I think B::Concise would tell you there was a regex involved, but not what it was.

Yes. You're actually searching for the match operator (not regexp construction), so it doesn't matter how the regexp was constructed, as long as the match operator is in static code.

>perl -MO=Concise -e "$re = eval 'qr/test3/'; '' =~ $re" | find "</>"
-e syntax OK
c  </> match() vKS
[download]

Keep in mind that '' =~ $re is short for '' =~ /$re/.