[llvm] [NVPTX] Improve lowering of v4i8 (PR #67866)

[Thomas Raoux via llvm-commits]

================
@@ -491,6 +497,10 @@ NVPTXTargetLowering::NVPTXTargetLowering(const NVPTXTargetMachine &TM,
   setOperationAction(ISD::INSERT_VECTOR_ELT, MVT::v2i16, Expand);
   setOperationAction(ISD::VECTOR_SHUFFLE, MVT::v2i16, Expand);
 
+  // TODO: we should eventually lower it as PRMT instruction.
+  setOperationAction(ISD::VECTOR_SHUFFLE, MVT::v4i8, Expand);
+  setOperationAction(ISD::BUILD_VECTOR, MVT::v4i8, Custom);
+
   // Operations not directly supported by NVPTX.
----------------
ThomasRaoux wrote:

It looks like we are missing some actions for v4i8 types like from line 639 to line 658.

```
  setI16x2OperationAction(ISD::ABS, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::SMIN, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::SMAX, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::UMIN, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::UMAX, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::CTPOP, MVT::v2i16, Legal, Expand);
  setI16x2OperationAction(ISD::CTLZ, MVT::v2i16, Legal, Expand);
  setI16x2OperationAction(ISD::ADD, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::SUB, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::MUL, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::SHL, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::SREM, MVT::v2i16, Legal, Custom);
  setI16x2OperationAction(ISD::UREM, MVT::v2i16, Legal, Custom);
  // Other arithmetic and logic ops are unsupported.
  setOperationAction({ISD::SDIV, ISD::UDIV, ISD::SRA, ISD::SRL, ISD::MULHS,
                      ISD::MULHU, ISD::FP_TO_SINT, ISD::FP_TO_UINT,
                      ISD::SINT_TO_FP, ISD::UINT_TO_FP},
                     MVT::v2i16, Expand);
```

https://github.com/llvm/llvm-project/pull/67866