bpo-31671: re: Convert RegexFlag to int before compile (GH-3862)

sre_compile does bit test (e.g. `flags & SRE_FLAG_IGNORECASE`) in loop. `IntFlag.__and__` and `IntFlag.__new__` made it slower. So this commit convert it to normal int before passing flags to `sre_compile()`.

Author: methane

Doc/whatsnew/3.7.rst

@@ -326,6 +326,11 @@ Optimizations
  expressions <re>`. Searching some patterns can now be up to 20 times faster.
  (Contributed by Serhiy Storchaka in :issue:`30285`.)
 
+* :func:`re.compile` now converts ``flags`` parameter to int object if
+ it is ``RegexFlag``. It is now as fast as Python 3.5, and faster than
+ Python 3.6 about 10% depending on the pattern.
+ (Contributed by INADA Naoki in :issue:`31671`.)
+
 * :meth:`selectors.EpollSelector.modify`, :meth:`selectors.PollSelector.modify`
  and :meth:`selectors.DevpollSelector.modify` may be around 10% faster under
  heavy loads. (Contributed by Giampaolo Rodola' in :issue:`30014`)

Lib/re.py

@@ -275,6 +275,8 @@ def escape(pattern):
 _MAXCACHE = 512
 def _compile(pattern, flags):
  # internal: compile pattern
+ if isinstance(flags, RegexFlag):
+ flags = flags.value
  try:
  return _cache[type(pattern), pattern, flags]
  except KeyError:
@@ -331,6 +333,8 @@ def _pickle(p):
 class Scanner:
  def __init__(self, lexicon, flags=0):
  from sre_constants import BRANCH, SUBPATTERN
+ if isinstance(flags, RegexFlag):
+ flags = flags.value
  self.lexicon = lexicon
  # combine phrases into a compound pattern
  p = []

Misc/NEWS.d/next/Library/2017-10-04-21-28-44.bpo-31671.E-zfc9.rst

@@ -0,0 +1,2 @@
+Now ``re.compile()`` converts passed RegexFlag to normal int object before
+compiling. bm_regex_compile benchmark shows 14% performance improvements.