https://github.com/python/cpython/commit/2dea1cf7fd9b1f6a914e363ecb17a853f4b99b6b
commit: 2dea1cf7fd9b1f6a914e363ecb17a853f4b99b6b
branch: main
author: Guido van Rossum <gu...@python.org>
committer: gvanrossum <gvanros...@gmail.com>
date: 2024-02-01T08:54:44-08:00
summary:
Write about Tier 2 and JIT in "what's new 3.13" (#114826)
(This will soon be superseded by Ken Jin's much more detailed version.)
files:
M Doc/whatsnew/3.13.rst
diff --git a/Doc/whatsnew/3.13.rst b/Doc/whatsnew/3.13.rst
index 6b94a3771406fa..887c3009f88504 100644
--- a/Doc/whatsnew/3.13.rst
+++ b/Doc/whatsnew/3.13.rst
@@ -81,6 +81,13 @@ Important deprecations, removals or restrictions:
* Python 3.13 and later have two years of full support,
followed by three years of security fixes.
+Interpreter improvements:
+
+* A basic :ref:`JIT compiler <whatsnew313-jit-compiler>` was added.
+ It is currently disabled by default (though we may turn it on later).
+ Performance improvements are modest -- we expect to be improving this
+ over the next few releases.
+
New Features
============
@@ -477,6 +484,46 @@ Optimizations
FreeBSD and Solaris. See the ``subprocess`` section above for details.
(Contributed by Jakub Kulik in :gh:`113117`.)
+.. _whatsnew313-jit-compiler:
+
+Experimental JIT Compiler
+=========================
+
+When CPython is configured using the ``--enable-experimental-jit`` option,
+a just-in-time compiler is added which can speed up some Python programs.
+
+The internal architecture is roughly as follows.
+
+* We start with specialized *Tier 1 bytecode*.
+ See :ref:`What's new in 3.11 <whatsnew311-pep659>` for details.
+
+* When the Tier 1 bytecode gets hot enough, it gets translated
+ to a new, purely internal *Tier 2 IR*, a.k.a. micro-ops ("uops").
+
+* The Tier 2 IR uses the same stack-based VM as Tier 1, but the
+ instruction format is better suited to translation to machine code.
+
+* We have several optimization passes for Tier 2 IR, which are applied
+ before it is interpreted or translated to machine code.
+
+* There is a Tier 2 interpreter, but it is mostly intended for debugging
+ the earlier stages of the optimization pipeline. If the JIT is not
+ enabled, the Tier 2 interpreter can be invoked by passing Python the
+ ``-X uops`` option or by setting the ``PYTHON_UOPS`` environment
+ variable to ``1``.
+
+* When the ``--enable-experimental-jit`` option is used, the optimized
+ Tier 2 IR is translated to machine code, which is then executed.
+ This does not require additional runtime options.
+
+* The machine code translation process uses an architecture called
+ *copy-and-patch*. It has no runtime dependencies, but there is a new
+ build-time dependency on LLVM.
+
+(JIT by Brandt Bucher, inspired by a paper by Haoran Xu and Fredrik Kjolstad.
+Tier 2 IR by Mark Shannon and Guido van Rossum.
+Tier 2 optimizer by Ken Jin.)
+
Deprecated
==========
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