gh-138497: Support LLVM_VERSION configuration via env by danigm · Pull Request #138498 · python/cpython · GitHub

This patch makes possible to override the llvm version used during build using "LLVM_VERSION" and "EXTERNALS_LLVM_TAG" environment variables.

This is useful to test the build with other LLVM versions without changing the sources, for example to build with llvm-20.

Related issue: #136895

Issue: Make LLVM_VERSION configurable with env variable #138497

If we do this:

We should do it in a manner similar to CFLAGS_JIT, where the env var is captured by the configure script and passed via the command-line to the build script.
EXTERNALS_LLVM_TAG should be left alone, I don't think it makes sense for anyone to override that (it's only used for Windows builds and it's literally a tag in a repo we control).

If we do this:

* We should do it in a manner similar to `CFLAGS_JIT`, where the env var is captured by the `configure` script and passed via the command-line to the build script.

* `EXTERNALS_LLVM_TAG` should be left alone, I don't think it makes sense for anyone to override that (it's only used for Windows builds and it's literally a tag in a repo we control).

I've done that way. Get the env variable in configure and pass to Tools/jit/build.py script as a new argument --llvm-version.

@savannahostrowski, thoughts on this change?

Thanks for this! I think this change is fair, so long as we only advertise that a single LLVM version is officially supported.

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Thanks for making the updates - I have a couple of other small wording suggestions but I think otherwise this looks good.

Would you also mind updating the Tools/jit/README.md to reflect this change? Right now, the README says that LLVM 19 is required. With this change, we should call out that LLVM 19 is the officially supported version, but that you can modify it if need be, using the env var.

…YXh.rst Rewording news entry Co-authored-by: Savannah Bailey <savannahostrowski@gmail.com>

Co-authored-by: Savannah Ostrowski <savannah@python.org>

@savannahostrowski conflict solved, I've rebased on top of main.

@danigm Please avoid rebasing and force pushing, it can result in lots of unrelated codeowners being summoned for a review.

It also makes it harder to review, and everything is squash merged anyway.

danigm requested review from brandtbucher, diegorusso and savannahostrowski as code owners September 4, 2025 10:23

bedevere-app Bot added the awaiting review label Sep 4, 2025

bedevere-app Bot mentioned this pull request Sep 4, 2025

Make LLVM_VERSION configurable with env variable #138497

Closed

danigm requested review from AA-Turner, corona10, emmatyping and erlend-aasland as code owners September 9, 2025 07:13

danigm force-pushed the llvm-version branch from e3a6760 to 8560996 Compare September 9, 2025 07:21

danigm force-pushed the llvm-version branch 2 times, most recently from b5b9649 to 4189a3e Compare September 9, 2025 08:03

emmatyping removed their request for review September 11, 2025 23:57

savannahostrowski requested changes Sep 15, 2025

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Comment thread Misc/NEWS.d/next/Build/2025-09-04-12-16-31.gh-issue-138497.Y_5YXh.rst Outdated

bedevere-app Bot added awaiting changes and removed awaiting review labels Sep 15, 2025

emmatyping reviewed Sep 16, 2025

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Comment thread Tools/jit/_llvm.py Outdated

bedevere-app Bot added awaiting change review and removed awaiting changes labels Sep 16, 2025

bedevere-app Bot requested a review from savannahostrowski September 16, 2025 05:45

savannahostrowski reviewed Sep 17, 2025

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Comment thread Misc/NEWS.d/next/Build/2025-09-04-12-16-31.gh-issue-138497.Y_5YXh.rst Outdated

Comment thread Tools/jit/build.py

Comment thread Tools/jit/_targets.py Outdated

danigm force-pushed the llvm-version branch from eb2a37a to 18f96e9 Compare September 17, 2025 11:08

danigm and others added 8 commits October 7, 2025 08:16

Reword news line with more information about LLVM

42d1d12

Set _LLVM_VERSION as default value for Target.llvm_version

4ce99f3

Do not set target.llvm_version on empty string

2a82537

Add warning when building with custom LLVM_VERSION

6528dae

Update Misc/NEWS.d/next/Build/2025-09-04-12-16-31.gh-issue-138497.Y_5…

c45361d

…YXh.rst Rewording news entry Co-authored-by: Savannah Bailey <savannahostrowski@gmail.com>

Move LLVM version warning to experimental banner

10175c7

Add LLVM_VERSION env info to Tools/jit/README.md

a60b02d

Fix warning synxtax in Tools/jit/_targets.py

8cea949

Co-authored-by: Savannah Ostrowski <savannah@python.org>

danigm force-pushed the llvm-version branch from de0d94d to 8cea949 Compare October 7, 2025 06:16

hugovk removed request for AA-Turner, AlexWaygood, FFY00, JelleZijlstra, abalkin, corona10, ericvsmith, erlend-aasland, gpshead, jaraco, lysnikolaou, pganssle, picnixz, rhettinger, vsajip and warsaw October 7, 2025 06:38

savannahostrowski mentioned this pull request Oct 26, 2025

gh-138451: Support custom LLVM installation path #138452

Merged

zanieb mentioned this pull request Jan 19, 2026

Upstream patch patch-jit-llvm-version-3.15.patch astral-sh/python-build-standalone#881

Closed

savannahostrowski mentioned this pull request Mar 11, 2026

Allow Clang-19+ for JIT (currently hard requires clang-19) #145800

Closed

gh-138497: Support LLVM_VERSION configuration via env by danigm · Pull Request #138498 · python/cpython · GitHub

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gh-138497: Support LLVM_VERSION configuration via env - #138498

gh-138497: Support LLVM_VERSION configuration via env#138498savannahostrowski merged 10 commits intopython:mainpython/cpython:mainfrom openSUSE-Python:llvm-versionopenSUSE-Python/cpython:llvm-versionCopy head branch name to clipboard

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gh-138497: Support LLVM_VERSION configuration via env#138498
savannahostrowski merged 10 commits into
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openSUSE-Python:llvm-version

danigm commented Sep 4, 2025 •
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