Re: [Perl/perl5] 502da7: make /p a no-op

Hi,

On Thu, Feb 12, 2026 at 06:00:35PM +0800, demerphq wrote:
> On my phone so forgive the double reply. The code i mean is something like
> this:
> 
> while (<>) {
>   while (/(.)/g) { $count++}
> }
> 
> Try that on a large file. If it appears to hang then /p should not be
> removed.

Thanks Yves for bringing up this issue.

I tried this (also reported on the GitHub ticket):

    $ time perl -E 'say $^V;while(<>){while(/(.)/g){$count++}}say$count' /tmp/big
    v5.36.0
    101876091
    
    real    0m16.232s
    user    0m16.208s
    sys     0m0.020s
    
    # this is the Perl built from https://github.com/Perl/perl5/pull/24191

    $ time ./perl -Ilib -E 'say $^V;while(<>){while(/(.)/g){$count++}}say$count' /tmp/big
    v5.43.8
    101876091
    
    real    0m48.173s
    user    0m48.110s
    sys     0m0.060s

So there's definitely a degradation.

> > Every time people proposed removing /p when I have  checked while /g it
> > has been broken.

I'm a little bit confused about the whole $& vs ${^MATCH} situation.
The docs keep saying there was horrible degradation before 5.20, but
that everything is fixed since 5.20 and COW. And still things don't
appear as simple.

Is there a difference between the punctuation variables ($`, $& and $')
and the long name versions (${^PREMATCH}, ${^MATCH} and ${^POSTMATCH})?
What is it? And what is the relation with PL_sawampersand, which has
apparently been disabled since 1a904fc88069e249a4bd0ef196a3f1a7f549e0fe
in 2012?

Should we open an issue to completely remove the code related to
PL_sawampersand?

I've tried these in the hope of understanding the relationship
between the puncation variables and the long name ones:

    # Using $& doesn't seem to make a difference

    $ time perl -E 'say $^V;while(<>){while(/(.)/g){$&;$count++}}say$count' /tmp/big
    v5.36.0
    101876091
    
    real    0m15.719s
    user    0m15.705s
    sys     0m0.013s
    
    # Using /p and ${^MATCH} doesn't seem to make a difference either

    $ time perl -E 'say $^V;while(<>){while(/(.)/gp){${^MATCH};$count++}}say$count' /tmp/big
    v5.36.0
    101876091
    
    real    0m15.739s
    user    0m15.723s
    sys     0m0.017s

(Both of those suck like the first example with my patch bleadperl,
of course.)

In my limited understanding, the change I made (removing a conditional
goto) was equivalent to having /p always enabled. That doesn't seem to
be the actual result.

I'm clearly out of my depth here.

I started looking at this, because I believe that for PPC0014 (English
name aliases) to be complete, we want the caret long name match variables
to be simple aliases to the punctuation ones. Which I think means /p
must be a true no-op.

-- 
 Philippe Bruhat (BooK)

 Garbage that is well-wrapped is still garbage.
                                    (Moral from Groo The Wanderer #64 (Epic))