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

[Artem Belevich via llvm-commits]

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@@ -18753,7 +18753,9 @@ SDValue DAGCombiner::rebuildSetCC(SDValue N) {
       EVT SetCCVT = N.getValueType();
       if (LegalTypes)
         SetCCVT = getSetCCResultType(SetCCVT);
-      // Replace the uses of XOR with SETCC
+      // Replace the uses of XOR with SETCC. Note, avoid this transformation if
+      // it would introduce illegal operations post-legalization as this can
+      // result in an infinite loop.
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Artem-B wrote:

"result in an infite loop" could use more details. " converting it to xor->setcc here, and expanding setcc->xor if the back-end requested it."

Speaking of which. I assume the infinite loop affects only targets that have `Expand` set on the op. Can we narrow the condition from `!Legal` to `==Expand` ?


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