[llvm] [AMDGPU][GlobalISel] Select s16 G_MERGE_VALUES into wider scalars (PR #207999)

[Petar Avramovic via llvm-commits]

petar-avramovic wrote:

thanks! Looks like legalizer is doing some real terrible lowering with G_EXTRACT, then lowers that extract and combiner could not deal with it. I don't have the best idea at the moment how to fix the terrible legalizer output in this case.
Generated code look fine

https://github.com/llvm/llvm-project/pull/207999