Prevent lwlock dtrace probes from unnecessary work

If dtrace is compiled in but disabled, the lwlock dtrace probes still
evaluate their arguments.  Since PostgreSQL 13, T_NAME(lock) does
nontrivial work, so it should be avoided if not needed.  To fix, make
these calls conditional on the *_ENABLED() macro corresponding to each
probe.

Reviewed-by: Craig Ringer <craig.ringer@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/CAGRY4nwxKUS_RvXFW-ugrZBYxPFFM5kjwKT5O+0+Stuga5b4+Q@mail.gmail.com

src/backend/storage/lmgr/lwlock.c

@@ -1318,6 +1318,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 #endif
 
 		LWLockReportWaitStart(lock);
+		if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
 
 		for (;;)
@@ -1340,6 +1341,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 		}
 #endif
 
+		if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
 		LWLockReportWaitEnd();
 
@@ -1349,6 +1351,7 @@ LWLockAcquire(LWLock *lock, LWLockMode mode)
 		result = false;
 	}
 
+	if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_ENABLED())
 		TRACE_POSTGRESQL_LWLOCK_ACQUIRE(T_NAME(lock), mode);
 
 	/* Add lock to list of locks held by this backend */
@@ -1400,6 +1403,7 @@ LWLockConditionalAcquire(LWLock *lock, LWLockMode mode)
 		RESUME_INTERRUPTS();
 
 		LOG_LWDEBUG("LWLockConditionalAcquire", lock, "failed");
+		if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_FAIL(T_NAME(lock), mode);
 	}
 	else
@@ -1407,6 +1411,7 @@ LWLockConditionalAcquire(LWLock *lock, LWLockMode mode)
 		/* Add lock to list of locks held by this backend */
 		held_lwlocks[num_held_lwlocks].lock = lock;
 		held_lwlocks[num_held_lwlocks++].mode = mode;
+		if (TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_CONDACQUIRE(T_NAME(lock), mode);
 	}
 	return !mustwait;
@@ -1479,6 +1484,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 #endif
 
 			LWLockReportWaitStart(lock);
+			if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
 				TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), mode);
 
 			for (;;)
@@ -1497,6 +1503,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 				Assert(nwaiters < MAX_BACKENDS);
 			}
 #endif
+			if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
 				TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), mode);
 			LWLockReportWaitEnd();
 
@@ -1527,6 +1534,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 		/* Failed to get lock, so release interrupt holdoff */
 		RESUME_INTERRUPTS();
 		LOG_LWDEBUG("LWLockAcquireOrWait", lock, "failed");
+		if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_FAIL(T_NAME(lock), mode);
 	}
 	else
@@ -1535,6 +1543,7 @@ LWLockAcquireOrWait(LWLock *lock, LWLockMode mode)
 		/* Add lock to list of locks held by this backend */
 		held_lwlocks[num_held_lwlocks].lock = lock;
 		held_lwlocks[num_held_lwlocks++].mode = mode;
+		if (TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_ACQUIRE_OR_WAIT(T_NAME(lock), mode);
 	}
 
@@ -1695,6 +1704,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
 #endif
 
 		LWLockReportWaitStart(lock);
+		if (TRACE_POSTGRESQL_LWLOCK_WAIT_START_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_WAIT_START(T_NAME(lock), LW_EXCLUSIVE);
 
 		for (;;)
@@ -1714,6 +1724,7 @@ LWLockWaitForVar(LWLock *lock, uint64 *valptr, uint64 oldval, uint64 *newval)
 		}
 #endif
 
+		if (TRACE_POSTGRESQL_LWLOCK_WAIT_DONE_ENABLED())
 			TRACE_POSTGRESQL_LWLOCK_WAIT_DONE(T_NAME(lock), LW_EXCLUSIVE);
 		LWLockReportWaitEnd();
 
@@ -1840,6 +1851,7 @@ LWLockRelease(LWLock *lock)
 	/* nobody else can have that kind of lock */
 	Assert(!(oldstate & LW_VAL_EXCLUSIVE));
 
+	if (TRACE_POSTGRESQL_LWLOCK_RELEASE_ENABLED())
 		TRACE_POSTGRESQL_LWLOCK_RELEASE(T_NAME(lock));
 
 	/*