[llvm] AMDGPU: Make v2f32 -> v2f16 legal when target supports v_cvt_pk_f16_f32 (PR #139956)

[Changpeng Fang via llvm-commits]

changpeng wrote:

> Then in what cases it refers to a destination type and in what cases it refers to the source operand type?

It is indeed very confusion. I was thinking it is hard to specify operand types (you may also have multiple operands).
I am not sure how does it work in details, but I am seeing:
   setOperationAction(ISD::STORE, MVT::v2f16, Promote);

https://github.com/llvm/llvm-project/pull/139956