[llvm] [AMDGPU] Add lit() asm operand modifier for SP3 compatibility. (PR #68839)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > abs(neg(x)) could be treated as abs(x).
> 
> So far I was under impression that these modifiers are supposed to designate corresponding encoding bits, just as our `id[:value]` instruction modifiers do, in which case the expectation would probably be to not allow combinations that are not supported by the target hardware.
> 
> Otherwise, if we see these more like generic expressions, then maybe using the good old minus sign would make more sense than `neg()`?

Fair point. I am happy for abs(neg(x)) to be an assembler error.

https://github.com/llvm/llvm-project/pull/68839