Even if it didn't turn that into a no-op, it won't make a whole lot of difference. A shift operation, even with loading and saving a variable from memory and then even with stack frame related overhead, will take maybe two dozen clock cycles on a bad day (cache misses et al) on modern CPUs. In comparison, even the simplest single operation in Perl will probably take a few hundred cycles (if not thousands).

If reports are to be believed though, Perl6 will be much faster at this, and native Parrot code should be on a par with C.

Makeshifts last the longest.