The event PLUGIN_PASS_EXECUTION passes the pointer to the executed pass
(the same as current_pass) as
gcc_data to the callback. You can also
inspect cfun to find out about which function this pass is executed for.
Note that this event will only be invoked if the gate check (if
applicable, modified by PLUGIN_OVERRIDE_GATE) succeeds.
You can use other hooks, like
PLUGIN_EARLY_GIMPLE_PASSES_END to manipulate global state
in your plugin(s) in order to get context for the pass execution.