You code causes the regex to be recompiled each time round the inner loop. A slight rearrangement should improve things: 
foreach my $sub ( keys %SUBS ) {
    my $re = qr/[^a-zA-Z]$sub[^a-zA-Z]*\(/;
    foreach my $line ( @sub_code ) {
        if ( $line =~ $re ) { push( @subs, $key ) }
    }
}

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Dave.

In reply to Re: Slow Regex - How to Optimize by dave_the_m
in thread Slow Regex - How to Optimize by noslenj123

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