[llvm] [NVPTX] Fix lowering of i1 SETCC (PR #115035)

[Justin Fargnoli via llvm-commits]

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@@ -11874,6 +11874,47 @@ bool TargetLowering::LegalizeSetCCCondCode(SelectionDAG &DAG, EVT VT,
       return true;
     }
 
+    // Special case: expand i1 comparisons using logical operations.
+    if (OpVT == MVT::i1) {
+      SDValue Ret;
+      switch (CCCode) {
+      default:
+        llvm_unreachable("Unknown integer setcc!");
+      case ISD::SETEQ: // X == Y  -->  ~(X ^ Y)
+        Ret = DAG.getNOT(dl, DAG.getNode(ISD::XOR, dl, MVT::i1, LHS, RHS),
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justinfargnoli wrote:

My question boils down to: will `xor` be legalized if it's generated for a target that doesn't support it? In other words, can `Expand` generate illegal code? 

My assumption was no, but based on your answer, I'm gathering that `Expand` can generate illegal code and rely on the legalizer to legalize it. Is that correct? 

https://github.com/llvm/llvm-project/pull/115035