[DAG][ARM] Define upwrapAddress for ARM backend.

[niravd]

Summary

Like with X86, this allows better DAG-level alias analysis and
alignment inference for wrapped addresses.

[efriedma]

Testcase?

[niravd]

This seems like it a natural thing to do as with the X86 backend, but since it doesn't make any test change differences, perhap it is unecessary.

llvm/lib/Target/ARM/ARMISelLowering.h

public:
 
     MachineBasicBlock *
     EmitInstrWithCustomInserter(MachineInstr &MI,
                                 MachineBasicBlock *MBB) const override;
 
     void AdjustInstrPostInstrSelection(MachineInstr &MI,
                                        SDNode *Node) const override;
 
+    SDValue unwrapAddress(SDValue N) const override;
+
     SDValue PerformCMOVCombine(SDNode *N, SelectionDAG &DAG) const;
     SDValue PerformBRCONDCombine(SDNode *N, SelectionDAG &DAG) const;
     SDValue PerformCMOVToBFICombine(SDNode *N, SelectionDAG &DAG) const;
     SDValue PerformDAGCombine(SDNode *N, DAGCombinerInfo &DCI) const override;
 
     bool isDesirableToTransformToIntegerOp(unsigned Opc, EVT VT) const override;
 
     /// allowsMisalignedMemoryAccesses - Returns true if the target allows

llvm/lib/Target/ARM/ARMISelLowering.cpp

void ARMTargetLowering::AdjustInstrPostInstrSelection(MachineInstr &MI,
 
   // If this instruction was defined with an optional CPSR def and its dag node
   // had a live implicit CPSR def, then activate the optional CPSR def.
   MachineOperand &MO = MI.getOperand(ccOutIdx);
   MO.setReg(ARM::CPSR);
   MO.setIsDef(true);
 }
 
+SDValue ARMTargetLowering::unwrapAddress(SDValue N) const {
+  if (N->getOpcode() == ARMISD::Wrapper ||
+      N->getOpcode() == ARMISD::WrapperPIC ||
+      N->getOpcode() == ARMISD::WrapperJT)
+    return N->getOperand(0);
+  return N;
+}
+
 //===----------------------------------------------------------------------===//
 //                           ARM Optimization Hooks
 //===----------------------------------------------------------------------===//
 
 // Helper function that checks if N is a null or all ones constant.
 static inline bool isZeroOrAllOnes(SDValue N, bool AllOnes) {
   return AllOnes ? isAllOnesConstant(N) : isNullConstant(N);
 }