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libstdc++: Minor codegen improvement for atomic wait spinloop 

This patch merges the spin loops in the atomic wait implementation which is a
minor codegen improvement.

libstdc++-v3/ChangeLog:
	* include/bits/atomic_wait.h (__atomic_spin): Merge spin loops.
This commit is contained in:
Thomas Rodgers 2022-07-05 17:42:42 -07:00
parent db613e8fa8
commit e75da2ace6
1 changed files with 7 additions and 10 deletions
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17
libstdc++-v3/include/bits/atomic_wait.h
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@ -142,8 +142,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#endif
}
constexpr auto __atomic_spin_count_1 = 12;
constexpr auto __atomic_spin_count_2 = 4;
constexpr auto __atomic_spin_count_relax = 12;
constexpr auto __atomic_spin_count = 16;
struct __default_spin_policy
{
@ -157,18 +157,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool
__atomic_spin(_Pred& __pred, _Spin __spin = _Spin{ }) noexcept
{
for (auto __i = 0; __i < __atomic_spin_count_1; ++__i)
for (auto __i = 0; __i < __atomic_spin_count; ++__i)
{
if (__pred())
return true;
__detail::__thread_relax();
}
for (auto __i = 0; __i < __atomic_spin_count_2; ++__i)
{
if (__pred())
return true;
__detail::__thread_yield();
if (__i < __atomic_spin_count_relax)
__detail::__thread_relax();
else
__detail::__thread_yield();
}
while (__spin())