[llvm] [Github] Skip .ll files with autogenerated MIR checks in undef deprecator (PR #206106)

[Frederik Harwath via llvm-commits]

frederik-h wrote:

> This PR makes the script skip too much, IMO.

The criterion is not very precise. Perhaps, instead of skipping the checks on files containing the autogen note, we could exclude comments/check lines from such files and only check the input IR? 

That said, the change from the PR skips only a small fraction of all .ll files as it is.
As expected, the matching files are almost all in `llvm/test/CodeGen`:
```
llvm-project/llvm/test $ find -iname "*.ll"  |& xargs grep -l  ".*gen.*update_mir" |& wc -l
479

llvm-project/llvm/test $ find CodeGen -iname "*.ll"  |& xargs grep -l  ".*gen.*update_mir" |& wc -l
475
```
The 4 exceptions are tests in `DebugInfo`.

Note that this is already quite a tiny fraction of all CodeGen tests that use LLVM IR:
```
llvm-project/llvm/test $ find CodeGen/ -iname "*.ll"  |& wc -l
26052
```

None of the matching tests seem to mix opt and llc `RUN:` lines.

> The warning is just a warning and can be ignored by reviewers if it's a false positive.

It causes CI runs to fail which is very distracting. Reviewers might consider the PR not to be ready for review and you would have to eventually merge the PR without a successful CI run if you do not add a workaround to your PR branch which would later need to be reverted - or did I simply miss an easy way to disable this check for CI runs?

https://github.com/llvm/llvm-project/pull/206106