[perl #129916] CV symbol table optimization only works in main::

On Wed, 19 Oct 2016 14:20:42 GMT, mauke- wrote:
> 
> This is a bug report for perl from l.mai@web.de,
> generated with the help of perlbug 1.40 running under perl 5.24.0.
> 
> 
> -----------------------------------------------------------------
> [Please describe your issue here]
> 
> Here's the merge I'm talking about:
> http://perl5.git.perl.org/perl.git/commitdiff/f9d9e965
> 
> Also listed in perl5220delta:
> 
> Subroutines in packages no longer need to be stored in typeglobs:
> declaring a subroutine will now put a simple sub reference directly in
> the stash if possible, saving memory.
> 
> This works fine for the main script:
> 
> $ perl -wE 'sub foo { 42 } say $main::{foo}'
> CODE(0xa06f668)
> 
> But not in other packages:
> 
> $ perl -wE 'package Other; sub foo { 42 } say $Other::{foo}'
> *Other::foo
> 
> I.e. this optimization doesn't apply to modules, which is where most
> subroutines come from.
> 
> -----
> 
> Speculation follows.
> 
> I suspect this is due to the following code in op.c
> (Perl_newATTRSUB_x):
> 
> const I32 flags =
>    ec ? GV_NOADD_NOINIT
>       :   PL_curstash != CopSTASH(PL_curcop)
>        || memchr(name, ':', namlen) || memchr(name, '\'', namlen)
>             ? gv_fetch_flags
>             : GV_ADDMULTI | GV_NOINIT | GV_NOTQUAL;
> gv = gv_fetchsv(cSVOPo->op_sv, flags, SVt_PVCV);
> 
> 'ec' stands for "error count"; this is normally false (unless we're
> parsing past a syntax error).
> 
> The 'name' check is fine (name = "foo", namlen = 3); what's tripping
> us
> up is the stash check.
> 
> PL_curstash is \%X:: in this situation, but CopSTASH(PL_curcop) is
> \%main::. So the stashes differ and we land in the gv_fetch_flags
> path,
> which adds a full typeglob.
> 

Is this something where, for the short run, we would be best off simply noting the phenomenon in the documentation?  I.e., something along the lines of:

#####
Contrary to what was stated in pod/perl5220delta.pod, ...
#####

Thank you very much.

-- 
James E Keenan (jkeenan@cpan.org)

---
via perlbug:  queue: perl5 status: new
https://rt.perl.org/Ticket/Display.html?id=129916

• [perl #129916] CV symbol table optimization only works in main:: by James E Keenan via RT