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//===- EmptyOpPatterns.cpp - Patterns related to tensor.empty folding ----===//
//
// 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/Tensor/IR/Tensor.h"
#include "mlir/Dialect/Tensor/Transforms/Transforms.h"
#include "mlir/IR/PatternMatch.h"
#include "llvm/Support/Debug.h"
using namespace mlir;
using namespace mlir::tensor;
namespace {
template <typename ReshapeOp>
struct FoldEmptyTensorWithReshapeOp : public OpRewritePattern<ReshapeOp> {
FoldEmptyTensorWithReshapeOp(MLIRContext *ctx, PatternBenefit benefit = 1,
bool foldSingleUseOnly = false)
: OpRewritePattern<ReshapeOp>(ctx, benefit),
foldSingleUseOnly(foldSingleUseOnly) {}
LogicalResult matchAndRewrite(ReshapeOp reshapeOp,
PatternRewriter &rewriter) const override {
// Check for tensor.empty source.
auto emptyOp = reshapeOp.getSrc().template getDefiningOp<EmptyOp>();
if (!emptyOp)
return failure();
// Check for single use.
if (foldSingleUseOnly && !llvm::hasSingleElement(emptyOp->getUses()))
return failure();
// Reify result shape.
Location loc = reshapeOp.getLoc();
ReifiedRankedShapedTypeDims resultShapes;
if (failed(reifyResultShapes(rewriter, reshapeOp, resultShapes)) ||
!llvm::hasSingleElement(resultShapes))
return failure();
// Create new tensor.empty op.
// TODO: Do not drop tensor type encoding.
Value emptyTensor = rewriter.create<EmptyOp>(
loc, resultShapes[0], reshapeOp.getResultType().getElementType());
if (emptyTensor.getType() != reshapeOp.getResultType()) {
rewriter.replaceOpWithNewOp<tensor::CastOp>(
reshapeOp, reshapeOp.getResultType(), emptyTensor);
} else {
rewriter.replaceOp(reshapeOp, emptyTensor);
}
return success();
}
private:
bool foldSingleUseOnly = false;
};
/// tensor.empty does not define any tensor contents, so a slice of a
/// tensor.empty can be folded to a smaller tensor.empty.
struct FoldEmptyTensorWithExtractSliceOp
: public OpRewritePattern<ExtractSliceOp> {
FoldEmptyTensorWithExtractSliceOp(MLIRContext *ctx,
PatternBenefit benefit = 1,
bool foldSingleUseOnly = false)
: OpRewritePattern<ExtractSliceOp>(ctx, benefit),
foldSingleUseOnly(foldSingleUseOnly) {}
LogicalResult matchAndRewrite(ExtractSliceOp sliceOp,
PatternRewriter &rewriter) const override {
// Check for tensor.empty source.
auto emptyOp = sliceOp.getSource().template getDefiningOp<EmptyOp>();
if (!emptyOp)
return failure();
// Check for single use.
if (foldSingleUseOnly && !llvm::hasSingleElement(emptyOp->getUses()))
return failure();
// Create new tensor.empty op. tensor.extract_slice may be rank-reducing;
// its dynamic sizes must be preserved as well as its result type.
auto tensorType = RankedTensorType::get(sliceOp.getType().getShape(),
sliceOp.getType().getElementType(),
sliceOp.getType().getEncoding());
rewriter.replaceOpWithNewOp<EmptyOp>(sliceOp, tensorType,
sliceOp.getSizes());
return success();
}
private:
bool foldSingleUseOnly = false;
};
/// tensor.empty does not define any tensor contents, so an unpadded pack
/// can be folded away.
struct FoldEmptyTensorWithPackOp : public OpRewritePattern<PackOp> {
using OpRewritePattern<PackOp>::OpRewritePattern;
LogicalResult matchAndRewrite(PackOp packOp,
PatternRewriter &rewriter) const override {
// Check for tensor.empty source.
auto emptyOp = packOp.getSource().getDefiningOp<EmptyOp>();
if (!emptyOp)
return failure();
// Check for padding.
// Packing with padding cannot be simply removed.
if (packOp.getPaddingValue())
return rewriter.notifyMatchFailure(packOp, "expects no padding value");
// Replace the pack directly with its destination.
rewriter.replaceOp(packOp, packOp.getDest());
return success();
}
};
/// tensor.empty does not define any tensor contents, so an unpack
/// can be folded away.
struct FoldEmptyTensorWithUnPackOp : public OpRewritePattern<UnPackOp> {
using OpRewritePattern<UnPackOp>::OpRewritePattern;
LogicalResult matchAndRewrite(UnPackOp unPackOp,
PatternRewriter &rewriter) const override {
// Check for tensor.empty source.
auto emptyOp = unPackOp.getSource().getDefiningOp<EmptyOp>();
if (!emptyOp)
return failure();
// Replace the unpack directly with its destination.
rewriter.replaceOp(unPackOp, unPackOp.getDest());
return success();
}
};
// Fold concat operation where all the operands are empty.
struct FoldConcatsOfEmpty : public OpRewritePattern<ConcatOp> {
using OpRewritePattern<ConcatOp>::OpRewritePattern;
LogicalResult matchAndRewrite(tensor::ConcatOp concatOp,
PatternRewriter &rewriter) const override {
auto concatOperands = concatOp.getInputs();
if (concatOperands.empty()) {
return failure();
}
auto firstEmptyOp = concatOperands.front().getDefiningOp<tensor::EmptyOp>();
if (!firstEmptyOp) {
return failure();
}
auto isDefinedByEmptyOp = [](Value v) -> bool {
return v.getDefiningOp<tensor::EmptyOp>();
};
if (!llvm::all_of(concatOperands.drop_front(), isDefinedByEmptyOp)) {
return rewriter.notifyMatchFailure(
concatOp, "not all operands are defined by an empty op");
}
SmallVector<SmallVector<OpFoldResult>> resultShape;
if (failed(concatOp.reifyResultShapes(rewriter, resultShape))) {
return rewriter.notifyMatchFailure(concatOp,
"failed to get result shape");
}
rewriter.replaceOpWithNewOp<tensor::EmptyOp>(
concatOp, resultShape[0], concatOp.getResultType().getElementType());
return success();
}
};
} // namespace
void mlir::tensor::populateFoldTensorEmptyPatterns(RewritePatternSet &patterns,
bool foldSingleUseOnly) {
patterns.add<FoldEmptyTensorWithExtractSliceOp,
FoldEmptyTensorWithReshapeOp<tensor::ExpandShapeOp>,
FoldEmptyTensorWithReshapeOp<tensor::CollapseShapeOp>>(
patterns.getContext(), /*benefit=*/1, foldSingleUseOnly);
patterns.add<FoldConcatsOfEmpty, FoldEmptyTensorWithPackOp,
FoldEmptyTensorWithUnPackOp>(patterns.getContext(),
/*benefit=*/1);
}
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