[llvm] [workflows] Build a container for running CI on github actions (PR #75286)

[Tom Stellard via llvm-commits]

tstellar wrote:

> Minor comments.
> 
> I'm assuming the plan is to migrate the key existing workflows to use the container image after this lands? We might also want to add a couple more dependencies or sub-containers (that use this one as their base image) for specific workflows as some of them (like the code formatting action) install packages through `apt-get` (or could).
> 

I thought about creating sub-containers, but I wasn't sure if all the extra complexity was actually worth it.  What's the advantage of having separate containers for different types of jobs?

> Installing python packages into a container would be nice as well for some of the jobs and would shave off a bit of setup time, but that's already mostly negated by the caching.
> 

I would like to install the python packages too, I wasn't sure the best way to implement this.  Should I copy all the requirements.txt files into the container directory and then add them to the container?

> For building LLVM/running tests, we'll probably need to make some changes to take more explicit control of the toolchain that we're using. For a build-once run many times container, I think a ThinLTO+PGO+BOLTed clang based toolchain would make a lot of sense, but that is irrelevant for this patch.

This is a good idea.  I've also thought about creating a container that has a pre-filled ccache cache to help speed up builds.



https://github.com/llvm/llvm-project/pull/75286