Hi All,
I did a quick benchmark test on his code using non threaded 5.8.0 and 5.6.1 and indeed there is a serious performance degradation.

It is the combination of the i and the g regex modifiers that causes the performance issue. If you remove one of them the performance is the sames as in 5.6.1. I did't not dig deeper into this, but there must be an explanation for this.

ps: this is the code I used

#!/usr/local/bin/perl5.8.0 or #!/usr/local/bin/perl5.6.1

use Benchmark; 
$main::x=join("",(a..z))x100;
 
&timethis(100,\&test);
 
sub test {
   $main::x =~ s/(.*?)I/$1/isge;
   }
[download]

update On popular demand, here are the benchmark results.

Perl 5.8.0
timethis 1000: 48 wallclock secs (46.76 usr +  0.02 sys = 46.78 CPU) @
+ 21.38/s (n=1000) 

Perl 5.6.1
timethis 1000:  1 wallclock secs ( 0.70 usr +  0.00 sys =  0.70 CPU) @
+ 1428.57/s (n=1000)
[download]

When debugging with use re "debug", there are some differences (I only post the last few lines) In 5.8.0, it gives

  Setting an EVAL scope, savestack=12
  24 <opqrstuvwx> <yz>    |  1:  OPEN1
  24 <opqrstuvwx> <yz>    |  3:  MINMOD
  24 <opqrstuvwx> <yz>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
  Setting an EVAL scope, savestack=12
  25 <opqrstuvwxy> <z>    |  1:  OPEN1
  25 <opqrstuvwxy> <z>    |  3:  MINMOD
  25 <opqrstuvwxy> <z>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
  Setting an EVAL scope, savestack=12
  26 <opqrstuvwxyz> <>    |  1:  OPEN1
  26 <opqrstuvwxyz> <>    |  3:  MINMOD
  26 <opqrstuvwxyz> <>    |  4:  STAR
  Setting an EVAL scope, savestack=12
                            failed...
Match failed
[download]

whilst in 5.6.1, it returns

                           SANY can match 1 times out of 1...
  23 <opqrstuvw> <xyz>    |  6:    CLOSE1
  23 <opqrstuvw> <xyz>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  24 <opqrstuvwx> <yz>    |  6:    CLOSE1
  24 <opqrstuvwx> <yz>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  25 <opqrstuvwxy> <z>    |  6:    CLOSE1
  25 <opqrstuvwxy> <z>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 1 times out of 1...
  26 <opqrstuvwxyz> <>    |  6:    CLOSE1
  26 <opqrstuvwxyz> <>    |  8:    EXACTF <I>
                              failed...
                           SANY can match 0 times out of 1...
                            failed...
Match failed
[download]

But, since I am not a regex expert, I have no clue what this means :-)
---------------------------
Dr. Mark Ceulemans
Senior Consultant
BMC, Belgium