bug#24037: [PATCH] grep: always match single line only with DFA superset

[Norihiro Tanaka]

When grep matcher uses DFA, I assumed that it might match multiline with
DFA superset, but it is wrong.  \n cannot occur inside a multibyte
character.  So an input always matches single line only with DFA superset.

Now set ALLOW_NL to 0, and remove loop.  It speeds up 2x in special case.

$ yes "$(printf 'a\nb')" | head -100000000 >k

(before)
$ time -p src/grep '\(a\|x\).\(b\|x\)' k
real 1.39
user 1.05
sys 0.31

(after)
$ time -p src/grep '\(a\|x\).\(b\|x\)' k
real 0.58
user 0.49
sys 0.09

0001-grep-always-match-single-line-only-with-DFA-superset.patch
Description: Text document