[llvm] [SelectionDAG] Handle more opcodes in canCreateUndefOrPoison (PR #84921)

[Nikita Popov via llvm-commits]

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@@ -5091,8 +5101,18 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
   case ISD::BITCAST:
   case ISD::BUILD_VECTOR:
   case ISD::BUILD_PAIR:
+  case ISD::SELECT:
     return false;
 
+  case ISD::SELECT_CC: {
+    // Integer select_cc cannot create undef or poison.
+    if (Op.getOperand(0).getValueType().isInteger())
+      return false;
+
+    // FIXME: Handle FP compares.
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nikic wrote:

Can this be combined with the following SETCC case, which has FP handling?

https://github.com/llvm/llvm-project/pull/84921