GH-120507: Lower the BEFORE_WITH and BEFORE_ASYNC_WITH instructions. (#120640)

* Remove BEFORE_WITH and BEFORE_ASYNC_WITH instructions.

* Add LOAD_SPECIAL instruction

* Reimplement `with` and `async with` statements using LOAD_SPECIAL

Author: markshannon

Doc/library/dis.rst

@@ -780,16 +780,6 @@ not have to be) the original ``STACK[-2]``.
    .. versionadded:: 3.12
 
 
-.. opcode:: BEFORE_ASYNC_WITH
-
-   Resolves ``__aenter__`` and ``__aexit__`` from ``STACK[-1]``.
-   Pushes ``__aexit__`` and result of ``__aenter__()`` to the stack::
-
-      STACK.extend((__aexit__, __aenter__())
-
-   .. versionadded:: 3.5
-
-
 
 **Miscellaneous opcodes**
 
@@ -944,18 +934,6 @@ iterations of the loop.
    Pushes :func:`!builtins.__build_class__` onto the stack.  It is later called
    to construct a class.
 
-
-.. opcode:: BEFORE_WITH
-
-   This opcode performs several operations before a with block starts.  First,
-   it loads :meth:`~object.__exit__` from the context manager and pushes it onto
-   the stack for later use by :opcode:`WITH_EXCEPT_START`.  Then,
-   :meth:`~object.__enter__` is called. Finally, the result of calling the
-   ``__enter__()`` method is pushed onto the stack.
-
-   .. versionadded:: 3.11
-
-
 .. opcode:: GET_LEN
 
    Perform ``STACK.append(len(STACK[-1]))``.
@@ -1812,6 +1790,17 @@ iterations of the loop.
    .. versionadded:: 3.12
 
 
+.. opcode:: LOAD_SPECIAL
+
+   Performs special method lookup on ``STACK[-1]``.
+   If ``type(STACK[-1]).__xxx__`` is a method, leave
+   ``type(STACK[-1]).__xxx__; STACK[-1]`` on the stack.
+   If ``type(STACK[-1]).__xxx__`` is not a method, leave
+   ``STACK[-1].__xxx__; NULL`` on the stack.
+
+   .. versionadded:: 3.14
+
+
 **Pseudo-instructions**
 
 These opcodes do not appear in Python bytecode. They are used by the compiler

Include/ceval.h

@@ -133,6 +133,13 @@ PyAPI_FUNC(void) PyEval_ReleaseThread(PyThreadState *tstate);
 #define FVS_MASK      0x4
 #define FVS_HAVE_SPEC 0x4
 
+/* Special methods used by LOAD_SPECIAL */
+#define SPECIAL___ENTER__   0
+#define SPECIAL___EXIT__    1
+#define SPECIAL___AENTER__  2
+#define SPECIAL___AEXIT__   3
+#define SPECIAL_MAX   3
+
 #ifndef Py_LIMITED_API
 #  define Py_CPYTHON_CEVAL_H
 #  include "cpython/ceval.h"

Include/internal/pycore_ceval.h

@@ -245,6 +245,13 @@ typedef PyObject *(*conversion_func)(PyObject *);
 PyAPI_DATA(const binaryfunc) _PyEval_BinaryOps[];
 PyAPI_DATA(const conversion_func) _PyEval_ConversionFuncs[];
 
+typedef struct _special_method {
+    PyObject *name;
+    const char *error;
+} _Py_SpecialMethod;
+
+PyAPI_DATA(const _Py_SpecialMethod) _Py_SpecialMethods[];
+
 PyAPI_FUNC(int) _PyEval_CheckExceptStarTypeValid(PyThreadState *tstate, PyObject* right);
 PyAPI_FUNC(int) _PyEval_CheckExceptTypeValid(PyThreadState *tstate, PyObject* right);
 PyAPI_FUNC(int) _PyEval_ExceptionGroupMatch(PyObject* exc_value, PyObject *match_type, PyObject **match, PyObject **rest);

Include/internal/pycore_object.h

@@ -709,6 +709,7 @@ extern int _PyObject_IsInstanceDictEmpty(PyObject *);
 
 // Export for 'math' shared extension
 PyAPI_FUNC(PyObject*) _PyObject_LookupSpecial(PyObject *, PyObject *);
+PyAPI_FUNC(PyObject*) _PyObject_LookupSpecialMethod(PyObject *self, PyObject *attr, PyObject **self_or_null);
 
 extern int _PyObject_IsAbstract(PyObject *);