely
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From: Jonathan Wakely @ 2021-09-02 17:53 UTC (permalink / raw)
To: libstdc++, gcc-patches
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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.
Tested x86_64-linux. Committed to trunk. I think we should backport
this to gcc-11 too, as it was a C++17 change and these assertions fail
for valid (if questionable) C++17 programs.
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commit dba1ab212292839572fda60df00965e094a11252
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Thu Sep 2 15:29:22 2021
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.
diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 20cf1343c58..cbe1da6d125 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 9b1fb15ac41..b395c65d468 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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2021-09-02 17:53 [committed] libstdc++: Remove "no stronger" assertion in compare exchange [PR102177] Jonathan Wakely
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