#summary Removing submatch information in some cases for speedup

= Introduction =

In a number of cases we only want to know if a
regexp matches, it doesn't matter what exactly it matches.  E.g. for
 this statement in a script:

       if text =~ pattern

In this case we should quit the regexp engine with a success result as
soon as a match is found.  That should be quite a speed improvement
compared to an engine that figures out exactly what is matched.

= How to get it done =

I plan to add two flags in addition to the second parameter of vim_regcomp().
namely,

{{{
#define RE_SUB0         8       /* need no submatch info */
#define RE_SUB1         16      /* need 1 submatch info */
}}}

then the caller can set it accordingly. This requires the caller explicitly
tell how many submatch will be used. If neither
is set then everything go as before.

= Scenarios =
A list of files showing where we could set submatch information for speedup.

==buffer.c== 
  * in buflist_findpat(),

  _before_:
{{{
  prog = vim_regcomp(p, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  prog = vim_regcomp(p, (p_magic ? RE_MAGIC : 0) + RE_SUB0);
}}}

  * in ExpandBufnames(),

  _before_:
{{{
  prog = vim_regcomp(patc + attempt * 11, RE_MAGIC);
}}}
{{{
  prog = vim_regcomp(patc + attempt * 11, RE_MAGIC + RE_SUB0);
}}}

==edit.c==
*ins_compl_files()* uses the submatch 0, the whole match string. Since it is the only
place where match takes place we can safely tell the two vim_regcomp()
calls in edit.c that we just want one submatch info.

  _before_:
{{{
  regmatch.regprog = vim_regcomp(ptr, RE_MAGIC);
  
  regmatch.regprog = vim_regcomp(pat, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(ptr, RE_MAGIC | RE_SUB1);
  
  regmatch.regprog = vim_regcomp(pat, (p_magic ? RE_MAGIC : 0) | RE_SUB1);
}}}

==eval.c==
  * in eval4(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(s2, RE_MAGIC + RE_STRING);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(s2,
                      RE_MAGIC + RE_STRING + RE_SUB0);
}}}

  * in find_some_match(), no change.

  * in f_split(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_STRING);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_STRING + RE_SUB1);
}}}

  * in ex_function(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(eap->arg + 1, RE_MAGIC);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(eap->arg + 1, RE_MAGIC + RE_SUB0);
}}}

  * in do_string_sub(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_STRING);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_STRING + RE_SUB1);
}}}

==ex_cmds.c==
  * in ex_sort(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(p + 1, RE_MAGIC + RE_SUB1);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(p + 1, RE_MAGIC + RE_SUB1);
}}}

==ex_cmds2.c==
  * in ex_breakadd(),

  _before_:
{{{ 
  bp->dbg_prog = vim_regcomp(pat, RE_MAGIC + RE_STRING);
}}}
  _after_:
{{{
  bp->dbg_prog = vim_regcomp(pat, RE_MAGIC + RE_STRING + RE_SUB0);
}}}

  * in do_arglist(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(p, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(p, (p_magic ? RE_MAGIC : 0)|RE_SUB0);
}}}

  * in ex_open(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(eap->arg, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(eap->arg, (p_magic ? RE_MAGIC : 0)|RE_SUB0);
}}}

  * in ex_match(),

*FIXME* No change here because I don't know where is the regexec().

==ex_getln.c==
  * in ExpandFromContext(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(pat, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(pat, (p_magic ? RE_MAGIC : 0)|RE_SUB0);
}}}

  * in del_history_entry(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(str, RE_MAGIC + RE_STRING)
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(str, RE_MAGIC + RE_STRING + RE_SUB0)
}}}

==fileio.c==
In match_file_pat(), no submatch info needed. So all three vim_regcomp() are added flag RE_SUB0.

==gui.c==
  * in gui_do_findrepl(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(ga.ga_data, RE_MAGIC + RE_STRING);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(ga.ga_data, RE_MAGIC + RE_STRING + RE_SUB1);
}}}

==misc1.c==
  * in get_number_indent(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(curbuf->b_p_flp, RE_MAGIC);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(curbuf->b_p_flp, RE_MAGIC + RE_SUB1);
}}}

  * in dos_expandpath(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_SUB0);
}}}

  * in unix_expandpath(),

  _before_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC);
}}}
  _after_:
{{{
  regmatch.regprog = vim_regcomp(pat, RE_MAGIC + RE_SUB0);
}}}

==option.c==

  * in check_clipboard_option(),

  _before_:
{{{
  new_exclude_prog = vim_regcomp(p, RE_MAGIC);
}}}
  _after_:
{{{
  new_exclude_prog = vim_regcomp(p, RE_MAGIC + RE_SUB0);
}}}

  * in compile_cap_prog(),

  _before_:
{{{
  buf->b_cap_prog = vim_regcomp(re, RE_MAGIC);
}}}
  _after_:
{{{
  buf->b_cap_prog = vim_regcomp(re, RE_MAGIC + RE_SUB0);
}}}

==tags.c==

  * in prepare_pats(),

  _before_:
{{{
  pats->regmatch.regprog = vim_regcomp(pats->pat, p_magic ? RE_MAGIC : 0);
}}}
  _after_:
{{{
  pats->regmatch.regprog = vim_regcomp(pats->pat, 
                                        (p_magic ? RE_MAGIC : 0) + RE_SUB1);
}}}