5.10.0 will feature assertions which can be active or inactive, which may do something of what you want. Also see the -P flag in perlrun.

If you are worried about overhead, you can do something like

# at the top
use constant DEBUG => $ENV{DEBUG};
...
# later
printDebug("some message") if DEBUG;
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Here the function call and if check are optimized away when not debugging, leaving only a very small statement stub.