ReshapePatterns.cpp

Go to the documentation of this file.

//===- RankReductionPatterns.cpp - Patterns related to rank reductions ----===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "mlir/Dialect/Affine/IR/AffineOps.h"
#include "mlir/Dialect/Arith/Utils/Utils.h"
#include "mlir/Dialect/Tensor/IR/Tensor.h"
#include "mlir/Dialect/Tensor/Transforms/Transforms.h"
#include "mlir/IR/PatternMatch.h"
#include "mlir/Interfaces/ValueBoundsOpInterface.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/LogicalResult.h"
 
using namespace mlir;
using namespace mlir::tensor;
 
namespace {
/// Fold expand_shape(extract_slice) ops that cancel itself out.
struct FoldExpandOfRankReducingExtract
    : public OpRewritePattern<ExpandShapeOp> {
  using OpRewritePattern<ExpandShapeOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(ExpandShapeOp expandShapeOp,
                                PatternRewriter &rewriter) const override {
    RankedTensorType resultType = expandShapeOp.getResultType();
    auto extractSliceOp =
        expandShapeOp.getSrc().getDefiningOp<ExtractSliceOp>();
    if (!extractSliceOp)
      return failure();
    RankedTensorType srcType = extractSliceOp.getSourceType();
 
    // Only cases where the ExpandShapeOp can be folded away entirely are
    // supported. Moreover, only simple cases where the resulting ExtractSliceOp
    // has no rank-reduction anymore are supported at the moment.
    RankedTensorType nonReducingExtractType = ExtractSliceOp::inferResultType(
        srcType, extractSliceOp.getStaticOffsets(),
        extractSliceOp.getStaticSizes(), extractSliceOp.getStaticStrides());
    if (nonReducingExtractType != resultType)
      return failure();
 
    SmallVector<OpFoldResult> mixedOffsets = extractSliceOp.getMixedOffsets();
    SmallVector<OpFoldResult> mixedSizes = extractSliceOp.getMixedSizes();
    SmallVector<OpFoldResult> mixedStrides = extractSliceOp.getMixedStrides();
    rewriter.replaceOpWithNewOp<tensor::ExtractSliceOp>(
        expandShapeOp, extractSliceOp.getSource(), mixedOffsets, mixedSizes,
        mixedStrides);
    return success();
  }
};
 
/// Fold collapse_shape which only removes static dimensions of size `1`
/// into extract_slice.
struct FoldUnPaddingCollapseIntoExtract
    : public OpRewritePattern<tensor::CollapseShapeOp> {
  using OpRewritePattern<tensor::CollapseShapeOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(tensor::CollapseShapeOp collapseShapeOp,
                                PatternRewriter &rewriter) const override {
    auto extractSliceOp =
        collapseShapeOp.getSrc().getDefiningOp<tensor::ExtractSliceOp>();
    // Collapse cannot be folded away with multiple users of the extract slice
    // and it is not necessarily beneficial to only convert the collapse into
    // another extract slice.
    if (!extractSliceOp || !extractSliceOp->hasOneUse())
      return failure();
 
    // Only fold away simple collapse where all removed dimensions have static
    // size `1`.
    SliceVerificationResult res = isRankReducedType(
        collapseShapeOp.getSrcType(), collapseShapeOp.getResultType());
    if (res != SliceVerificationResult::Success)
      return rewriter.notifyMatchFailure(collapseShapeOp,
                                         "expected unpadding collapse");
 
    Value unPaddedExtractSlice = rewriter.create<tensor::ExtractSliceOp>(
        extractSliceOp.getLoc(), collapseShapeOp.getResultType(),
        extractSliceOp.getSource(), extractSliceOp.getMixedOffsets(),
        extractSliceOp.getMixedSizes(), extractSliceOp.getMixedStrides());
    rewriter.replaceOp(collapseShapeOp, unPaddedExtractSlice);
    return success();
  }
};
 
/// Fold insert_slice(collapse_shape) ops that cancel itself out.
template <typename OpTy>
struct FoldInsertOfRankReducingInsert : public OpRewritePattern<OpTy> {
  using OpRewritePattern<OpTy>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(OpTy insertSliceOp,
                                PatternRewriter &rewriter) const override {
    auto collapseShapeOp =
        insertSliceOp.getSource().template getDefiningOp<CollapseShapeOp>();
    if (!collapseShapeOp)
      return failure();
    RankedTensorType srcType = collapseShapeOp.getSrcType();
 
    // Only cases where the CollapseShapeOp can be folded away entirely are
    // supported. Moreover, only simple cases where the resulting InsertSliceOp
    // has no rank-reduction anymore are supported at the moment.
    RankedTensorType nonReducingInsertType =
        RankedTensorType::get(insertSliceOp.getStaticSizes(),
                              insertSliceOp.getDestType().getElementType());
    if (nonReducingInsertType != srcType)
      return failure();
 
    SmallVector<OpFoldResult> mixedOffsets = insertSliceOp.getMixedOffsets();
    SmallVector<OpFoldResult> mixedSizes = insertSliceOp.getMixedSizes();
    SmallVector<OpFoldResult> mixedStrides = insertSliceOp.getMixedStrides();
    rewriter.replaceOpWithNewOp<OpTy>(insertSliceOp, collapseShapeOp.getSrc(),
                                      insertSliceOp.getDest(), mixedOffsets,
                                      mixedSizes, mixedStrides);
    return success();
  }
};
 
/// Fold expand_shape which only adds static dimensions of size `1`
/// into insert_slice.
template <typename OpTy>
struct FoldPaddingExpandIntoInsert : public OpRewritePattern<OpTy> {
  using OpRewritePattern<OpTy>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(OpTy insertSliceOp,
                                PatternRewriter &rewriter) const override {
    auto expandShapeOp = insertSliceOp.getSource()
                             .template getDefiningOp<tensor::ExpandShapeOp>();
    if (!expandShapeOp)
      return failure();
 
    // Only fold away simple expansion where all added dimensions have static
    // size `1`.
    SliceVerificationResult res = isRankReducedType(
        expandShapeOp.getResultType(), expandShapeOp.getSrcType());
    if (res != SliceVerificationResult::Success)
      return rewriter.notifyMatchFailure(insertSliceOp,
                                         "expected rank increasing expansion");
 
    rewriter.modifyOpInPlace(insertSliceOp, [&]() {
      insertSliceOp.getSourceMutable().assign(expandShapeOp.getSrc());
    });
    return success();
  }
};
 
/// Pattern to bubble up a tensor.expand_shape op through a producer
/// tensor.collapse_shape op that has non intersecting reassociations.
struct BubbleUpExpandThroughParallelCollapse
    : public OpRewritePattern<tensor::ExpandShapeOp> {
  using OpRewritePattern<tensor::ExpandShapeOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(tensor::ExpandShapeOp expandOp,
                                PatternRewriter &rewriter) const override {
    auto collapseOp =
        expandOp.getSrc().getDefiningOp<tensor::CollapseShapeOp>();
    if (!collapseOp)
      return failure();
    auto expandReInds = expandOp.getReassociationIndices();
    auto collapseReInds = collapseOp.getReassociationIndices();
 
    // Special case where the collapsed tensor to expand is a 0-D tensor,
    // then the reassociation maps will be empty and not produce valid results.
    if (expandReInds.size() == 0) {
      return failure();
    }
 
    // Reshapes are parallel to each other (by construction the number of
    // reassociations specified in the collapse and expand are the same), if at
    // any position
    // 1. either the reassociation indices are of the same size, or
    // 2. either the reassociation in the collapse or the expand is of size 1.
    ArrayRef<int64_t> staticSourceSize = collapseOp.getSrcType().getShape();
    ArrayRef<int64_t> staticResultSize = expandOp.getStaticOutputShape();
    for (auto [expandReassociation, collapseReassociation] :
         llvm::zip_equal(expandReInds, collapseReInds)) {
      if (collapseReassociation.size() == expandReassociation.size()) {
        // Even if the reassociations are the same, the collapse/expand should
        // result in the same dimensions. i.e  4x8x2 into 64 should be expanded
        // into 4x8x2 again. In presense of dynamic dimensions one can only
        // verify "equality" when there is only one dynamic dimension present,
        // and all other static dimensions are equal.
        ArrayRef<int64_t> collapsedStaticShapes = staticSourceSize.slice(
            collapseReassociation.front(), collapseReassociation.size());
        int64_t numCollapsedDynamic =
            llvm::count_if(collapsedStaticShapes,
                           [](int64_t d) { return ShapedType::isDynamic(d); });
        ArrayRef<int64_t> expandedStaticShapes = staticResultSize.slice(
            expandReassociation.front(), expandReassociation.size());
        int64_t numExpandedDynamic =
            llvm::count_if(expandedStaticShapes,
                           [](int64_t d) { return ShapedType::isDynamic(d); });
        if (numCollapsedDynamic > 1 || numExpandedDynamic > 1 ||
            collapsedStaticShapes != expandedStaticShapes) {
          return failure();
        }
        continue;
      }
      // If the reassociations are not same, one or the other needs to be of
      // size one.
      if (collapseReassociation.size() != 1 && expandReassociation.size() != 1)
        return failure();
    }
 
    // Compute new reassociation indices and expanded/collaped shapes.
    SmallVector<ReassociationIndices> newExpandReInds, newCollapseReInds;
    Location loc = expandOp->getLoc();
    SmallVector<OpFoldResult> sourceSizes =
        tensor::getMixedSizes(rewriter, loc, collapseOp.getSrc());
    SmallVector<OpFoldResult> resultSizes = expandOp.getMixedOutputShape();
    SmallVector<OpFoldResult> newExpandSizes;
 
    int64_t newExpandIndex = 0, newCollapseIndex = 0, sourceSizeIndex = 0,
            resultSizeIndex = 0;
 
    for (size_t idx = 0, idxEnd = collapseReInds.size(); idx < idxEnd; idx++) {
      auto &collapseReassociation = collapseReInds[idx];
      auto &expandReassociation = expandReInds[idx];
 
      // Case 1. The reassociations are same in the collapse producer
      // and expand consumer. In the swapped expand, each of the final
      // dimensions are kept as is in the expand and the collapse. So,
      // for every element in the `ReassocationIndices` vector add a new
      // `ReassociationIndices` vector for the swapped expand and collapse
      // (of size 1).
      if (collapseReassociation.size() == expandReassociation.size()) {
        for (size_t i = 0; i < collapseReassociation.size(); ++i) {
          newCollapseReInds.push_back({newCollapseIndex++});
          newExpandReInds.push_back({newExpandIndex++});
          newExpandSizes.push_back(resultSizes[resultSizeIndex++]);
          sourceSizeIndex++;
        }
        continue;
      }
 
      // Case 2. The `ReassociationIndices` in the collapse is of size > 1 (and
      // in the expand is of size == 1). In this case, the original dimensions
      // are preserved on expansion and collapsed subsequently.
      if (collapseReassociation.size() != 1) {
        ReassociationIndices newCollapseReassociation;
        for (size_t i = 0; i < collapseReassociation.size(); ++i) {
          newCollapseReassociation.push_back(newCollapseIndex++);
          newExpandReInds.push_back({newExpandIndex++});
          newExpandSizes.push_back(sourceSizes[sourceSizeIndex++]);
        }
        resultSizeIndex++;
        newCollapseReInds.push_back(newCollapseReassociation);
        continue;
      }
 
      // Case 3. The `ReassociationIndices` in the expand is of size > 1 (and
      // in the collapse is of size == 1). In this case, the expansion happens
      // first and the expanded dimensions are preserved on collapse.
      ReassociationIndices newExpandReassociation;
      for (size_t i = 0; i < expandReassociation.size(); ++i) {
        newExpandReassociation.push_back(newExpandIndex++);
        newCollapseReInds.push_back({newCollapseIndex++});
        newExpandSizes.push_back(resultSizes[resultSizeIndex++]);
      }
      newExpandReInds.push_back(newExpandReassociation);
      sourceSizeIndex++;
    }
 
    // Swap reshape order.
    SmallVector<Value> dynamicSizes;
    SmallVector<int64_t> staticSizes;
    dispatchIndexOpFoldResults(newExpandSizes, dynamicSizes, staticSizes);
    auto expandResultType = expandOp.getResultType().clone(staticSizes);
    Value newCollapseSrc = collapseOp.getSrc();
    // If the number of reassociation indices in the new `expand_shape` op
    // matches the number of dimensions of the result, then the expand_shape
    // is a no-op.
    if (newExpandReInds.size() != newExpandSizes.size()) {
      newCollapseSrc = rewriter.create<tensor::ExpandShapeOp>(
          loc, expandResultType, newCollapseSrc, newExpandReInds,
          newExpandSizes);
    }
 
    // If the number of reassociation indices in the new `collapse_shape` op
    // matches the number of dimensions of the source, then the collapse_shape
    // is a no-op.
    Value replacement = newCollapseSrc;
    if (newCollapseReInds.size() != newExpandSizes.size()) {
      replacement = rewriter.create<tensor::CollapseShapeOp>(
          loc, newCollapseSrc, newCollapseReInds);
    }
    rewriter.replaceOp(expandOp, replacement);
    return success();
  }
};
 
/// Converts `tensor.extract_slice(tensor.expand_shape)` to
/// `tensor.expand_shape(tensor.extract_slice)`.
///
/// For this transformation to be possible, the slice must be fully contiguous
/// within each reassociation group of the expand_shape. A slice is defined as
/// fully contiguous within a reassociation group if after flattening the
/// reassociation group to a single 1D range, then the slice taken out of the
/// group could be defined as a single contiguous subrange within that range.
///
/// Rank reducing slices are not supported.
///
/// Example:
/// The transformation is possible because each reassociation group has a
/// contiguous slice (i.e., [2x4->2x4], [2x8->1x5], [4x2x4->1x1x4]).
/// ```
/// BEFORE:
/// %reshape = tensor.expand_shape %in [[0, 1], [2, 3], [4, 5, 6]]
///     tensor<8x16x32xf32> to tensor<2x4x2x8x4x2x4xf32>
/// %slice = tensor.extract_slice %reshape ...
///     tensor<2x4x2x8x4x2x4xf32> to tensor<2x4x1x5x1x1x4xf32>
///
/// AFTER:
/// %slice = tensor.extract_slice %in ...
///     tensor<8x16x32xf32> to tensor<8x5x4xf32>
/// %reshape = tensor.expand_shape %slice [[0, 1], [2, 3], [4, 5, 6]]
///     tensor<8x5x4xf32> to tensor<2x4x1x5x1x1x4xf32>
/// ```
///
/// Note - this pattern could be extended to be a swap pattern between
/// `tensor.expand_shape` and `tensor.extract_slice`, but is currently
/// implemented only as a bubble up pattern for `tensor.extract_slice`.
struct BubbleUpExpandShapeThroughExtractSlice
    : public OpRewritePattern<tensor::ExtractSliceOp> {
  using OpRewritePattern<tensor::ExtractSliceOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(tensor::ExtractSliceOp sliceOp,
                                PatternRewriter &rewriter) const override {
    auto expandShapeOp =
        sliceOp.getSource().getDefiningOp<tensor::ExpandShapeOp>();
 
    if (checkPreconditionForBubbleUpExtractSlice(sliceOp, expandShapeOp,
                                                 rewriter)
            .failed())
      return failure();
 
    // The tensor.extract_slice before applying the pattern works on the result
    // of the tensor.expand_shape, so variables (i.e. inputs for ExtractSliceOp)
    // referring to the state before applying the pattern are named with the
    // prefix "expanded", and ones referring to the state after applying the
    // pattern are named with the prefix "collapsed".
    SmallVector<OpFoldResult> expandedOffsets = sliceOp.getMixedOffsets();
    SmallVector<OpFoldResult> expandedSizes = sliceOp.getMixedSizes();
    SmallVector<OpFoldResult> expandedShape =
        getMixedValues(expandShapeOp.getStaticOutputShape(),
                       expandShapeOp.getOutputShape(), rewriter);
 
    // Helper variables and function for accumulating the size values.
    Location loc = expandShapeOp->getLoc();
    AffineExpr d0, d1, d2;
    bindDims(rewriter.getContext(), d0, d1, d2);
    // Multiply two integers.
    auto mul = [&](OpFoldResult v1, OpFoldResult v2) {
      auto mulMap = AffineMap::get(2, 0, {d0 * d1});
      return affine::makeComposedFoldedAffineApply(rewriter, loc, mulMap,
                                                   {v1, v2});
    };
 
    // Compute new offsets, sizes, and strides for tensor.extract_slice.
    // The new tensor.extract_slice will work on a tensor that has has a rank of
    // ReassociationIndices.size(). In the loop a single offset, size, and
    // stride value is computed per reassociation group.
    SmallVector<OpFoldResult> collapsedOffsets, collapsedSizes,
        collapsedStrides;
    for (const ReassociationIndices &indices :
         expandShapeOp.getReassociationIndices()) {
      // collapsedSize will hold the size of the single dim that represents the
      // reassociation group in the non expanded tensor.
      OpFoldResult collapsedSize = rewriter.getIndexAttr(1);
      // The reassocGroupSizes and reassocGroupOffsets are used to create an
      // affine.linearize_index op to linearize the single offset value required
      // for this reassociation group.
      SmallVector<OpFoldResult> reassocGroupSizes, reassocGroupOffsets;
 
      for (long expandedDim : indices) {
        // reassocGroupSizes and reassocGroupOffsets can be obtained directly
        // from the expanded state, but the collapsed size requires calculation
        // as it did not previously exist.
        reassocGroupSizes.push_back(expandedShape[expandedDim]);
        reassocGroupOffsets.push_back(expandedOffsets[expandedDim]);
        collapsedSize = mul(collapsedSize, expandedSizes[expandedDim]);
      }
 
      SmallVector<Value> offsetVals =
          llvm::map_to_vector(reassocGroupOffsets, [&](OpFoldResult ofr) {
            return getValueOrCreateConstantIndexOp(rewriter, loc, ofr);
          });
      OpFoldResult collapsedOffset =
          rewriter
              .create<affine::AffineLinearizeIndexOp>(loc, offsetVals,
                                                      reassocGroupSizes,
                                                      /*disjoint=*/true)
              .getResult();
      collapsedOffsets.push_back(collapsedOffset);
      collapsedSizes.push_back(collapsedSize);
 
      // Only unit stride is supported.
      collapsedStrides.push_back(rewriter.getIndexAttr(1));
    }
 
    // The shape of the result can be obtained from the sizes passed in.
    SmallVector<Value> dynDims;
    SmallVector<int64_t> shape;
    dispatchIndexOpFoldResults(expandedSizes, dynDims, shape);
    RankedTensorType resultType = RankedTensorType::get(
        shape, expandShapeOp.getResultType().getElementType());
 
    // Create a new ExtractSliceOp and ExpandShapeOp.
    Value newSliceOp = rewriter.create<tensor::ExtractSliceOp>(
        loc, expandShapeOp.getSrc(), collapsedOffsets, collapsedSizes,
        collapsedStrides);
    rewriter.replaceOpWithNewOp<tensor::ExpandShapeOp>(
        sliceOp, resultType, newSliceOp,
        expandShapeOp.getReassociationIndices(), expandedSizes);
    return success();
  }
 
  // Helper function to check if all the required conditions for the
  // tensor.extract_slice to be bubbled up through the tensor.expand_shape are
  // met.
  LogicalResult
  checkPreconditionForBubbleUpExtractSlice(tensor::ExtractSliceOp sliceOp,
                                           tensor::ExpandShapeOp expandShapeOp,
                                           PatternRewriter &rewriter) const {
 
    if (!expandShapeOp) {
      return rewriter.notifyMatchFailure(
          sliceOp, "tensor.extract_slice source not produced by expand_shape");
    }
 
    if (!sliceOp.hasUnitStride()) {
      return rewriter.notifyMatchFailure(
          sliceOp, "unsupported: non-unit stride. Only contiguous slices can "
                   "be supported in this transformation.");
    }
 
    SmallVector<OpFoldResult> offsets = sliceOp.getMixedOffsets();
    SmallVector<OpFoldResult> sizes = sliceOp.getMixedSizes();
 
    if (static_cast<size_t>(sliceOp.getResultType().getRank()) !=
        sizes.size()) {
      return rewriter.notifyMatchFailure(sliceOp,
                                         "unimplemented: rank reducing slice");
    }
 
    SmallVector<OpFoldResult> outputShape =
        getMixedValues(expandShapeOp.getStaticOutputShape(),
                       expandShapeOp.getOutputShape(), rewriter);
 
    std::function<bool(OpFoldResult, OpFoldResult, OpFoldResult)>
        isZeroOffsetAndFullSize =
            [](OpFoldResult offset, OpFoldResult sliceSize, OpFoldResult size) {
              if (!isConstantIntValue(offset, 0))
                return false;
              FailureOr<bool> maybeEqual =
                  ValueBoundsConstraintSet::areEqual(sliceSize, size);
              return llvm::succeeded(maybeEqual) && maybeEqual.value();
            };
 
    // Check that the slice is contiguous within each reassociation group.
    // The slice is contiguous only if after the first dimension where a non
    // unit slice is taken, the slice size on all subsequent dimensions of the
    // group is equal to the entire size of the dimension.
    // Examples of contiguous slices:
    //   full sizes: [8, 8, 10] slice offsets: [0, 0, 0] slice sizes: [1, 1, 10]
    //   full sizes: [5, 10] slice offsets: [3, 0] slice sizes: [2, 10]
    // Examples of non contiguous slices:
    //   full sizes: [8, 8, 10] slice offsets: [0, 0, 0] slice sizes: [1, 2, 5]
    //   full sizes: [5, 10] slice offsets: [0, 4] slice sizes: [2, 5]
    for (const ReassociationIndices &indices :
         expandShapeOp.getReassociationIndices()) {
      int64_t i = 0;
      int64_t e = indices.size();
      // Find the first expanded dim after the first dim with non-unit extracted
      // size.
      for (; i < e; ++i) {
        if (!isConstantIntValue(sizes[indices[i]], 1)) {
          // +1 to skip the first non-unit size dim.
          i++;
          break;
        }
      }
 
      // Verify that all subsequent dimensions extract the full size of the
      // source tensor.
      for (; i < e; ++i) {
        int64_t expandedDim = indices[i];
        if (!isZeroOffsetAndFullSize(offsets[expandedDim], sizes[expandedDim],
                                     outputShape[expandedDim])) {
          return rewriter.notifyMatchFailure(
              sliceOp, "Not a contiguous slice of the expanded tensor.");
        }
      }
    }
 
    return success();
  }
};
 
/// Converts `tensor.extract_slice(tensor.collapse_shape)` to
///          `tensor.collapse_shape(tensor.extract_slice)`.
///
/// For this transformation to be possible - after bubbling up, the extraction
/// of the contiguous slice must be representable as a single slice obtained via
/// tensor.extract_slice within each reassociation group of the src.
///
/// In case the size and offset extracted are static then this is possible if
/// the following conditions are met within each reassociation group:
/// Let T be a tensor of shape [A0, A1, ..., An] (these are the sizes of the
/// dimensions in the reassociation group), and let S = [S0, S1, ..., Sn] be the
/// shape of a desired slice. A slice of shape S can be extracted as a
/// contiguous span of elements if and only if there exists an index k in {0, 1,
/// ..., n} such that:
///      S_i = 1 for all i < k (that is, all leading dimensions are singleton),
///      1 <= S_k <= A_k (that is, non trivial slicing occurs along exactly
///                       one dimension),
///      S_i = A_i for all i > k (that is, all trailing dimensions are preserved
///      in full).
/// In other words, the slice shape S must be of the form:
/// [ 1, 1, ..., 1, Sk, Ak + 1, Ak + 2, ...,An ]
///
/// In case the size and/or offset extracted are dynamic then this is possible
/// only if there is single dimension in the reassociation group that has a size
/// not equal to 1.
/// In other words, the tensor shape must be of the form:
/// [ 1, 1, ..., 1, A, 1, ...,1 ]
/// Note - it might be possible to enable this pattern for more cases when the
/// size/offset are dynamic via performing an analysis of the possible values
/// that could be given to the size/offset.
///
/// Example:
/// The transformation is possible because each reassociation group can be
/// represented as a contiguous slice (i.e., [8x16->2x16], [1x7->1x?],
/// [20->10]).
/// ```
/// BEFORE:
/// %collapse = tensor.collapse_shape %src [[0, 1], [2, 3], [4]] ...
///     tensor<8x16x1x7x20f32> to tensor<128x7x20xf32>
/// %slice = tensor.extract_slice %slice [0, 0, 0][32, %size, 10][1, 1, 1]
///     tensor<128x7x20xf32> to tensor<32x?x10xf32>
///
/// AFTER:
/// %slice = tensor.extract_slice %src [0, 0, 0, 0, 0][2, 16, 1, %size, 10]
//           [1, 1, 1, 1, 1] : tensor<8x16x1x7x20f32> to tensor<2x16x1x?x10xf32>
/// %collapse = tensor.collapse_shape %slice [[0, 1], [2, 3], [4]] ...
///     tensor<2x16x1x?x10xf32> to tensor<32x?x10xf32>
/// ```
///
/// Negative example:
/// The transformation is not possible because we cannot use a single slice to
/// represent the reassociation group [2x3x10->???]. If we would want the
/// collapse to be after the extraction, we would need to extract multiple
/// slices and concat them together.
/// ```
/// %collapse = tensor.collapse_shape %src [[0, 1, 2]] : tensor<2x3x10xf32> into
/// tensor<60xf32> %extract = tensor.extract_slice %collapse[0][15][1] :
///                                      tensor<60xf32> to tensor<15xf32>
/// ```
/// If we would want the collapse to be after the extraction, a possible
/// alternate transformation could be to extract multiple slices and concat them
/// together:
/// ```
/// %extract_1 = tensor.extract_slice %src[0, 0, 0][1, 1, 10] :
///                               tensor<2x3x10xf32> to tensor <1x1x10xf32>
/// %extract_2 = tensor.extract_slice %src[0, 1, 0][1, 1, 5] :
///                               tensor<2x3x10xf32> to tensor <1x1x5xf32>
/// %concat = tosa.concat %extract_1, %extract_2 {axis = 0 : i32} :
///                    (<1x1x10xf32>, <1x1x5xf32>) -> <1x1x15xf32>
/// %collapse = tensor.collapse_shape %concat [[0, 1, 2]] : tensor<1x1x15xf32>
///                                                       to tensor<15xf32>
/// ```
/// But this is not the intended purpose of the transformation.
struct BubbleUpCollapseShapeThroughExtractSlice
    : public OpRewritePattern<tensor::ExtractSliceOp> {
  using OpRewritePattern<tensor::ExtractSliceOp>::OpRewritePattern;
 
  LogicalResult matchAndRewrite(tensor::ExtractSliceOp sliceOp,
                                PatternRewriter &rewriter) const override {
    auto collapseShapeOp =
        sliceOp.getSource().getDefiningOp<tensor::CollapseShapeOp>();
    if (!collapseShapeOp) {
      return rewriter.notifyMatchFailure(
          sliceOp,
          "tensor.extract_slice source not produced by tensor.collapse_shape");
    }
 
    if (!sliceOp.hasUnitStride()) {
      return rewriter.notifyMatchFailure(
          sliceOp, "unsupported: non-unit stride. Only contiguous slices can "
                   "be supported in this transformation.");
    }
 
    // The tensor.extract_slice before applying the pattern works on the result
    // of the tensor.collapse_shape, so variables (i.e. inputs for
    // ExtractSliceOp) referring to the state before applying the pattern are
    // named with the prefix "collapsed", and ones referring to the state after
    // applying the pattern are named with the prefix "expanded".
    SmallVector<OpFoldResult> collapsedOffsets = sliceOp.getMixedOffsets();
    SmallVector<OpFoldResult> collapsedSizes = sliceOp.getMixedSizes();
 
    if (static_cast<size_t>(sliceOp.getResultType().getRank()) !=
        collapsedSizes.size()) {
      return rewriter.notifyMatchFailure(sliceOp,
                                         "unimplemented: rank reducing slice");
    }
 
    ArrayRef<int64_t> srcShape = collapseShapeOp.getSrcType().getShape();
    SmallVector<ReassociationIndices, 4> reassociationIndices =
        collapseShapeOp.getReassociationIndices();
 
    // Compute new offsets, sizes, and strides for tensor.extract_slice.
    // The new tensor.extract_slice will work on a tensor that has has a rank
    // equal to the rank of the src of the collapse_shape. In each iteration of
    // the loop, the offsets and sizes will be computed per reassociation group.
    SmallVector<OpFoldResult> expandedOffsets, expandedSizes;
    SmallVector<OpFoldResult> expandedStrides(srcShape.size(),
                                              rewriter.getIndexAttr(1));
 
    for (auto [collapsedSize, collapsedOffset, reassocIndices] :
         llvm::zip_equal(collapsedSizes, collapsedOffsets,
                         collapseShapeOp.getReassociationIndices())) {
      // CASE #1 - size and/or offset are dynamic.
      // In this case, the slice can be represented as a contiguous slice only
      // if there is a single dimension in the reassociation group that has a
      // size not equal to 1.
      if (isa<Value>(collapsedSize) || isa<Value>(collapsedOffset)) {
        int nonUnitSizeCount = 0;
        for (int64_t expandedShapeIdx : reassocIndices) {
          if (srcShape[expandedShapeIdx] != 1) {
            nonUnitSizeCount++;
            expandedSizes.push_back(collapsedSize);
            expandedOffsets.push_back(collapsedOffset);
            continue;
          }
 
          expandedSizes.push_back(rewriter.getIndexAttr(1));
          expandedOffsets.push_back(rewriter.getIndexAttr(0));
        }
 
        if (nonUnitSizeCount != 1) {
          return rewriter.notifyMatchFailure(
              sliceOp,
              "unsupported: slice cannot be verified to be contiguous");
        }
        continue;
      }
 
      // CASE #2 = size and offset are static.
      // Verify that the slice can be represented as a contiguous slice of the
      // src of the collapse_shape.
      // Checking this is done on order of most internal dimensions first,
      // so traversal is done in reverse order of the reassociation group.
      // If the expected slice shape is [1, 1, ..., 1, Sk, Ak + 1, Ak + 2,
      // ...,An] then we first find the size and offset for n...k+1 then for k
      // and then for k-1...0.
 
      // currentCollapsedsize and currentCollapsedOffset are initialized with
      // the original collapsed size and offset and divided by the expanded
      // shape size in each dimension as we go along the reassociation group.
      // In essence we are spreading the original collapsed size and offset over
      // the various expanded slice dimensions.
      // The variables are used both to check the validity of the slice and to
      // compute the expanded sizes and offsets.
      int64_t currentCollapsedsize = getConstantIntValue(collapsedSize).value();
      int64_t currentCollapsedOffset =
          getConstantIntValue(collapsedOffset).value();
 
      SmallVector<OpFoldResult> groupExpandedSizes, groupExpandedOffsets;
 
      ReassociationIndices reversedReassocIndices(reassocIndices.rbegin(),
                                                  reassocIndices.rend());
      int64_t idx = 0;
      int64_t reassocGroupSize = reassocIndices.size();
 
      // First handle the trailing dimensions where the slice size should be
      // equal to the tensor shape and the offset should be 0 (n...k+1).
      for (; idx < reassocGroupSize; ++idx) {
        int64_t expandedShapeSize = srcShape[reversedReassocIndices[idx]];
 
        if (currentCollapsedsize < expandedShapeSize)
          break;
 
        // We need to make sure that the slice size can be set to the shape size
        // and the offset to 0.
        if ((currentCollapsedsize % expandedShapeSize) != 0 ||
            (currentCollapsedOffset % expandedShapeSize) != 0) {
          return rewriter.notifyMatchFailure(
              sliceOp, "unsupported: cannot be extracted as a contiguous slice "
                       "of the src of the collapse_shape");
        }
 
        groupExpandedSizes.push_back(rewriter.getIndexAttr(expandedShapeSize));
        groupExpandedOffsets.push_back(rewriter.getIndexAttr(0));
 
        currentCollapsedsize /= expandedShapeSize;
        currentCollapsedOffset /= expandedShapeSize;
      }
 
      // Now handle the first dim where slicing occurs on (k).
      if (idx < reassocGroupSize) {
        int64_t expandedShapeSize = srcShape[reversedReassocIndices[idx]];
        int64_t offsetInDim = currentCollapsedOffset % expandedShapeSize;
        // We need to make sure that the slice size in this dim + offset will
        // not exceed the shape size.
        if ((currentCollapsedsize + offsetInDim) >= expandedShapeSize) {
          return rewriter.notifyMatchFailure(
              sliceOp, "unsupported: slice cannot be extracted as a contiguous "
                       "slice of the src of the collapse_shape");
        }
 
        groupExpandedSizes.push_back(
            rewriter.getIndexAttr(currentCollapsedsize));
        groupExpandedOffsets.push_back(rewriter.getIndexAttr(offsetInDim));
 
        currentCollapsedOffset /= expandedShapeSize;
      }
 
      // Now handle the leading dimensions where the slice size is equal to 1
      // (k-1...0).
      // The size for these dimensions must be 1 because of how we constructed
      // the slice size of the expanded shape. We spread the original collapsed
      // size over the expanded shape sizes until we reached dimension k where
      // the remaining size was smaller than the expanded shape size, and spread
      // the remaining size on it. So, now we are left with only 1s.
      for (idx++; idx < reassocGroupSize; ++idx) {
        int64_t expandedShapeSize = srcShape[reversedReassocIndices[idx]];
        int64_t offsetInDim = currentCollapsedOffset % expandedShapeSize;
        groupExpandedSizes.push_back(rewriter.getIndexAttr(1));
        groupExpandedOffsets.push_back(rewriter.getIndexAttr(offsetInDim));
        currentCollapsedOffset /= expandedShapeSize;
      }
 
      expandedSizes.append(groupExpandedSizes.rbegin(),
                           groupExpandedSizes.rend());
      expandedOffsets.append(groupExpandedOffsets.rbegin(),
                             groupExpandedOffsets.rend());
    }
 
    Value newSliceOp = rewriter.create<tensor::ExtractSliceOp>(
        collapseShapeOp->getLoc(), collapseShapeOp.getSrc(), expandedOffsets,
        expandedSizes, expandedStrides);
    rewriter.replaceOpWithNewOp<tensor::CollapseShapeOp>(
        sliceOp, sliceOp.getResultType(), newSliceOp,
        collapseShapeOp.getReassociationIndices());
 
    return success();
  }
};
 
} // namespace
 
void mlir::tensor::populateReassociativeReshapeFoldingPatterns(
    RewritePatternSet &patterns) {
  patterns
      .add<FoldExpandOfRankReducingExtract, FoldUnPaddingCollapseIntoExtract,
           FoldInsertOfRankReducingInsert<tensor::InsertSliceOp>,
           FoldInsertOfRankReducingInsert<tensor::ParallelInsertSliceOp>,
           FoldPaddingExpandIntoInsert<tensor::InsertSliceOp>,
           FoldPaddingExpandIntoInsert<tensor::ParallelInsertSliceOp>>(
          patterns.getContext());
}
 
void mlir::tensor::populateBubbleUpExpandShapePatterns(
    RewritePatternSet &patterns) {
  patterns.add<BubbleUpExpandThroughParallelCollapse>(patterns.getContext());
}
 
void mlir::tensor::populateBubbleUpExtractSliceOpPatterns(
    RewritePatternSet &patterns) {
  patterns.add<BubbleUpExpandShapeThroughExtractSlice,
               BubbleUpCollapseShapeThroughExtractSlice>(patterns.getContext());
}