[llvm] [AMDGPU] selecting v_sat_pk instruction, version 2 (PR #123297)

[Pierre van Houtryve via llvm-commits]

================
@@ -332,6 +332,9 @@ def AMDGPUumed3 : SDNode<"AMDGPUISD::UMED3", AMDGPUDTIntTernaryOp,
   []
 >;
 
+// Special node to handle v_sat_pk to avoid v2i8
----------------
Pierre-vh wrote:

```suggestion
// Special node to pack v2i8 into i16 for v_sat_pk lowering.
```

https://github.com/llvm/llvm-project/pull/123297