Speed up recursive type check (#14326)

Use a faster type query visitor and reuse visitor across calls.

This should speed up type checking slightly. My measurements show a
~0.5% improvement, but it may be below the noise floor.

misc/perf_compare.py

@@ -0,0 +1,101 @@
+"""Compare performance of mypyc-compiled mypy between two or more commits/branches.
+
+Simple usage:
+
+  python misc/perf_compare.py my-branch master
+
+What this does:
+
+ * Create a temp clone of the mypy repo for each target commit
+ * Checkout a target commit in each of the clones
+ * Compile mypyc in each of the clones in parallel
+ * Create another temp clone of the mypy repo as the code to self check
+ * Self check with each of the compiled mypys N times
+ * Report the average runtimes and relative performance
+"""
+
+from __future__ import annotations
+
+import argparse
+import glob
+import os
+import shutil
+import statistics
+import subprocess
+import sys
+import threading
+import time
+
+
+def build_mypy(target_dir: str) -> None:
+    env = os.environ.copy()
+    env["CC"] = "clang"
+    env["MYPYC_OPT_LEVEL"] = "2"
+    cmd = ["python3", "setup.py", "--use-mypyc", "build_ext", "--inplace"]
+    subprocess.run(cmd, env=env, check=True, cwd=target_dir)
+
+
+def clone(target_dir: str, commit: str | None) -> None:
+    repo_dir = os.getcwd()
+    if os.path.isdir(target_dir):
+        print(f"{target_dir} exists: deleting")
+        input()
+        shutil.rmtree(target_dir)
+    print(f"cloning mypy to {target_dir}")
+    subprocess.run(["git", "clone", repo_dir, target_dir], check=True)
+    if commit:
+        subprocess.run(["git", "checkout", commit], check=True, cwd=target_dir)
+
+
+def run_benchmark(compiled_dir: str, check_dir: str) -> float:
+    env = os.environ.copy()
+    env["PYTHONPATH"] = os.path.abspath(compiled_dir)
+    cmd = ["python3", "-m", "mypy", "--config-file", "mypy_self_check.ini"]
+    cmd += glob.glob("mypy/*.py", root_dir=check_dir)
+    cmd += glob.glob("mypy/*/*.py", root_dir=check_dir)
+    t0 = time.time()
+    subprocess.run(cmd, cwd=check_dir, env=env)
+    return time.time() - t0
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser()
+    parser.add_argument("commit", nargs="+")
+    args = parser.parse_args()
+    commits = args.commit
+    num_bench = 2
+
+    if not os.path.isdir(".git") or not os.path.isdir("mypyc"):
+        sys.exit("error: Run this the mypy repo root")
+
+    build_threads = []
+    target_dirs = []
+    for i, commit in enumerate(commits):
+        target_dir = f"mypy.{i}.tmpdir"
+        target_dirs.append(target_dir)
+        clone(target_dir, commit)
+        t = threading.Thread(target=lambda: build_mypy(target_dir))
+        t.start()
+        build_threads.append(t)
+
+    self_check_dir = "mypy.self.tmpdir"
+    clone(self_check_dir, None)
+
+    for t in build_threads:
+        t.join()
+
+    print(f"built mypy at {len(commits)} commits")
+
+    results: dict[str, list[float]] = {}
+    for i in range(num_bench):
+        for i, commit in enumerate(commits):
+            tt = run_benchmark(target_dirs[i], self_check_dir)
+            results.setdefault(commit, []).append(tt)
+
+    for commit in commits:
+        tt = statistics.mean(results[commit])
+        print(f"commit: {tt:.1f}s")
+
+
+if __name__ == "__main__":
+    main()