[llvm] [AMDGPU][True16][CodeGen] readfirstlane for vgpr16 copy to sgpr32 (PR #137848)

[Brox Chen via llvm-commits]

broxigarchen wrote:

There is a PR https://github.com/llvm/llvm-project/pull/118037 created before. Trim the patch and reopened here

https://github.com/llvm/llvm-project/pull/137848