From f281d9dd1ed63825efa234df63d3f2ae6cc9022a Mon Sep 17 00:00:00 2001 From: Thomas Rodgers Date: Tue, 5 Jul 2022 17:42:42 -0700 Subject: [PATCH] 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. (cherry picked from commit e75da2ace6b6f634237259ef62cfb2d3d34adb10) --- 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 125b1cad8868..a6d55d3af8ae 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()) -- 2.47.2