Use pg_memory_is_all_zeros() in pgstatfuncs.c.

There are a few places in this file that use memset() and memcmp()
to determine whether a section of memory is all zeros.  This commit
modifies them to use pg_memory_is_all_zeros() instead.  These
aren't expected to be hot code paths, but this may optimize them a
bit.  Plus, this allows us to remove some variables that were only
needed for the memset() and memcmp().

Author: Bertrand Drouvot
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/Z1hNubHfvMxlW6eu%40ip-10-97-1-34.eu-west-3.compute.internal

src/backend/utils/adt/pgstatfuncs.c

@@ -361,7 +361,6 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 		/* Values only available to role member or pg_read_all_stats */
 		if (HAS_PGSTAT_PERMISSIONS(beentry->st_userid))
 		{
-			SockAddr	zero_clientaddr;
 			char	   *clipped_activity;
 
 			switch (beentry->st_state)
@@ -483,9 +482,8 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 				nulls[11] = true;
 
 			/* A zeroed client addr means we don't know */
-			memset(&zero_clientaddr, 0, sizeof(zero_clientaddr));
-			if (memcmp(&(beentry->st_clientaddr), &zero_clientaddr,
-					   sizeof(zero_clientaddr)) == 0)
+			if (pg_memory_is_all_zeros(&beentry->st_clientaddr,
+									   sizeof(beentry->st_clientaddr)))
 			{
 				nulls[12] = true;
 				nulls[13] = true;
@@ -880,7 +878,6 @@ pg_stat_get_backend_client_addr(PG_FUNCTION_ARGS)
 {
 	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
-	SockAddr	zero_clientaddr;
 	char		remote_host[NI_MAXHOST];
 	int			ret;
 
@@ -891,9 +888,8 @@ pg_stat_get_backend_client_addr(PG_FUNCTION_ARGS)
 		PG_RETURN_NULL();
 
 	/* A zeroed client addr means we don't know */
-	memset(&zero_clientaddr, 0, sizeof(zero_clientaddr));
-	if (memcmp(&(beentry->st_clientaddr), &zero_clientaddr,
-			   sizeof(zero_clientaddr)) == 0)
+	if (pg_memory_is_all_zeros(&beentry->st_clientaddr,
+							   sizeof(beentry->st_clientaddr)))
 		PG_RETURN_NULL();
 
 	switch (beentry->st_clientaddr.addr.ss_family)
@@ -925,7 +921,6 @@ pg_stat_get_backend_client_port(PG_FUNCTION_ARGS)
 {
 	int32		procNumber = PG_GETARG_INT32(0);
 	PgBackendStatus *beentry;
-	SockAddr	zero_clientaddr;
 	char		remote_port[NI_MAXSERV];
 	int			ret;
 
@@ -936,9 +931,8 @@ pg_stat_get_backend_client_port(PG_FUNCTION_ARGS)
 		PG_RETURN_NULL();
 
 	/* A zeroed client addr means we don't know */
-	memset(&zero_clientaddr, 0, sizeof(zero_clientaddr));
-	if (memcmp(&(beentry->st_clientaddr), &zero_clientaddr,
-			   sizeof(zero_clientaddr)) == 0)
+	if (pg_memory_is_all_zeros(&beentry->st_clientaddr,
+							   sizeof(beentry->st_clientaddr)))
 		PG_RETURN_NULL();
 
 	switch (beentry->st_clientaddr.addr.ss_family)