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Extend getBackwardSlice to track values captured from above #113478

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Merged
merged 3 commits into from
Oct 31, 2024
Merged

Extend getBackwardSlice to track values captured from above #113478

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2920933
Add `omitUsesFromAbove` to getBackwardsSlice
IanWood1 Oct 23, 2024
3e8b47a
Cleanup impl & add test
IanWood1 Oct 30, 2024
9f7ea3c
Use lambda to reuse logic
IanWood1 Oct 30, 2024
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5 changes: 5 additions & 0 deletions mlir/include/mlir/Analysis/SliceAnalysis.h
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,11 @@ struct BackwardSliceOptions : public SliceOptions {
/// backward slice computation traverses block arguments and asserts that the
/// parent op has a single region with a single block.
bool omitBlockArguments = false;

/// When omitUsesFromAbove is true, the backward slice computation omits
/// traversing values that are captured from above.
/// TODO: this should default to `false` after users have been updated.
bool omitUsesFromAbove = true;
};

using ForwardSliceOptions = SliceOptions;
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9 changes: 8 additions & 1 deletion mlir/lib/Analysis/SliceAnalysis.cpp
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Expand Up @@ -16,6 +16,7 @@
#include "mlir/IR/Operation.h"
#include "mlir/Interfaces/SideEffectInterfaces.h"
#include "mlir/Support/LLVM.h"
#include "mlir/Transforms/RegionUtils.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"

Expand Down Expand Up @@ -91,7 +92,13 @@ static void getBackwardSliceImpl(Operation *op,
if (options.filter && !options.filter(op))
return;

for (const auto &en : llvm::enumerate(op->getOperands())) {
auto operands = op->getOperands();
SetVector<Value> valuesToFollow(operands.begin(), operands.end());
if (!options.omitUsesFromAbove) {
getUsedValuesDefinedAbove(op->getRegions(), valuesToFollow);
}

for (const auto &en : llvm::enumerate(valuesToFollow)) {
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@joker-eph joker-eph Oct 30, 2024 •
edited
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The way you can make it "free" when there are no regions is to define this code as a lambda that operates on an ValueRange.

auto processValues = [&] (ValueRange valuesToFollow) {
  ...
};

And then dispatch like this:

  processValues(op->getOperands());

  if (!options.omitUsesFromAbove) {
    SetVector<Value> valuesToFollow;
    getUsedValuesDefinedAbove(op->getRegions(), valuesToFollow);
    processValues(valuesToFollow);
  }

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@IanWood1 IanWood1 Oct 30, 2024

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Thank you, that's a good solution.

I tweaked it a bit to take a Value so it can get passed to visitValuesDefinedAbove which takes a lambda with an OpOperand* arg. This prevents storing the values in a set (backwardSlice->count ensures they are still only visited once)

auto operand = en.value();
if (auto *definingOp = operand.getDefiningOp()) {
if (backwardSlice->count(definingOp) == 0)
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28 changes: 27 additions & 1 deletion mlir/test/IR/slice.mlir
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@@ -1,4 +1,4 @@
// RUN: mlir-opt -slice-analysis-test %s | FileCheck %s
// RUN: mlir-opt -slice-analysis-test -split-input-file %s | FileCheck %s

func.func @slicing_linalg_op(%arg0 : index, %arg1 : index, %arg2 : index) {
%a = memref.alloc(%arg0, %arg2) : memref<?x?xf32>
Expand Down Expand Up @@ -33,3 +33,29 @@ func.func @slicing_linalg_op(%arg0 : index, %arg1 : index, %arg2 : index) {
// CHECK-DAG: %[[B:.+]] = memref.alloc(%[[ARG2]], %[[ARG1]]) : memref<?x?xf32>
// CHECK-DAG: %[[C:.+]] = memref.alloc(%[[ARG0]], %[[ARG1]]) : memref<?x?xf32>
// CHECK: return

// -----

#map = affine_map<(d0, d1) -> (d0, d1)>
func.func @slice_use_from_above(%arg0: tensor<5x5xf32>, %arg1: tensor<5x5xf32>) {
%0 = linalg.generic {indexing_maps = [#map, #map], iterator_types = ["parallel", "parallel"]} ins(%arg0 : tensor<5x5xf32>) outs(%arg1 : tensor<5x5xf32>) {
^bb0(%in: f32, %out: f32):
%2 = arith.addf %in, %in : f32
linalg.yield %2 : f32
} -> tensor<5x5xf32>
%collapsed = tensor.collapse_shape %0 [[0, 1]] : tensor<5x5xf32> into tensor<25xf32>
%1 = linalg.generic {indexing_maps = [#map, #map], iterator_types = ["parallel", "parallel"]} ins(%0 : tensor<5x5xf32>) outs(%arg1 : tensor<5x5xf32>) {
^bb0(%in: f32, %out: f32):
%c2 = arith.constant 2 : index
%extracted = tensor.extract %collapsed[%c2] : tensor<25xf32>
%2 = arith.addf %extracted, %extracted : f32
linalg.yield %2 : f32
} -> tensor<5x5xf32>
return
}

// CHECK-LABEL: func @slice_use_from_above__backward_slice__0
// CHECK-SAME: %[[ARG0:[a-zA-Z0-9_]+]]: tensor
// CHECK: %[[A:.+]] = linalg.generic {{.*}} ins(%[[ARG0]]
// CHECK: %[[B:.+]] = tensor.collapse_shape %[[A]]
// CHECK: return
2 changes: 2 additions & 0 deletions mlir/test/lib/IR/TestSlicing.cpp
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Expand Up @@ -39,6 +39,8 @@ static LogicalResult createBackwardSliceFunction(Operation *op,
SetVector<Operation *> slice;
BackwardSliceOptions options;
options.omitBlockArguments = omitBlockArguments;
// TODO: Make this default.
options.omitUsesFromAbove = false;
getBackwardSlice(op, &slice, options);
for (Operation *slicedOp : slice)
builder.clone(*slicedOp, mapper);
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