From: H.J. Lu <hjl.tools@gmail.com>
Date: Fri, 12 Nov 2021 19:47:42 +0000 (-0800)
Subject: Move assignment out of the CAS condition
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=60b8295333a076ff853c1093c502c7bf5197ab2e;p=thirdparty%2Fglibc.git

Move assignment out of the CAS condition

Update

commit 49302b8fdf9103b6fc0a398678668a22fa19574c
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:54:01 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_clocklock_common [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

and

commit 0b82747dc48d5bf0871bdc6da8cb6eec1256355f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Nov 11 06:31:51 2021 -0800

    Avoid extra load with CAS in __pthread_mutex_lock_full [BZ #28537]

    Replace boolean CAS with value CAS to avoid the extra load.

by moving assignment out of the CAS condition.

(cherry picked from commit 120ac6d238825452e8024e2f627da33b2508dfd3)
---

diff --git a/nptl/pthread_mutex_lock.c b/nptl/pthread_mutex_lock.c
index ac8a472c08d..2895926953e 100644
--- a/nptl/pthread_mutex_lock.c
+++ b/nptl/pthread_mutex_lock.c
@@ -296,10 +296,9 @@ __pthread_mutex_lock_full (pthread_mutex_t *mutex)
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;
diff --git a/nptl/pthread_mutex_timedlock.c b/nptl/pthread_mutex_timedlock.c
index 541ec189384..22174f74c9b 100644
--- a/nptl/pthread_mutex_timedlock.c
+++ b/nptl/pthread_mutex_timedlock.c
@@ -247,10 +247,9 @@ __pthread_mutex_clocklock_common (pthread_mutex_t *mutex,
 	     meantime.  */
 	  if ((oldval & FUTEX_WAITERS) == 0)
 	    {
-	      int val;
-	      if ((val = atomic_compare_and_exchange_val_acq
-		   (&mutex->__data.__lock, oldval | FUTEX_WAITERS,
-		    oldval)) != oldval)
+	      int val = atomic_compare_and_exchange_val_acq
+		(&mutex->__data.__lock, oldval | FUTEX_WAITERS, oldval);
+	      if (val != oldval)
 		{
 		  oldval = val;
 		  continue;