[gcc r13-1849] libstdc++: Minor codegen improvement for atomic wait spinloop
Thomas Rodgers
rodgertq@gcc.gnu.org
Tue Jul 26 22:26:13 GMT 2022
https://gcc.gnu.org/g:e75da2ace6b6f634237259ef62cfb2d3d34adb10
commit r13-1849-ge75da2ace6b6f634237259ef62cfb2d3d34adb10
Author: Thomas Rodgers <trodgers@redhat.com>
Date: Tue Jul 5 17:42:42 2022 -0700
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.
Diff:
---
libstdc++-v3/include/bits/atomic_wait.h | 17 +++++++----------
1 file changed, 7 insertions(+), 10 deletions(-)
diff --git a/libstdc++-v3/include/bits/atomic_wait.h b/libstdc++-v3/include/bits/atomic_wait.h
index 125b1cad886..a6d55d3af8a 100644
--- a/libstdc++-v3/include/bits/atomic_wait.h
+++ b/libstdc++-v3/include/bits/atomic_wait.h
@@ -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())
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