simplify and optimize pthread_mutex_trylock

src/thread/pthread_mutex_trylock.c

@@ -2,24 +2,23 @@
 
 int pthread_mutex_trylock(pthread_mutex_t *m)
 {
-	pthread_t self;
-	if (m->_m_type != PTHREAD_MUTEX_NORMAL) {
-		self = pthread_self();
-		if (m->_m_type == PTHREAD_MUTEX_RECURSIVE
-		 && m->_m_owner == self->tid) {
-			if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
-			m->_m_count++;
-			return 0;
-		}
-	}
+	int tid;
+
+	if (m->_m_type == PTHREAD_MUTEX_NORMAL)
+		return -a_xchg(&m->_m_lock, 1) & EBUSY;
 
-	if (a_xchg(&m->_m_lock, 1))
-		if (m->_m_type == PTHREAD_MUTEX_ERRORCHECK
-		 && m->_m_owner == self->tid) return EDEADLK;
-		else return EBUSY;
-	if (m->_m_type != PTHREAD_MUTEX_NORMAL) {
-		m->_m_owner = self->tid;
-		m->_m_count = 1;
+	tid = pthread_self()->tid;
+
+	if (m->_m_owner == tid) {
+		if (m->_m_type != PTHREAD_MUTEX_RECURSIVE)
+			return EDEADLK;
+		if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
+		m->_m_count++;
+		return 0;
 	}
+
+	if (a_xchg(&m->_m_lock, 1)) return EBUSY;
+	m->_m_owner = tid;
+	m->_m_count = 1;
 	return 0;
 }