static std::string getEdgeAttributes(const void *Node, EdgeIter EI) {
   SDOperand Op = EI.getNode()->getOperand(EI.getOperand());
   MVT::ValueType VT = Op.getValueType();
   if (VT == MVT::Flag)
     return "color=red,style=bold";
   else if (VT == MVT::Other)
     return "style=dashed";
   return "";
 }
SDOperand AlphaTargetLowering::CustomPromoteOperation(SDOperand Op, 
                                                      SelectionDAG &DAG) {
  assert(Op.getValueType() == MVT::i32 && 
         Op.getOpcode() == ISD::VAARG &&
         "Unknown node to custom promote!");
  
  // The code in LowerOperation already handles i32 vaarg
  return LowerOperation(Op, DAG);
}
static SDOperand LowerJumpTable(SDOperand Op, SelectionDAG &DAG) {
  MVT::ValueType PtrVT = Op.getValueType();
  JumpTableSDNode *JT = cast<JumpTableSDNode>(Op);
  SDOperand JTI = DAG.getTargetJumpTable(JT->getIndex(), PtrVT);
  SDOperand Zero = DAG.getConstant(0, PtrVT);
  
  SDOperand Hi = DAG.getNode(AlphaISD::GPRelHi,  MVT::i64, JTI,
                             DAG.getNode(ISD::GLOBAL_OFFSET_TABLE, MVT::i64));
  SDOperand Lo = DAG.getNode(AlphaISD::GPRelLo, MVT::i64, JTI, Hi);
  return Lo;
}
/// LowerOperation - Provide custom lowering hooks for some operations.
///
SDOperand AlphaTargetLowering::LowerOperation(SDOperand Op, SelectionDAG &DAG) {
  switch (Op.getOpcode()) {
  default: assert(0 && "Wasn't expecting to be able to lower this!");
  case ISD::FORMAL_ARGUMENTS: return LowerFORMAL_ARGUMENTS(Op, DAG, 
                                                           VarArgsBase,
                                                           VarArgsOffset);

  case ISD::RET: return LowerRET(Op,DAG);
  case ISD::JumpTable: return LowerJumpTable(Op, DAG);

  case ISD::SINT_TO_FP: {
    assert(MVT::i64 == Op.getOperand(0).getValueType() && 
           "Unhandled SINT_TO_FP type in custom expander!");
    SDOperand LD;
    bool isDouble = MVT::f64 == Op.getValueType();
    LD = DAG.getNode(ISD::BIT_CONVERT, MVT::f64, Op.getOperand(0));
    SDOperand FP = DAG.getNode(isDouble?AlphaISD::CVTQT_:AlphaISD::CVTQS_,
                               isDouble?MVT::f64:MVT::f32, LD);
    return FP;
  }
  case ISD::FP_TO_SINT: {
    bool isDouble = MVT::f64 == Op.getOperand(0).getValueType();
    SDOperand src = Op.getOperand(0);

    if (!isDouble) //Promote
      src = DAG.getNode(ISD::FP_EXTEND, MVT::f64, src);
    
    src = DAG.getNode(AlphaISD::CVTTQ_, MVT::f64, src);

    return DAG.getNode(ISD::BIT_CONVERT, MVT::i64, src);
  }
  case ISD::ConstantPool: {
    ConstantPoolSDNode *CP = cast<ConstantPoolSDNode>(Op);
    Constant *C = CP->getConstVal();
    SDOperand CPI = DAG.getTargetConstantPool(C, MVT::i64, CP->getAlignment());
    
    SDOperand Hi = DAG.getNode(AlphaISD::GPRelHi,  MVT::i64, CPI,
                               DAG.getNode(ISD::GLOBAL_OFFSET_TABLE, MVT::i64));
    SDOperand Lo = DAG.getNode(AlphaISD::GPRelLo, MVT::i64, CPI, Hi);
    return Lo;
  }
  case ISD::GlobalAddress: {
    GlobalAddressSDNode *GSDN = cast<GlobalAddressSDNode>(Op);
    GlobalValue *GV = GSDN->getGlobal();
    SDOperand GA = DAG.getTargetGlobalAddress(GV, MVT::i64, GSDN->getOffset());

    //    if (!GV->hasWeakLinkage() && !GV->isDeclaration() && !GV->hasLinkOnceLinkage()) {
    if (GV->hasInternalLinkage()) {
      SDOperand Hi = DAG.getNode(AlphaISD::GPRelHi,  MVT::i64, GA,
                                DAG.getNode(ISD::GLOBAL_OFFSET_TABLE, MVT::i64));
      SDOperand Lo = DAG.getNode(AlphaISD::GPRelLo, MVT::i64, GA, Hi);
      return Lo;
    } else
      return DAG.getNode(AlphaISD::RelLit, MVT::i64, GA, 
                         DAG.getNode(ISD::GLOBAL_OFFSET_TABLE, MVT::i64));
  }
  case ISD::ExternalSymbol: {
    return DAG.getNode(AlphaISD::RelLit, MVT::i64, 
                       DAG.getTargetExternalSymbol(cast<ExternalSymbolSDNode>(Op)
                                                   ->getSymbol(), MVT::i64),
                       DAG.getNode(ISD::GLOBAL_OFFSET_TABLE, MVT::i64));
  }

  case ISD::UREM:
  case ISD::SREM:
    //Expand only on constant case
    if (Op.getOperand(1).getOpcode() == ISD::Constant) {
      MVT::ValueType VT = Op.Val->getValueType(0);
      SDOperand Tmp1 = Op.Val->getOpcode() == ISD::UREM ?
        BuildUDIV(Op.Val, DAG, NULL) :
        BuildSDIV(Op.Val, DAG, NULL);
      Tmp1 = DAG.getNode(ISD::MUL, VT, Tmp1, Op.getOperand(1));
      Tmp1 = DAG.getNode(ISD::SUB, VT, Op.getOperand(0), Tmp1);
      return Tmp1;
    }
    //fall through
  case ISD::SDIV:
  case ISD::UDIV:
    if (MVT::isInteger(Op.getValueType())) {
      if (Op.getOperand(1).getOpcode() == ISD::Constant)
        return Op.getOpcode() == ISD::SDIV ? BuildSDIV(Op.Val, DAG, NULL) 
          : BuildUDIV(Op.Val, DAG, NULL);
      const char* opstr = 0;
      switch (Op.getOpcode()) {
      case ISD::UREM: opstr = "__remqu"; break;
      case ISD::SREM: opstr = "__remq";  break;
      case ISD::UDIV: opstr = "__divqu"; break;
      case ISD::SDIV: opstr = "__divq";  break;
      }
      SDOperand Tmp1 = Op.getOperand(0),
        Tmp2 = Op.getOperand(1),
        Addr = DAG.getExternalSymbol(opstr, MVT::i64);
      return DAG.getNode(AlphaISD::DivCall, MVT::i64, Addr, Tmp1, Tmp2);
    }
    break;

  case ISD::VAARG: {
    SDOperand Chain = Op.getOperand(0);
    SDOperand VAListP = Op.getOperand(1);
    SrcValueSDNode *VAListS = cast<SrcValueSDNode>(Op.getOperand(2));
    
    SDOperand Base = DAG.getLoad(MVT::i64, Chain, VAListP, VAListS->getValue(),
                                 VAListS->getOffset());
    SDOperand Tmp = DAG.getNode(ISD::ADD, MVT::i64, VAListP,
                                DAG.getConstant(8, MVT::i64));
    SDOperand Offset = DAG.getExtLoad(ISD::SEXTLOAD, MVT::i64, Base.getValue(1),
                                      Tmp, NULL, 0, MVT::i32);
    SDOperand DataPtr = DAG.getNode(ISD::ADD, MVT::i64, Base, Offset);
    if (MVT::isFloatingPoint(Op.getValueType()))
    {
      //if fp && Offset < 6*8, then subtract 6*8 from DataPtr
      SDOperand FPDataPtr = DAG.getNode(ISD::SUB, MVT::i64, DataPtr,
                                        DAG.getConstant(8*6, MVT::i64));
      SDOperand CC = DAG.getSetCC(MVT::i64, Offset,
                                  DAG.getConstant(8*6, MVT::i64), ISD::SETLT);
      DataPtr = DAG.getNode(ISD::SELECT, MVT::i64, CC, FPDataPtr, DataPtr);
    }

    SDOperand NewOffset = DAG.getNode(ISD::ADD, MVT::i64, Offset,
                                      DAG.getConstant(8, MVT::i64));
    SDOperand Update = DAG.getTruncStore(Offset.getValue(1), NewOffset,
                                         Tmp, NULL, 0, MVT::i32);
    
    SDOperand Result;
    if (Op.getValueType() == MVT::i32)
      Result = DAG.getExtLoad(ISD::SEXTLOAD, MVT::i64, Update, DataPtr,
                              NULL, 0, MVT::i32);
    else
      Result = DAG.getLoad(Op.getValueType(), Update, DataPtr, NULL, 0);
    return Result;
  }
  case ISD::VACOPY: {
    SDOperand Chain = Op.getOperand(0);
    SDOperand DestP = Op.getOperand(1);
    SDOperand SrcP = Op.getOperand(2);
    SrcValueSDNode *DestS = cast<SrcValueSDNode>(Op.getOperand(3));
    SrcValueSDNode *SrcS = cast<SrcValueSDNode>(Op.getOperand(4));
    
    SDOperand Val = DAG.getLoad(getPointerTy(), Chain, SrcP,
                                SrcS->getValue(), SrcS->getOffset());
    SDOperand Result = DAG.getStore(Val.getValue(1), Val, DestP, DestS->getValue(),
                                    DestS->getOffset());
    SDOperand NP = DAG.getNode(ISD::ADD, MVT::i64, SrcP, 
                               DAG.getConstant(8, MVT::i64));
    Val = DAG.getExtLoad(ISD::SEXTLOAD, MVT::i64, Result, NP, NULL,0, MVT::i32);
    SDOperand NPD = DAG.getNode(ISD::ADD, MVT::i64, DestP,
                                DAG.getConstant(8, MVT::i64));
    return DAG.getTruncStore(Val.getValue(1), Val, NPD, NULL, 0, MVT::i32);
  }
  case ISD::VASTART: {
    SDOperand Chain = Op.getOperand(0);
    SDOperand VAListP = Op.getOperand(1);
    SrcValueSDNode *VAListS = cast<SrcValueSDNode>(Op.getOperand(2));
    
    // vastart stores the address of the VarArgsBase and VarArgsOffset
    SDOperand FR  = DAG.getFrameIndex(VarArgsBase, MVT::i64);
    SDOperand S1  = DAG.getStore(Chain, FR, VAListP, VAListS->getValue(),
                                 VAListS->getOffset());
    SDOperand SA2 = DAG.getNode(ISD::ADD, MVT::i64, VAListP,
                                DAG.getConstant(8, MVT::i64));
    return DAG.getTruncStore(S1, DAG.getConstant(VarArgsOffset, MVT::i64),
                             SA2, NULL, 0, MVT::i32);
  }
  case ISD::RETURNADDR:        
    return DAG.getNode(AlphaISD::GlobalRetAddr, MVT::i64);
      //FIXME: implement
  case ISD::FRAMEADDR:          break;
  }
  
  return SDOperand();
}
Ejemplo n.º 5
0
SDOperand IA64TargetLowering::
LowerOperation(SDOperand Op, SelectionDAG &DAG) {
  switch (Op.getOpcode()) {
  default: assert(0 && "Should not custom lower this!");
  case ISD::GlobalTLSAddress:
    assert(0 && "TLS not implemented for IA64.");
  case ISD::RET: {
    SDOperand AR_PFSVal, Copy;
    
    switch(Op.getNumOperands()) {
     default:
      assert(0 && "Do not know how to return this many arguments!");
      abort();
    case 1: 
      AR_PFSVal = DAG.getCopyFromReg(Op.getOperand(0), VirtGPR, MVT::i64);
      AR_PFSVal = DAG.getCopyToReg(AR_PFSVal.getValue(1), IA64::AR_PFS, 
                                   AR_PFSVal);
      return DAG.getNode(IA64ISD::RET_FLAG, MVT::Other, AR_PFSVal);
    case 3: {
      // Copy the result into the output register & restore ar.pfs
      MVT::ValueType ArgVT = Op.getOperand(1).getValueType();
      unsigned ArgReg = MVT::isInteger(ArgVT) ? IA64::r8 : IA64::F8;

      AR_PFSVal = DAG.getCopyFromReg(Op.getOperand(0), VirtGPR, MVT::i64);
      Copy = DAG.getCopyToReg(AR_PFSVal.getValue(1), ArgReg, Op.getOperand(1),
                              SDOperand());
      AR_PFSVal = DAG.getCopyToReg(Copy.getValue(0), IA64::AR_PFS, AR_PFSVal,
                                   Copy.getValue(1));
      return DAG.getNode(IA64ISD::RET_FLAG, MVT::Other,
                         AR_PFSVal, AR_PFSVal.getValue(1));
    }
    }
    return SDOperand();
  }
  case ISD::VAARG: {
    MVT::ValueType VT = getPointerTy();
    const Value *SV = cast<SrcValueSDNode>(Op.getOperand(2))->getValue();
    SDOperand VAList = DAG.getLoad(VT, Op.getOperand(0), Op.getOperand(1), 
                                   SV, 0);
    // Increment the pointer, VAList, to the next vaarg
    SDOperand VAIncr = DAG.getNode(ISD::ADD, VT, VAList, 
                                   DAG.getConstant(MVT::getSizeInBits(VT)/8, 
                                                   VT));
    // Store the incremented VAList to the legalized pointer
    VAIncr = DAG.getStore(VAList.getValue(1), VAIncr,
                          Op.getOperand(1), SV, 0);
    // Load the actual argument out of the pointer VAList
    return DAG.getLoad(Op.getValueType(), VAIncr, VAList, NULL, 0);
  }
  case ISD::VASTART: {
    // vastart just stores the address of the VarArgsFrameIndex slot into the
    // memory location argument.
    SDOperand FR = DAG.getFrameIndex(VarArgsFrameIndex, MVT::i64);
    const Value *SV = cast<SrcValueSDNode>(Op.getOperand(2))->getValue();
    return DAG.getStore(Op.getOperand(0), FR, Op.getOperand(1), SV, 0);
  }
  // Frame & Return address.  Currently unimplemented
  case ISD::RETURNADDR:         break;
  case ISD::FRAMEADDR:          break;
  }
  return SDOperand();
}
Ejemplo n.º 6
0
std::pair<SDOperand, SDOperand>
IA64TargetLowering::LowerCallTo(SDOperand Chain, const Type *RetTy,
                                bool RetSExt, bool RetZExt,
                                bool isVarArg, unsigned CallingConv, 
                                bool isTailCall, SDOperand Callee, 
                                ArgListTy &Args, SelectionDAG &DAG) {

  MachineFunction &MF = DAG.getMachineFunction();

  unsigned NumBytes = 16;
  unsigned outRegsUsed = 0;

  if (Args.size() > 8) {
    NumBytes += (Args.size() - 8) * 8;
    outRegsUsed = 8;
  } else {
    outRegsUsed = Args.size();
  }

  // FIXME? this WILL fail if we ever try to pass around an arg that
  // consumes more than a single output slot (a 'real' double, int128
  // some sort of aggregate etc.), as we'll underestimate how many 'outX'
  // registers we use. Hopefully, the assembler will notice.
  MF.getInfo<IA64FunctionInfo>()->outRegsUsed=
    std::max(outRegsUsed, MF.getInfo<IA64FunctionInfo>()->outRegsUsed);

  // keep stack frame 16-byte aligned
  // assert(NumBytes==((NumBytes+15) & ~15) && 
  //        "stack frame not 16-byte aligned!");
  NumBytes = (NumBytes+15) & ~15;
  
  Chain = DAG.getCALLSEQ_START(Chain,DAG.getConstant(NumBytes, getPointerTy()));

  SDOperand StackPtr;
  std::vector<SDOperand> Stores;
  std::vector<SDOperand> Converts;
  std::vector<SDOperand> RegValuesToPass;
  unsigned ArgOffset = 16;
  
  for (unsigned i = 0, e = Args.size(); i != e; ++i)
    {
      SDOperand Val = Args[i].Node;
      MVT::ValueType ObjectVT = Val.getValueType();
      SDOperand ValToStore(0, 0), ValToConvert(0, 0);
      unsigned ObjSize=8;
      switch (ObjectVT) {
      default: assert(0 && "unexpected argument type!");
      case MVT::i1:
      case MVT::i8:
      case MVT::i16:
      case MVT::i32: {
        //promote to 64-bits, sign/zero extending based on type
        //of the argument
        ISD::NodeType ExtendKind = ISD::ANY_EXTEND;
        if (Args[i].isSExt)
          ExtendKind = ISD::SIGN_EXTEND;
        else if (Args[i].isZExt)
          ExtendKind = ISD::ZERO_EXTEND;
        Val = DAG.getNode(ExtendKind, MVT::i64, Val);
        // XXX: fall through
      }
      case MVT::i64:
        //ObjSize = 8;
        if(RegValuesToPass.size() >= 8) {
          ValToStore = Val;
        } else {
          RegValuesToPass.push_back(Val);
        }
        break;
      case MVT::f32:
        //promote to 64-bits
        Val = DAG.getNode(ISD::FP_EXTEND, MVT::f64, Val);
        // XXX: fall through
      case MVT::f64:
        if(RegValuesToPass.size() >= 8) {
          ValToStore = Val;
        } else {
          RegValuesToPass.push_back(Val);
          if(1 /* TODO: if(calling external or varadic function)*/ ) {
            ValToConvert = Val; // additionally pass this FP value as an int
          }
        }
        break;
      }
      
      if(ValToStore.Val) {
        if(!StackPtr.Val) {
          StackPtr = DAG.getRegister(IA64::r12, MVT::i64);
        }
        SDOperand PtrOff = DAG.getConstant(ArgOffset, getPointerTy());
        PtrOff = DAG.getNode(ISD::ADD, MVT::i64, StackPtr, PtrOff);
        Stores.push_back(DAG.getStore(Chain, ValToStore, PtrOff, NULL, 0));
        ArgOffset += ObjSize;
      }

      if(ValToConvert.Val) {
        Converts.push_back(DAG.getNode(IA64ISD::GETFD, MVT::i64, ValToConvert)); 
      }
    }

  // Emit all stores, make sure they occur before any copies into physregs.
  if (!Stores.empty())
    Chain = DAG.getNode(ISD::TokenFactor, MVT::Other, &Stores[0],Stores.size());

  static const unsigned IntArgRegs[] = {
    IA64::out0, IA64::out1, IA64::out2, IA64::out3, 
    IA64::out4, IA64::out5, IA64::out6, IA64::out7
  };

  static const unsigned FPArgRegs[] = {
    IA64::F8,  IA64::F9,  IA64::F10, IA64::F11, 
    IA64::F12, IA64::F13, IA64::F14, IA64::F15
  };

  SDOperand InFlag;
  
  // save the current GP, SP and RP : FIXME: do we need to do all 3 always?
  SDOperand GPBeforeCall = DAG.getCopyFromReg(Chain, IA64::r1, MVT::i64, InFlag);
  Chain = GPBeforeCall.getValue(1);
  InFlag = Chain.getValue(2);
  SDOperand SPBeforeCall = DAG.getCopyFromReg(Chain, IA64::r12, MVT::i64, InFlag);
  Chain = SPBeforeCall.getValue(1);
  InFlag = Chain.getValue(2);
  SDOperand RPBeforeCall = DAG.getCopyFromReg(Chain, IA64::rp, MVT::i64, InFlag);
  Chain = RPBeforeCall.getValue(1);
  InFlag = Chain.getValue(2);

  // Build a sequence of copy-to-reg nodes chained together with token chain
  // and flag operands which copy the outgoing integer args into regs out[0-7]
  // mapped 1:1 and the FP args into regs F8-F15 "lazily"
  // TODO: for performance, we should only copy FP args into int regs when we
  // know this is required (i.e. for varardic or external (unknown) functions)

  // first to the FP->(integer representation) conversions, these are
  // flagged for now, but shouldn't have to be (TODO)
  unsigned seenConverts = 0;
  for (unsigned i = 0, e = RegValuesToPass.size(); i != e; ++i) {
    if(MVT::isFloatingPoint(RegValuesToPass[i].getValueType())) {
      Chain = DAG.getCopyToReg(Chain, IntArgRegs[i], Converts[seenConverts++], 
                               InFlag);
      InFlag = Chain.getValue(1);
    }
  }

  // next copy args into the usual places, these are flagged
  unsigned usedFPArgs = 0;
  for (unsigned i = 0, e = RegValuesToPass.size(); i != e; ++i) {
    Chain = DAG.getCopyToReg(Chain,
      MVT::isInteger(RegValuesToPass[i].getValueType()) ?
        IntArgRegs[i] : FPArgRegs[usedFPArgs++], RegValuesToPass[i], InFlag);
    InFlag = Chain.getValue(1);
  }

  // If the callee is a GlobalAddress node (quite common, every direct call is)
  // turn it into a TargetGlobalAddress node so that legalize doesn't hack it.
/*
  if (GlobalAddressSDNode *G = dyn_cast<GlobalAddressSDNode>(Callee)) {
    Callee = DAG.getTargetGlobalAddress(G->getGlobal(), MVT::i64);
  }
*/

  std::vector<MVT::ValueType> NodeTys;
  std::vector<SDOperand> CallOperands;
  NodeTys.push_back(MVT::Other);   // Returns a chain
  NodeTys.push_back(MVT::Flag);    // Returns a flag for retval copy to use.
  CallOperands.push_back(Chain);
  CallOperands.push_back(Callee);

  // emit the call itself
  if (InFlag.Val)
    CallOperands.push_back(InFlag);
  else
    assert(0 && "this should never happen!\n");

  // to make way for a hack:
  Chain = DAG.getNode(IA64ISD::BRCALL, NodeTys,
                      &CallOperands[0], CallOperands.size());
  InFlag = Chain.getValue(1);

  // restore the GP, SP and RP after the call  
  Chain = DAG.getCopyToReg(Chain, IA64::r1, GPBeforeCall, InFlag);
  InFlag = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, IA64::r12, SPBeforeCall, InFlag);
  InFlag = Chain.getValue(1);
  Chain = DAG.getCopyToReg(Chain, IA64::rp, RPBeforeCall, InFlag);
  InFlag = Chain.getValue(1);
 
  std::vector<MVT::ValueType> RetVals;
  RetVals.push_back(MVT::Other);
  RetVals.push_back(MVT::Flag);
 
  MVT::ValueType RetTyVT = getValueType(RetTy);
  SDOperand RetVal;
  if (RetTyVT != MVT::isVoid) {
    switch (RetTyVT) {
    default: assert(0 && "Unknown value type to return!");
    case MVT::i1: { // bools are just like other integers (returned in r8)
      // we *could* fall through to the truncate below, but this saves a
      // few redundant predicate ops
      SDOperand boolInR8 = DAG.getCopyFromReg(Chain, IA64::r8, MVT::i64,InFlag);
      InFlag = boolInR8.getValue(2);
      Chain = boolInR8.getValue(1);
      SDOperand zeroReg = DAG.getCopyFromReg(Chain, IA64::r0, MVT::i64, InFlag);
      InFlag = zeroReg.getValue(2);
      Chain = zeroReg.getValue(1);
      
      RetVal = DAG.getSetCC(MVT::i1, boolInR8, zeroReg, ISD::SETNE);
      break;
    }
    case MVT::i8:
    case MVT::i16:
    case MVT::i32:
      RetVal = DAG.getCopyFromReg(Chain, IA64::r8, MVT::i64, InFlag);
      Chain = RetVal.getValue(1);
      
      // keep track of whether it is sign or zero extended (todo: bools?)
/* XXX
      RetVal = DAG.getNode(RetTy->isSigned() ? ISD::AssertSext :ISD::AssertZext,
                           MVT::i64, RetVal, DAG.getValueType(RetTyVT));
*/
      RetVal = DAG.getNode(ISD::TRUNCATE, RetTyVT, RetVal);
      break;
    case MVT::i64:
      RetVal = DAG.getCopyFromReg(Chain, IA64::r8, MVT::i64, InFlag);
      Chain = RetVal.getValue(1);
      InFlag = RetVal.getValue(2); // XXX dead
      break;
    case MVT::f32:
      RetVal = DAG.getCopyFromReg(Chain, IA64::F8, MVT::f64, InFlag);
      Chain = RetVal.getValue(1);
      RetVal = DAG.getNode(ISD::TRUNCATE, MVT::f32, RetVal);
      break;
    case MVT::f64:
      RetVal = DAG.getCopyFromReg(Chain, IA64::F8, MVT::f64, InFlag);
      Chain = RetVal.getValue(1);
      InFlag = RetVal.getValue(2); // XXX dead
      break;
    }
  }
  
  Chain = DAG.getCALLSEQ_END(Chain,
                             DAG.getConstant(NumBytes, getPointerTy()),
                             DAG.getConstant(0, getPointerTy()),
                             SDOperand());
  return std::make_pair(RetVal, Chain);
}