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Fidget-Spinner merged 3 commits into from
Apr 10, 2026
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gh-139038: Credit more people for JIT in 3.15 #148359

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Credit more people for JIT in 3.15
Fidget-Spinner Apr 10, 2026
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Address review, use name
Fidget-Spinner Apr 10, 2026
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review round 2
Fidget-Spinner Apr 10, 2026
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19 changes: 11 additions & 8 deletions Doc/whatsnew/3.15.rst
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Expand Up @@ -1428,7 +1428,6 @@ end users running Python do not need LLVM installed. Instructions for
installing LLVM can be found in the `JIT compiler documentation
<https://github.com/python/cpython/blob/main/Tools/jit/README.md>`__
for all supported platforms.

(Contributed by Savannah Ostrowski in :gh:`140973`.)

.. rubric:: A new tracing frontend
Expand All @@ -1440,7 +1439,6 @@ code. For example, simple Python object creation is now understood by the
supported. This was made possible by an overhauled JIT tracing frontend
that records actual execution paths through code, rather than estimating
them as the previous implementation did.

(Contributed by Ken Jin in :gh:`139109`. Support for Windows added by
Mark Shannon in :gh:`141703`.)

Expand All @@ -1450,35 +1448,40 @@ A basic form of register allocation has been added to the JIT compiler's
optimizer. This allows the JIT compiler to avoid certain stack operations
altogether and instead operate on registers. This allows the JIT to produce
more efficient traces by avoiding reads and writes to memory.

(Contributed by Mark Shannon in :gh:`135379`.)

.. rubric:: More JIT optimizations

More `constant-propagation <https://en.wikipedia.org/wiki/Constant_folding>`__
is now performed. This means when the JIT compiler detects that certain user
code results in constants, the code can be simplified by the JIT.

(Contributed by Ken Jin and Savannah Ostrowski in :gh:`132732`.)

The JIT avoids :term:`reference count`\ s where possible. This generally
:term:`Reference count`\ s are avoided whenever it is safe to do so. This generally
reduces the cost of most operations in Python.

(Contributed by Ken Jin, Donghee Na, Zheao Li, Hai Zhu, Savannah Ostrowski,
Reiden Ong, Noam Cohen, Tomas Roun, PuQing, Cajetan Rodrigues, and Sacul in :gh:`134584`.)

The JIT optimizer now supports significantly more operations than in 3.14.
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@sharktide sharktide Apr 10, 2026

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Suggested change
The JIT optimizer now supports significantly more operations than in 3.14.
The JIT optimizer now supports significantly more operations than the JIT optimizer in 3.14

Small suggestion for clarity

(Contributed by Kumar Aditya, Ken Jin, and Sacul in :gh:`131798`.)

.. rubric:: Better machine code generation

The JIT compiler's machine code generator now produces better machine code
for x86-64 and AArch64 macOS and Linux targets. In general, users should
experience lower memory usage for generated machine code and more efficient
machine code versus the old JIT.

machine code versus 3.14.
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@sharktide sharktide Apr 10, 2026

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Suggested change
machine code versus 3.14.
machine code versus the machine code generated by the 3.14 JIT compiler.

Same here

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@Fidget-Spinner Fidget-Spinner Apr 10, 2026

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I think this is already implied. It would also be dishonest of us to compare to something else, so I hope people think the same.

(Contributed by Brandt Bucher in :gh:`136528` and :gh:`136528`.
Implementation for AArch64 contributed by Mark Shannon in :gh:`139855`.
Additional optimizations for AArch64 contributed by Mark Shannon and
Diego Russo in :gh:`140683` and :gh:`142305`.)

.. rubric:: Maintainability

The JIT optimizer's operations have been simplified.
This was made possible by a refactoring of JIT data structures.
(Contributed by Zhongtian Zheng in :gh:`148211` and Hai Zhu in :gh:`143421`.)


Removed
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