[llvm] [Github][RFC] Add workflow to diff codegen on llvm-test-suite (PR #190010)

[Konrad Kleine via llvm-commits]

https://github.com/kwk commented:

I think I can only comment and not help out that much. I'm not familiar with the `utils/tdiff.py` script. But I think the overall approach looks good, although very complex and probably tedious to maintain.

Are there easy steps that you could print to repeat a build locally?

Maybe it makes sense to have one comment that shows the process of how the build is going? I have something like the following in mind:

1. Create comment (aka build log comment) as a reaction to the `/test-suite` comment (aka trigger comment) and say:

```html
<!-- {github trigger comment id} -->
Thank you @${event.comment.user.login} for using the <a href="todo:link-to-documentation-here"><code>/test-suite</code></a> command <a href="${event.comment.htmlurl}">here</a>!
<sub>This very comment will be used to continuously log build state changes for your request. We decided to do this in addition to using Github's Check Runs below so you can inspect previous check runs better.</sub>
```

2. If the PR is not mergeable you can append to the comment:

```html
Sorry, but this pull request is currently not mergeable.
```

3. You might also want to prevent retriggering `/test-suite` for the same git SHA to prevent attacks or duplicate works and then append to the build log comment:

```html
The same build request exists for this pull request's SHA (<ENTER SHA JERE>) <a href="<ENTER ACTIONS LOG URL>">here</a>.
```

I hope you get the idea. For starters I've added comment about adding reactions to the initial trigger comment.


https://github.com/llvm/llvm-project/pull/190010