GH-89987: Shrink the BINARY_SUBSCR caches (GH-103022)

1 files changed, 11 insertions, 0 deletions

diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 859ffb9..98cc51c 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -234,7 +234,18 @@ struct _typeobject {
  * It should should be treated as an opaque blob
  * by code other than the specializer and interpreter. */
 struct _specialization_cache {
+    // In order to avoid bloating the bytecode with lots of inline caches, the
+    // members of this structure have a somewhat unique contract. They are set
+    // by the specialization machinery, and are invalidated by PyType_Modified.
+    // The rules for using them are as follows:
+    // - If getitem is non-NULL, then it is the same Python function that
+    //   PyType_Lookup(cls, "__getitem__") would return.
+    // - If getitem is NULL, then getitem_version is meaningless.
+    // - If getitem->func_version == getitem_version, then getitem can be called
+    //   with two positional arguments and no keyword arguments, and has neither
+    //   *args nor **kwargs (as required by BINARY_SUBSCR_GETITEM):
     PyObject *getitem;
+    uint32_t getitem_version;
 };
 
 /* The *real* layout of a type object when allocated on the heap */