--- a/mercurial/commands.py	Wed Sep 09 15:23:49 2020 +0900
+++ b/mercurial/commands.py	Wed Sep 09 15:56:40 2020 +0900
@@ -3398,9 +3398,11 @@
     if opts.get(b'print0'):
         sep = eol = b'\0'
 
-    getfile = util.lrucachefunc(repo.file)
-    matches = {}
-    copies = {}
+    searcher = grepmod.grepsearcher(ui, repo, regexp)
+
+    getfile = searcher._getfile
+    matches = searcher._matches
+    copies = searcher._copies
 
     def grepbody(fn, rev, body):
         matches[rev].setdefault(fn, [])
@@ -3520,12 +3522,12 @@
             fm.data(matched=False)
         fm.end()
 
-    skip = set()
-    revfiles = {}
+    skip = searcher._skip
+    revfiles = searcher._revfiles
     found = False
     follow = opts.get(b'follow')
 
-    getrenamed = scmutil.getrenamedfn(repo)
+    getrenamed = searcher._getrenamed
 
     def readfile(ctx, fn):
         rev = ctx.rev()

--- a/mercurial/grep.py	Wed Sep 09 15:23:49 2020 +0900
+++ b/mercurial/grep.py	Wed Sep 09 15:56:40 2020 +0900
@@ -9,7 +9,11 @@
 
 import difflib
 
-from . import pycompat
+from . import (
+    pycompat,
+    scmutil,
+    util,
+)
 
 
 def matchlines(body, regexp):
@@ -69,3 +73,20 @@
                 yield (b'-', a[i])
             for i in pycompat.xrange(blo, bhi):
                 yield (b'+', b[i])
+
+
+class grepsearcher(object):
+    """Search files and revisions for lines matching the given pattern"""
+
+    def __init__(self, ui, repo, regexp):
+        self._ui = ui
+        self._repo = repo
+        self._regexp = regexp
+
+        self._getfile = util.lrucachefunc(repo.file)
+        self._getrenamed = scmutil.getrenamedfn(repo)
+
+        self._matches = {}
+        self._copies = {}
+        self._skip = set()
+        self._revfiles = {}