if (wsrep_debug) { } is required since it is otherwise in the error log a lot.
b) srv_conc_enter_innodb_without_atomics seems to be only place where trx->wsrep_event is used, srv_conc_enter_innodb_without_atomics is called only when ATOMIC_BUILTINS are not defined. Hence, it makes sense to wrap wsrep_srv_conc_cancel_wait and its calls inside #ifdef HAVE_ATOMIC_BUILTINS as well.
a) If this is redundant, then a
if (wsrep_debug) { } is required since it is otherwise in the error log a lot.
b) srv_conc_ enter_innodb_ without_ atomics seems to be only place where trx->wsrep_event is used, srv_conc_ enter_innodb_ without_ atomics is called only when ATOMIC_BUILTINS are not defined. Hence, it makes sense to wrap wsrep_srv_ conc_cancel_ wait and its calls inside #ifdef HAVE_ATOMIC_ BUILTINS as well.