Add clang link to PATH.

[ysiraichi]

This PR install the clang and clang++ alternative links using update-alternatives. This is so we don't need to specify a the Clang version inside bazelrc in #8665. Therefore, instead of setting CC=/usr/lib/llvm-17/bin/clang, we can just set CC=clang.

[yaoshiang]

Can you document this in an existing or new guide in the contributing section so that users can discover support for clang? And also speak to the value of doing so? (faster compile / better debugging symbols / etc)?

[ysiraichi]

I wouldn't say that we support Clang, yet. Support for it is coming in #8665, alongside hermetic CUDA. The reason we are transitioning to Clang is because that's the only way to make hermetic CUDA work. There may be other benefits to which I'm not aware, though.

In summary, this PR is only making it possible to use clang from the generated docker images, without having to specify the version, e.g. clang-17.

That said, I agree it would be nice to say somewhere that we have to use Clang because of hermetic CUDA. I can do that after we land the hermetic CUDA PR.

[yaoshiang]

Sounds good. Would you mind filing an issue and making sure we do in fact document these flags in a future PR? I personally would have liked to use clang instead of GCc…

[bhavya01]

Will this change also build cuda plugin using clang. I recently ran into an issue that was caused by our gcc use openxla/xla#25801

[ysiraichi]

@bhavya01 Yes.

[ysiraichi]

@yaoshiang Could you stamp this PR?

[yaoshiang]

I'm not an expert on the PT/XLA and PT build systems, so I'll refrain from trying to be helpful, other than to say, let's just try to keep it as consistent with PT as possible, and to document all the controls a contributor gets.

[ysiraichi]

@yaoshiang Right. I requested your review because I believe your request for changes is blocking this PR to land.

dismissing

[yaoshiang]

@yaoshiang Right. I requested your review because I believe your request for changes is blocking this PR to land.

Yup, I dismissed my prior review so you should be clear - thanks.

[bhavya01]

@ysiraichi This PR broke our nightly builds

Can we revert, fix and then try to land this change again?

[ysiraichi]

This is odd. I can't reproduce that.
I'm starting from python:3.8-bullseye, and running:

$ ansible-playbook playbook.yaml -e "stage=build" -e "accelerator=cuda" -e "arch=amd64" -e "python_version=3.8" -e "cuda_version=12.3" --tags="bazel,configure_env,install_deps"

Everything runs as expected. Could you share the full log?