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brandtbucher merged 4 commits into from
May 6, 2025
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GH-113464: Add the JIT to What's New #133486

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Add the JIT to What's New and update some related docs
brandtbucher May 6, 2025
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Add the JIT to What's New and update some related docs
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@brandtbucher
brandtbucher committed May 6, 2025
commit 6c8cf59a7a2efbb2de4faae1fd7c76f4699dc87b
25 changes: 17 additions & 8 deletions Doc/using/configure.rst
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Expand Up @@ -302,14 +302,23 @@ General Options

.. option:: --enable-experimental-jit=[no|yes|yes-off|interpreter]

Indicate how to integrate the :ref:`JIT compiler <whatsnew313-jit-compiler>`.

* ``no`` - build the interpreter without the JIT.
* ``yes`` - build the interpreter with the JIT.
* ``yes-off`` - build the interpreter with the JIT but disable it by default.
* ``interpreter`` - build the interpreter without the JIT, but with the tier 2 enabled interpreter.

By convention, ``--enable-experimental-jit`` is a shorthand for ``--enable-experimental-jit=yes``.
Indicate how to integrate the :ref:`experimental just-in-time compiler
<whatsnew314-jit-compiler>`.

* ``no``: Don't build the JIT.
* ``yes``: Enable the JIT. To disable it at runtime, set the environment
variable :envvar:`PYTHON_JIT=0 <PYTHON_JIT>`.
* ``yes-off``: Build the JIT, but disable it by default. To enable it at
runtime, set the environment variable :envvar:`PYTHON_JIT=1 <PYTHON_JIT>`.
* ``interpreter``: Enable the "JIT interpreter" (only useful for those
debugging the JIT itself). To disable the JIT at runtime, set the
environment variable :envvar:`PYTHON_JIT=0 <PYTHON_JIT>`.

By convention, ``--enable-experimental-jit`` is shorthand for
``--enable-experimental-jit=yes``. ``--enable-experimental-jit=no`` is the
default behavior if the option is not provided. See
:file:`Tools/jit/README.md` for more information, including how to install
the necessary build-time dependencies.

.. note::

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28 changes: 28 additions & 0 deletions Doc/whatsnew/3.14.rst
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Expand Up @@ -77,6 +77,7 @@ Summary -- release highlights
:ref:`argparse <whatsnew314-color-argparse>`,
:ref:`json <whatsnew314-color-json>` and
:ref:`calendar <whatsnew314-color-calendar>` CLIs
* :ref:`An experimental just-in-time compiler <whatsnew314-jit-compiler>`


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Expand Down Expand Up @@ -715,6 +716,33 @@ in the :envvar:`PYTHONSTARTUP` script.
(Contributed by 艁ukasz Langa in :gh:`131507`.)


.. _whatsnew314-jit-compiler:

An experimental just-in-time compiler
-------------------------------------
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Official macOS and Windows release binaries now include an *experimental* JIT
compiler. Although it is **not** recommended for production use, it can be
enabled by setting the :envvar:`PYTHON_JIT` environment variable. Downstream
source builds can be configured with :option:`--enable-experimental-jit=yes-off`
for similar behavior.

This is still early, foundational work; the performance impact of enabling the
JIT typically ranges from 10% slower to 20% faster, depending on workload. The
most significant missing functionality at this time is the inability for native
debuggers and profilers like ``gdb`` and ``perf`` to unwind through JIT frames
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(Python debuggers and profilers, like :mod:`pdb` or :mod:`profile`, work without
modification). Free-threaded builds do not support JIT compilation.

:func:`sys._jit.is_available` can be used to determine if your Python executable
supports JIT compilation. To tell if JIT compilation has been enabled for the
current process, use :func:`sys._jit.is_enabled`.

Please report any bugs or major performance regressions that you encounter!
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.. seealso:: :pep:`744`


Other language changes
======================

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6 changes: 3 additions & 3 deletions Tools/jit/README.md
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Expand Up @@ -54,13 +54,13 @@ choco install llvm --version=19.1.0

## Building

For `PCbuild`-based builds, pass the new `--experimental-jit` option to `build.bat`.
For `PCbuild`-based builds, pass the `--experimental-jit` option to `build.bat`.

For all other builds, pass the new `--enable-experimental-jit` option to `configure`.
For all other builds, pass the `--enable-experimental-jit` option to `configure`.

Otherwise, just configure and build as you normally would. Cross-compiling "just works", since the JIT is built for the host platform.

The JIT can also be enabled or disabled using the `PYTHON_JIT` environment variable, even on builds where it is enabled or disabled by default. More details about configuring CPython with the JIT and optional values for `--enable-experimental-jit` can be found [here](https://docs.python.org/dev/whatsnew/3.13.html#experimental-jit-compiler).
The JIT can also be enabled or disabled using the `PYTHON_JIT` environment variable, even on builds where it is enabled or disabled by default. More details about configuring CPython with the JIT and optional values for `--enable-experimental-jit` can be found [here](https://docs.python.org/dev/using/configure.html#cmdoption-enable-experimental-jit).

[^pep-744]: [PEP 744](https://peps.python.org/pep-0744/)

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