[llvm] Nvptx port LowerBITCAST to SelectionDAG (PR #120903)

[via llvm-commits]

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@@ -2619,7 +2595,7 @@ NVPTXTargetLowering::LowerOperation(SDValue Op, SelectionDAG &DAG) const {
   case ISD::BUILD_VECTOR:
     return LowerBUILD_VECTOR(Op, DAG);
   case ISD::BITCAST:
-    return LowerBITCAST(Op, DAG);
+    return SDValue();
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GrumpyPigSkin wrote:

Hi, I had a look at `DAGTypeLegalizer::ExpandRes_BITCAST` it is close to what I want but it emits the store/load.
I managed to get the code working for the NVPTX test case by removing the `setOperationAction`. Please will look at the newer code and see if the idea is on the right track? 

https://github.com/llvm/llvm-project/pull/120903