MLIR  21.0.0git
Fusion.cpp
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1 //===- Fusion.cpp - Implementation of linalg Fusion -----------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements the linalg dialect Fusion pass.
10 //
11 //===----------------------------------------------------------------------===//
12 
22 #include "mlir/IR/AffineExpr.h"
23 #include "mlir/IR/AffineMap.h"
24 #include "mlir/IR/Dominance.h"
25 #include "mlir/Support/LLVM.h"
28 #include "llvm/ADT/MapVector.h"
29 #include "llvm/ADT/ScopeExit.h"
30 #include "llvm/ADT/SmallBitVector.h"
31 #include "llvm/Support/CommandLine.h"
32 #include "llvm/Support/Debug.h"
33 
34 #include <optional>
35 #include <set>
36 
37 #define DEBUG_TYPE "linalg-fusion"
38 
39 using namespace mlir;
40 using namespace mlir::linalg;
41 
42 /// Implements a simple high-level fusion pass on linalg structured operations.
43 ///
44 /// In each block, linalg ops are processed in reverse textual order.
45 /// Given a linalg op `O`, fusion occurs by:
46 /// 1. inspecting the linalg ops that write into the views read by `O`. There
47 /// are 2 cases:
48 /// a) buffer case: use the SSA value of the views and a simple alias
49 /// analysis on subview ops to determine producer-consumer dependences;
50 /// b) tensor case: use SSA use-def chains on extract_slice ops;
51 /// 2. greedily fuse the linalg ops that produce the subview/extract_slice.
52 /// 3. inspect the fused ops and determine whether they have other remaining
53 /// LinalgOp uses. If not, then erase the original producing linalg op.
54 ///
55 /// More advanced use cases, analyses as well as profitability heuristics are
56 /// left for future work.
57 
60  unsigned dimension;
61 };
62 
63 // Given an `op`, returns the first (`shape`, `dimension`) pair that identifies
64 // the loop range at `loopDepth`. The semantics of the loopToOperandRangesMaps
65 // guarantees at least one such dimension is found. If multiple candidates exist
66 // they must agree by construction (i.e. have the same size) and we just return
67 // the first one.
68 static ShapeDimension
69 getShapeDefiningLoopRange(LinalgOp op, unsigned loopDepth,
70  bool fromSubViewOpOnly = false) {
71  // Iterate over the inputs and outputs in order.
72  // Extract the subranges from the linearized ranges.
73  for (OpOperand &opOperand : op->getOpOperands()) {
74  // The method `getRangeFromOperandShape` requires using SubViewOp or
75  // ExtractSliceOps. If the value isn't defined from there continue.
76  // todo: The method should be adapted to get the values from
77  // `ViewInterface`. The interface needs a `getOrCreateRanges` method which
78  // currently returns a `linalg.range`. The fix here is to move this op to
79  // `std` dialect and add the method to `ViewInterface`.
80  if (fromSubViewOpOnly &&
81  !isa_and_nonnull<memref::SubViewOp, tensor::ExtractSliceOp>(
82  opOperand.get().getDefiningOp()))
83  continue;
84 
85  AffineMap map = op.getMatchingIndexingMap(&opOperand);
86  LLVM_DEBUG(llvm::dbgs() << "getShapeDefiningLoopRange I/O idx: "
87  << opOperand.getOperandNumber() << "\n");
88  LLVM_DEBUG(llvm::dbgs()
89  << "getShapeDefiningLoopRange map: " << map << "\n");
90  for (const auto &en : llvm::enumerate(map.getResults())) {
91  auto dimExpr = dyn_cast<AffineDimExpr>(en.value());
92  if (!dimExpr)
93  continue;
94  if (loopDepth == cast<AffineDimExpr>(en.value()).getPosition()) {
95  LLVM_DEBUG(llvm::dbgs() << "getShapeDefiningLoopRange loopDepth: "
96  << loopDepth << "\n");
97  LLVM_DEBUG(llvm::dbgs() << "getShapeDefiningLoopRange shape: "
98  << opOperand.get() << "\n");
99  return ShapeDimension{opOperand.get(),
100  static_cast<unsigned>(en.index())};
101  }
102  }
103  }
104  llvm_unreachable("Expect to be able to extract a shape defining loop range");
105 }
106 
107 static SmallVector<Value> getTiledOperands(LinalgOp producer) {
108  return producer->getOperands();
109 }
110 
111 /// Fuses the producer by cloning the `producer`. The `fusedLoopsAndRanges`
112 /// provides the loop range information for the fused loops. The rest are
113 /// obtained from the producer itself, since they are not tiled + fused.
114 static LinalgOp fuse(OpBuilder &b, LinalgOp producer,
115  const DenseMap<unsigned, Range> &fusedLoopsAndRanges) {
116  SmallVector<OpFoldResult> ivs, tileSizes, sizeBounds;
117  SmallVector<Range> loopRanges;
118  Location loc = producer.getLoc();
119 
120  for (unsigned i = 0, e = producer.getNumLoops(); i < e; ++i) {
121  auto shapeDim = getShapeDefiningLoopRange(producer, i);
122  OpFoldResult dim =
123  createFoldedDimOp(b, loc, shapeDim.shape, shapeDim.dimension);
124  sizeBounds.push_back(dim);
125  auto it = fusedLoopsAndRanges.find(i);
126  if (it != fusedLoopsAndRanges.end()) {
127  ivs.push_back(it->second.offset);
128  tileSizes.push_back(it->second.size);
129  loopRanges.push_back(it->second);
130  LLVM_DEBUG(llvm::dbgs() << "tiled loop#" << i << " with LoopRange "
131  << loopRanges.back() << "\n");
132  } else {
133  tileSizes.push_back(b.getIndexAttr(0));
134  loopRanges.push_back(Range{b.getIndexAttr(0), dim, b.getIndexAttr(1)});
135  LLVM_DEBUG(llvm::dbgs() << "full loop#" << i << " with LoopRange "
136  << loopRanges.back() << "\n");
137  }
138  }
139 
140  SmallVector<Value, 8> clonedShapes;
141  clonedShapes.reserve(producer->getNumOperands());
142 
143  // Compute subranges for all tensor input/output operands.
144  clonedShapes.append(makeTiledShapes(
145  b, loc, producer, getTiledOperands(producer), ivs, tileSizes, sizeBounds,
146  /**omitPartialTileCheck=*/false));
147 
148  // Take result types from the tiled init operands.
149  MutableOperandRange producerDpsInits = producer.getDpsInitsMutable();
150  SmallVector<Type, 4> resultTypes;
151  resultTypes.reserve(producer->getNumResults());
152  int64_t firstInitOperandIdx =
153  producerDpsInits.getAsOperandRange().getBeginOperandIndex();
154  for (int64_t i = 0, e = producer->getNumResults(); i < e; ++i) {
155  resultTypes.push_back(clonedShapes[firstInitOperandIdx + i].getType());
156  }
157 
158  // Clone the producer with new operands and result types.
159  LinalgOp clonedOp = clone(b, producer, resultTypes, clonedShapes);
160 
161  // Shift all IndexOp results by the tile offset.
162  SmallVector<OpFoldResult> allIvs = llvm::to_vector(
163  llvm::map_range(loopRanges, [&](Range range) { return range.offset; }));
164  offsetIndices(b, clonedOp, allIvs);
165 
166  return clonedOp;
167 }
168 
169 /// Get the loop range for a dimension `dim` based on the `shapedOperand`. It is
170 /// expected to be defined by a subview op or an extract_slice op.
172  Value shapedOperand, unsigned dim) {
173  Operation *shapeProducingOp = shapedOperand.getDefiningOp();
174  if (auto subViewOp = dyn_cast<memref::SubViewOp>(shapeProducingOp))
175  return subViewOp.getOrCreateRanges(b, loc)[dim];
176  if (auto sliceOp = dyn_cast<tensor::ExtractSliceOp>(shapeProducingOp))
177  return sliceOp.getOrCreateRanges(b, loc)[dim];
178  llvm_unreachable("SubviewOp or ExtractSliceOp expected");
179 }
180 
181 /// Fuses the producer into the loop immediately enclosing the consumer.
182 /// This is achieved by "recomputing" the producer at the time it
183 /// is needed just before the consumer.
184 static LinalgOp fuse(OpBuilder &b, LinalgOp producerOp, AffineMap producerMap,
185  OpOperand &consumerOpOperand) {
186  LLVM_DEBUG(llvm::dbgs() << "Producer map: " << producerMap << "\n");
187  DenseMap<unsigned, Range> fusedLoopsAndRanges;
188  Value shapedOperand = consumerOpOperand.get();
189  for (const auto &en : llvm::enumerate(producerMap.getResults())) {
190  unsigned posInProducerLoop = cast<AffineDimExpr>(en.value()).getPosition();
191  fusedLoopsAndRanges[posInProducerLoop] = getRangeFromOperandShape(
192  b, consumerOpOperand.getOwner()->getLoc(), shapedOperand, en.index());
193  }
194  return fuse(b, producerOp, fusedLoopsAndRanges);
195 }
196 
197 /// Walk back use-def chain through scf::For yields.
198 /// Sets `producer` and `outputIndex` if it finds a producer LinalgOp
199 
200 // TODO(ravishankarm, ntv): This can be moved into the dependence graphs
201 // dependence tracking since the dependence tracking is similar to what is done
202 // w.r.t to buffers.
203 static void getProducerOfTensor(Value tensor, OpResult &opResult) {
204  if (!isa<RankedTensorType>(tensor.getType()))
205  return;
206 
207  while (true) {
208  LLVM_DEBUG(llvm::dbgs() << "\ngetProducerOfTensor: " << tensor);
209  if (auto linalgOp = tensor.getDefiningOp<LinalgOp>()) {
210  opResult = cast<OpResult>(tensor);
211  return;
212  }
213  if (auto sliceOp = tensor.getDefiningOp<tensor::ExtractSliceOp>()) {
214  tensor = sliceOp.getSource();
215  continue;
216  }
217  if (auto blockArg = dyn_cast<BlockArgument>(tensor)) {
218  if (auto forOp = blockArg.getDefiningOp<scf::ForOp>()) {
219  tensor = forOp.getInitArgs()[blockArg.getArgNumber()];
220  continue;
221  }
222  }
223  return;
224  }
225 }
226 
227 FailureOr<FusionInfo>
229  Value inputTensor = consumerOpOperand.get();
230  OpResult producerOpResult;
231  getProducerOfTensor(inputTensor, producerOpResult);
232  if (!producerOpResult) {
233  LLVM_DEBUG(llvm::dbgs() << "\nUnable to find producer");
234  return failure();
235  }
236  return fuseProducerOfTensor(b, producerOpResult, consumerOpOperand);
237 }
238 
239 FailureOr<FusionInfo>
241  OpOperand &consumerOpOperand) {
242  auto producerOp = dyn_cast<LinalgOp>(producerOpResult.getOwner());
243  if (!producerOp)
244  return failure();
245 
246  LinalgOp consumerOp = dyn_cast<LinalgOp>(consumerOpOperand.getOwner());
247  if (!consumerOp)
248  return failure();
249 
250  Value inputTensor = consumerOpOperand.get();
251 
252  // Must be an extract_slice op to guarantee there are loops we can fuse into.
253  auto sliceOp = inputTensor.getDefiningOp<tensor::ExtractSliceOp>();
254  if (!sliceOp) {
255  LLVM_DEBUG(llvm::dbgs()
256  << "\nNot fusable, not an extract_slice op: " << inputTensor);
257  return failure();
258  }
259 
260  // If producer is already in the same block as consumer, we are done.
261  if (consumerOpOperand.get().getParentBlock() ==
262  producerOpResult.getParentBlock())
263  return failure();
264 
265  // Insert fused `producer` just before `consumer`.
267  b.setInsertionPoint(consumerOp);
268  LLVM_DEBUG(llvm::dbgs() << "Fuse into consumer: " << *consumerOp << "\n");
269  OpOperand *opOperand =
270  producerOp.getDpsInitOperand(producerOpResult.getResultNumber());
271  LinalgOp fusedProducer =
272  fuse(b, producerOp, producerOp.getMatchingIndexingMap(opOperand),
273  consumerOpOperand);
274 
275  // Replace use.
276  Value def = fusedProducer->getResult(producerOpResult.getResultNumber());
277  Type consumerType = consumerOpOperand.get().getType();
278  // Check if rank-reduction occurred as part of the extract_slice. If yes,
279  // collapse the dropped dimensions.
280  if (cast<ShapedType>(consumerType).getRank() !=
281  cast<ShapedType>(def.getType()).getRank()) {
282  llvm::SmallBitVector droppedDims = sliceOp.getDroppedDims();
283  def =
284  tensor::dropGivenUnitDims(b, fusedProducer.getLoc(), def, droppedDims);
285  }
286  // Canonicalizations are not guaranteed to have happened before constructing
287  // `fusedProducer`. In the tensor case this can result in temporary type
288  // mismatches. Insert a `tensor.cast` op to propagate the transformation
289  // invariant that types are compatible.
290  if (consumerType != def.getType())
291  def = b.create<tensor::CastOp>(fusedProducer.getLoc(), consumerType, def);
292  consumerOpOperand.set(def);
293  return FusionInfo{cast<LinalgOp>(producerOpResult.getOwner()), fusedProducer};
294 }
static LinalgOp fuse(OpBuilder &b, LinalgOp producer, const DenseMap< unsigned, Range > &fusedLoopsAndRanges)
Fuses the producer by cloning the producer.
Definition: Fusion.cpp:114
static void getProducerOfTensor(Value tensor, OpResult &opResult)
Walk back use-def chain through scf::For yields.
Definition: Fusion.cpp:203
static SmallVector< Value > getTiledOperands(LinalgOp producer)
Definition: Fusion.cpp:107
static ShapeDimension getShapeDefiningLoopRange(LinalgOp op, unsigned loopDepth, bool fromSubViewOpOnly=false)
Definition: Fusion.cpp:69
static Range getRangeFromOperandShape(OpBuilder &b, Location loc, Value shapedOperand, unsigned dim)
Get the loop range for a dimension dim based on the shapedOperand.
Definition: Fusion.cpp:171
A multi-dimensional affine map Affine map's are immutable like Type's, and they are uniqued.
Definition: AffineMap.h:46
ArrayRef< AffineExpr > getResults() const
Definition: AffineMap.cpp:403
IntegerAttr getIndexAttr(int64_t value)
Definition: Builders.cpp:103
IRValueT get() const
Return the current value being used by this operand.
Definition: UseDefLists.h:160
void set(IRValueT newValue)
Set the current value being used by this operand.
Definition: UseDefLists.h:163
This class defines the main interface for locations in MLIR and acts as a non-nullable wrapper around...
Definition: Location.h:76
This class provides a mutable adaptor for a range of operands.
Definition: ValueRange.h:118
OperandRange getAsOperandRange() const
Explicit conversion to an OperandRange.
RAII guard to reset the insertion point of the builder when destroyed.
Definition: Builders.h:346
This class helps build Operations.
Definition: Builders.h:205
void setInsertionPoint(Block *block, Block::iterator insertPoint)
Set the insertion point to the specified location.
Definition: Builders.h:396
Operation * create(const OperationState &state)
Creates an operation given the fields represented as an OperationState.
Definition: Builders.cpp:452
This class represents a single result from folding an operation.
Definition: OpDefinition.h:271
This class represents an operand of an operation.
Definition: Value.h:257
This is a value defined by a result of an operation.
Definition: Value.h:447
Operation * getOwner() const
Returns the operation that owns this result.
Definition: Value.h:456
unsigned getResultNumber() const
Returns the number of this result.
Definition: Value.h:459
unsigned getBeginOperandIndex() const
Return the operand index of the first element of this range.
Operation is the basic unit of execution within MLIR.
Definition: Operation.h:88
Location getLoc()
The source location the operation was defined or derived from.
Definition: Operation.h:223
Instances of the Type class are uniqued, have an immutable identifier and an optional mutable compone...
Definition: Types.h:74
This class represents an instance of an SSA value in the MLIR system, representing a computable value...
Definition: Value.h:96
Type getType() const
Return the type of this value.
Definition: Value.h:105
Block * getParentBlock()
Return the Block in which this Value is defined.
Definition: Value.cpp:48
Operation * getDefiningOp() const
If this value is the result of an operation, return the operation that defines it.
Definition: Value.cpp:20
Operation * getOwner() const
Return the owner of this operand.
Definition: UseDefLists.h:38
constexpr void enumerate(std::tuple< Tys... > &tuple, CallbackT &&callback)
Definition: Matchers.h:344
FailureOr< FusionInfo > fuseProducerOfTensor(OpBuilder &b, OpOperand &consumerOpOperand)
This implements the fusion part of the "tileAndFuse on tensors" transformation and thus requires the ...
Definition: Fusion.cpp:228
SmallVector< Value > makeTiledShapes(OpBuilder &builder, Location loc, LinalgOp linalgOp, ValueRange valuesToTile, ArrayRef< OpFoldResult > ivs, ArrayRef< OpFoldResult > tileSizes, ArrayRef< OpFoldResult > sizeBounds, bool omitPartialTileCheck)
Creates extract_slice/subview ops for all valuesToTile of the given linalgOp with builder,...
Definition: Utils.cpp:865
OpFoldResult createFoldedDimOp(OpBuilder &b, Location loc, Value val, int64_t dim)
Create one memref::DimOp or tensor::DimOp depending on the type of val.
Definition: LinalgOps.cpp:108
void offsetIndices(OpBuilder &b, LinalgOp linalgOp, ArrayRef< OpFoldResult > offests)
Add the specified offsets to any linalg.index ops contained in the given linalgOp.
Definition: Utils.cpp:887
CollapseShapeOp dropGivenUnitDims(OpBuilder &b, Location loc, Value src, const llvm::SmallBitVector &dropDims)
Create tensor.collapse_shape to drop unit dimensions in dropDims in tensor src.
Definition: Utils.cpp:97
Include the generated interface declarations.
Type getType(OpFoldResult ofr)
Returns the int type of the integer in ofr.
Definition: Utils.cpp:305
Operation * clone(OpBuilder &b, Operation *op, TypeRange newResultTypes, ValueRange newOperands)
Implements a simple high-level fusion pass on linalg structured operations.
Definition: Fusion.cpp:58
unsigned dimension
Definition: Fusion.cpp:60
Value shape
Definition: Fusion.cpp:59
Represents a range (offset, size, and stride) where each element of the triple may be dynamic or stat...
OpFoldResult offset
A struct containing the Linalg producer before and after fusion.
Definition: Utils.h:233