From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 2267B3857828; Fri, 22 Oct 2021 03:31:06 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 2267B3857828 From: "crazylht at gmail dot com" To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/102566] [i386] GCC should emit LOCK BTS for simple bit-test-and-set operations with std::atomic Date: Fri, 22 Oct 2021 03:31:05 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: middle-end X-Bugzilla-Version: 12.0 X-Bugzilla-Keywords: missed-optimization X-Bugzilla-Severity: enhancement X-Bugzilla-Who: crazylht at gmail dot com X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 22 Oct 2021 03:31:06 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D102566 --- Comment #28 from Hongtao.liu --- Can be optimize int gomp_futex_wake =3D FUTEX_WAKE | FUTEX_PRIVATE_FLAG; int gomp_futex_wait =3D FUTEX_WAIT | FUTEX_PRIVATE_FLAG; void gomp_mutex_lock_slow (gomp_mutex_t *mutex, int oldval) { /* First loop spins a while. */ while (oldval =3D=3D 1) { if (do_spin (mutex, 1)) { /* Spin timeout, nothing changed. Set waiting flag. */ oldval =3D __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE); if (oldval =3D=3D 0) return; futex_wait (mutex, -1); break; } else { /* Something changed. If now unlocked, we're good to go. */ oldval =3D 0; if (__atomic_compare_exchange_n (mutex, &oldval, 1, false, MEMMODEL_ACQUIRE, MEMMODEL_RELAX= ED)) return; } } /* Second loop waits until mutex is unlocked. We always exit this loop with wait flag set, so next unlock will awaken a thread. */ while ((oldval =3D __atomic_exchange_n (mutex, -1, MEMMODEL_ACQUIRE))) do_wait (mutex, -1); } with _atomic_fetch_or/and/xor ?=