Add RestructureNonConstantAxes pass to address reduce op tests failin…

…g on non constant axes (llvm#3600)

include/torch-mlir/Dialect/Torch/Transforms/Passes.h

@@ -149,6 +149,12 @@ StringRef getAbstractInterpLibrary();
 
 static const char kTorchOpPrefix[] = R"(torch.)";
 
+void populateRestructureNonConstantAxesPattern(RewritePatternSet &patterns,
+                                               MLIRContext *context);
+
+std::unique_ptr<OperationPass<func::FuncOp>>
+createRestructureNonConstantAxesPass();
+
 } // namespace Torch
 
 /// Registers all Torch transformation passes.

include/torch-mlir/Dialect/Torch/Transforms/Passes.td

@@ -431,4 +431,24 @@ def VerifyBackendContractNoDecompositions
   }];
 }
 
+def RestructureNonConstantAxes
+    : Pass<"torch-restructure-non-constant-axes", "func::FuncOp"> {
+  let summary = "Ensure that every Reduction.cpp op has a constant reduction axis.";
+  let constructor = [{
+    mlir::torch::Torch::createRestructureNonConstantAxesPass()
+  }];
+  let description = [{
+    This pass ensures that every Reduction.cpp op has a constant reduction axis.
+
+    It does so using reshapes. For example, a <1,2,3,4,5> tensor will be reshaped to a <?,?,?> tensor
+    and reduced on axis 1 to produce a <?,1,?> tensor. The resulting tensor will be reshaped back to the original shape.
+
+    Then when the axis is supplied at runtime (say axis = -2), the shapes will be computed as so:
+    <?,?,?> becomes <6,4,5>
+    which gets reduced to <6,1,5>
+    and rehsaped back to the original reduction op's output shape,
+    <1,2,3,1,5>
+  }];
+}
+
 #endif // TORCHMLIR_TORCH_PASSES

lib/Dialect/Torch/Transforms/CMakeLists.txt

@@ -17,6 +17,7 @@ add_mlir_library(TorchMLIRTorchPasses
   ReifyShapeCalculations.cpp
   ReifyDtypeCalculations.cpp
   ReifyAbstractInterpCalculationsUtils.cpp
+  RestructureNonConstantAxes.cpp
   ScalarizeShapes.cpp
   AbstractInterpLibrary.cpp
   SimplifyShapeCalculations.cpp

lib/Dialect/Torch/Transforms/RestructureNonConstantAxes.cpp

@@ -0,0 +1,277 @@
+//===- RestructureNonConstantAxes.cpp --------------------------------*-
+// C++-*-===//
+//
+// This file is licensed 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
+// Also available under a BSD-style license. See LICENSE.
+//
+//===----------------------------------------------------------------------===//
+
+#include "PassDetail.h"
+
+#include "mlir/IR/BuiltinOps.h"
+#include "mlir/Pass/PassManager.h"
+#include "mlir/Transforms/DialectConversion.h"
+#include "mlir/Transforms/GreedyPatternRewriteDriver.h"
+#include "torch-mlir/Dialect/Torch/IR/TorchDialect.h"
+#include "torch-mlir/Dialect/Torch/IR/TorchOps.h"
+#include "torch-mlir/Dialect/Torch/Transforms/Passes.h"
+#include "torch-mlir/Dialect/Torch/Utils/Utils.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/Support/Debug.h"
+
+#define DEBUG_TYPE "torch-lower-to-backend-contract"
+
+using namespace mlir;
+using namespace mlir::torch;
+using namespace mlir::torch::Torch;
+
+namespace {
+
+template <typename SrcOp>
+class ConstantifyDimArgument : public OpRewritePattern<SrcOp> {
+public:
+  using OpRewritePattern<SrcOp>::OpRewritePattern;
+
+  bool isDimConstant(SrcOp op) const {
+    SmallVector<int64_t> dimList;
+    int64_t dim;
+    return matchPattern(op.getDim(), m_TorchListOfConstantInts(dimList)) ||
+           matchPattern(op.getDim(), m_TorchConstantInt(&dim));
+  }
+
+  /*
+  This function renders the reduction dim constant by reshaping the input tensor
+  such that the dim argument is the middle dimension.
+
+  For example, if the input tensor has shape [3,4,5,6,7] and the dim argument is
+  -2, the input tensor is reshaped to [3,4,5,6,7] -> [12,5,42], the reduction
+  operation is applied, and the result is reshaped back to [3,4,1,6,7].
+
+  Since we don't know the dim argument at compile time, we need to compute the
+  arguments to the reshape op at runtime. We do this by computing the new shape
+  of the tensor by multiplying the shapes of the tensor before and after the dim
+  argument, and then reshaping the tensor to this new shape.
+  */
+  LogicalResult matchAndRewrite(SrcOp op,
+                                PatternRewriter &rewriter) const override {
+    Location loc = op->getLoc();
+
+    Value self = op.getSelf();
+    Value dim = op.getDim();
+
+    if (isDimConstant(op)) {
+      return rewriter.notifyMatchFailure(op,
+                                         "dim argument is already constant");
+    }
+
+    if (isa<Torch::NoneType>(dim.getType())) {
+      return rewriter.notifyMatchFailure(
+          op, "RestructureNonConstantAxes does not support None dim");
+    }
+
+    // when keepdim is not constant, check the ranks of the input and output
+    // tensors
+    ValueTensorType selfTy =
+        llvm::cast<ValueTensorType>(op.getSelf().getType());
+    ValueTensorType resultTy =
+        llvm::cast<ValueTensorType>(op.getResult().getType());
+    if (selfTy.hasSizes() && resultTy.hasSizes() &&
+        selfTy.getSizes().size() != resultTy.getSizes().size()) {
+      return rewriter.notifyMatchFailure(
+          op,
+          "RestructureNonConstantAxes does not yet support keepdim=false, but "
+          "the input and output tensors have different ranks");
+    }
+
+    Type intType = rewriter.getType<Torch::IntType>();
+    Type boolType = rewriter.getType<Torch::BoolType>();
+    auto createInt = [&](int value) {
+      return rewriter.create<Torch::ConstantIntOp>(
+          loc, intType,
+          rewriter.getIntegerAttr(rewriter.getIntegerType(64), value));
+    };
+    Value zero = createInt(0);
+    Value one = createInt(1);
+
+    // handle when dim is a single element list
+    bool oldDimIsList = isa<Torch::ListType>(dim.getType());
+    if (oldDimIsList) {
+      Value len = rewriter.create<Torch::AtenLenTOp>(loc, intType, dim);
+      Value dimListIsLengthOne =
+          rewriter.create<Torch::AtenEqIntOp>(loc, boolType, len, one);
+      rewriter.create<Torch::RuntimeAssertOp>(
+          loc, dimListIsLengthOne,
+          rewriter.getStringAttr("RestructureNonConstantAxes does not support "
+                                 "dim lists with more than one element"));
+      dim = rewriter.create<Torch::Aten__Getitem__TOp>(loc, intType, dim, zero);
+    }
+
+    // Normalize negative dim
+    Value rank = rewriter.create<Torch::AtenDimOp>(loc, intType, self);
+    Value isNegative = rewriter.create<Torch::AtenLtIntOp>(loc, dim, zero);
+    Value rankOffset = rewriter.create<Torch::AtenMulIntOp>(
+        loc, intType,
+        rewriter.create<Torch::AtenIntBoolOp>(loc, intType, isNegative), rank);
+    dim = rewriter.create<Torch::AtenAddIntOp>(loc, intType, dim, rankOffset);
+
+    auto createConditionalMult = [&](Value self, Value multiplier,
+                                     Value condition) {
+      // compute:
+      // result = codition ? (self * multiplier) : self
+      // via
+      // result = self * (1 + (multiplier - 1) * condition)
+      // which translates to:
+
+      // result = multiplier - 1
+      Value result = rewriter.create<Torch::AtenSubIntOp>(
+          loc, intType, multiplier, createInt(1));
+      // result = result * condition
+      result =
+          rewriter.create<Torch::AtenMulIntOp>(loc, intType, result, condition);
+      // result = result + 1
+      result = rewriter.create<Torch::AtenAddIntOp>(loc, intType, result,
+                                                    createInt(1));
+      // result = self * result
+      result = rewriter.create<Torch::AtenMulIntOp>(loc, intType, self, result);
+      return result;
+    };
+
+    // new shape = [beforeDim, dimSize, afterDim]
+    Value beforeProd = createInt(1);
+    Value afterProd = createInt(1);
+    Value dimSize = createInt(1);
+
+    for (size_t i = 0; i < selfTy.getSizes().size(); ++i) {
+      Value idx = createInt(i);
+      Value size =
+          rewriter.create<Torch::AtenSizeIntOp>(loc, intType, self, idx);
+
+      Value isBeforeDim =
+          rewriter.create<Torch::AtenLtIntOp>(loc, boolType, idx, dim);
+      isBeforeDim =
+          rewriter.create<Torch::AtenIntBoolOp>(loc, intType, isBeforeDim);
+      Value isAfterDim =
+          rewriter.create<Torch::AtenGtIntOp>(loc, boolType, idx, dim);
+      isAfterDim =
+          rewriter.create<Torch::AtenIntBoolOp>(loc, intType, isAfterDim);
+
+      Value isEqualToDim =
+          rewriter.create<Torch::AtenEqIntOp>(loc, boolType, idx, dim);
+      isEqualToDim =
+          rewriter.create<Torch::AtenIntBoolOp>(loc, intType, isEqualToDim);
+      dimSize = createConditionalMult(dimSize, size, isEqualToDim);
+
+      beforeProd = createConditionalMult(beforeProd, size, isBeforeDim);
+      afterProd = createConditionalMult(afterProd, size, isAfterDim);
+    }
+
+    Value newShape = rewriter.create<Torch::PrimListConstructOp>(
+        loc, rewriter.getType<Torch::ListType>(intType),
+        ValueRange{beforeProd, dimSize, afterProd});
+
+    // Reshape input
+    auto newSelfTy = selfTy.getWithSizesAndDtype(
+        SmallVector<int64_t>{Torch::kUnknownSize, Torch::kUnknownSize,
+                             Torch::kUnknownSize},
+        selfTy.getDtype());
+    Value reshapedSelf =
+        rewriter.create<Torch::AtenViewOp>(loc, newSelfTy, self, newShape);
+
+    // construct new operange range where self is replaced with reshapedSelf
+    // tensor, and dim is replaced with 1
+    Value newDim;
+    if (oldDimIsList) {
+      newDim = rewriter.create<Torch::PrimListConstructOp>(
+          loc, rewriter.getType<Torch::ListType>(intType), ValueRange{one});
+    } else {
+      newDim = one;
+    }
+    ValueRange oldOperands = op->getOperands();
+    SmallVector<Value> newOperandsVect;
+    for (size_t i = 0; i < oldOperands.size(); ++i) {
+      if (oldOperands[i] == op.getSelf()) {
+        newOperandsVect.push_back(reshapedSelf);
+      } else if (oldOperands[i] == op.getDim()) {
+        newOperandsVect.push_back(newDim);
+      } else {
+        newOperandsVect.push_back(oldOperands[i]);
+      }
+    }
+    ValueRange newOperands = ValueRange(newOperandsVect);
+
+    // construct new reduction op result type
+    ValueTensorType newResultTy =
+        cast<ValueTensorType>(resultTy.getWithSizesAndDtype(
+            SmallVector<int64_t>{Torch::kUnknownSize, 1, Torch::kUnknownSize},
+            resultTy.getDtype()));
+
+    Value newReductionOp =
+        rewriter.create<SrcOp>(loc, newResultTy, newOperands, op->getAttrs());
+
+    // Reshape the result back to original shape
+    ValueTensorType oldResultTy =
+        cast<ValueTensorType>(op.getResult().getType());
+    SmallVector<Value> shapeValues;
+    for (auto dim : oldResultTy.getSizes()) {
+      shapeValues.push_back(createInt(dim));
+    }
+    Value originalShape = rewriter.create<Torch::PrimListConstructOp>(
+        loc, rewriter.getType<Torch::ListType>(intType), shapeValues);
+    Value result = rewriter.create<Torch::AtenViewOp>(
+        loc, op->getResult(0).getType(), newReductionOp, originalShape);
+
+    rewriter.replaceOp(op, result);
+    return success();
+  };
+};
+
+template <typename... OpTypes>
+void addConstantifyDimArgumentPatterns(RewritePatternSet &patterns,
+                                       MLIRContext *context) {
+  // simple variadic template to sugar up adding the patterns
+  (patterns.add<ConstantifyDimArgument<OpTypes>>(context), ...);
+}
+
+void populateRestructureNonConstantAxesPattern(RewritePatternSet &patterns,
+                                               MLIRContext *context) {
+  // these are the reduction ops with a dim argument
+
+  addConstantifyDimArgumentPatterns<
+      // not supported because they have multiple results
+      // AtenMaxDimOp,
+      // AtenMinDimOp,
+      AtenSumDimIntListOp, AtenAllDimOp, AtenLinalgVectorNormOp,
+      AtenFrobeniusNormDimOp>(patterns, context);
+}
+
+class RestructureNonConstantAxesPass
+    : public RestructureNonConstantAxesBase<RestructureNonConstantAxesPass> {
+public:
+  RestructureNonConstantAxesPass() = default;
+
+  void runOnOperation() override {
+    MLIRContext *context = &getContext();
+
+    RewritePatternSet patterns(context);
+
+    populateRestructureNonConstantAxesPattern(patterns, context);
+
+    // TODO: Debug visitation order to make this more efficient.
+    // A single linear scan should suffice.
+    GreedyRewriteConfig config;
+    config.useTopDownTraversal = true;
+    config.maxIterations = GreedyRewriteConfig::kNoLimit;
+    if (failed(applyPatternsAndFoldGreedily(getOperation(), std::move(patterns),
+                                            config))) {
+      return signalPassFailure();
+    }
+  }
+};
+} // namespace
+
+std::unique_ptr<OperationPass<func::FuncOp>>
+mlir::torch::Torch::createRestructureNonConstantAxesPass() {
+  return std::make_unique<RestructureNonConstantAxesPass>();
+}

lib/Dialect/TorchConversion/Transforms/Passes.cpp

@@ -64,6 +64,10 @@ void mlir::torch::registerTorchConversionPasses() {
 
 void TorchConversion::createTorchBackendToLinalgOnTensorsBackendPipeline(
     OpPassManager &pm) {
+  // Fix non constant dims passed to reduction ops
+  pm.addNestedPass<func::FuncOp>(
+      torch::Torch::createRestructureNonConstantAxesPass());
+
   // We want to fuse quantized operations together before lowering to linalg.
   pm.addNestedPass<func::FuncOp>(Torch::createFuseQuantizedOpsPass());
   pm.addNestedPass<func::FuncOp>(Torch::createScalarizeShapesPass());