filter-repo: cache file renaming and filtering

We repeatedly hit the same filenames over and over as we traverse
history, but our expressions for renaming or filtering within the
newname() function are based solely on the filename and thus will always
give the same answer.  So record any answer we get and just use it
whenever we hit the same filename again.

If the filtering expressions contain only a single short pathname, this
has no measurable effect, but for several paths (e.g. listing all
builtin/*.c files individually in git.git) it can add up to a few
percent of overall runtime.

Signed-off-by: Elijah Newren <newren@gmail.com>

git-filter-repo

@@ -2537,6 +2537,7 @@ class RepoFilter(object):
     # Other vars
     self._sanity_checks_handled = False
     self._orig_refs = None
+    self._newnames = {}
 
   def _run_sanity_checks(self):
     self._sanity_checks_handled = True
@@ -2630,8 +2631,7 @@ class RepoFilter(object):
       for regex,   replacement in args.replace_text['regexes']:
         blob.data = regex.sub(replacement, blob.data)
 
-  @staticmethod
-  def tweak_commit(args, commit):
+  def tweak_commit(self, args, commit):
     def filename_matches(path_expression, pathname):
       if path_expression == '':
         return True
@@ -2675,8 +2675,12 @@ class RepoFilter(object):
     # Filter the list of file changes
     new_file_changes = {}
     for change in commit.file_changes:
-      change.filename = newname(args.path_changes, change.filename,
-                                args.inclusive)
+      if change.filename in self._newnames:
+        change.filename = self._newnames[change.filename]
+      else:
+        change.filename = newname(args.path_changes, change.filename,
+                                  args.inclusive)
+        self._newnames[change.filename] = change.filename
       if not change.filename:
         continue # Filtering criteria excluded this file; move on to next one
       if change.filename in new_file_changes:
@@ -2852,7 +2856,7 @@ class RepoFilter(object):
         RepoFilter.tweak_blob(self._args, b)
         self._blob_callback and self._blob_callback(b)
       def actual_commit_callback(c):
-        RepoFilter.tweak_commit(self._args, c)
+        self.tweak_commit(self._args, c)
         self._commit_callback and self._commit_callback(c)
       def actual_tag_callback(t):
         RepoFilter.handle_tag(self._args, t, shortname = True)