bug#34910: 27.0.50; Too much matching reentrancy

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Sat, 30 Mar 2019 14:05:50 +0100
> Cc: Eli Zaretskii <eliz@gnu.org>, dancol@dancol.org, 34910@debbugs.gnu.org
> 
> 30 mars 2019 kl. 13.55 skrev Stefan Monnier <monnier@IRO.UMontreal.CA>:
> > 
> > It was probably just an oversight, because whether we're searching
> > within strings or within buffers the same problems appear with \{N\}
> > repetitions (where the counter is stored directly inside the
> > regexp-byte-code) and with on-the-fly strength-reduction (where we
> > replace some byte-code with cheaper ones (where applicable) on the first
> > pass through the regexp).
> 
> Is the reentrancy just in preparation for future needs, or is it possible to 
> re-enter the regexp code right now?

I think the former, since reentrance could only happen if a Lisp
thread yields while inside a regexp function, which I think is not
possible, since we never call 'select' or any Lisp from there, do we?