Extend getBackwardSlice to track values captured from above

mlir/include/mlir/Analysis/SliceAnalysis.h

@@ -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;

mlir/lib/Analysis/SliceAnalysis.cpp

@@ -16,6 +16,8 @@
 #include "mlir/IR/Operation.h"
 #include "mlir/Interfaces/SideEffectInterfaces.h"
 #include "mlir/Support/LLVM.h"
+#include "mlir/Transforms/RegionUtils.h"
+#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 
@@ -91,14 +93,13 @@ static void getBackwardSliceImpl(Operation *op,
   if (options.filter && !options.filter(op))
     return;
 
-  for (const auto &en : llvm::enumerate(op->getOperands())) {
-    auto operand = en.value();
-    if (auto *definingOp = operand.getDefiningOp()) {
+  auto processValue = [&](Value value) {
+    if (auto *definingOp = value.getDefiningOp()) {
       if (backwardSlice->count(definingOp) == 0)
         getBackwardSliceImpl(definingOp, backwardSlice, options);
-    } else if (auto blockArg = dyn_cast<BlockArgument>(operand)) {
+    } else if (auto blockArg = dyn_cast<BlockArgument>(value)) {
       if (options.omitBlockArguments)
-        continue;
+        return;
 
       Block *block = blockArg.getOwner();
       Operation *parentOp = block->getParentOp();
@@ -113,7 +114,14 @@ static void getBackwardSliceImpl(Operation *op,
     } else {
       llvm_unreachable("No definingOp and not a block argument.");
     }
+  };
+
+  if (!options.omitUsesFromAbove) {
+    visitUsedValuesDefinedAbove(op->getRegions(), [&](OpOperand *operand) {
+      processValue(operand->get());
+    });
   }
+  llvm::for_each(op->getOperands(), processValue);
 
   backwardSlice->insert(op);
 }

mlir/test/IR/slice.mlir

@@ -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>
@@ -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

mlir/test/lib/IR/TestSlicing.cpp

@@ -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);