So I use a $ENV{DEBUG_LEVEL} flag to turn on/off debugging in my project similar to this: 
#!/usr/bin/env perl
use constant DEBUG => $ENV{DEBUG_LEVEL};

sub debug {
    my $level = shift;
    return if ($level > DEBUG);
    print STDERR "($level/" . DEBUG . ") @_\n";
}


sub helpful {
    my $int = shift;
    debug(1, "called with: ", $int);
    ## do stuff here ...
    my $val = $int * $int;
    debug(3, "output: ", $val);
    print "$int becomes: $val \n";
}

for ( 1..5 ) {
  helpful( $_ );
}

[download]

After a while, the debug() statements become sprinkled all over the place. For me, it is helpful. But I am wondering if there is a cost to all these calls.

I tried testing this theory with:

DEBUG_LEVEL=3 perl -MO=Concise ./debug_onoff.pl

DEBUG_LEVEL=2 perl -MO=Concise ./debug_onoff.pl

DEBUG_LEVEL=0 perl -MO=Concise ./debug_onoff.pl

but the output is the same. See for related topic.

So the questions is:

  1. does the perl compiler optimize away the debug's when the ENV{DEBUG_LEVEL} is 0?
  2. is there a cost to leaving the debug()'s inline?
  3. should I remove them to improve performance overall?
  4. is there a better way to accomplish the goal of simple on/off for debugging one's code?

Thanks for your insight.

In reply to perl compiler optimizer curiosity by smile4me

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