[AArch64] canCreateUndefOrPoisonForTargetNode - AArch64ISD::MOVI opcodes can't create undef/poison

Possible fix for failed fold in llvm#148191

Author: RKSimon

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -30398,6 +30398,23 @@ bool AArch64TargetLowering::SimplifyDemandedBitsForTargetNode(
       Op, OriginalDemandedBits, OriginalDemandedElts, Known, TLO, Depth);
 }
 
+bool AArch64TargetLowering::canCreateUndefOrPoisonForTargetNode(
+    SDValue Op, const APInt &DemandedElts, const SelectionDAG &DAG,
+    bool PoisonOnly, bool ConsiderFlags, unsigned Depth) const {
+
+  // TODO: Add more target nodes.
+  switch (Op.getOpcode()) {
+  case AArch64ISD::MOVI:
+  case AArch64ISD::MOVIedit:
+  case AArch64ISD::MOVImsl:
+  case AArch64ISD::MOVIshift:
+  case AArch64ISD::MVNIshift:
+    return false;
+  }
+  return TargetLowering::canCreateUndefOrPoisonForTargetNode(
+      Op, DemandedElts, DAG, PoisonOnly, ConsiderFlags, Depth);
+}
+
 bool AArch64TargetLowering::isTargetCanonicalConstantNode(SDValue Op) const {
   return Op.getOpcode() == AArch64ISD::DUP ||
          Op.getOpcode() == AArch64ISD::MOVI ||

llvm/lib/Target/AArch64/AArch64ISelLowering.h

@@ -851,6 +851,12 @@ class AArch64TargetLowering : public TargetLowering {
                                          TargetLoweringOpt &TLO,
                                          unsigned Depth) const override;
 
+  bool canCreateUndefOrPoisonForTargetNode(SDValue Op,
+                                           const APInt &DemandedElts,
+                                           const SelectionDAG &DAG,
+                                           bool PoisonOnly, bool ConsiderFlags,
+                                           unsigned Depth) const override;
+
   bool isTargetCanonicalConstantNode(SDValue Op) const override;
 
   // With the exception of data-predicate transitions, no instructions are