How does execution of iRules work together with APM evaluation

As we know, HTTP_REQUEST event is triggered very early before APM evaluations happens. What if iRule associated with HTTP_REQUEST tries to pool or call "HTTP::Respond", how the entire processing flow will be affected. Normally the pooling step will occur after APM-allow. Since now the iRule tries pooling earlier, will APM evaluation be skipped and directly jumps to pooling step? I hope that someone could shed the light on it.

Thanks in advance!

when HTTP_REQUEST { switch -regexp -- [string tolower [HTTP::path]] {

"^/special-case$" { pool prod_linux_varnish return } } }