[llvm] [AArch64] Initial compiler support for SVE unwind on Windows. (PR #138609)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> Those two crashes are the ones I've seen, yes, and are addressed by the hack.

Oh, right, the other issue is also silenced by the hack - sorry, I had missed that.

> The issue is that the projects detect SVE without debug info, then try to build with debug info?

In this case, I think they do apply the same debug info options both when detecting and building, the problem is that the issue with debug info doesn't show up on a trivial sized detection snippet. I did contribute a big enough snippet that did trigger when we don't support generating unwind info, https://aomedia.googlesource.com/aom/+/5ccdc66ab6eb8eb300eda854fab4ff250b2c2f92%5E%21/, but it doesn't trigger the issues with debug info.

> So... I have the following options here right now:
> 
> * Add a temporary disabled-by-default flag for SVE on Windows, so projects can't detect the SVE support.
> * Add some form of debug info hack: either intentionally add incorrect mappings, or somehow drop the bits of debug info that would depend on those mappings.
> 
> Longer-term, we're reaching out to Microsoft for more information here, but not sure how long that will take.

I can work around it in my test setups temporarily by not enabling codeview debug info for aarch64 windows, but by the time of the 21.x branch (which should be in 5-7 weeks roughly?) I think it would be good to apply either of those kinds of fixes - no strong opinion on which one.

https://github.com/llvm/llvm-project/pull/138609