Do gube's original question and the fine answers above not point also to some optomization (a single instance in the symbol table of the two identical if...} clauses?

No^*. It all has to do with match positions not being reset until a match failed, if /g is in effect.

Without /g, those internal state variables are reset before each match; with /g, they are reset after a match failed.

*) which doesn't mean there isn't such optimization, merely that the behaviour gives no evidence about that.

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}