1 //===-------- LegalizeTypesGeneric.cpp - Generic type legalization --------===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements generic type expansion and splitting for LegalizeTypes.
11 // The routines here perform legalization when the details of the type (such as
12 // whether it is an integer or a float) do not matter.
13 // Expansion is the act of changing a computation in an illegal type to be a
14 // computation in two identical registers of a smaller type. The Lo/Hi part
15 // is required to be stored first in memory on little/big-endian machines.
16 // Splitting is the act of changing a computation in an illegal type to be a
17 // computation in two not necessarily identical registers of a smaller type.
18 // There are no requirements on how the type is represented in memory.
20 //===----------------------------------------------------------------------===//
22 #include "LegalizeTypes.h"
23 #include "llvm/IR/DataLayout.h"
26 #define DEBUG_TYPE "legalize-types"
28 //===----------------------------------------------------------------------===//
29 // Generic Result Expansion.
30 //===----------------------------------------------------------------------===//
32 // These routines assume that the Lo/Hi part is stored first in memory on
33 // little/big-endian machines, followed by the Hi/Lo part. This means that
34 // they cannot be used as is on vectors, for which Lo is always stored first.
35 void DAGTypeLegalizer::ExpandRes_MERGE_VALUES(SDNode *N, unsigned ResNo,
36 SDValue &Lo, SDValue &Hi) {
37 SDValue Op = DisintegrateMERGE_VALUES(N, ResNo);
38 GetExpandedOp(Op, Lo, Hi);
41 void DAGTypeLegalizer::ExpandRes_BITCAST(SDNode *N, SDValue &Lo, SDValue &Hi) {
42 EVT OutVT = N->getValueType(0);
43 EVT NOutVT = TLI.getTypeToTransformTo(*DAG.getContext(), OutVT);
44 SDValue InOp = N->getOperand(0);
45 EVT InVT = InOp.getValueType();
48 // Handle some special cases efficiently.
49 switch (getTypeAction(InVT)) {
50 case TargetLowering::TypeLegal:
51 case TargetLowering::TypePromoteInteger:
53 case TargetLowering::TypePromoteFloat:
54 llvm_unreachable("Bitcast of a promotion-needing float should never need"
56 case TargetLowering::TypeSoftenFloat:
57 // Convert the integer operand instead.
58 SplitInteger(GetSoftenedFloat(InOp), Lo, Hi);
59 Lo = DAG.getNode(ISD::BITCAST, dl, NOutVT, Lo);
60 Hi = DAG.getNode(ISD::BITCAST, dl, NOutVT, Hi);
62 case TargetLowering::TypeExpandInteger:
63 case TargetLowering::TypeExpandFloat: {
64 auto &DL = DAG.getDataLayout();
65 // Convert the expanded pieces of the input.
66 GetExpandedOp(InOp, Lo, Hi);
67 if (TLI.hasBigEndianPartOrdering(InVT, DL) !=
68 TLI.hasBigEndianPartOrdering(OutVT, DL))
70 Lo = DAG.getNode(ISD::BITCAST, dl, NOutVT, Lo);
71 Hi = DAG.getNode(ISD::BITCAST, dl, NOutVT, Hi);
74 case TargetLowering::TypeSplitVector:
75 GetSplitVector(InOp, Lo, Hi);
76 if (TLI.hasBigEndianPartOrdering(OutVT, DAG.getDataLayout()))
78 Lo = DAG.getNode(ISD::BITCAST, dl, NOutVT, Lo);
79 Hi = DAG.getNode(ISD::BITCAST, dl, NOutVT, Hi);
81 case TargetLowering::TypeScalarizeVector:
82 // Convert the element instead.
83 SplitInteger(BitConvertToInteger(GetScalarizedVector(InOp)), Lo, Hi);
84 Lo = DAG.getNode(ISD::BITCAST, dl, NOutVT, Lo);
85 Hi = DAG.getNode(ISD::BITCAST, dl, NOutVT, Hi);
87 case TargetLowering::TypeWidenVector: {
88 assert(!(InVT.getVectorNumElements() & 1) && "Unsupported BITCAST");
89 InOp = GetWidenedVector(InOp);
91 std::tie(LoVT, HiVT) = DAG.GetSplitDestVTs(InVT);
92 std::tie(Lo, Hi) = DAG.SplitVector(InOp, dl, LoVT, HiVT);
93 if (TLI.hasBigEndianPartOrdering(OutVT, DAG.getDataLayout()))
95 Lo = DAG.getNode(ISD::BITCAST, dl, NOutVT, Lo);
96 Hi = DAG.getNode(ISD::BITCAST, dl, NOutVT, Hi);
101 if (InVT.isVector() && OutVT.isInteger()) {
102 // Handle cases like i64 = BITCAST v1i64 on x86, where the operand
103 // is legal but the result is not.
104 unsigned NumElems = 2;
106 EVT NVT = EVT::getVectorVT(*DAG.getContext(), ElemVT, NumElems);
108 // If <ElemVT * N> is not a legal type, try <ElemVT/2 * (N*2)>.
109 while (!isTypeLegal(NVT)) {
110 unsigned NewSizeInBits = ElemVT.getSizeInBits() / 2;
111 // If the element size is smaller than byte, bail.
112 if (NewSizeInBits < 8)
115 ElemVT = EVT::getIntegerVT(*DAG.getContext(), NewSizeInBits);
116 NVT = EVT::getVectorVT(*DAG.getContext(), ElemVT, NumElems);
119 if (isTypeLegal(NVT)) {
120 SDValue CastInOp = DAG.getNode(ISD::BITCAST, dl, NVT, InOp);
122 SmallVector<SDValue, 8> Vals;
123 for (unsigned i = 0; i < NumElems; ++i)
124 Vals.push_back(DAG.getNode(
125 ISD::EXTRACT_VECTOR_ELT, dl, ElemVT, CastInOp,
126 DAG.getConstant(i, dl, TLI.getVectorIdxTy(DAG.getDataLayout()))));
128 // Build Lo, Hi pair by pairing extracted elements if needed.
130 for (unsigned e = Vals.size(); e - Slot > 2; Slot += 2, e += 1) {
131 // Each iteration will BUILD_PAIR two nodes and append the result until
132 // there are only two nodes left, i.e. Lo and Hi.
133 SDValue LHS = Vals[Slot];
134 SDValue RHS = Vals[Slot + 1];
136 if (DAG.getDataLayout().isBigEndian())
139 Vals.push_back(DAG.getNode(ISD::BUILD_PAIR, dl,
142 LHS.getValueType().getSizeInBits() << 1),
148 if (DAG.getDataLayout().isBigEndian())
155 // Lower the bit-convert to a store/load from the stack.
156 assert(NOutVT.isByteSized() && "Expanded type not byte sized!");
158 // Create the stack frame object. Make sure it is aligned for both
159 // the source and expanded destination types.
160 unsigned Alignment = DAG.getDataLayout().getPrefTypeAlignment(
161 NOutVT.getTypeForEVT(*DAG.getContext()));
162 SDValue StackPtr = DAG.CreateStackTemporary(InVT, Alignment);
163 int SPFI = cast<FrameIndexSDNode>(StackPtr.getNode())->getIndex();
164 MachinePointerInfo PtrInfo = MachinePointerInfo::getFixedStack(SPFI);
166 // Emit a store to the stack slot.
167 SDValue Store = DAG.getStore(DAG.getEntryNode(), dl, InOp, StackPtr, PtrInfo,
170 // Load the first half from the stack slot.
171 Lo = DAG.getLoad(NOutVT, dl, Store, StackPtr, PtrInfo,
172 false, false, false, 0);
174 // Increment the pointer to the other half.
175 unsigned IncrementSize = NOutVT.getSizeInBits() / 8;
176 StackPtr = DAG.getNode(ISD::ADD, dl, StackPtr.getValueType(), StackPtr,
177 DAG.getConstant(IncrementSize, dl,
178 StackPtr.getValueType()));
180 // Load the second half from the stack slot.
181 Hi = DAG.getLoad(NOutVT, dl, Store, StackPtr,
182 PtrInfo.getWithOffset(IncrementSize), false,
183 false, false, MinAlign(Alignment, IncrementSize));
185 // Handle endianness of the load.
186 if (TLI.hasBigEndianPartOrdering(OutVT, DAG.getDataLayout()))
190 void DAGTypeLegalizer::ExpandRes_BUILD_PAIR(SDNode *N, SDValue &Lo,
192 // Return the operands.
193 Lo = N->getOperand(0);
194 Hi = N->getOperand(1);
197 void DAGTypeLegalizer::ExpandRes_EXTRACT_ELEMENT(SDNode *N, SDValue &Lo,
199 GetExpandedOp(N->getOperand(0), Lo, Hi);
200 SDValue Part = cast<ConstantSDNode>(N->getOperand(1))->getZExtValue() ?
203 assert(Part.getValueType() == N->getValueType(0) &&
204 "Type twice as big as expanded type not itself expanded!");
206 GetPairElements(Part, Lo, Hi);
209 void DAGTypeLegalizer::ExpandRes_EXTRACT_VECTOR_ELT(SDNode *N, SDValue &Lo,
211 SDValue OldVec = N->getOperand(0);
212 unsigned OldElts = OldVec.getValueType().getVectorNumElements();
213 EVT OldEltVT = OldVec.getValueType().getVectorElementType();
216 // Convert to a vector of the expanded element type, for example
217 // <3 x i64> -> <6 x i32>.
218 EVT OldVT = N->getValueType(0);
219 EVT NewVT = TLI.getTypeToTransformTo(*DAG.getContext(), OldVT);
221 if (OldVT != OldEltVT) {
222 // The result of EXTRACT_VECTOR_ELT may be larger than the element type of
223 // the input vector. If so, extend the elements of the input vector to the
224 // same bitwidth as the result before expanding.
225 assert(OldEltVT.bitsLT(OldVT) && "Result type smaller then element type!");
226 EVT NVecVT = EVT::getVectorVT(*DAG.getContext(), OldVT, OldElts);
227 OldVec = DAG.getNode(ISD::ANY_EXTEND, dl, NVecVT, N->getOperand(0));
230 SDValue NewVec = DAG.getNode(ISD::BITCAST, dl,
231 EVT::getVectorVT(*DAG.getContext(),
235 // Extract the elements at 2 * Idx and 2 * Idx + 1 from the new vector.
236 SDValue Idx = N->getOperand(1);
238 Idx = DAG.getNode(ISD::ADD, dl, Idx.getValueType(), Idx, Idx);
239 Lo = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, NewVT, NewVec, Idx);
241 Idx = DAG.getNode(ISD::ADD, dl, Idx.getValueType(), Idx,
242 DAG.getConstant(1, dl, Idx.getValueType()));
243 Hi = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, dl, NewVT, NewVec, Idx);
245 if (DAG.getDataLayout().isBigEndian())
249 void DAGTypeLegalizer::ExpandRes_NormalLoad(SDNode *N, SDValue &Lo,
251 assert(ISD::isNormalLoad(N) && "This routine only for normal loads!");
254 LoadSDNode *LD = cast<LoadSDNode>(N);
255 EVT ValueVT = LD->getValueType(0);
256 EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), ValueVT);
257 SDValue Chain = LD->getChain();
258 SDValue Ptr = LD->getBasePtr();
259 unsigned Alignment = LD->getAlignment();
260 bool isVolatile = LD->isVolatile();
261 bool isNonTemporal = LD->isNonTemporal();
262 bool isInvariant = LD->isInvariant();
263 AAMDNodes AAInfo = LD->getAAInfo();
265 assert(NVT.isByteSized() && "Expanded type not byte sized!");
267 Lo = DAG.getLoad(NVT, dl, Chain, Ptr, LD->getPointerInfo(),
268 isVolatile, isNonTemporal, isInvariant, Alignment,
271 // Increment the pointer to the other half.
272 unsigned IncrementSize = NVT.getSizeInBits() / 8;
273 Ptr = DAG.getNode(ISD::ADD, dl, Ptr.getValueType(), Ptr,
274 DAG.getConstant(IncrementSize, dl, Ptr.getValueType()));
275 Hi = DAG.getLoad(NVT, dl, Chain, Ptr,
276 LD->getPointerInfo().getWithOffset(IncrementSize),
277 isVolatile, isNonTemporal, isInvariant,
278 MinAlign(Alignment, IncrementSize), AAInfo);
280 // Build a factor node to remember that this load is independent of the
282 Chain = DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo.getValue(1),
285 // Handle endianness of the load.
286 if (TLI.hasBigEndianPartOrdering(ValueVT, DAG.getDataLayout()))
289 // Modified the chain - switch anything that used the old chain to use
291 ReplaceValueWith(SDValue(N, 1), Chain);
294 void DAGTypeLegalizer::ExpandRes_VAARG(SDNode *N, SDValue &Lo, SDValue &Hi) {
295 EVT OVT = N->getValueType(0);
296 EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), OVT);
297 SDValue Chain = N->getOperand(0);
298 SDValue Ptr = N->getOperand(1);
300 const unsigned Align = N->getConstantOperandVal(3);
302 Lo = DAG.getVAArg(NVT, dl, Chain, Ptr, N->getOperand(2), Align);
303 Hi = DAG.getVAArg(NVT, dl, Lo.getValue(1), Ptr, N->getOperand(2), 0);
305 // Handle endianness of the load.
306 if (TLI.hasBigEndianPartOrdering(OVT, DAG.getDataLayout()))
309 // Modified the chain - switch anything that used the old chain to use
311 ReplaceValueWith(SDValue(N, 1), Hi.getValue(1));
315 //===--------------------------------------------------------------------===//
316 // Generic Operand Expansion.
317 //===--------------------------------------------------------------------===//
319 void DAGTypeLegalizer::IntegerToVector(SDValue Op, unsigned NumElements,
320 SmallVectorImpl<SDValue> &Ops,
322 assert(Op.getValueType().isInteger());
326 if (NumElements > 1) {
328 SplitInteger(Op, Parts[0], Parts[1]);
329 if (DAG.getDataLayout().isBigEndian())
330 std::swap(Parts[0], Parts[1]);
331 IntegerToVector(Parts[0], NumElements, Ops, EltVT);
332 IntegerToVector(Parts[1], NumElements, Ops, EltVT);
334 Ops.push_back(DAG.getNode(ISD::BITCAST, DL, EltVT, Op));
338 SDValue DAGTypeLegalizer::ExpandOp_BITCAST(SDNode *N) {
340 if (N->getValueType(0).isVector()) {
341 // An illegal expanding type is being converted to a legal vector type.
342 // Make a two element vector out of the expanded parts and convert that
343 // instead, but only if the new vector type is legal (otherwise there
344 // is no point, and it might create expansion loops). For example, on
345 // x86 this turns v1i64 = BITCAST i64 into v1i64 = BITCAST v2i32.
347 // FIXME: I'm not sure why we are first trying to split the input into
348 // a 2 element vector, so I'm leaving it here to maintain the current
350 unsigned NumElts = 2;
351 EVT OVT = N->getOperand(0).getValueType();
352 EVT NVT = EVT::getVectorVT(*DAG.getContext(),
353 TLI.getTypeToTransformTo(*DAG.getContext(), OVT),
355 if (!isTypeLegal(NVT)) {
356 // If we can't find a legal type by splitting the integer in half,
357 // then we can use the node's value type.
358 NumElts = N->getValueType(0).getVectorNumElements();
359 NVT = N->getValueType(0);
362 SmallVector<SDValue, 8> Ops;
363 IntegerToVector(N->getOperand(0), NumElts, Ops, NVT.getVectorElementType());
365 SDValue Vec = DAG.getNode(ISD::BUILD_VECTOR, dl, NVT,
366 makeArrayRef(Ops.data(), NumElts));
367 return DAG.getNode(ISD::BITCAST, dl, N->getValueType(0), Vec);
370 // Otherwise, store to a temporary and load out again as the new type.
371 return CreateStackStoreLoad(N->getOperand(0), N->getValueType(0));
374 SDValue DAGTypeLegalizer::ExpandOp_BUILD_VECTOR(SDNode *N) {
375 // The vector type is legal but the element type needs expansion.
376 EVT VecVT = N->getValueType(0);
377 unsigned NumElts = VecVT.getVectorNumElements();
378 EVT OldVT = N->getOperand(0).getValueType();
379 EVT NewVT = TLI.getTypeToTransformTo(*DAG.getContext(), OldVT);
382 assert(OldVT == VecVT.getVectorElementType() &&
383 "BUILD_VECTOR operand type doesn't match vector element type!");
385 // Build a vector of twice the length out of the expanded elements.
386 // For example <3 x i64> -> <6 x i32>.
387 std::vector<SDValue> NewElts;
388 NewElts.reserve(NumElts*2);
390 for (unsigned i = 0; i < NumElts; ++i) {
392 GetExpandedOp(N->getOperand(i), Lo, Hi);
393 if (DAG.getDataLayout().isBigEndian())
395 NewElts.push_back(Lo);
396 NewElts.push_back(Hi);
399 SDValue NewVec = DAG.getNode(ISD::BUILD_VECTOR, dl,
400 EVT::getVectorVT(*DAG.getContext(),
401 NewVT, NewElts.size()),
404 // Convert the new vector to the old vector type.
405 return DAG.getNode(ISD::BITCAST, dl, VecVT, NewVec);
408 SDValue DAGTypeLegalizer::ExpandOp_EXTRACT_ELEMENT(SDNode *N) {
410 GetExpandedOp(N->getOperand(0), Lo, Hi);
411 return cast<ConstantSDNode>(N->getOperand(1))->getZExtValue() ? Hi : Lo;
414 SDValue DAGTypeLegalizer::ExpandOp_INSERT_VECTOR_ELT(SDNode *N) {
415 // The vector type is legal but the element type needs expansion.
416 EVT VecVT = N->getValueType(0);
417 unsigned NumElts = VecVT.getVectorNumElements();
420 SDValue Val = N->getOperand(1);
421 EVT OldEVT = Val.getValueType();
422 EVT NewEVT = TLI.getTypeToTransformTo(*DAG.getContext(), OldEVT);
424 assert(OldEVT == VecVT.getVectorElementType() &&
425 "Inserted element type doesn't match vector element type!");
427 // Bitconvert to a vector of twice the length with elements of the expanded
428 // type, insert the expanded vector elements, and then convert back.
429 EVT NewVecVT = EVT::getVectorVT(*DAG.getContext(), NewEVT, NumElts*2);
430 SDValue NewVec = DAG.getNode(ISD::BITCAST, dl,
431 NewVecVT, N->getOperand(0));
434 GetExpandedOp(Val, Lo, Hi);
435 if (DAG.getDataLayout().isBigEndian())
438 SDValue Idx = N->getOperand(2);
439 Idx = DAG.getNode(ISD::ADD, dl, Idx.getValueType(), Idx, Idx);
440 NewVec = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, NewVecVT, NewVec, Lo, Idx);
441 Idx = DAG.getNode(ISD::ADD, dl,
442 Idx.getValueType(), Idx,
443 DAG.getConstant(1, dl, Idx.getValueType()));
444 NewVec = DAG.getNode(ISD::INSERT_VECTOR_ELT, dl, NewVecVT, NewVec, Hi, Idx);
446 // Convert the new vector to the old vector type.
447 return DAG.getNode(ISD::BITCAST, dl, VecVT, NewVec);
450 SDValue DAGTypeLegalizer::ExpandOp_SCALAR_TO_VECTOR(SDNode *N) {
452 EVT VT = N->getValueType(0);
453 assert(VT.getVectorElementType() == N->getOperand(0).getValueType() &&
454 "SCALAR_TO_VECTOR operand type doesn't match vector element type!");
455 unsigned NumElts = VT.getVectorNumElements();
456 SmallVector<SDValue, 16> Ops(NumElts);
457 Ops[0] = N->getOperand(0);
458 SDValue UndefVal = DAG.getUNDEF(Ops[0].getValueType());
459 for (unsigned i = 1; i < NumElts; ++i)
461 return DAG.getNode(ISD::BUILD_VECTOR, dl, VT, Ops);
464 SDValue DAGTypeLegalizer::ExpandOp_NormalStore(SDNode *N, unsigned OpNo) {
465 assert(ISD::isNormalStore(N) && "This routine only for normal stores!");
466 assert(OpNo == 1 && "Can only expand the stored value so far");
469 StoreSDNode *St = cast<StoreSDNode>(N);
470 EVT ValueVT = St->getValue().getValueType();
471 EVT NVT = TLI.getTypeToTransformTo(*DAG.getContext(), ValueVT);
472 SDValue Chain = St->getChain();
473 SDValue Ptr = St->getBasePtr();
474 unsigned Alignment = St->getAlignment();
475 bool isVolatile = St->isVolatile();
476 bool isNonTemporal = St->isNonTemporal();
477 AAMDNodes AAInfo = St->getAAInfo();
479 assert(NVT.isByteSized() && "Expanded type not byte sized!");
480 unsigned IncrementSize = NVT.getSizeInBits() / 8;
483 GetExpandedOp(St->getValue(), Lo, Hi);
485 if (TLI.hasBigEndianPartOrdering(ValueVT, DAG.getDataLayout()))
488 Lo = DAG.getStore(Chain, dl, Lo, Ptr, St->getPointerInfo(),
489 isVolatile, isNonTemporal, Alignment, AAInfo);
491 Ptr = DAG.getNode(ISD::ADD, dl, Ptr.getValueType(), Ptr,
492 DAG.getConstant(IncrementSize, dl, Ptr.getValueType()));
493 Hi = DAG.getStore(Chain, dl, Hi, Ptr,
494 St->getPointerInfo().getWithOffset(IncrementSize),
495 isVolatile, isNonTemporal,
496 MinAlign(Alignment, IncrementSize), AAInfo);
498 return DAG.getNode(ISD::TokenFactor, dl, MVT::Other, Lo, Hi);
502 //===--------------------------------------------------------------------===//
503 // Generic Result Splitting.
504 //===--------------------------------------------------------------------===//
506 // Be careful to make no assumptions about which of Lo/Hi is stored first in
507 // memory (for vectors it is always Lo first followed by Hi in the following
508 // bytes; for integers and floats it is Lo first if and only if the machine is
511 void DAGTypeLegalizer::SplitRes_MERGE_VALUES(SDNode *N, unsigned ResNo,
512 SDValue &Lo, SDValue &Hi) {
513 SDValue Op = DisintegrateMERGE_VALUES(N, ResNo);
514 GetSplitOp(Op, Lo, Hi);
517 void DAGTypeLegalizer::SplitRes_SELECT(SDNode *N, SDValue &Lo,
519 SDValue LL, LH, RL, RH, CL, CH;
521 GetSplitOp(N->getOperand(1), LL, LH);
522 GetSplitOp(N->getOperand(2), RL, RH);
524 SDValue Cond = N->getOperand(0);
526 if (Cond.getValueType().isVector()) {
527 // Check if there are already splitted versions of the vector available and
528 // use those instead of splitting the mask operand again.
529 if (getTypeAction(Cond.getValueType()) == TargetLowering::TypeSplitVector)
530 GetSplitVector(Cond, CL, CH);
532 std::tie(CL, CH) = DAG.SplitVector(Cond, dl);
535 Lo = DAG.getNode(N->getOpcode(), dl, LL.getValueType(), CL, LL, RL);
536 Hi = DAG.getNode(N->getOpcode(), dl, LH.getValueType(), CH, LH, RH);
539 void DAGTypeLegalizer::SplitRes_SELECT_CC(SDNode *N, SDValue &Lo,
541 SDValue LL, LH, RL, RH;
543 GetSplitOp(N->getOperand(2), LL, LH);
544 GetSplitOp(N->getOperand(3), RL, RH);
546 Lo = DAG.getNode(ISD::SELECT_CC, dl, LL.getValueType(), N->getOperand(0),
547 N->getOperand(1), LL, RL, N->getOperand(4));
548 Hi = DAG.getNode(ISD::SELECT_CC, dl, LH.getValueType(), N->getOperand(0),
549 N->getOperand(1), LH, RH, N->getOperand(4));
552 void DAGTypeLegalizer::SplitRes_UNDEF(SDNode *N, SDValue &Lo, SDValue &Hi) {
554 std::tie(LoVT, HiVT) = DAG.GetSplitDestVTs(N->getValueType(0));
555 Lo = DAG.getUNDEF(LoVT);
556 Hi = DAG.getUNDEF(HiVT);