Vector/Transforms/VectorTransferSplitRewritePatterns.cpp

//===- VectorTransferSplitRewritePatterns.cpp - Transfer Split Rewrites ---===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements target-independent patterns to rewrite a vector.transfer
// op into a fully in-bounds part and a partial part.
//
//===----------------------------------------------------------------------===//

#include <type_traits>

#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
#include "mlir/Dialect/Linalg/IR/Linalg.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Dialect/SCF/SCF.h"
#include "mlir/Dialect/StandardOps/IR/Ops.h"
#include "mlir/Dialect/Utils/StructuredOpsUtils.h"

#include "mlir/Dialect/Vector/Transforms/VectorTransforms.h"
#include "mlir/IR/Matchers.h"
#include "mlir/IR/PatternMatch.h"
#include "mlir/Interfaces/VectorInterfaces.h"

#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"

#define DEBUG_TYPE "vector-transfer-split"

using namespace mlir;
using namespace mlir::vector;

static Optional<int64_t> extractConstantIndex(Value v) {
  if (auto cstOp = v.getDefiningOp<arith::ConstantIndexOp>())
    return cstOp.value();
  if (auto affineApplyOp = v.getDefiningOp<AffineApplyOp>())
    if (affineApplyOp.getAffineMap().isSingleConstant())
      return affineApplyOp.getAffineMap().getSingleConstantResult();
  return None;
}

// Missing foldings of scf.if make it necessary to perform poor man's folding
// eagerly, especially in the case of unrolling. In the future, this should go
// away once scf.if folds properly.
static Value createFoldedSLE(RewriterBase &b, Value v, Value ub) {
  auto maybeCstV = extractConstantIndex(v);
  auto maybeCstUb = extractConstantIndex(ub);
  if (maybeCstV && maybeCstUb && *maybeCstV < *maybeCstUb)
    return Value();
  return b.create<arith::CmpIOp>(v.getLoc(), arith::CmpIPredicate::sle, v, ub);
}

/// Build the condition to ensure that a particular VectorTransferOpInterface
/// is in-bounds.
static Value createInBoundsCond(RewriterBase &b,
                                VectorTransferOpInterface xferOp) {
  assert(xferOp.permutation_map().isMinorIdentity() &&
         "Expected minor identity map");
  Value inBoundsCond;
  xferOp.zipResultAndIndexing([&](int64_t resultIdx, int64_t indicesIdx) {
    // Zip over the resulting vector shape and memref indices.
    // If the dimension is known to be in-bounds, it does not participate in
    // the construction of `inBoundsCond`.
    if (xferOp.isDimInBounds(resultIdx))
      return;
    // Fold or create the check that `index + vector_size` <= `memref_size`.
    Location loc = xferOp.getLoc();
    int64_t vectorSize = xferOp.getVectorType().getDimSize(resultIdx);
    auto d0 = getAffineDimExpr(0, xferOp.getContext());
    auto vs = getAffineConstantExpr(vectorSize, xferOp.getContext());
    Value sum =
        makeComposedAffineApply(b, loc, d0 + vs, xferOp.indices()[indicesIdx]);
    Value cond = createFoldedSLE(
        b, sum, vector::createOrFoldDimOp(b, loc, xferOp.source(), indicesIdx));
    if (!cond)
      return;
    // Conjunction over all dims for which we are in-bounds.
    if (inBoundsCond)
      inBoundsCond = b.create<arith::AndIOp>(loc, inBoundsCond, cond);
    else
      inBoundsCond = cond;
  });
  return inBoundsCond;
}

/// Split a vector.transfer operation into an in-bounds (i.e., no out-of-bounds
/// masking) fastpath and a slowpath.
/// If `ifOp` is not null and the result is `success, the `ifOp` points to the
/// newly created conditional upon function return.
/// To accomodate for the fact that the original vector.transfer indexing may be
/// arbitrary and the slow path indexes @[0...0] in the temporary buffer, the
/// scf.if op returns a view and values of type index.
/// At this time, only vector.transfer_read case is implemented.
///
/// Example (a 2-D vector.transfer_read):
/// ```
///    %1 = vector.transfer_read %0[...], %pad : memref<A...>, vector<...>
/// ```
/// is transformed into:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      // fastpath, direct cast
///      memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view : compatibleMemRefType, index, index
///    } else {
///      // slowpath, not in-bounds vector.transfer or linalg.copy.
///      memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %4 : compatibleMemRefType, index, index
//     }
///    %0 = vector.transfer_read %1#0[%1#1, %1#2] {in_bounds = [true ... true]}
/// ```
/// where `alloc` is a top of the function alloca'ed buffer of one vector.
///
/// Preconditions:
///  1. `xferOp.permutation_map()` must be a minor identity map
///  2. the rank of the `xferOp.memref()` and the rank of the `xferOp.vector()`
///  must be equal. This will be relaxed in the future but requires
///  rank-reducing subviews.
static LogicalResult
splitFullAndPartialTransferPrecondition(VectorTransferOpInterface xferOp) {
  // TODO: support 0-d corner case.
  if (xferOp.getTransferRank() == 0)
    return failure();

  // TODO: expand support to these 2 cases.
  if (!xferOp.permutation_map().isMinorIdentity())
    return failure();
  // Must have some out-of-bounds dimension to be a candidate for splitting.
  if (!xferOp.hasOutOfBoundsDim())
    return failure();
  // Don't split transfer operations directly under IfOp, this avoids applying
  // the pattern recursively.
  // TODO: improve the filtering condition to make it more applicable.
  if (isa<scf::IfOp>(xferOp->getParentOp()))
    return failure();
  return success();
}

/// Given two MemRefTypes `aT` and `bT`, return a MemRefType to which both can
/// be cast. If the MemRefTypes don't have the same rank or are not strided,
/// return null; otherwise:
///   1. if `aT` and `bT` are cast-compatible, return `aT`.
///   2. else return a new MemRefType obtained by iterating over the shape and
///   strides and:
///     a. keeping the ones that are static and equal across `aT` and `bT`.
///     b. using a dynamic shape and/or stride for the dimensions that don't
///        agree.
static MemRefType getCastCompatibleMemRefType(MemRefType aT, MemRefType bT) {
  if (memref::CastOp::areCastCompatible(aT, bT))
    return aT;
  if (aT.getRank() != bT.getRank())
    return MemRefType();
  int64_t aOffset, bOffset;
  SmallVector<int64_t, 4> aStrides, bStrides;
  if (failed(getStridesAndOffset(aT, aStrides, aOffset)) ||
      failed(getStridesAndOffset(bT, bStrides, bOffset)) ||
      aStrides.size() != bStrides.size())
    return MemRefType();

  ArrayRef<int64_t> aShape = aT.getShape(), bShape = bT.getShape();
  int64_t resOffset;
  SmallVector<int64_t, 4> resShape(aT.getRank(), 0),
      resStrides(bT.getRank(), 0);
  for (int64_t idx = 0, e = aT.getRank(); idx < e; ++idx) {
    resShape[idx] =
        (aShape[idx] == bShape[idx]) ? aShape[idx] : ShapedType::kDynamicSize;
    resStrides[idx] = (aStrides[idx] == bStrides[idx])
                          ? aStrides[idx]
                          : ShapedType::kDynamicStrideOrOffset;
  }
  resOffset =
      (aOffset == bOffset) ? aOffset : ShapedType::kDynamicStrideOrOffset;
  return MemRefType::get(
      resShape, aT.getElementType(),
      makeStridedLinearLayoutMap(resStrides, resOffset, aT.getContext()));
}

/// Operates under a scoped context to build the intersection between the
/// view `xferOp.source()` @ `xferOp.indices()` and the view `alloc`.
// TODO: view intersection/union/differences should be a proper std op.
static std::pair<Value, Value>
createSubViewIntersection(RewriterBase &b, VectorTransferOpInterface xferOp,
                          Value alloc) {
  Location loc = xferOp.getLoc();
  int64_t memrefRank = xferOp.getShapedType().getRank();
  // TODO: relax this precondition, will require rank-reducing subviews.
  assert(memrefRank == alloc.getType().cast<MemRefType>().getRank() &&
         "Expected memref rank to match the alloc rank");
  ValueRange leadingIndices =
      xferOp.indices().take_front(xferOp.getLeadingShapedRank());
  SmallVector<OpFoldResult, 4> sizes;
  sizes.append(leadingIndices.begin(), leadingIndices.end());
  auto isaWrite = isa<vector::TransferWriteOp>(xferOp);
  xferOp.zipResultAndIndexing([&](int64_t resultIdx, int64_t indicesIdx) {
    using MapList = ArrayRef<ArrayRef<AffineExpr>>;
    Value dimMemRef = vector::createOrFoldDimOp(b, xferOp.getLoc(),
                                                xferOp.source(), indicesIdx);
    Value dimAlloc = b.create<memref::DimOp>(loc, alloc, resultIdx);
    Value index = xferOp.indices()[indicesIdx];
    AffineExpr i, j, k;
    bindDims(xferOp.getContext(), i, j, k);
    SmallVector<AffineMap, 4> maps =
        AffineMap::inferFromExprList(MapList{{i - j, k}});
    // affine_min(%dimMemRef - %index, %dimAlloc)
    Value affineMin = b.create<AffineMinOp>(
        loc, index.getType(), maps[0], ValueRange{dimMemRef, index, dimAlloc});
    sizes.push_back(affineMin);
  });

  SmallVector<OpFoldResult> srcIndices = llvm::to_vector<4>(llvm::map_range(
      xferOp.indices(), [](Value idx) -> OpFoldResult { return idx; }));
  SmallVector<OpFoldResult> destIndices(memrefRank, b.getIndexAttr(0));
  SmallVector<OpFoldResult> strides(memrefRank, b.getIndexAttr(1));
  auto copySrc = b.create<memref::SubViewOp>(
      loc, isaWrite ? alloc : xferOp.source(), srcIndices, sizes, strides);
  auto copyDest = b.create<memref::SubViewOp>(
      loc, isaWrite ? xferOp.source() : alloc, destIndices, sizes, strides);
  return std::make_pair(copySrc, copyDest);
}

/// Given an `xferOp` for which:
///   1. `inBoundsCond` and a `compatibleMemRefType` have been computed.
///   2. a memref of single vector `alloc` has been allocated.
/// Produce IR resembling:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      %view = memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view, ... : compatibleMemRefType, index, index
///    } else {
///      %2 = linalg.fill(%pad, %alloc)
///      %3 = subview %view [...][...][...]
///      %4 = subview %alloc [0, 0] [...] [...]
///      linalg.copy(%3, %4)
///      %5 = memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %5, ... : compatibleMemRefType, index, index
///   }
/// ```
/// Return the produced scf::IfOp.
static scf::IfOp
createFullPartialLinalgCopy(RewriterBase &b, vector::TransferReadOp xferOp,
                            TypeRange returnTypes, Value inBoundsCond,
                            MemRefType compatibleMemRefType, Value alloc) {
  Location loc = xferOp.getLoc();
  Value zero = b.create<arith::ConstantIndexOp>(loc, 0);
  Value memref = xferOp.source();
  return b.create<scf::IfOp>(
      loc, returnTypes, inBoundsCond,
      [&](OpBuilder &b, Location loc) {
        Value res = memref;
        if (compatibleMemRefType != xferOp.getShapedType())
          res = b.create<memref::CastOp>(loc, memref, compatibleMemRefType);
        scf::ValueVector viewAndIndices{res};
        viewAndIndices.insert(viewAndIndices.end(), xferOp.indices().begin(),
                              xferOp.indices().end());
        b.create<scf::YieldOp>(loc, viewAndIndices);
      },
      [&](OpBuilder &b, Location loc) {
        b.create<linalg::FillOp>(loc, xferOp.padding(), alloc);
        // Take partial subview of memref which guarantees no dimension
        // overflows.
        IRRewriter rewriter(b);
        std::pair<Value, Value> copyArgs = createSubViewIntersection(
            rewriter, cast<VectorTransferOpInterface>(xferOp.getOperation()),
            alloc);
        b.create<linalg::CopyOp>(loc, copyArgs.first, copyArgs.second);
        Value casted =
            b.create<memref::CastOp>(loc, alloc, compatibleMemRefType);
        scf::ValueVector viewAndIndices{casted};
        viewAndIndices.insert(viewAndIndices.end(), xferOp.getTransferRank(),
                              zero);
        b.create<scf::YieldOp>(loc, viewAndIndices);
      });
}

/// Given an `xferOp` for which:
///   1. `inBoundsCond` and a `compatibleMemRefType` have been computed.
///   2. a memref of single vector `alloc` has been allocated.
/// Produce IR resembling:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view, ... : compatibleMemRefType, index, index
///    } else {
///      %2 = vector.transfer_read %view[...], %pad : memref<A...>, vector<...>
///      %3 = vector.type_cast %extra_alloc :
///        memref<...> to memref<vector<...>>
///      store %2, %3[] : memref<vector<...>>
///      %4 = memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %4, ... : compatibleMemRefType, index, index
///   }
/// ```
/// Return the produced scf::IfOp.
static scf::IfOp createFullPartialVectorTransferRead(
    RewriterBase &b, vector::TransferReadOp xferOp, TypeRange returnTypes,
    Value inBoundsCond, MemRefType compatibleMemRefType, Value alloc) {
  Location loc = xferOp.getLoc();
  scf::IfOp fullPartialIfOp;
  Value zero = b.create<arith::ConstantIndexOp>(loc, 0);
  Value memref = xferOp.source();
  return b.create<scf::IfOp>(
      loc, returnTypes, inBoundsCond,
      [&](OpBuilder &b, Location loc) {
        Value res = memref;
        if (compatibleMemRefType != xferOp.getShapedType())
          res = b.create<memref::CastOp>(loc, memref, compatibleMemRefType);
        scf::ValueVector viewAndIndices{res};
        viewAndIndices.insert(viewAndIndices.end(), xferOp.indices().begin(),
                              xferOp.indices().end());
        b.create<scf::YieldOp>(loc, viewAndIndices);
      },
      [&](OpBuilder &b, Location loc) {
        Operation *newXfer = b.clone(*xferOp.getOperation());
        Value vector = cast<VectorTransferOpInterface>(newXfer).vector();
        b.create<memref::StoreOp>(
            loc, vector,
            b.create<vector::TypeCastOp>(
                loc, MemRefType::get({}, vector.getType()), alloc));

        Value casted =
            b.create<memref::CastOp>(loc, alloc, compatibleMemRefType);
        scf::ValueVector viewAndIndices{casted};
        viewAndIndices.insert(viewAndIndices.end(), xferOp.getTransferRank(),
                              zero);
        b.create<scf::YieldOp>(loc, viewAndIndices);
      });
}

/// Given an `xferOp` for which:
///   1. `inBoundsCond` and a `compatibleMemRefType` have been computed.
///   2. a memref of single vector `alloc` has been allocated.
/// Produce IR resembling:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view, ... : compatibleMemRefType, index, index
///    } else {
///      %3 = vector.type_cast %extra_alloc :
///        memref<...> to memref<vector<...>>
///      %4 = memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %4, ... : compatibleMemRefType, index, index
///   }
/// ```
static ValueRange
getLocationToWriteFullVec(RewriterBase &b, vector::TransferWriteOp xferOp,
                          TypeRange returnTypes, Value inBoundsCond,
                          MemRefType compatibleMemRefType, Value alloc) {
  Location loc = xferOp.getLoc();
  Value zero = b.create<arith::ConstantIndexOp>(loc, 0);
  Value memref = xferOp.source();
  return b
      .create<scf::IfOp>(
          loc, returnTypes, inBoundsCond,
          [&](OpBuilder &b, Location loc) {
            Value res = memref;
            if (compatibleMemRefType != xferOp.getShapedType())
              res = b.create<memref::CastOp>(loc, memref, compatibleMemRefType);
            scf::ValueVector viewAndIndices{res};
            viewAndIndices.insert(viewAndIndices.end(),
                                  xferOp.indices().begin(),
                                  xferOp.indices().end());
            b.create<scf::YieldOp>(loc, viewAndIndices);
          },
          [&](OpBuilder &b, Location loc) {
            Value casted =
                b.create<memref::CastOp>(loc, alloc, compatibleMemRefType);
            scf::ValueVector viewAndIndices{casted};
            viewAndIndices.insert(viewAndIndices.end(),
                                  xferOp.getTransferRank(), zero);
            b.create<scf::YieldOp>(loc, viewAndIndices);
          })
      ->getResults();
}

/// Given an `xferOp` for which:
///   1. `inBoundsCond` has been computed.
///   2. a memref of single vector `alloc` has been allocated.
///   3. it originally wrote to %view
/// Produce IR resembling:
/// ```
///    %notInBounds = arith.xori %inBounds, %true
///    scf.if (%notInBounds) {
///      %3 = subview %alloc [...][...][...]
///      %4 = subview %view [0, 0][...][...]
///      linalg.copy(%3, %4)
///   }
/// ```
static void createFullPartialLinalgCopy(RewriterBase &b,
                                        vector::TransferWriteOp xferOp,
                                        Value inBoundsCond, Value alloc) {
  Location loc = xferOp.getLoc();
  auto notInBounds = b.create<arith::XOrIOp>(
      loc, inBoundsCond, b.create<arith::ConstantIntOp>(loc, true, 1));
  b.create<scf::IfOp>(loc, notInBounds, [&](OpBuilder &b, Location loc) {
    IRRewriter rewriter(b);
    std::pair<Value, Value> copyArgs = createSubViewIntersection(
        rewriter, cast<VectorTransferOpInterface>(xferOp.getOperation()),
        alloc);
    b.create<linalg::CopyOp>(loc, copyArgs.first, copyArgs.second);
    b.create<scf::YieldOp>(loc, ValueRange{});
  });
}

/// Given an `xferOp` for which:
///   1. `inBoundsCond` has been computed.
///   2. a memref of single vector `alloc` has been allocated.
///   3. it originally wrote to %view
/// Produce IR resembling:
/// ```
///    %notInBounds = arith.xori %inBounds, %true
///    scf.if (%notInBounds) {
///      %2 = load %alloc : memref<vector<...>>
///      vector.transfer_write %2, %view[...] : memref<A...>, vector<...>
///   }
/// ```
static void createFullPartialVectorTransferWrite(RewriterBase &b,
                                                 vector::TransferWriteOp xferOp,
                                                 Value inBoundsCond,
                                                 Value alloc) {
  Location loc = xferOp.getLoc();
  auto notInBounds = b.create<arith::XOrIOp>(
      loc, inBoundsCond, b.create<arith::ConstantIntOp>(loc, true, 1));
  b.create<scf::IfOp>(loc, notInBounds, [&](OpBuilder &b, Location loc) {
    BlockAndValueMapping mapping;
    Value load = b.create<memref::LoadOp>(
        loc, b.create<vector::TypeCastOp>(
                 loc, MemRefType::get({}, xferOp.vector().getType()), alloc));
    mapping.map(xferOp.vector(), load);
    b.clone(*xferOp.getOperation(), mapping);
    b.create<scf::YieldOp>(loc, ValueRange{});
  });
}

/// Split a vector.transfer operation into an in-bounds (i.e., no out-of-bounds
/// masking) fastpath and a slowpath.
///
/// For vector.transfer_read:
/// If `ifOp` is not null and the result is `success, the `ifOp` points to the
/// newly created conditional upon function return.
/// To accomodate for the fact that the original vector.transfer indexing may be
/// arbitrary and the slow path indexes @[0...0] in the temporary buffer, the
/// scf.if op returns a view and values of type index.
///
/// Example (a 2-D vector.transfer_read):
/// ```
///    %1 = vector.transfer_read %0[...], %pad : memref<A...>, vector<...>
/// ```
/// is transformed into:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      // fastpath, direct cast
///      memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view : compatibleMemRefType, index, index
///    } else {
///      // slowpath, not in-bounds vector.transfer or linalg.copy.
///      memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %4 : compatibleMemRefType, index, index
//     }
///    %0 = vector.transfer_read %1#0[%1#1, %1#2] {in_bounds = [true ... true]}
/// ```
/// where `alloc` is a top of the function alloca'ed buffer of one vector.
///
/// For vector.transfer_write:
/// There are 2 conditional blocks. First a block to decide which memref and
/// indices to use for an unmasked, inbounds write. Then a conditional block to
/// further copy a partial buffer into the final result in the slow path case.
///
/// Example (a 2-D vector.transfer_write):
/// ```
///    vector.transfer_write %arg, %0[...], %pad : memref<A...>, vector<...>
/// ```
/// is transformed into:
/// ```
///    %1:3 = scf.if (%inBounds) {
///      memref.cast %A: memref<A...> to compatibleMemRefType
///      scf.yield %view : compatibleMemRefType, index, index
///    } else {
///      memref.cast %alloc: memref<B...> to compatibleMemRefType
///      scf.yield %4 : compatibleMemRefType, index, index
///     }
///    %0 = vector.transfer_write %arg, %1#0[%1#1, %1#2] {in_bounds = [true ...
///                                                                    true]}
///    scf.if (%notInBounds) {
///      // slowpath: not in-bounds vector.transfer or linalg.copy.
///    }
/// ```
/// where `alloc` is a top of the function alloca'ed buffer of one vector.
///
/// Preconditions:
///  1. `xferOp.permutation_map()` must be a minor identity map
///  2. the rank of the `xferOp.source()` and the rank of the `xferOp.vector()`
///  must be equal. This will be relaxed in the future but requires
///  rank-reducing subviews.
LogicalResult mlir::vector::splitFullAndPartialTransfer(
    RewriterBase &b, VectorTransferOpInterface xferOp,
    VectorTransformsOptions options, scf::IfOp *ifOp) {
  if (options.vectorTransferSplit == VectorTransferSplit::None)
    return failure();

  SmallVector<bool, 4> bools(xferOp.getTransferRank(), true);
  auto inBoundsAttr = b.getBoolArrayAttr(bools);
  if (options.vectorTransferSplit == VectorTransferSplit::ForceInBounds) {
    xferOp->setAttr(xferOp.getInBoundsAttrName(), inBoundsAttr);
    return success();
  }

  // Assert preconditions. Additionally, keep the variables in an inner scope to
  // ensure they aren't used in the wrong scopes further down.
  {
    assert(succeeded(splitFullAndPartialTransferPrecondition(xferOp)) &&
           "Expected splitFullAndPartialTransferPrecondition to hold");

    auto xferReadOp = dyn_cast<vector::TransferReadOp>(xferOp.getOperation());
    auto xferWriteOp = dyn_cast<vector::TransferWriteOp>(xferOp.getOperation());

    if (!(xferReadOp || xferWriteOp))
      return failure();
    if (xferWriteOp && xferWriteOp.mask())
      return failure();
    if (xferReadOp && xferReadOp.mask())
      return failure();
  }

  RewriterBase::InsertionGuard guard(b);
  b.setInsertionPoint(xferOp);
  Value inBoundsCond = createInBoundsCond(
      b, cast<VectorTransferOpInterface>(xferOp.getOperation()));
  if (!inBoundsCond)
    return failure();

  // Top of the function `alloc` for transient storage.
  Value alloc;
  {
    FuncOp funcOp = xferOp->getParentOfType<FuncOp>();
    RewriterBase::InsertionGuard guard(b);
    b.setInsertionPointToStart(&funcOp.getRegion().front());
    auto shape = xferOp.getVectorType().getShape();
    Type elementType = xferOp.getVectorType().getElementType();
    alloc = b.create<memref::AllocaOp>(funcOp.getLoc(),
                                       MemRefType::get(shape, elementType),
                                       ValueRange{}, b.getI64IntegerAttr(32));
  }

  MemRefType compatibleMemRefType =
      getCastCompatibleMemRefType(xferOp.getShapedType().cast<MemRefType>(),
                                  alloc.getType().cast<MemRefType>());
  if (!compatibleMemRefType)
    return failure();

  SmallVector<Type, 4> returnTypes(1 + xferOp.getTransferRank(),
                                   b.getIndexType());
  returnTypes[0] = compatibleMemRefType;

  if (auto xferReadOp =
          dyn_cast<vector::TransferReadOp>(xferOp.getOperation())) {
    // Read case: full fill + partial copy -> in-bounds vector.xfer_read.
    scf::IfOp fullPartialIfOp =
        options.vectorTransferSplit == VectorTransferSplit::VectorTransfer
            ? createFullPartialVectorTransferRead(b, xferReadOp, returnTypes,
                                                  inBoundsCond,
                                                  compatibleMemRefType, alloc)
            : createFullPartialLinalgCopy(b, xferReadOp, returnTypes,
                                          inBoundsCond, compatibleMemRefType,
                                          alloc);
    if (ifOp)
      *ifOp = fullPartialIfOp;

    // Set existing read op to in-bounds, it always reads from a full buffer.
    for (unsigned i = 0, e = returnTypes.size(); i != e; ++i)
      xferReadOp.setOperand(i, fullPartialIfOp.getResult(i));

    xferOp->setAttr(xferOp.getInBoundsAttrName(), inBoundsAttr);

    return success();
  }

  auto xferWriteOp = cast<vector::TransferWriteOp>(xferOp.getOperation());

  // Decide which location to write the entire vector to.
  auto memrefAndIndices = getLocationToWriteFullVec(
      b, xferWriteOp, returnTypes, inBoundsCond, compatibleMemRefType, alloc);

  // Do an in bounds write to either the output or the extra allocated buffer.
  // The operation is cloned to prevent deleting information needed for the
  // later IR creation.
  BlockAndValueMapping mapping;
  mapping.map(xferWriteOp.source(), memrefAndIndices.front());
  mapping.map(xferWriteOp.indices(), memrefAndIndices.drop_front());
  auto *clone = b.clone(*xferWriteOp, mapping);
  clone->setAttr(xferWriteOp.getInBoundsAttrName(), inBoundsAttr);

  // Create a potential copy from the allocated buffer to the final output in
  // the slow path case.
  if (options.vectorTransferSplit == VectorTransferSplit::VectorTransfer)
    createFullPartialVectorTransferWrite(b, xferWriteOp, inBoundsCond, alloc);
  else
    createFullPartialLinalgCopy(b, xferWriteOp, inBoundsCond, alloc);

  xferOp->erase();

  return success();
}

LogicalResult mlir::vector::VectorTransferFullPartialRewriter::matchAndRewrite(
    Operation *op, PatternRewriter &rewriter) const {
  auto xferOp = dyn_cast<VectorTransferOpInterface>(op);
  if (!xferOp || failed(splitFullAndPartialTransferPrecondition(xferOp)) ||
      failed(filter(xferOp)))
    return failure();
  rewriter.startRootUpdate(xferOp);
  if (succeeded(splitFullAndPartialTransfer(rewriter, xferOp, options))) {
    rewriter.finalizeRootUpdate(xferOp);
    return success();
  }
  rewriter.cancelRootUpdate(xferOp);
  return failure();
}