[llvm] AMDGPU/GlobalISel: Legalize G_ANYEXT s16 to s64 (PR #205470)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

ok, so G_ANYEXT s16 to s64 really exists on true16.
And it needs to be expanded to reg-sequence/merge-values at some point, now I am not sure what is the best place for it. Probably best to do it as late as possible since combines like anyext compared to tracking through merge-values. 
Legalizer is fine but I see we deal with 16->s64 extends in regbanklegalize so probably best to not make exceptions? what do you think

https://github.com/llvm/llvm-project/pull/205470