[llvm] [StackFrameLayoutAnalysis] Add basic Scalable stack slot output (PR #99883)

[Paul Kirth via llvm-commits]

ilovepi wrote:

> > I’ll see if I can find a way to sort out the offsets being incorrect.
> 
> Thanks folks. I'd be interested if there was a good way to handle this. Unfortunately we might need to invent something. The AArch64 stack frame can have scalable and fixed-width objects combined in its layout, where some parts are fp-based and others are sp. I don't know if there is a way at the moment to get the real offset and was wondering what the best way to add it might be.

Yeah, I think this will probably take some surgery to work out. I know the DWARF for RISC-V vector spills is pretty complicated, too, so I doubt it will be simple to fix. 

I’m probably going to have to rethink a few assumptions this pass made. I wonder if BOLT has some tricks for this kind of thing? Anyway, lots to think about. 

https://github.com/llvm/llvm-project/pull/99883