Raptor/src/PIM/Conversion/ONNXToSpatial/Patterns/Math/ReduceMean.cpp

#include "mlir/Dialect/Tensor/IR/Tensor.h"
#include "mlir/Transforms/DialectConversion.h"

#include "llvm/ADT/SmallVector.h"

#include <algorithm>

#include "src/Accelerators/PIM/Conversion/ONNXToSpatial/Common.hpp"
#include "src/Accelerators/PIM/Conversion/ONNXToSpatial/Patterns.hpp"
#include "src/Accelerators/PIM/Dialect/Spatial/SpatialOps.hpp"
#include "src/Dialect/ONNX/ONNXOps.hpp"

using namespace mlir;

namespace onnx_mlir {
namespace {

static SmallVector<int64_t> normalizeAxes(ArrayAttr axesAttr, int64_t rank) {
  SmallVector<int64_t> normalizedAxes;
  if (!axesAttr) {
    normalizedAxes.reserve(rank);
    for (int64_t axis = 0; axis < rank; axis++)
      normalizedAxes.push_back(axis);
    return normalizedAxes;
  }

  normalizedAxes.reserve(axesAttr.size());
  for (Attribute attr : axesAttr) {
    int64_t axis = cast<IntegerAttr>(attr).getInt();
    normalizedAxes.push_back(axis >= 0 ? axis : rank + axis);
  }

  llvm::sort(normalizedAxes);
  normalizedAxes.erase(std::unique(normalizedAxes.begin(), normalizedAxes.end()), normalizedAxes.end());
  return normalizedAxes;
}

static SmallVector<bool> buildReducedAxesMask(ArrayRef<int64_t> axes, int64_t rank) {
  SmallVector<bool> reducedAxes(rank, false);
  for (int64_t axis : axes) {
    if (axis < 0 || axis >= rank)
      return {};
    reducedAxes[axis] = true;
  }
  return reducedAxes;
}

static RankedTensorType getAllOnesType(RankedTensorType inputType, Type elementType) {
  return RankedTensorType::get(SmallVector<int64_t>(inputType.getRank(), 1), elementType);
}

static SmallVector<ReassociationIndices> buildCollapseReassociation(ArrayRef<bool> reducedAxes) {
  SmallVector<ReassociationIndices> reassociation;
  ReassociationIndices currentGroup;

  for (auto [axis, isReduced] : llvm::enumerate(reducedAxes)) {
    currentGroup.push_back(axis);
    if (!isReduced) {
      reassociation.push_back(currentGroup);
      currentGroup.clear();
    }
  }

  if (!currentGroup.empty()) {
    if (reassociation.empty())
      reassociation.push_back(std::move(currentGroup));
    else
      reassociation.back().append(currentGroup.begin(), currentGroup.end());
  }

  return reassociation;
}

static Value createAverageCompute(Value input,
                                  RankedTensorType resultType,
                                  ConversionPatternRewriter& rewriter,
                                  Location loc) {
  constexpr size_t numInputs = 1;
  auto computeOp = createSpatCompute<numInputs>(rewriter, loc, resultType, {}, ValueRange {input}, [&](Value x) {
    auto avgOp = spatial::SpatVAvgOp::create(rewriter, loc, resultType, x);
    spatial::SpatYieldOp::create(rewriter, loc, avgOp.getResult());
  });
  return computeOp.getResult(0);
}

static Value buildReduceMeanKeepdims(Value input,
                                     ArrayRef<bool> reducedAxes,
                                     int64_t axis,
                                     RankedTensorType leafType,
                                     ConversionPatternRewriter& rewriter,
                                     Location loc) {
  int64_t rank = cast<RankedTensorType>(input.getType()).getRank();
  if (axis == rank)
    return createAverageCompute(input, leafType, rewriter, loc);

  if (reducedAxes[axis])
    return buildReduceMeanKeepdims(input, reducedAxes, axis + 1, leafType, rewriter, loc);

  SmallVector<Value> slices = sliceTensor(input, axis, /*sliceSize=*/1, rewriter, loc);
  SmallVector<Value> reducedSlices;
  reducedSlices.reserve(slices.size());
  for (Value slice : slices)
    reducedSlices.push_back(buildReduceMeanKeepdims(slice, reducedAxes, axis + 1, leafType, rewriter, loc));

  return reducedSlices.size() == 1 ? reducedSlices.front()
                                   : tensor::ConcatOp::create(rewriter, loc, axis, reducedSlices).getResult();
}

static Value squeezeReducedAxes(Value keepdimsValue,
                                RankedTensorType resultType,
                                ArrayRef<bool> reducedAxes,
                                ConversionPatternRewriter& rewriter,
                                Location loc) {
  if (resultType.getRank() == 0) {
    SmallVector<Value> indices(cast<RankedTensorType>(keepdimsValue.getType()).getRank(),
                               arith::ConstantIndexOp::create(rewriter, loc, 0));
    Value element = tensor::ExtractOp::create(rewriter, loc, keepdimsValue, indices);
    return tensor::FromElementsOp::create(rewriter, loc, resultType, ValueRange {element});
  }

  return tensor::CollapseShapeOp::create(
           rewriter, loc, resultType, keepdimsValue, buildCollapseReassociation(reducedAxes))
    .getResult();
}

struct ReduceMeanToSpatialCompute : OpConversionPattern<ONNXReduceMeanV13Op> {
  using OpConversionPattern::OpConversionPattern;

  LogicalResult matchAndRewrite(ONNXReduceMeanV13Op reduceMeanOp,
                                ONNXReduceMeanV13OpAdaptor adaptor,
                                ConversionPatternRewriter& rewriter) const override {
    auto inputType = dyn_cast<RankedTensorType>(adaptor.getData().getType());
    auto resultType = dyn_cast<RankedTensorType>(reduceMeanOp.getReduced().getType());
    if (!inputType || !resultType || !inputType.hasStaticShape() || !resultType.hasStaticShape())
      return failure();

    SmallVector<int64_t> axes = normalizeAxes(reduceMeanOp.getAxesAttr(), inputType.getRank());
    SmallVector<bool> reducedAxes = buildReducedAxesMask(axes, inputType.getRank());
    if (reducedAxes.empty() && inputType.getRank() != 0)
      return failure();

    Location loc = reduceMeanOp.getLoc();
    RankedTensorType leafType = getAllOnesType(inputType, resultType.getElementType());
    Value reducedKeepdims = buildReduceMeanKeepdims(adaptor.getData(), reducedAxes, /*axis=*/0, leafType, rewriter, loc);

    if (reduceMeanOp.getKeepdims() != 0) {
      rewriter.replaceOp(reduceMeanOp, reducedKeepdims);
      return success();
    }

    Value reduced = squeezeReducedAxes(reducedKeepdims, resultType, reducedAxes, rewriter, loc);
    rewriter.replaceOp(reduceMeanOp, reduced);
    return success();
  }
};

} // namespace

void populateReduceMeanPatterns(RewritePatternSet& patterns, MLIRContext* ctx) {
  patterns.add<ReduceMeanToSpatialCompute>(ctx);
}

} // namespace onnx_mlir