[SelectionDAG] replace duplicated peekThroughBitcast helper functions; NFCI

[spatel]

Summary

x86 had 2 versions of peekThroughBitcast. DAGCombiner had 1. Plus, it had a 1-off implementation for the one-use variant.
The new code mimics the IR version where we have an optional param if the one-use constraint is requested. No functional change intended.

I'm proposing to put this next to isBitwiseNot() because I am planning to use it in there. Another option is next to the helpers in the ISD namespace (eg, ISD::isConstantSplatVector()). But if there's no good reason for those to be there, I'd prefer to pull everything over here if possible.

[RKSimon]

Would we be better off keeping the separate peekThroughOneUseBitcasts helper for clarity? Still putting them both in SelectionDAG

[spatel]

In D52285#1240311, @RKSimon wrote:

Would we be better off keeping the separate peekThroughOneUseBitcasts helper for clarity? Still putting them both in SelectionDAG

Either way is ok with me. I took this option since it's what we do in IR, but spelling it out in the name does enforce better readability. Anyone else have a preference?

[spatel]

Patch updated:
Use separate functions to differentiate the one-use constraint. This is effectively transferring the x86 code with the same names, so it's a smaller patch.

Implementation detail: the x86 code was checking for 'V.getNode()', but I'm not sure how that could be false, so I left that out of the new code.

[lebedev.ri]

Unless there is a need to conditionally use the one-use variant,
two separate functions seem cleaner. But no strong opinion here.

[RKSimon]

LGTM - thanks

include/llvm/CodeGen/SelectionDAGNodes.h

 bool isNullFPConstant(SDValue V);
 
 /// Returns true if \p V is an integer constant with all bits set.
 bool isAllOnesConstant(SDValue V);
 
 /// Returns true if \p V is a constant integer one.
 bool isOneConstant(SDValue V);
 
+/// Return the non-bitcasted source operand of \p V if it exists.
+/// If \p V is not a bitcasted value, it is returned as-is.
+SDValue peekThroughBitcasts(SDValue V);
+
+/// Return the non-bitcasted and one-use source operand of \p V if it exists.
+/// If \p V is not a bitcasted one-use value, it is returned as-is.
+SDValue peekThroughOneUseBitcasts(SDValue V);
+
 /// Returns true if \p V is a bitwise not operation. Assumes that an all ones
 /// constant is canonicalized to be operand 1.
 bool isBitwiseNot(SDValue V);
 
 /// Returns the SDNode if it is a constant splat BuildVector or constant int.
 ConstantSDNode *isConstOrConstSplat(SDValue N);
 
 /// Returns the SDNode if it is a constant splat BuildVector or constant float.

lib/CodeGen/SelectionDAG/DAGCombiner.cpp

 /// it is profitable to do so.
 bool DAGCombiner::isOneUseSetCC(SDValue N) const {
   SDValue N0, N1, N2;
   if (isSetCCEquivalent(N, N0, N1, N2) && N.getNode()->hasOneUse())
     return true;
   return false;
 }
 
-static SDValue peekThroughBitcast(SDValue V) {
-  while (V.getOpcode() == ISD::BITCAST)
-    V = V.getOperand(0);
-  return V;
-}
-
 // Returns the SDNode if it is a constant float BuildVector
 // or constant float.
 static SDNode *isConstantFPBuildVectorOrConstantFP(SDValue N) {
   if (isa<ConstantFPSDNode>(N))
     return N.getNode();
   if (ISD::isBuildVectorOfConstantFPSDNodes(N.getNode()))
     return N.getNode();
   return nullptr;
if (ConstantSDNode *Splat = isConstOrConstSplat(N))
     return Splat->isOne() && Splat->getAPIntValue().getBitWidth() == BitWidth;
   return false;
 }
 
 // Determines if it is a constant integer of all ones or a splatted vector of a
 // constant integer of all ones (with no undefs).
 // Do not permit build vector implicit truncation.
 static bool isAllOnesConstantOrAllOnesSplatConstant(SDValue N) {
-  N = peekThroughBitcast(N);
+  N = peekThroughBitcasts(N);
   unsigned BitWidth = N.getScalarValueSizeInBits();
   if (ConstantSDNode *Splat = isConstOrConstSplat(N))
     return Splat->isAllOnesValue() &&
            Splat->getAPIntValue().getBitWidth() == BitWidth;
   return false;
 }
 
 // Determines if a BUILD_VECTOR is composed of all-constants possibly mixed with
bool DAGCombiner::MergeStoresOfConstantsOrVecElts(
   if (UseVector) {
     if (IsConstantSrc) {
       SmallVector<SDValue, 8> BuildVector;
       for (unsigned I = 0; I != NumStores; ++I) {
         StoreSDNode *St = cast<StoreSDNode>(StoreNodes[I].MemNode);
         SDValue Val = St->getValue();
         // If constant is of the wrong type, convert it now.
         if (MemVT != Val.getValueType()) {
-          Val = peekThroughBitcast(Val);
+          Val = peekThroughBitcasts(Val);
           // Deal with constants of wrong size.
           if (ElementSizeBits != Val.getValueSizeInBits()) {
             EVT IntMemVT =
                 EVT::getIntegerVT(*DAG.getContext(), MemVT.getSizeInBits());
             if (isa<ConstantFPSDNode>(Val)) {
               // Not clear how to truncate FP values.
               return false;
             } else if (auto *C = dyn_cast<ConstantSDNode>(Val))
if (IsConstantSrc) {
       }
       StoredVal = DAG.getNode(MemVT.isVector() ? ISD::CONCAT_VECTORS
                                                : ISD::BUILD_VECTOR,
                               DL, StoreTy, BuildVector);
     } else {
       SmallVector<SDValue, 8> Ops;
       for (unsigned i = 0; i < NumStores; ++i) {
         StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
-        SDValue Val = peekThroughBitcast(St->getValue());
+        SDValue Val = peekThroughBitcasts(St->getValue());
         // All operands of BUILD_VECTOR / CONCAT_VECTOR must be of
         // type MemVT. If the underlying value is not the correct
         // type, but it is an extraction of an appropriate vector we
         // can recast Val to be of the correct type. This may require
         // converting between EXTRACT_VECTOR_ELT and
         // EXTRACT_SUBVECTOR.
         if ((MemVT != Val.getValueType()) &&
             (Val.getOpcode() == ISD::EXTRACT_VECTOR_ELT ||
if (UseVector) {
     // Construct a single integer constant which is made of the smaller
     // constant inputs.
     bool IsLE = DAG.getDataLayout().isLittleEndian();
     for (unsigned i = 0; i < NumStores; ++i) {
       unsigned Idx = IsLE ? (NumStores - 1 - i) : i;
       StoreSDNode *St  = cast<StoreSDNode>(StoreNodes[Idx].MemNode);
 
       SDValue Val = St->getValue();
-      Val = peekThroughBitcast(Val);
+      Val = peekThroughBitcasts(Val);
       StoreInt <<= ElementSizeBits;
       if (ConstantSDNode *C = dyn_cast<ConstantSDNode>(Val)) {
         StoreInt |= C->getAPIntValue()
                         .zextOrTrunc(ElementSizeBits)
                         .zextOrTrunc(SizeInBits);
       } else if (ConstantFPSDNode *C = dyn_cast<ConstantFPSDNode>(Val)) {
         StoreInt |= C->getValueAPF()
                         .bitcastToAPInt()

 void DAGCombiner::getStoreMergeCandidates(
     StoreSDNode *St, SmallVectorImpl<MemOpLink> &StoreNodes,
     SDNode *&RootNode) {
   // This holds the base pointer, index, and the offset in bytes from the base
   // pointer.
   BaseIndexOffset BasePtr = BaseIndexOffset::match(St, DAG);
   EVT MemVT = St->getMemoryVT();
 
-  SDValue Val = peekThroughBitcast(St->getValue());
+  SDValue Val = peekThroughBitcasts(St->getValue());
   // We must have a base and an offset.
   if (!BasePtr.getBase().getNode())
     return;
 
   // Do not handle stores to undef base pointers.
   if (BasePtr.getBase().isUndef())
     return;
 
if (IsLoadSrc) {
     // The memory operands must not be volatile.
     if (Ld->isVolatile() || Ld->isIndexed())
       return;
   }
   auto CandidateMatch = [&](StoreSDNode *Other, BaseIndexOffset &Ptr,
                             int64_t &Offset) -> bool {
     if (Other->isVolatile() || Other->isIndexed())
       return false;
-    SDValue Val = peekThroughBitcast(Other->getValue());
+    SDValue Val = peekThroughBitcasts(Other->getValue());
     // Allow merging constants of different types as integers.
     bool NoTypeMatch = (MemVT.isInteger()) ? !MemVT.bitsEq(Other->getMemoryVT())
                                            : Other->getMemoryVT() != MemVT;
     if (IsLoadSrc) {
       if (NoTypeMatch)
         return false;
       // The Load's Base Ptr must also match
       if (LoadSDNode *OtherLd = dyn_cast<LoadSDNode>(Val)) {
bool DAGCombiner::MergeConsecutiveStores(StoreSDNode *St) {
   if (ElementSizeBytes * 8 != MemVT.getSizeInBits())
     return false;
 
   if (!MemVT.isSimple())
     return false;
 
   // Perform an early exit check. Do not bother looking at stored values that
   // are not constants, loads, or extracted vector elements.
-  SDValue StoredVal = peekThroughBitcast(St->getValue());
+  SDValue StoredVal = peekThroughBitcasts(St->getValue());
   bool IsLoadSrc = isa<LoadSDNode>(StoredVal);
   bool IsConstantSrc = isa<ConstantSDNode>(StoredVal) ||
                        isa<ConstantFPSDNode>(StoredVal);
   bool IsExtractVecSrc = (StoredVal.getOpcode() == ISD::EXTRACT_VECTOR_ELT ||
                           StoredVal.getOpcode() == ISD::EXTRACT_SUBVECTOR);
 
   if (!IsConstantSrc && !IsLoadSrc && !IsExtractVecSrc)
     return false;
while (StoreNodes.size() > 1) {
     SmallVector<MemOpLink, 8> LoadNodes;
 
     // Find acceptable loads. Loads need to have the same chain (token factor),
     // must not be zext, volatile, indexed, and they must be consecutive.
     BaseIndexOffset LdBasePtr;
 
     for (unsigned i = 0; i < NumConsecutiveStores; ++i) {
       StoreSDNode *St = cast<StoreSDNode>(StoreNodes[i].MemNode);
-      SDValue Val = peekThroughBitcast(St->getValue());
+      SDValue Val = peekThroughBitcasts(St->getValue());
       LoadSDNode *Ld = cast<LoadSDNode>(Val);
 
       BaseIndexOffset LdPtr = BaseIndexOffset::match(Ld, DAG);
       // If this is not the first ptr that we check.
       int64_t LdOffset = 0;
       if (LdBasePtr.getBase().getNode()) {
         // The base ptr must be the same.
         if (!LdBasePtr.equalBaseIndex(LdPtr, DAG, LdOffset))
SDValue DAGCombiner::visitBUILD_VECTOR(SDNode *N) {
   // For example:
   //   (build_vector (i64 (bitcast (v2i32 X))), (i64 (bitcast (v2i32 X)))) ->
   //     (v2i64 (bitcast (concat_vectors (v2i32 X), (v2i32 X))))
   //
   // If X is a build_vector itself, the concat can become a larger build_vector.
   // TODO: Maybe this is useful for non-splat too?
   if (!LegalOperations) {
     if (SDValue Splat = cast<BuildVectorSDNode>(N)->getSplatValue()) {
-      Splat = peekThroughBitcast(Splat);
+      Splat = peekThroughBitcasts(Splat);
       EVT SrcVT = Splat.getValueType();
       if (SrcVT.isVector()) {
         unsigned NumElts = N->getNumOperands() * SrcVT.getVectorNumElements();
         EVT NewVT = EVT::getVectorVT(*DAG.getContext(),
                                      SrcVT.getVectorElementType(), NumElts);
         if (!LegalTypes || TLI.isTypeLegal(NewVT)) {
           SmallVector<SDValue, 8> Ops(N->getNumOperands(), Splat);
           SDValue Concat = DAG.getNode(ISD::CONCAT_VECTORS, SDLoc(N),
static SDValue combineConcatVectorOfExtracts(SDNode *N, SelectionDAG &DAG) {
   EVT OpVT = N->getOperand(0).getValueType();
   int NumElts = VT.getVectorNumElements();
   int NumOpElts = OpVT.getVectorNumElements();
 
   SDValue SV0 = DAG.getUNDEF(VT), SV1 = DAG.getUNDEF(VT);
   SmallVector<int, 8> Mask;
 
   for (SDValue Op : N->ops()) {
-    // Peek through any bitcast.
-    Op = peekThroughBitcast(Op);
+    Op = peekThroughBitcasts(Op);
 
     // UNDEF nodes convert to UNDEF shuffle mask values.
     if (Op.isUndef()) {
       Mask.append((unsigned)NumOpElts, -1);
       continue;
     }
 
     if (Op.getOpcode() != ISD::EXTRACT_SUBVECTOR)
       return SDValue();
 
     // What vector are we extracting the subvector from and at what index?
     SDValue ExtVec = Op.getOperand(0);
 
     // We want the EVT of the original extraction to correctly scale the
     // extraction index.
     EVT ExtVT = ExtVec.getValueType();
-
-    // Peek through any bitcast.
-    ExtVec = peekThroughBitcast(ExtVec);
+    ExtVec = peekThroughBitcasts(ExtVec);
 
     // UNDEF nodes convert to UNDEF shuffle mask values.
     if (ExtVec.isUndef()) {
       Mask.append((unsigned)NumOpElts, -1);
       continue;
     }
 
     if (!isa<ConstantSDNode>(Op.getOperand(1)))
static SDValue narrowExtractedVectorBinOp(SDNode *Extract, SelectionDAG &DAG) {
   unsigned NumElems = VT.getVectorNumElements();
   assert((ExtractIndex->getZExtValue() % NumElems) == 0 &&
          "Extract index is not a multiple of the vector length.");
   if (Extract->getOperand(0).getValueSizeInBits() != VT.getSizeInBits() * 2)
     return SDValue();
 
   // We are looking for an optionally bitcasted wide vector binary operator
   // feeding an extract subvector.
-  SDValue BinOp = peekThroughBitcast(Extract->getOperand(0));
+  SDValue BinOp = peekThroughBitcasts(Extract->getOperand(0));
 
   // TODO: The motivating case for this transform is an x86 AVX1 target. That
   // target has temptingly almost legal versions of bitwise logic ops in 256-bit
   // flavors, but no other 256-bit integer support. This could be extended to
   // handle any binop, but that may require fixing/adding other folds to avoid
   // codegen regressions.
   unsigned BOpcode = BinOp.getOpcode();
   if (BOpcode != ISD::AND && BOpcode != ISD::OR && BOpcode != ISD::XOR)
     return SDValue();
 
   // The binop must be a vector type, so we can chop it in half.
   EVT WideBVT = BinOp.getValueType();
   if (!WideBVT.isVector())
     return SDValue();
 
   // Bail out if the target does not support a narrower version of the binop.
   EVT NarrowBVT = EVT::getVectorVT(*DAG.getContext(), WideBVT.getScalarType(),
                                    WideBVT.getVectorNumElements() / 2);
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
   if (!TLI.isOperationLegalOrCustomOrPromote(BOpcode, NarrowBVT))
     return SDValue();
 
-  // Peek through bitcasts of the binary operator operands if needed.
-  SDValue LHS = peekThroughBitcast(BinOp.getOperand(0));
-  SDValue RHS = peekThroughBitcast(BinOp.getOperand(1));
+  SDValue LHS = peekThroughBitcasts(BinOp.getOperand(0));
+  SDValue RHS = peekThroughBitcasts(BinOp.getOperand(1));
 
   // We need at least one concatenation operation of a binop operand to make
   // this transform worthwhile. The concat must double the input vector sizes.
   // TODO: Should we also handle INSERT_SUBVECTOR patterns?
   bool ConcatL =
       LHS.getOpcode() == ISD::CONCAT_VECTORS && LHS.getNumOperands() == 2;
   bool ConcatR =
       RHS.getOpcode() == ISD::CONCAT_VECTORS && RHS.getNumOperands() == 2;
if (V->getOpcode() == ISD::CONCAT_VECTORS &&
       V->getOperand(0).getValueType() == NVT) {
     unsigned Idx = N->getConstantOperandVal(1);
     unsigned NumElems = NVT.getVectorNumElements();
     assert((Idx % NumElems) == 0 &&
            "IDX in concat is not a multiple of the result vector length.");
     return V->getOperand(Idx / NumElems);
   }
 
-  // Skip bitcasting
-  V = peekThroughBitcast(V);
+  V = peekThroughBitcasts(V);
 
   // If the input is a build vector. Try to make a smaller build vector.
   if (V->getOpcode() == ISD::BUILD_VECTOR) {
     if (auto *Idx = dyn_cast<ConstantSDNode>(N->getOperand(1))) {
       EVT InVT = V->getValueType(0);
       unsigned ExtractSize = NVT.getSizeInBits();
       unsigned EltSize = InVT.getScalarSizeInBits();
       // Only do this if we won't split any elements.
static SDValue combineTruncationShuffle(ShuffleVectorSDNode *SVN,
                                         SelectionDAG &DAG) {
   EVT VT = SVN->getValueType(0);
   bool IsBigEndian = DAG.getDataLayout().isBigEndian();
 
   // TODO Add support for big-endian when we have a test case.
   if (!VT.isInteger() || IsBigEndian)
     return SDValue();
 
-  SDValue N0 = peekThroughBitcast(SVN->getOperand(0));
+  SDValue N0 = peekThroughBitcasts(SVN->getOperand(0));
 
   unsigned Opcode = N0.getOpcode();
   if (Opcode != ISD::ANY_EXTEND_VECTOR_INREG &&
       Opcode != ISD::SIGN_EXTEND_VECTOR_INREG &&
       Opcode != ISD::ZERO_EXTEND_VECTOR_INREG)
     return SDValue();
 
   SDValue N00 = N0.getOperand(0);
if (SDValue Res = combineShuffleOfScalars(SVN, DAG, TLI))
       return Res;
 
   // If this shuffle only has a single input that is a bitcasted shuffle,
   // attempt to merge the 2 shuffles and suitably bitcast the inputs/output
   // back to their original types.
   if (N0.getOpcode() == ISD::BITCAST && N0.hasOneUse() &&
       N1.isUndef() && Level < AfterLegalizeVectorOps &&
       TLI.isTypeLegal(VT)) {
-
-    // Peek through the bitcast only if there is one user.
-    SDValue BC0 = N0;
-    while (BC0.getOpcode() == ISD::BITCAST) {
-      if (!BC0.hasOneUse())
-        break;
-      BC0 = BC0.getOperand(0);
-    }
-
     auto ScaleShuffleMask = [](ArrayRef<int> Mask, int Scale) {
       if (Scale == 1)
         return SmallVector<int, 8>(Mask.begin(), Mask.end());
 
       SmallVector<int, 8> NewMask;
       for (int M : Mask)
         for (int s = 0; s != Scale; ++s)
           NewMask.push_back(M < 0 ? -1 : Scale * M + s);
       return NewMask;
     };
     
+    SDValue BC0 = peekThroughOneUseBitcasts(N0);
     if (BC0.getOpcode() == ISD::VECTOR_SHUFFLE && BC0.hasOneUse()) {
       EVT SVT = VT.getScalarType();
       EVT InnerVT = BC0->getValueType(0);
       EVT InnerSVT = InnerVT.getScalarType();
 
       // Determine which shuffle works with the smaller scalar type.
       EVT ScaleVT = SVT.bitsLT(InnerSVT) ? VT : InnerVT;
       EVT ScaleSVT = ScaleVT.getScalarType();

 /// with the destination vector and a zero vector.
 /// e.g. AND V, <0xffffffff, 0, 0xffffffff, 0>. ==>
 ///      vector_shuffle V, Zero, <0, 4, 2, 4>
 SDValue DAGCombiner::XformToShuffleWithZero(SDNode *N) {
   assert(N->getOpcode() == ISD::AND && "Unexpected opcode!");
 
   EVT VT = N->getValueType(0);
   SDValue LHS = N->getOperand(0);
-  SDValue RHS = peekThroughBitcast(N->getOperand(1));
+  SDValue RHS = peekThroughBitcasts(N->getOperand(1));
   SDLoc DL(N);
 
   // Make sure we're not running after operation legalization where it
   // may have custom lowered the vector shuffles.
   if (LegalOperations)
     return SDValue();
 
   if (RHS.getOpcode() != ISD::BUILD_VECTOR)

lib/CodeGen/SelectionDAG/SelectionDAG.cpp

bool llvm::isAllOnesConstant(SDValue V) {
   return Const != nullptr && Const->isAllOnesValue();
 }
 
 bool llvm::isOneConstant(SDValue V) {
   ConstantSDNode *Const = dyn_cast<ConstantSDNode>(V);
   return Const != nullptr && Const->isOne();
 }
 
+SDValue llvm::peekThroughBitcasts(SDValue V) {
+  while (V.getOpcode() == ISD::BITCAST)
+    V = V.getOperand(0);
+  return V;
+}
+
+SDValue llvm::peekThroughOneUseBitcasts(SDValue V) {
+  while (V.getOpcode() == ISD::BITCAST && V.getOperand(0).hasOneUse())
+    V = V.getOperand(0);
+  return V;
+}
+
 bool llvm::isBitwiseNot(SDValue V) {
   if (V.getOpcode() != ISD::XOR)
     return false;
   ConstantSDNode *C = isConstOrConstSplat(V.getOperand(1));
   return C && C->isAllOnesValue();
 }
 
 ConstantSDNode *llvm::isConstOrConstSplat(SDValue N) {

lib/Target/X86/X86ISelLowering.cpp

static SDValue getShuffleVectorZeroOrUndef(SDValue V2, int Idx,
   int NumElems = VT.getVectorNumElements();
   SmallVector<int, 16> MaskVec(NumElems);
   for (int i = 0; i != NumElems; ++i)
     // If this is the insertion idx, put the low elt of V2 here.
     MaskVec[i] = (i == Idx) ? NumElems : i;
   return DAG.getVectorShuffle(VT, SDLoc(V2), V1, V2, MaskVec);
 }
 
-static SDValue peekThroughBitcasts(SDValue V) {
-  while (V.getNode() && V.getOpcode() == ISD::BITCAST)
-    V = V.getOperand(0);
-  return V;
-}
-
-static SDValue peekThroughOneUseBitcasts(SDValue V) {
-  while (V.getNode() && V.getOpcode() == ISD::BITCAST &&
-         V.getOperand(0).hasOneUse())
-    V = V.getOperand(0);
-  return V;
-}
-
 // Peek through EXTRACT_SUBVECTORs - typically used for AVX1 256-bit intops.
 static SDValue peekThroughEXTRACT_SUBVECTORs(SDValue V) {
   while (V.getOpcode() == ISD::EXTRACT_SUBVECTOR)
     V = V.getOperand(0);
   return V;
 }
 
 static const Constant *getTargetConstantFromNode(SDValue Op) {