bug#63225: Compiling regexp patterns (and REGEXP_CACHE_SIZE in search.c)

[Ihor Radchenko <yantar92@posteo.net>]

Mattias Engdegård <mattias.engdegard@gmail.com> writes:

>> Ideally, the compiler should do something similar to
>> what https://www.colm.net/open-source/ragel/ does.
>
> Yes, constructing a DFA would be more realistic when it's less in danger of being thrown away at any time.

I tried to look closer into regex-emacs.c and I note that the regexp
compiler basically generates a specialized bytecode to be executed by
regexp matcher later.

So, may the existing vector type be reused to store compiled regexp
pattern objects?

AFIU, pvec_type will need to have one more item and reader/printer will
need to be modified for a specialized print representation. The compiled
regexp itself will be stored as unibyte string, containing the
instructions.

This will also open a possibility to compile regexp patterns from Elisp,
if necessary.

-- 
Ihor Radchenko // yantar92,
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