[llvm] [AMDGPU] fix SIPeepholeSDWA optimization for fp16 (PR #109395)

[Matt Arsenault via llvm-commits]

arsenm wrote:

> WORD0,WORD1,DWORD enum values here are 4,5,6

This is still unreadable. I have to figure out which operands are which indexes. What does this print as, in human readable form, out of the asm printer? 

https://github.com/llvm/llvm-project/pull/109395