mlir/test/lib/Analysis/DataFlow/TestSparseBackwardDataFlowAnalysis.cpp

//===- TestBackwardDataFlowAnalysis.cpp - Test dead code analysis ---------===//
//
// 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/Analysis/DataFlow/SparseAnalysis.h"
#include "mlir/Analysis/DataFlow/Utils.h"
#include "mlir/Dialect/MemRef/IR/MemRef.h"
#include "mlir/Interfaces/SideEffectInterfaces.h"
#include "mlir/Pass/Pass.h"

using namespace mlir;
using namespace mlir::dataflow;

namespace {

/// Lattice value storing the a set of memory resources that something
/// is written to.
struct WrittenToLatticeValue {
  bool operator==(const WrittenToLatticeValue &other) {
    return this->writes == other.writes;
  }

  static WrittenToLatticeValue meet(const WrittenToLatticeValue &lhs,
                                    const WrittenToLatticeValue &rhs) {
    WrittenToLatticeValue res = lhs;
    (void)res.addWrites(rhs.writes);

    return res;
  }

  static WrittenToLatticeValue join(const WrittenToLatticeValue &lhs,
                                    const WrittenToLatticeValue &rhs) {
    // Should not be triggered by this test, but required by `Lattice<T>`
    llvm_unreachable("Join should not be triggered by this test");
  }

  ChangeResult addWrites(const SetVector<StringAttr> &writes) {
    int sizeBefore = this->writes.size();
    this->writes.insert_range(writes);
    int sizeAfter = this->writes.size();
    return sizeBefore == sizeAfter ? ChangeResult::NoChange
                                   : ChangeResult::Change;
  }

  void print(raw_ostream &os) const {
    os << "[";
    llvm::interleave(
        writes, os, [&](const StringAttr &a) { os << a.str(); }, " ");
    os << "]";
  }

  void clear() { writes.clear(); }

  SetVector<StringAttr> writes;
};

/// This lattice represents, for a given value, the set of memory resources that
/// this value, or anything derived from this value, is potentially written to.
struct WrittenTo : public Lattice<WrittenToLatticeValue> {
  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(WrittenTo)
  using Lattice::Lattice;
};

/// An analysis that, by going backwards along the dataflow graph, annotates
/// each value with all the memory resources it (or anything derived from it)
/// is eventually written to.
class WrittenToAnalysis : public SparseBackwardDataFlowAnalysis<WrittenTo> {
public:
  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(WrittenToAnalysis)

  WrittenToAnalysis(DataFlowSolver &solver, SymbolTableCollection &symbolTable,
                    bool assumeFuncWrites)
      : SparseBackwardDataFlowAnalysis(solver, symbolTable),
        assumeFuncWrites(assumeFuncWrites) {}

  LogicalResult visitOperation(Operation *op, ArrayRef<WrittenTo *> operands,
                               ArrayRef<const WrittenTo *> results) override;

  void visitBranchOperand(OpOperand &operand) override;

  void visitCallOperand(OpOperand &operand) override;

  void
  visitNonControlFlowArguments(RegionSuccessor &successor,
                               ArrayRef<BlockArgument> arguments) override {}

  void visitExternalCall(CallOpInterface call, ArrayRef<WrittenTo *> operands,
                         ArrayRef<const WrittenTo *> results) override;

  void setToExitState(WrittenTo *lattice) override {
    lattice->getValue().clear();
  }

private:
  bool assumeFuncWrites;
};

LogicalResult
WrittenToAnalysis::visitOperation(Operation *op, ArrayRef<WrittenTo *> operands,
                                  ArrayRef<const WrittenTo *> results) {
  if (auto store = dyn_cast<memref::StoreOp>(op)) {
    SetVector<StringAttr> newWrites;
    newWrites.insert(op->getDiscardableAttrOfType<StringAttr>("tag_name"));
    propagateIfChanged(operands[0],
                       operands[0]->getValue().addWrites(newWrites));
    return success();
  } // By default, every result of an op depends on every operand.
  for (const WrittenTo *r : results) {
    for (WrittenTo *operand : operands) {
      meet(operand, *r);
    }
    addDependency(const_cast<WrittenTo *>(r), getProgramPointAfter(op));
  }
  return success();
}

void WrittenToAnalysis::visitBranchOperand(OpOperand &operand) {
  // Mark branch operands as "brancharg%d", with %d the operand number.
  WrittenTo *lattice = getLatticeElement(operand.get());
  SetVector<StringAttr> newWrites;
  newWrites.insert(
      StringAttr::get(operand.getOwner()->getContext(),
                      "brancharg" + Twine(operand.getOperandNumber())));
  propagateIfChanged(lattice, lattice->getValue().addWrites(newWrites));
}

void WrittenToAnalysis::visitCallOperand(OpOperand &operand) {
  // Mark call operands as "callarg%d", with %d the operand number.
  WrittenTo *lattice = getLatticeElement(operand.get());
  SetVector<StringAttr> newWrites;
  newWrites.insert(
      StringAttr::get(operand.getOwner()->getContext(),
                      "callarg" + Twine(operand.getOperandNumber())));
  propagateIfChanged(lattice, lattice->getValue().addWrites(newWrites));
}

void WrittenToAnalysis::visitExternalCall(CallOpInterface call,
                                          ArrayRef<WrittenTo *> operands,
                                          ArrayRef<const WrittenTo *> results) {
  if (!assumeFuncWrites) {
    return SparseBackwardDataFlowAnalysis::visitExternalCall(call, operands,
                                                             results);
  }

  for (WrittenTo *lattice : operands) {
    SetVector<StringAttr> newWrites;
    StringAttr name = call->getDiscardableAttrOfType<StringAttr>("tag_name");
    if (!name) {
      name = StringAttr::get(call->getContext(),
                             call.getOperation()->getName().getStringRef());
    }
    newWrites.insert(name);
    propagateIfChanged(lattice, lattice->getValue().addWrites(newWrites));
  }
}

} // end anonymous namespace

namespace {
struct TestWrittenToPass
    : public PassWrapper<TestWrittenToPass, OperationPass<>> {
  MLIR_DEFINE_EXPLICIT_INTERNAL_INLINE_TYPE_ID(TestWrittenToPass)

  TestWrittenToPass() = default;
  TestWrittenToPass(const TestWrittenToPass &other) : PassWrapper(other) {
    interprocedural = other.interprocedural;
    assumeFuncWrites = other.assumeFuncWrites;
  }

  StringRef getArgument() const override { return "test-written-to"; }

  Option<bool> interprocedural{
      *this, "interprocedural", llvm::cl::init(true),
      llvm::cl::desc("perform interprocedural analysis")};
  Option<bool> assumeFuncWrites{
      *this, "assume-func-writes", llvm::cl::init(false),
      llvm::cl::desc(
          "assume external functions have write effect on all arguments")};

  void runOnOperation() override {
    Operation *op = getOperation();

    SymbolTableCollection symbolTable;

    DataFlowSolver solver(DataFlowConfig().setInterprocedural(interprocedural));
    loadBaselineAnalyses(solver);
    solver.load<WrittenToAnalysis>(symbolTable, assumeFuncWrites);
    if (failed(solver.initializeAndRun(op)))
      return signalPassFailure();

    raw_ostream &os = llvm::outs();
    op->walk([&](Operation *op) {
      auto tag = op->getDiscardableAttrOfType<StringAttr>("tag");
      if (!tag)
        return;
      os << "test_tag: " << tag.getValue() << ":\n";
      for (auto [index, operand] : llvm::enumerate(op->getOperands())) {
        const WrittenTo *writtenTo = solver.lookupState<WrittenTo>(operand);
        if (!writtenTo) {
          // The lattice may not be computed for values in unreachable code
          // (e.g., private functions not called from anywhere in
          // interprocedural analysis mode).
          os << " operand #" << index << ": <not computed>\n";
          continue;
        }
        os << " operand #" << index << ": ";
        writtenTo->print(os);
        os << "\n";
      }
      for (auto [index, operand] : llvm::enumerate(op->getResults())) {
        const WrittenTo *writtenTo = solver.lookupState<WrittenTo>(operand);
        if (!writtenTo) {
          os << " result #" << index << ": <not computed>\n";
          continue;
        }
        os << " result #" << index << ": ";
        writtenTo->print(os);
        os << "\n";
      }
    });
  }
};
} // end anonymous namespace

namespace mlir {
namespace test {
void registerTestWrittenToPass() { PassRegistration<TestWrittenToPass>(); }
} // end namespace test
} // end namespace mlir