Stop aelemfast from crashing on GVs with null AVs
As reported at nntp://nntp.perl.org/
1298599236.4753.72.camel@p100 (and
respaced for readability):
#!perl5.12.0
$r=q/
print __FILE__;
local *dbline = $main::{"_<".__FILE__};
print $dbline[0]
/;
eval $r;'
__END__
(eval 1)
Bus error
This only seems to happen in non-threaded perls.
It can be reduced to this:
*d = *a; print $d[0];
The $d[0] is optimised into an aelemfast op (instead of the usual aelem
with an rv2av kid). pp_aelemfast is at fault, as evidenced by the fact
that this does not crash (the ${\...} prevents the optimisation):
*d = *a; print $d[${\0}];
pp_aelemfast uses GvAV instead of GvAVn. Usually $d[0] will autovivify
@d, but the glob assignment leaves $d[0] pointing to a glob (*d) with
no array. Then pp_alemfast passes a null pointer around.