blob: cb92185394938c7f801cb876debe6c122facca6b [file] [log] [blame]
//===- DropUnitDims.cpp - Pass to drop use of unit-extent for broadcasting ===//
//
// 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 patterns/pass to remove usage of unit-extent dimensions
// to specify broadcasting in favor of more canonical representation of the
// computation
//
//===----------------------------------------------------------------------===//
#include "PassDetail.h"
#include "mlir/Dialect/Arithmetic/IR/Arithmetic.h"
#include "mlir/Dialect/Linalg/IR/LinalgOps.h"
#include "mlir/Dialect/Linalg/IR/LinalgTypes.h"
#include "mlir/Dialect/Linalg/Passes.h"
#include "mlir/Dialect/Linalg/Transforms/Transforms.h"
#include "mlir/Dialect/Linalg/Utils/Utils.h"
#include "mlir/Dialect/Tensor/IR/Tensor.h"
#include "mlir/IR/AffineExpr.h"
#include "mlir/IR/AffineMap.h"
#include "mlir/IR/BuiltinTypes.h"
#include "mlir/Transforms/FoldUtils.h"
#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Debug.h"
#define DEBUG_TYPE "linalg-drop-unit-dims"
using namespace mlir;
using namespace mlir::linalg;
/// Implements a pass that canonicalizes the uses of unit-extent dimensions for
/// broadcasting. For example,
///
/// ```mlir
/// #accesses = [
/// affine_map<(d0, d1) -> (0, d1)>,
/// affine_map<(d0, d1) -> (d0, 0)>,
/// affine_map<(d0, d1) -> (d0, d1)>
/// ]
///
/// #trait = {
/// args_in = 2,
/// args_out = 1,
/// indexing_maps = #accesses,
/// iterator_types = ["parallel", "parallel"],
/// library_call = "some_external_fn"
/// }
///
/// func @broadcast_test(%arg0 : tensor<5xf32>, %arg1 : tensor<5xf32>) ->
/// tensor<5x5xf32>
/// {
/// %0 = linalg.tensor_reshape %arg0 [affine_map<(d0, d1) -> (d0, d1)>] :
/// tensor<5xf32> into tensor<1x5xf32>
/// %1 = linalg.tensor_reshape %arg1 [affine_map<(d0, d1) -> (d0, d1)>] :
/// tensor<5xf32> into tensor<5x1xf32>
/// %2 = linalg.generic #trait %0, %1 {
/// ^bb0(%arg2: f32, %arg3: f32):
/// %3 = arith.addf %arg2, %arg3 : f32
/// linalg.yield %3 : f32
/// } : tensor<1x5xf32>, tensor<5x1xf32> -> tensor<5x5xf32>
/// return %2 : tensor<5x5xf32>
/// }
///
/// would canonicalize to
///
/// ```mlir
/// #accesses = [
/// affine_map<(d0, d1) -> (d1)>,
/// affine_map<(d0, d1) -> (d0)>,
/// affine_map<(d0, d1) -> (d0, d1)>
/// ]
///
/// #trait = {
/// args_in = 2,
/// args_out = 1,
/// indexing_maps = #accesses,
/// iterator_types = ["parallel", "parallel"],
/// library_call = "some_external_fn"
/// }
///
/// func @broadcast_test(%arg0 : tensor<5xf32>, %arg1 : tensor<5xf32>) ->
/// tensor<5x5xf32>
/// {
/// %0 = linalg.generic #trait %arg0, %arg1 {
/// ^bb0(%arg2: f32, %arg3: f32):
/// %3 = arith.addf %arg2, %arg3 : f32
/// linalg.yield %3 : f32
/// } : tensor<5xf32>, tensor<5xf32> -> tensor<5x5xf32>
/// return %0 : tensor<5x5xf32>
/// }
/// Given dims of the iteration space of a structured op that are known to be
/// single trip count (`unitDims`), return the indexing maps to use in the
/// canonicalized op with these dims removed, given the original `indexingMaps`.
static ArrayAttr replaceUnitDims(DenseSet<unsigned> &unitDims,
ArrayRef<AffineMap> indexingMaps,
MLIRContext *context) {
if (indexingMaps.empty())
return nullptr;
unsigned numIterationDims = indexingMaps.front().getNumDims();
unsigned numSymbols = indexingMaps.front().getNumSymbols();
// Compute the replacement for each dim expr.
SmallVector<AffineExpr, 4> dimReplacements;
dimReplacements.reserve(numIterationDims);
unsigned numKeptDims = 0;
for (unsigned dim : llvm::seq<unsigned>(0, numIterationDims)) {
if (unitDims.count(dim))
dimReplacements.push_back(getAffineConstantExpr(0, context));
else
dimReplacements.push_back(getAffineDimExpr(numKeptDims++, context));
}
// Symbols remain the same.
SmallVector<AffineExpr, 4> symReplacements;
symReplacements.reserve(numSymbols);
for (unsigned symbol : llvm::seq<unsigned>(0, numSymbols))
symReplacements.push_back(getAffineSymbolExpr(symbol, context));
SmallVector<AffineMap, 4> newIndexingMaps;
newIndexingMaps.reserve(indexingMaps.size());
for (AffineMap operandMap : indexingMaps) {
// Expected indexing maps to have no symbols.
if (operandMap.getNumSymbols())
return nullptr;
newIndexingMaps.push_back(simplifyAffineMap(
operandMap.replaceDimsAndSymbols(dimReplacements, symReplacements,
numIterationDims - unitDims.size(),
numSymbols)));
}
// Check that the new index maps are invertible. If not, something went
// wrong, so abort.
if (!inversePermutation(concatAffineMaps(newIndexingMaps)))
return nullptr;
return ArrayAttr::get(context,
llvm::to_vector<4>(llvm::map_range(
newIndexingMaps, [](AffineMap map) -> Attribute {
return AffineMapAttr::get(map);
})));
}
/// Update the index accesses of linalg operations having index semantics.
static void replaceUnitDimIndexOps(GenericOp genericOp,
const DenseSet<unsigned> &unitDims,
PatternRewriter &rewriter) {
for (IndexOp indexOp :
llvm::make_early_inc_range(genericOp.getBody()->getOps<IndexOp>())) {
OpBuilder::InsertionGuard guard(rewriter);
rewriter.setInsertionPoint(indexOp);
if (unitDims.count(indexOp.dim()) != 0) {
rewriter.replaceOpWithNewOp<arith::ConstantIndexOp>(indexOp, 0);
} else {
// Update the dimension of the index operation if needed.
unsigned droppedDims = llvm::count_if(
unitDims, [&](unsigned dim) { return dim < indexOp.dim(); });
if (droppedDims != 0)
rewriter.replaceOpWithNewOp<IndexOp>(indexOp,
indexOp.dim() - droppedDims);
}
}
}
namespace {
/// Pattern to fold unit-trip count loops in GenericOps.
struct FoldUnitDimLoops : public OpRewritePattern<GenericOp> {
using OpRewritePattern<GenericOp>::OpRewritePattern;
LogicalResult matchAndRewrite(GenericOp genericOp,
PatternRewriter &rewriter) const override {
SmallVector<AffineMap, 4> indexingMaps = genericOp.getIndexingMaps();
if (indexingMaps.empty())
return failure();
// Check if any of the iteration dimensions are unit-trip count. They will
// end up being unit-trip count if they are used to index into a unit-dim
// tensor/memref.
AffineMap invertedMap = inversePermutation(concatAffineMaps(indexingMaps));
if (!invertedMap)
return failure();
SmallVector<int64_t> dims = genericOp.getStaticShape();
DenseSet<unsigned> unitDims;
SmallVector<unsigned, 4> unitDimsReductionLoops;
ArrayAttr iteratorTypes = genericOp.iterator_types();
for (auto expr : enumerate(invertedMap.getResults())) {
if (AffineDimExpr dimExpr = expr.value().dyn_cast<AffineDimExpr>())
if (dims[dimExpr.getPosition()] == 1)
unitDims.insert(expr.index());
}
if (unitDims.empty())
return failure();
// Compute the modified indexing maps.
MLIRContext *context = rewriter.getContext();
ArrayAttr newIndexingMapAttr =
replaceUnitDims(unitDims, indexingMaps, context);
if (!newIndexingMapAttr)
return genericOp.emitError("unable to compute modified indexing_maps");
// Compute the iterator types of the modified op by dropping the one-trip
// count loops.
SmallVector<Attribute, 4> newIteratorTypes;
for (auto attr : llvm::enumerate(iteratorTypes)) {
if (!unitDims.count(attr.index()))
newIteratorTypes.push_back(attr.value());
}
rewriter.startRootUpdate(genericOp);
genericOp.indexing_mapsAttr(newIndexingMapAttr);
genericOp.iterator_typesAttr(ArrayAttr::get(context, newIteratorTypes));
replaceUnitDimIndexOps(genericOp, unitDims, rewriter);
rewriter.finalizeRootUpdate(genericOp);
return success();
}
};
struct UnitExtentReplacementInfo {
Type type;
AffineMap indexMap;
ArrayAttr reassociation;
};
} // namespace
/// Utility function for replacing operands/results to a linalg generic
/// operation with unit-extent dimensions. These can be replaced with
/// an operand/result with the unit-extent dimension removed. This is only done
/// if the indexing map used to access that didimensionmension has a
/// AffineConstantExpr of value 0. Given the `type` of an result/operand of a
/// Linalg op, and its `indexMap` the utility function returns:
/// - the new type with dimensions of size 1 removed.
/// - modified index map that can be used to access the replaced result/operand
/// - the reassociation that converts from the original tensor type to the
/// modified tensor type.
static llvm::Optional<UnitExtentReplacementInfo>
replaceUnitExtents(GenericOp genericOp, OpOperand *opOperand,
MLIRContext *context) {
AffineMap indexingMap = genericOp.getTiedIndexingMap(opOperand);
ArrayRef<int64_t> shape = genericOp.getShape(opOperand);
ArrayRef<AffineExpr> exprs = indexingMap.getResults();
SmallVector<AffineExpr> reassociations;
SmallVector<Attribute> reassociationMaps;
SmallVector<AffineExpr> newIndexExprs;
SmallVector<int64_t> newShape;
int64_t origRank = genericOp.getRank(opOperand);
AffineExpr zeroExpr = getAffineConstantExpr(0, context);
auto isUnitExtent = [&](int64_t dim) -> bool {
return shape[dim] == 1 && exprs[dim] == zeroExpr;
};
// Early return for memrefs with affine maps to represent that we will always
// leave them unchanged.
Type actualType = opOperand->get().getType();
if (auto memref = actualType.dyn_cast<MemRefType>()) {
if (!memref.getLayout().isIdentity())
return llvm::None;
}
int64_t dim = 0;
// Fold dimensions that are unit-extent at the beginning of the tensor.
while (dim < origRank && isUnitExtent(dim))
reassociations.push_back(getAffineDimExpr(dim++, context));
while (dim < origRank) {
reassociations.push_back(getAffineDimExpr(dim, context));
newIndexExprs.push_back(exprs[dim]);
newShape.push_back(shape[dim]);
// Fold all following dimensions that are unit-extent.
while (dim + 1 < origRank && isUnitExtent(dim + 1)) {
++dim;
reassociations.push_back(getAffineDimExpr(dim, context));
}
reassociationMaps.push_back(AffineMapAttr::get(AffineMap::get(
origRank, /*symbolCount = */ 0, reassociations, context)));
reassociations.clear();
++dim;
}
// Compute the tensor or scalar replacement type.
Type elementType = getElementTypeOrSelf(opOperand->get());
Type replacementType;
if (elementType == opOperand->get().getType()) {
replacementType = elementType;
} else if (actualType.isa<RankedTensorType>()) {
replacementType = RankedTensorType::get(newShape, elementType);
} else if (actualType.isa<MemRefType>()) {
replacementType = MemRefType::get(newShape, elementType);
}
assert(replacementType && "unsupported shaped type");
UnitExtentReplacementInfo info = {replacementType,
AffineMap::get(indexingMap.getNumDims(),
indexingMap.getNumSymbols(),
newIndexExprs, context),
ArrayAttr::get(context, reassociationMaps)};
return info;
}
namespace {
SmallVector<ReassociationExprs, 2>
convertAffineMapArrayToExprs(ArrayAttr affineMapArrayAttr) {
SmallVector<ReassociationExprs, 2> reassociationExprs;
for (auto attr : affineMapArrayAttr)
reassociationExprs.push_back(
llvm::to_vector<4>(attr.cast<AffineMapAttr>().getValue().getResults()));
return reassociationExprs;
}
/// Pattern to replace tensor/buffer operands/results that are unit extents.
struct ReplaceUnitExtents : public OpRewritePattern<GenericOp> {
using OpRewritePattern<GenericOp>::OpRewritePattern;
// Return the original value if the type is unchanged, or reshape it. Return a
// nullptr if this is an unsupported type.
Value maybeExpand(Value result, Type origResultType,
ArrayAttr reassociationMap, Location loc,
PatternRewriter &rewriter) const {
if (origResultType == result.getType())
return result;
if (origResultType.isa<RankedTensorType>()) {
return rewriter.create<linalg::TensorExpandShapeOp>(
loc, origResultType, result,
convertAffineMapArrayToExprs(reassociationMap));
}
if (origResultType.isa<MemRefType>()) {
return rewriter.create<memref::ExpandShapeOp>(
loc, origResultType, result,
convertAffineMapArrayToExprs(reassociationMap));
}
return nullptr;
};
// Return the original value if the type is unchanged, or reshape it. Return a
// nullptr if this is an unsupported type.
Value maybeCollapse(Value operand, Type newInputOutputType,
ArrayAttr reassociationMap, Location loc,
PatternRewriter &rewriter) const {
auto operandType = operand.getType();
if (operandType == newInputOutputType)
return operand;
if (operandType.isa<MemRefType>()) {
return rewriter.create<memref::CollapseShapeOp>(
loc, newInputOutputType, operand,
convertAffineMapArrayToExprs(reassociationMap));
}
if (operandType.isa<RankedTensorType>()) {
return rewriter.create<linalg::TensorCollapseShapeOp>(
loc, newInputOutputType, operand,
convertAffineMapArrayToExprs(reassociationMap));
}
return nullptr;
};
LogicalResult matchAndRewrite(GenericOp genericOp,
PatternRewriter &rewriter) const override {
// Skip the pattern if the op has any tensor with special encoding.
if (llvm::any_of(genericOp->getOperandTypes(), [](Type type) {
auto tensorType = type.dyn_cast<RankedTensorType>();
return tensorType && tensorType.getEncoding() != nullptr;
}))
return failure();
MLIRContext *context = rewriter.getContext();
Location loc = genericOp.getLoc();
SmallVector<AffineMap> newIndexingMaps;
SmallVector<ArrayAttr> reassociationMaps;
SmallVector<Type> newInputOutputTypes;
bool doCanonicalization = false;
for (OpOperand *opOperand : genericOp.getInputAndOutputOperands()) {
auto replacementInfo = replaceUnitExtents(genericOp, opOperand, context);
if (replacementInfo) {
reassociationMaps.push_back(replacementInfo->reassociation);
newIndexingMaps.push_back(replacementInfo->indexMap);
newInputOutputTypes.push_back(replacementInfo->type);
doCanonicalization |=
replacementInfo->type != opOperand->get().getType();
} else {
// If replaceUnitExtents cannot handle this case, maintain the same
// type, indexing map, and create a set of mappings representing an
// identity matrix.
newInputOutputTypes.push_back(opOperand->get().getType());
newIndexingMaps.push_back(genericOp.getTiedIndexingMap(opOperand));
int64_t origRank = genericOp.getRank(opOperand);
auto maps = llvm::to_vector<8>(llvm::map_range(
llvm::seq<int64_t>(0, origRank), [&](int64_t dim) -> Attribute {
return AffineMapAttr::get(
AffineMap::get(origRank, /*symbolCount = */ 0,
getAffineDimExpr(dim, context), context));
}));
reassociationMaps.push_back(ArrayAttr::get(context, maps));
}
}
// If the indexing maps of the result operation are not invertible (i.e. not
// legal), abort.
if (!doCanonicalization ||
!inversePermutation(concatAffineMaps(newIndexingMaps)))
return failure();
// If any operand type change, insert a reshape to convert from the original
// type to the new type.
// TODO: get rid of flattenedIdx which assumes operand order and contiguity.
unsigned flattenedIdx = 0;
auto insertReshapes = [&](ValueRange values) {
SmallVector<Value, 4> res;
res.reserve(values.size());
for (auto operand : values) {
auto reshapedValue =
maybeCollapse(operand, newInputOutputTypes[flattenedIdx],
reassociationMaps[flattenedIdx], loc, rewriter);
assert(reshapedValue &&
"expected ranked MemRef or Tensor operand type");
res.push_back(reshapedValue);
++flattenedIdx;
}
return res;
};
SmallVector<Value, 4> newInputs = insertReshapes(genericOp.inputs());
SmallVector<Value, 4> newOutputs = insertReshapes(genericOp.outputs());
// If any result type changes, insert a reshape to convert from the original
// type to the new type.
SmallVector<Type, 4> resultTypes;
resultTypes.reserve(genericOp.getNumResults());
for (unsigned i : llvm::seq<unsigned>(0, genericOp.getNumResults()))
resultTypes.push_back(newInputOutputTypes[i + genericOp.getNumInputs()]);
GenericOp replacementOp = rewriter.create<GenericOp>(
loc, resultTypes, newInputs, newOutputs, newIndexingMaps,
llvm::to_vector<4>(
genericOp.iterator_types().template getAsValueRange<StringAttr>()));
rewriter.inlineRegionBefore(genericOp.region(), replacementOp.region(),
replacementOp.region().begin());
// If any result tensor has a modified shape, then add reshape to recover
// the original shape.
SmallVector<Value, 4> resultReplacements;
for (auto result : llvm::enumerate(replacementOp.getResults())) {
unsigned index = result.index() + replacementOp.getNumInputs();
auto origResultType = genericOp.getResult(result.index()).getType();
auto newResult = maybeExpand(result.value(), origResultType,
reassociationMaps[index], loc, rewriter);
assert(newResult &&
"unexpected output type other than ranked MemRef or Tensor");
resultReplacements.push_back(newResult);
}
rewriter.replaceOp(genericOp, resultReplacements);
return success();
}
};
} // namespace
/// Get the reassociation maps to fold the result of a extract_slice (or source
/// of a insert_slice) operation with given offsets, and sizes to its
/// rank-reduced version. This is only done for the cases where the size is 1
/// and offset is 0. Strictly speaking the offset 0 is not required in general,
/// but non-zero offsets are not handled by SPIR-V backend at this point (and
/// potentially cannot be handled).
static Optional<SmallVector<ReassociationIndices>>
getReassociationMapForFoldingUnitDims(ArrayRef<OpFoldResult> mixedSizes) {
SmallVector<ReassociationIndices> reassociation;
ReassociationIndices curr;
for (auto it : llvm::enumerate(mixedSizes)) {
auto dim = it.index();
auto size = it.value();
curr.push_back(dim);
auto attr = size.dyn_cast<Attribute>();
if (attr && attr.cast<IntegerAttr>().getInt() == 1)
continue;
reassociation.emplace_back(ReassociationIndices{});
std::swap(reassociation.back(), curr);
}
// When the reassociations are not empty, then fold the remaining
// unit-dimensions into the last dimension. If the reassociations so far is
// empty, then leave it emtpy. This will fold everything to a rank-0 tensor.
if (!curr.empty() && !reassociation.empty())
reassociation.back().append(curr.begin(), curr.end());
return reassociation;
}
namespace {
/// Convert `extract_slice` operations to rank-reduced versions.
struct UseRankReducedExtractSliceOp
: public OpRewritePattern<tensor::ExtractSliceOp> {
using OpRewritePattern<tensor::ExtractSliceOp>::OpRewritePattern;
LogicalResult matchAndRewrite(tensor::ExtractSliceOp sliceOp,
PatternRewriter &rewriter) const override {
RankedTensorType resultType = sliceOp.getType();
SmallVector<OpFoldResult> offsets = sliceOp.getMixedOffsets();
SmallVector<OpFoldResult> sizes = sliceOp.getMixedSizes();
SmallVector<OpFoldResult> strides = sliceOp.getMixedStrides();
auto reassociation = getReassociationMapForFoldingUnitDims(sizes);
if (!reassociation ||
reassociation->size() == static_cast<size_t>(resultType.getRank()))
return failure();
auto rankReducedType = tensor::ExtractSliceOp::inferRankReducedResultType(
reassociation->size(), sliceOp.getSourceType(),
offsets, sizes, strides)
.cast<RankedTensorType>();
Location loc = sliceOp.getLoc();
Value newSlice = rewriter.create<tensor::ExtractSliceOp>(
loc, rankReducedType, sliceOp.source(), offsets, sizes, strides);
rewriter.replaceOpWithNewOp<TensorExpandShapeOp>(sliceOp, resultType,
newSlice, *reassociation);
return success();
}
};
/// Convert `insert_slice` operations to rank-reduced versions.
struct UseRankReducedInsertSliceOp
: public OpRewritePattern<tensor::InsertSliceOp> {
using OpRewritePattern<tensor::InsertSliceOp>::OpRewritePattern;
LogicalResult matchAndRewrite(tensor::InsertSliceOp insertOp,
PatternRewriter &rewriter) const override {
RankedTensorType sourceType = insertOp.getSourceType();
SmallVector<OpFoldResult> offsets = insertOp.getMixedOffsets();
SmallVector<OpFoldResult> sizes = insertOp.getMixedSizes();
SmallVector<OpFoldResult> strides = insertOp.getMixedStrides();
auto reassociation = getReassociationMapForFoldingUnitDims(sizes);
if (!reassociation ||
reassociation->size() == static_cast<size_t>(sourceType.getRank()))
return failure();
Location loc = insertOp.getLoc();
auto reshapedSource = rewriter.create<TensorCollapseShapeOp>(
loc, insertOp.source(), *reassociation);
rewriter.replaceOpWithNewOp<tensor::InsertSliceOp>(
insertOp, reshapedSource, insertOp.dest(), insertOp.getMixedOffsets(),
insertOp.getMixedSizes(), insertOp.getMixedStrides());
return success();
}
};
} // namespace
/// Patterns that are used to canonicalize the use of unit-extent dims for
/// broadcasting.
void mlir::linalg::populateFoldUnitExtentDimsPatterns(
RewritePatternSet &patterns) {
auto *context = patterns.getContext();
patterns.add<FoldUnitDimLoops, ReplaceUnitExtents,
UseRankReducedExtractSliceOp, UseRankReducedInsertSliceOp>(
context);
TensorCollapseShapeOp::getCanonicalizationPatterns(patterns, context);
TensorExpandShapeOp::getCanonicalizationPatterns(patterns, context);
}
namespace {
/// Pass that removes unit-extent dims within generic ops.
struct LinalgFoldUnitExtentDimsPass
: public LinalgFoldUnitExtentDimsBase<LinalgFoldUnitExtentDimsPass> {
void runOnFunction() override {
FuncOp funcOp = getFunction();
MLIRContext *context = funcOp.getContext();
RewritePatternSet patterns(context);
if (foldOneTripLoopsOnly)
patterns.add<FoldUnitDimLoops>(context);
else
populateFoldUnitExtentDimsPatterns(patterns);
(void)applyPatternsAndFoldGreedily(funcOp.getBody(), std::move(patterns));
}
};
} // namespace
std::unique_ptr<OperationPass<FuncOp>>
mlir::createLinalgFoldUnitExtentDimsPass() {
return std::make_unique<LinalgFoldUnitExtentDimsPass>();
}