From 31828a693f35c829fa52a44c9eeab8bc92ba7692 Mon Sep 17 00:00:00 2001
From: Batuhan Taskaya <isidentical@gmail.com>
Date: Mon, 10 Jan 2022 21:00:19 +0300
Subject: [PATCH] Add changelog / some nits

---
 CHANGES.md                  |  2 ++
 src/blib2to3/pgen2/parse.py | 13 +++++--------
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/CHANGES.md b/CHANGES.md
index d5cfb623c9a..52ac49f1438 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -17,6 +17,8 @@
 - Tuple unpacking on `return` and `yield` constructs now implies 3.8+ (#2700)
 - Unparenthesized tuples on annotated assignments (e.g
   `values: Tuple[int, ...] = 1, 2, 3`) now implies 3.8+ (#2708)
+- Speed-up the new backtracking parser about 4X in general (enabled when
+  `--target-version` is set to 3.10 and higher). (#2728)
 
 ## 21.12b0
 
diff --git a/src/blib2to3/pgen2/parse.py b/src/blib2to3/pgen2/parse.py
index e25f583d11c..8fe96672897 100644
--- a/src/blib2to3/pgen2/parse.py
+++ b/src/blib2to3/pgen2/parse.py
@@ -73,7 +73,7 @@ def ilabels(self) -> Set[int]:
 
     @contextmanager
     def switch_to(self, ilabel: int) -> Iterator[None]:
-        with self.patch():
+        with self.backtrack():
             self.parser.stack = self._points[ilabel]
             try:
                 yield
@@ -83,12 +83,11 @@ def switch_to(self, ilabel: int) -> Iterator[None]:
                 self.parser.stack = self._start_point
 
     @contextmanager
-    def patch(self) -> Iterator[None]:
+    def backtrack(self) -> Iterator[None]:
         """
-        Patch basic state operations (push/pop/shift) with node-level
-        immutable variants. These still will operate on the stack; but
-        they won't create any new nodes, or modify the contents of any
-        other existing nodes.
+        Use the node-level invariant ones for basic parsing operations (push/pop/shift).
+        These still will operate on the stack; but they won't create any new nodes, or
+        modify the contents of any other existing nodes.
 
         This saves us a ton of time when we are backtracking, since we
         want to restore to the initial state as quick as possible, which
@@ -349,8 +348,6 @@ def classify(self, type: int, value: Text, context: Context) -> List[int]:
             raise ParseError("bad token", type, value, context)
         return [ilabel]
 
-    STATE_OPERATIONS = ["shift", "push", "pop"]
-
     def shift(self, type: int, value: Text, newstate: int, context: Context) -> None:
         """Shift a token.  (Internal)"""
         if self.is_backtracking: