[llvm] [GlobalISel] Fall back for bf16 conversions. (PR #71470)

[David Green via llvm-commits]

davemgreen wrote:

Nice. I was thinking of adding this check for aarch64 at least, it makes sense to do it generically.

How do we think bf16 should be supported? As far as I understand the options would be
- to have it as part of the type information (bf16 as opposed to s16)
- to have it as a different operation (G_FADDBF16 as opposed to G_FADD)
- or to have it as an flag on the existing operations (G_FADD bf16 as opposed to G_FADD [ieee] maybe).

Maybe there are other options too? There are other (multiple) fp8 types being proposed currently. Any thought so far on what the best way to support them would be?

https://github.com/llvm/llvm-project/pull/71470