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[3.11] gh-95913: Edit, expand & format Bytecode sect in 3.11 WhatsNew (GH-98559) #98597

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Oct 24, 2022
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[3.11] gh-95913: Edit, expand & format Bytecode sect in 3.11 WhatsNew (GH-98559) #98597

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120 changes: 81 additions & 39 deletions Doc/whatsnew/3.11.rst
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Expand Up @@ -1481,58 +1481,100 @@ contributors are volunteers from the community.
CPython bytecode changes
========================

* The bytecode now contains inline cache entries, which take the form of
:opcode:`CACHE` instructions. Many opcodes expect to be followed by an exact
number of caches, and instruct the interpreter to skip over them at runtime.
Populated caches can look like arbitrary instructions, so great care should be
taken when reading or modifying raw, adaptive bytecode containing quickened
data.
The bytecode now contains inline cache entries,
which take the form of the newly-added :opcode:`CACHE` instructions.
Many opcodes expect to be followed by an exact number of caches,
and instruct the interpreter to skip over them at runtime.
Populated caches can look like arbitrary instructions,
so great care should be taken when reading or modifying
raw, adaptive bytecode containing quickened data.

* Replaced all numeric ``BINARY_*`` and ``INPLACE_*`` instructions with a single
:opcode:`BINARY_OP` implementation.

* Replaced the three call instructions: :opcode:`CALL_FUNCTION`,
:opcode:`CALL_FUNCTION_KW` and :opcode:`CALL_METHOD` with
:opcode:`PUSH_NULL`, :opcode:`PRECALL`, :opcode:`CALL`,
and :opcode:`KW_NAMES`.
This decouples the argument shifting for methods from the handling of
keyword arguments and allows better specialization of calls.
.. _whatsnew311-added-opcodes:

* Removed ``COPY_DICT_WITHOUT_KEYS`` and ``GEN_START``.
New opcodes
-----------

* :opcode:`ASYNC_GEN_WRAP`, :opcode:`RETURN_GENERATOR` and :opcode:`SEND`,
used in generators and co-routines.

* :opcode:`MATCH_CLASS` and :opcode:`MATCH_KEYS` no longer push an additional
boolean value indicating whether the match succeeded or failed. Instead, they
indicate failure with :const:`None` (where a tuple of extracted values would
otherwise be).
* :opcode:`COPY_FREE_VARS`,
which avoids needing special caller-side code for closures.

* Replace several stack manipulation instructions (``DUP_TOP``, ``DUP_TOP_TWO``,
``ROT_TWO``, ``ROT_THREE``, ``ROT_FOUR``, and ``ROT_N``) with new
:opcode:`COPY` and :opcode:`SWAP` instructions.
* :opcode:`JUMP_BACKWARD_NO_INTERRUPT`,
for use in certain loops where handling interrupts is undesirable.

* Replaced :opcode:`JUMP_IF_NOT_EXC_MATCH` by :opcode:`CHECK_EXC_MATCH` which
performs the check but does not jump.
* :opcode:`MAKE_CELL`, to create :ref:`cell-objects`.

* Replaced :opcode:`JUMP_IF_NOT_EG_MATCH` by :opcode:`CHECK_EG_MATCH` which
performs the check but does not jump.
* :opcode:`CHECK_EG_MATCH` and :opcode:`PREP_RERAISE_STAR`,
to handle the :ref:`new exception groups and except* <whatsnew311-pep654>`
added in :pep:`654`.

* Replaced :opcode:`JUMP_ABSOLUTE` by the relative :opcode:`JUMP_BACKWARD`.
* :opcode:`PUSH_EXC_INFO`, for use in exception handlers.

* Added :opcode:`JUMP_BACKWARD_NO_INTERRUPT`, which is used in certain loops where it
is undesirable to handle interrupts.
* :opcode:`RESUME`, a no-op,
for internal tracing, debugging and optimization checks.

* Replaced :opcode:`POP_JUMP_IF_TRUE` and :opcode:`POP_JUMP_IF_FALSE` by
the relative :opcode:`POP_JUMP_FORWARD_IF_TRUE`, :opcode:`POP_JUMP_BACKWARD_IF_TRUE`,
:opcode:`POP_JUMP_FORWARD_IF_FALSE` and :opcode:`POP_JUMP_BACKWARD_IF_FALSE`.

* Added :opcode:`POP_JUMP_FORWARD_IF_NOT_NONE`, :opcode:`POP_JUMP_BACKWARD_IF_NOT_NONE`,
:opcode:`POP_JUMP_FORWARD_IF_NONE` and :opcode:`POP_JUMP_BACKWARD_IF_NONE`
opcodes to speed up conditional jumps.
.. _whatsnew311-replaced-opcodes:

* :opcode:`JUMP_IF_TRUE_OR_POP` and :opcode:`JUMP_IF_FALSE_OR_POP` are now
relative rather than absolute.
Replaced opcodes
----------------

* :opcode:`RESUME` has been added. It is a no-op. Performs internal tracing,
debugging and optimization checks.
+------------------------------------+-----------------------------------+-----------------------------------------+
| Replaced Opcode(s) | New Opcode(s) | Notes |
+====================================+===================================+=========================================+
| | :opcode:`!BINARY_*` | :opcode:`BINARY_OP` | Replaced all numeric binary/in-place |
| | :opcode:`!INPLACE_*` | | opcodes with a single opcode |
+------------------------------------+-----------------------------------+-----------------------------------------+
| | :opcode:`!CALL_FUNCTION` | | :opcode:`CALL` | Decouples argument shifting for methods |
| | :opcode:`!CALL_FUNCTION_KW` | | :opcode:`KW_NAMES` | from handling of keyword arguments; |
| | :opcode:`!CALL_METHOD` | | :opcode:`PRECALL` | allows better specialization of calls |
| | | :opcode:`PUSH_NULL` | |
+------------------------------------+-----------------------------------+-----------------------------------------+
| | :opcode:`!DUP_TOP` | | :opcode:`COPY` | Stack manipulation instructions |
| | :opcode:`!DUP_TOP_TWO` | | :opcode:`SWAP` | |
| | :opcode:`!ROT_TWO` | | |
| | :opcode:`!ROT_THREE` | | |
| | :opcode:`!ROT_FOUR` | | |
| | :opcode:`!ROT_N` | | |
+------------------------------------+-----------------------------------+-----------------------------------------+
| | :opcode:`!JUMP_IF_NOT_EXC_MATCH` | | :opcode:`CHECK_EXC_MATCH` | Now performs check but doesn't jump |
+------------------------------------+-----------------------------------+-----------------------------------------+
| | :opcode:`!JUMP_ABSOLUTE` | | :opcode:`JUMP_BACKWARD` | See [#bytecode-jump]_; |
| | :opcode:`!POP_JUMP_IF_FALSE` | | :opcode:`POP_JUMP_BACKWARD_IF_* | ``TRUE``, ``FALSE``, |
| | :opcode:`!POP_JUMP_IF_TRUE` | <POP_JUMP_BACKWARD_IF_TRUE>` | ``NONE`` and ``NOT_NONE`` variants |
| | | :opcode:`POP_JUMP_FORWARD_IF_* | for each direction |
| | <POP_JUMP_FORWARD_IF_TRUE>` | |
+------------------------------------+-----------------------------------+-----------------------------------------+
| | :opcode:`!SETUP_WITH` | :opcode:`BEFORE_WITH` | :keyword:`with` block setup |
| | :opcode:`!SETUP_ASYNC_WITH` | | |
+------------------------------------+-----------------------------------+-----------------------------------------+

.. [#bytecode-jump] All jump opcodes are now relative, including the
existing :opcode:`JUMP_IF_TRUE_OR_POP` and :opcode:`JUMP_IF_FALSE_OR_POP`.
The argument is now an offset from the current instruction
rather than an absolute location.


.. _whatsnew311-changed-opcodes:
.. _whatsnew311-removed-opcodes:
.. _whatsnew311-changed-removed-opcodes:

Changed/removed opcodes
-----------------------

* Changed :opcode:`MATCH_CLASS` and :opcode:`MATCH_KEYS`
to no longer push an additional boolean value to indicate success/failure.
Instead, ``None`` is pushed on failure
in place of the tuple of extracted values.

* Changed opcodes that work with exceptions to reflect them
now being represented as one item on the stack instead of three
(see :gh:`89874`).

* Removed :opcode:`!COPY_DICT_WITHOUT_KEYS`, :opcode:`!GEN_START`,
:opcode:`!POP_BLOCK`, :opcode:`!SETUP_FINALLY` and :opcode:`!YIELD_FROM`.


.. _whatsnew311-deprecated:
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