Re: Very promising results with libpcre2

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> On Sat, Apr 1, 2017 at 12:48 AM, Junio C Hamano <gitster@pobox.com> wrote:
>>> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>>>
>>>> That enables the new JIT support in pcre v2:
>>>>
>>>>       s/iter    rx fixed   prx
>>>> rx      2.19    --  -33%  -44%
>>>> fixed   1.47   49%    --  -17%
>>>> prx     1.22   79%   20%    --
>>>
>>> The numbers with JIT does look "interesting".
>>>
>>> I couldn't quite tell if there are major incompatibilities in the
>>> regex language itself between two versions from their documentation,
>>> but assuming that there isn't (modulo bugfixes and enhancements) and
>>> assuming that we are going to use their standard matcher, it may be
>>> OK to just use the newer one without linking both.
>>
>> There's no incompatibilities in the regex language itself (modulo bugs
>> etc). So yeah, I'll prepare some patch to use v2.
>
> Just to make sure that we are on the same page.  While I do not see
> the need to link with both variants and allow users to choose
> between them at runtime, I do not know if the whole world is ready
> to drop pcre1 and use pcre2 (the latter of which has only been
> around for a bit over two years).
>
> So we'd probably want to do
>
>  (1) keep USE_LIBPCRE and enable v1 when set;
>  (2) add USE_LIBPCRE2 and enable v2 when set;
>  (3) make sure to error out when both are set.
>
> or something like that.  It is tempting to allow us to say
>
>     make USE_LIBPCRE=2
>
> but the existing builds are likely to be depending on "is it set to
> anything? then use PCRE1" behaviour, so we unfortunately cannot take
> that route.