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gh-138451: Support custom LLVM installation path #138452

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gh-138451: Support custom LLVM installation path #138452

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9af482d
Support custom LLVM installation path
xhochy Sep 3, 2025
0bd8352
📜🤖 Added by blurb_it.
blurb-it[bot] Sep 3, 2025
859bfbd
Use `LLVM_TOOLS_INSTALL_DIR` to search for LLVM tools
xhochy Sep 5, 2025
9492d92
Don't join on empty values.
xhochy Sep 7, 2025
788de07
Fix syntax error
xhochy Sep 7, 2025
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Build/2025-09-03-14-55-59.gh-issue-138451.-Qzh2S.rst
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@@ -0,0 +1 @@
Search for LLVM tools in ``LLVM_TOOLS_INSTALL_DIR`` during the build.
5 changes: 5 additions & 0 deletions Tools/jit/_llvm.py
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Expand Up @@ -69,6 +69,11 @@ async def _get_brew_llvm_prefix(*, echo: bool = False) -> str | None:

@_async_cache
async def _find_tool(tool: str, *, echo: bool = False) -> str | None:
# Explicitly defined LLVM installation location
if (llvm_tools_dir := os.getenv("LLVM_TOOLS_INSTALL_DIR")) is not None:
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Should we document this somewhere? If it gets a NEWS entry, then we probably have (or need) a list of environment variables that may need to be set when building.

I'd expect the list to be in the devguide, really, which is a different repo. But do we have one in the main repo?

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Also:

Suggested change
if (llvm_tools_dir := os.getenv("LLVM_TOOLS_INSTALL_DIR")) is not None:
if llvm_tools_dir := os.getenv("LLVM_TOOLS_INSTALL_DIR")):

We shouldn't join to an empty value either (since that's interchangeable with "not set"). And possibly we should make sure it's an absolute path as well, though that may not matter so much.

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Considering the JIT is still experimental, I don't think we should document this in the CPython docs. I agree that it should be in the devguide.

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As I did not know about the devguide before this review: Where should I add something? On first sight there was no section obvious to me.

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I assume it's somewhere on this page, but to be honest I didn't read the whole thing: https://github.com/python/devguide/blob/main/getting-started/setup-building.rst

Possibly we need a new section here anyway for building the JIT? @savannahostrowski @brandtbucher are there JIT-specific build docs somewhere to document a relevant environment variable?

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We have docs for building in https://github.com/python/cpython/blob/main/Tools/jit/README.md#building. We'd probably want to update this for now.

path = os.path.join(llvm_tools_dir, tool)
if await _check_tool_version(path, echo=echo):
return path
# Unversioned executables:
path = tool
if await _check_tool_version(path, echo=echo):
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