argument_spec.cpp

#include <torch/csrc/jit/argument_spec.h>

namespace torch {
namespace jit {

void ArgumentSpecCreator::scan(
    const TypePtr& typ,
    size_t depth,
    const WrittenSlots& written_slots) {
  auto finishAggregate = [&](size_t pos) {
    // it is possible after all the work we did to scan this aggregate,
    // we found no tensors to specialize. In this case, just generate
    // a skip for the whole aggregate.
    bool any_spec = std::any_of(
        instructions_.begin() + pos, instructions_.end(), [](Inst i) {
          return i == SPECIALIZE_TENSOR;
        });
    if (!any_spec) {
      instructions_[pos] = SKIP;
      instructions_.resize(pos + 1);
    } else {
      instructions_.emplace_back(LEAVE);
    }
  };
  // the simple vm that scans instructions_ has a limited stack depth,
  // this prevents going deeper than that.
  if (depth >= DEPTH_LIMIT) {
    instructions_.emplace_back(SKIP);
  }
  if (typ->isSubtypeOf(TensorType::get())) {
    num_tensors_++;
    instructions_.emplace_back(SPECIALIZE_TENSOR);
  } else if (auto tup = typ->cast<TupleType>()) {
    size_t pos = instructions_.size();
    instructions_.emplace_back(ENTER_TUPLE);
    for (const auto& elem : tup->containedTypes()) {
      scan(elem, depth + 1, written_slots);
    }
    finishAggregate(pos);
  } else if (auto cls = typ->cast<ClassType>()) {
    size_t pos = instructions_.size();
    instructions_.emplace_back(ENTER_OBJECT);
    for (size_t i = 0; i < cls->numAttributes(); ++i) {
      auto key = cls->name() + cls->attributeNames().at(i);
      // it is only safe to specialize because someone might have written to it
      if (!written_slots.count(key)) {
        scan(cls->containedTypes().at(i), depth + 1, written_slots);
      } else {
        instructions_.emplace_back(SKIP);
      }
    }
    finishAggregate(pos);
  } else {
    instructions_.emplace_back(SKIP);
  }
};

// this is a coarse-grained guarentee that the slots of a class will not be
// modified by the function. It works fine for things that used be read-only
// modules, but will be overly conservative when some classes are written to.
// Doing alias analysis and looking for writes to the class would be more
// accurate.
static void scanWrittenSlots(
    Block* block,
    ArgumentSpecCreator::WrittenSlots& written_slots) {
  for (Node* n : block->nodes()) {
    if (n->kind() == prim::SetAttr) {
      if (auto cls = n->inputs().at(0)->type()->cast<ClassType>()) {
        written_slots.insert(cls->name() + n->s(attr::name));
      }
    }
    for (Block* subblock : n->blocks()) {
      scanWrittenSlots(subblock, written_slots);
    }
    if (n->hasAttribute(attr::Subgraph)) {
      scanWrittenSlots(n->g(attr::Subgraph)->block(), written_slots);
    }
  }
}

ArgumentSpecCreator::ArgumentSpecCreator(Graph& graph)
    : num_inputs_(graph.inputs().size()) {
  WrittenSlots written_slots;
  scanWrittenSlots(graph.block(), written_slots);
  for (Value* input : graph.inputs()) {
    scan(input->type(), 0, written_slots);
  }
}

void ArgumentSpecCreator::dump() const {
  for (Inst inst : instructions_) {
    switch (inst) {
      case LEAVE:
        std::cout << "] ";
        break;
      case ENTER_TUPLE:
        std::cout << "Tuple[";
        break;
      case ENTER_OBJECT:
        std::cout << "Object[";
        break;
      case SKIP:
        std::cout << "Skip ";
        break;
      case SPECIALIZE_TENSOR:
        std::cout << "SpecializeTensor ";
        break;
    }
  }
  std::cout << "\n";
}

ArgumentSpec ArgumentSpecCreator::create(bool with_grad, const Stack& input)
    const {
  ArgumentSpec spec(num_tensors_);
  const IValue* stack[DEPTH_LIMIT]; // The stack of IValue lists
  // The stack gets initialized with the input list
  stack[0] = last(input, num_inputs_).begin();
  size_t stack_top = 0; // offset to the top of the stack
  for (Inst inst : instructions_) {
    switch (inst) {
      case SPECIALIZE_TENSOR:
        // consume a tensor and add to the argspec
        spec.addTensor(*stack[stack_top]++, with_grad);
        break;
      case ENTER_TUPLE: {
        // consume tuple
        const IValue* iv = stack[stack_top]++;
        AT_ASSERT(iv->isTuple());
        // see [argspec refcounting]
        auto p = *reinterpret_cast<const at::ivalue::Tuple* const*>(iv);
        auto tup_ptr = &p->elements()[0];
        // push list of tuple elements to the stack
        stack[++stack_top] = tup_ptr;
      } break;
      case ENTER_OBJECT: {
        // consume object
        const IValue* iv = stack[stack_top]++;
        AT_ASSERT(iv->isObject());
        iv->toObject();
        // see [argspec refcounting]
        auto p = *reinterpret_cast<const at::ivalue::Object* const*>(iv);
        auto obj_ptr = &p->slots()[0];
        // push list of object elements to the stack
        stack[++stack_top] = obj_ptr;
      } break;
      case SKIP:
        // consume and skip an element
        stack[stack_top]++;
        break;
      case LEAVE:
        --stack_top;
        break;
    }
  }
  return spec;
}

// For every input of a given graph, returns a most detailed type that can be
// inferred for it based on this ArgumentSpec.
std::vector<TypePtr> ArgumentSpecCreator::getSpecializedTypes(
    Graph& graph,
    const ArgumentSpec& spec) const {
  auto input_types =
      fmap(graph.inputs(), [](Value* input) { return input->type(); });
  std::vector<std::vector<TypePtr>> result_stack;
  result_stack.emplace_back();
  std::vector<const TypePtr*> input_stack = {input_types.data()};
  std::vector<std::function<TypePtr()>> aggregate_creators;

  size_t arg_spec_offset = 0; // number of specialized tensors seen so far

  for (Inst inst : instructions_) {
    switch (inst) {
      case SPECIALIZE_TENSOR: {
        input_stack.back()++;
        auto& arg = spec.at(arg_spec_offset++);
        if (!arg.defined()) {
          result_stack.back().emplace_back(AutogradZeroTensorType::get());
        } else {
          result_stack.back().emplace_back(DimensionedTensorType::create(
              arg.type(),
              ConvertIntToCPUOrCUDA(arg.device()),
              arg.dim(),
              arg.requires_grad()));
        }
      } break;
      case ENTER_TUPLE: {
        auto tup = (*input_stack.back()++)->expect<TupleType>();
        input_stack.emplace_back(tup->elements().data());
        result_stack.emplace_back();
        aggregate_creators.emplace_back(
            [&] { return TupleType::create(result_stack.back()); });
      } break;
      case ENTER_OBJECT: {
        auto cls = (*input_stack.back()++)->expect<ClassType>();
        input_stack.emplace_back(cls->containedTypes().data());
        result_stack.emplace_back();
        aggregate_creators.emplace_back(
            [&result_stack, cls] { return cls->refine(result_stack.back()); });
      } break;
      case SKIP:
        result_stack.back().emplace_back(*input_stack.back()++);
        break;
      case LEAVE:
        TypePtr result = aggregate_creators.back()();
        result_stack.pop_back();
        aggregate_creators.pop_back();
        input_stack.pop_back();
        result_stack.back().emplace_back(std::move(result));
        break;
    }
  }
  AT_ASSERT(result_stack.size() == 1);
  return result_stack.back();
}

void ArgumentSpecCreator::setInputTypes(Graph& g, const ArgumentSpec& spec)
    const {
  auto input_types = getSpecializedTypes(g, spec);
  auto inputs = g.inputs();
  for (size_t i = 0; i < inputs.size(); ++i) {
    inputs[i]->setType(input_types[i]);
  }
}

} // namespace jit
} // namespace torch