perf: return from is_subtype early (#19400)

sterliakov · web-flow · commit edd491f30aa6 · 2025-07-16T15:19:38.000+01:00
Our equality implementation is conservative: if two types compare equal,
we know for sure they do indeed refer to the same type, and any type is
subtype of itself. This saved 0.9% in my local benchmark run.
diff --git a/misc/perf_compare.py b/misc/perf_compare.py
@@ -1,3 +1,5 @@
+#! /usr/bin/env python
+
 """Compare performance of mypyc-compiled mypy between one or more commits/branches.
 
 Simple usage:
diff --git a/mypy/subtypes.py b/mypy/subtypes.py
@@ -145,6 +145,8 @@ def is_subtype(
     between the type arguments (e.g., A and B), taking the variance of the
     type var into account.
     """
+    if left == right:
+        return True
     if subtype_context is None:
         subtype_context = SubtypeContext(
             ignore_type_params=ignore_type_params,
@@ -206,6 +208,8 @@ def is_proper_subtype(
     (this is useful for runtime isinstance() checks). If keep_erased_types is True,
     do not consider ErasedType a subtype of all types (used by type inference against unions).
     """
+    if left == right:
+        return True
     if subtype_context is None:
         subtype_context = SubtypeContext(
             ignore_promotions=ignore_promotions,
diff --git a/mypy/types.py b/mypy/types.py
@@ -2272,6 +2272,8 @@ def __eq__(self, other: object) -> bool:
                 and self.name == other.name
                 and self.is_type_obj() == other.is_type_obj()
                 and self.is_ellipsis_args == other.is_ellipsis_args
+                and self.type_guard == other.type_guard
+                and self.type_is == other.type_is
                 and self.fallback == other.fallback
             )
         else:
diff --git a/test-data/unit/check-generics.test b/test-data/unit/check-generics.test
@@ -2929,8 +2929,8 @@ def mix(fs: List[Callable[[S], T]]) -> Callable[[S], List[T]]:
 def id(__x: U) -> U:
     ...
 fs = [id, id, id]
-reveal_type(mix(fs))  # N: Revealed type is "def [S] (S`11) -> builtins.list[S`11]"
-reveal_type(mix([id, id, id]))  # N: Revealed type is "def [S] (S`13) -> builtins.list[S`13]"
+reveal_type(mix(fs))  # N: Revealed type is "def [S] (S`7) -> builtins.list[S`7]"
+reveal_type(mix([id, id, id]))  # N: Revealed type is "def [S] (S`9) -> builtins.list[S`9]"
 [builtins fixtures/list.pyi]
 
 [case testInferenceAgainstGenericCurry]
diff --git a/test-data/unit/check-parameter-specification.test b/test-data/unit/check-parameter-specification.test
@@ -921,8 +921,8 @@ class A:
     def func(self, action: Callable[_P, _R], *args: _P.args, **kwargs: _P.kwargs) -> _R:
         ...
 
-reveal_type(A.func)  # N: Revealed type is "def [_P, _R] (self: __main__.A, action: def (*_P.args, **_P.kwargs) -> _R`6, *_P.args, **_P.kwargs) -> _R`6"
-reveal_type(A().func)  # N: Revealed type is "def [_P, _R] (action: def (*_P.args, **_P.kwargs) -> _R`10, *_P.args, **_P.kwargs) -> _R`10"
+reveal_type(A.func)  # N: Revealed type is "def [_P, _R] (self: __main__.A, action: def (*_P.args, **_P.kwargs) -> _R`4, *_P.args, **_P.kwargs) -> _R`4"
+reveal_type(A().func)  # N: Revealed type is "def [_P, _R] (action: def (*_P.args, **_P.kwargs) -> _R`8, *_P.args, **_P.kwargs) -> _R`8"
 
 def f(x: int) -> int:
     ...
@@ -953,8 +953,8 @@ class A:
     def func(self, action: Job[_P, None]) -> Job[_P, None]:
         ...
 
-reveal_type(A.func)  # N: Revealed type is "def [_P] (self: __main__.A, action: __main__.Job[_P`4, None]) -> __main__.Job[_P`4, None]"
-reveal_type(A().func)  # N: Revealed type is "def [_P] (action: __main__.Job[_P`6, None]) -> __main__.Job[_P`6, None]"
+reveal_type(A.func)  # N: Revealed type is "def [_P] (self: __main__.A, action: __main__.Job[_P`3, None]) -> __main__.Job[_P`3, None]"
+reveal_type(A().func)  # N: Revealed type is "def [_P] (action: __main__.Job[_P`5, None]) -> __main__.Job[_P`5, None]"
 reveal_type(A().func(Job(lambda x: x)))  # N: Revealed type is "__main__.Job[[x: Any], None]"
 
 def f(x: int, y: int) -> None: ...
