>perl -Mre=debug -e"/$_/ for qw( foo bar bar foo )" 2>&1 | find "Compiling"
Compiling REx `foo'
Compiling REx `bar'
Compiling REx `foo'

>perl -Mre=debug -e"qr/$_/ for qw( foo bar bar foo )" 2>&1 | find "Compiling"
Compiling REx `foo'
Compiling REx `bar'
Compiling REx `foo'