[llvm] [SelectionDAG] Propagate poison in getNode with two operands if the input is poison. (PR #135387)

[Amy Kwan via llvm-commits]

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@@ -7601,16 +7604,20 @@ SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
     case ISD::SDIV:
     case ISD::UREM:
     case ISD::SREM:
-      return getUNDEF(VT);       // fold op(arg1, undef) -> undef
+      // fold op(arg1, undef) -> undef, // fold op(arg1, poison) -> poison.
+      return N2.getOpcode() == ISD::POISON ? getPOISON(VT) : getUNDEF(VT);
     case ISD::MUL:
     case ISD::AND:
     case ISD::SSUBSAT:
     case ISD::USUBSAT:
-      return getConstant(0, DL, VT);  // fold op(arg1, undef) -> 0
+      // fold op(arg1, undef) -> 0, fold op(arg1, poison) -> poison.
+      return N2.getOpcode() == ISD::POISON ? getPOISON(VT)
+                                           : getConstant(0, DL, VT);
     case ISD::OR:
     case ISD::SADDSAT:
     case ISD::UADDSAT:
-      return getAllOnesConstant(DL, VT);
+      return N2.getOpcode() == ISD::POISON ? getPOISON(VT)
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amy-kwan wrote:

Nit: maybe we can add a similar comment, like the other cases?

https://github.com/llvm/llvm-project/pull/135387