#include <torch/csrc/jit/passes/peephole.h>

#include <ATen/core/jit_type.h>
#include <c10/util/irange.h>
#include <torch/csrc/jit/ir/ir_views.h>
#include <torch/csrc/jit/jit_log.h>

namespace torch {
namespace jit {

namespace {

/**
 * Check whether the arithmetic node is binary between integers, and return a
 * constant int value if there exists one.
 *
 * @pre node is integer arithmetic.
 * @post if there's one constant in two oprands, then the second operand is
 *       constant.
 */
c10::optional<int64_t> checkArithNode(Node& node) {
  if (node.inputs().size() != 2 || node.input(0)->type() != IntType::get() ||
      node.input(1)->type() != IntType::get()) {
    return {};
  }

  if (node.kind() == aten::mul || node.kind() == aten::add) {
    if (auto i = constant_as<int64_t>(node.input(0))) {
      node.permuteInputs({1, 0});
      return i;
    }
  }

  return constant_as<int64_t>(node.input(1));
}

/**
 * Remove a mul/floordiv node if it is multiplication or division by 1.
 *
 * @pre node is either aten::mul, aten::floordiv or aten::div
 */
bool trySimplifyMulOrDiv(Node& node) {
  auto constant = checkArithNode(node);
  if (!constant || *constant != 1) {
    return false;
  }

  node.output()->replaceAllUsesWith(node.inputs()[0]);
  return true;
}

/**
 * Simplify an add/sub node with its input node, i.e. merge the constant parts
 * together.
 *
 * @pre node is either aten::add or aten::sub
 */
bool trySimplifyAddOrSub(Node& node) {
  auto constant = checkArithNode(node);
  if (!constant) {
    return false;
  }

  if (constant == 0) {
    node.output()->replaceAllUsesWith(node.input(0));
    return true;
  }

  auto& dep = *node.inputs()[0]->node();
  if (dep.kind() != aten::add && dep.kind() != aten::sub) {
    return false;
  }

  auto delta = checkArithNode(dep);
  if (!delta) {
    return false;
  }
  auto merged =
      dep.kind() == node.kind() ? *constant + *delta : *constant - *delta;

  if (merged == 0) {
    node.output()->replaceAllUsesWith(dep.inputs()[0]);
  } else {
    WithInsertPoint g(&node);
    node.replaceInput(0, dep.inputs()[0]);
    node.replaceInput(1, node.owningGraph()->insertConstant(merged));
  }
  return true;
}

} // namespace

struct PeepholeOptimizeNonTensorImpl {
  // NOLINTNEXTLINE(modernize-pass-by-value)
  PeepholeOptimizeNonTensorImpl(const std::shared_ptr<Graph>& graph)
      : graph_(graph) {}

  bool run() {
    return optimizeBlock(graph_->block());
  }

  bool optimizeBlock(Block* block) {
    bool changed = false;
    for (auto it = block->nodes().begin(); it != block->nodes().end(); ++it) {
      auto* node = *it;

      for (Block* sub_block : node->blocks()) {
        changed |= optimizeBlock(sub_block);
      }

      if (node->kind() != prim::Constant) {
        WithInsertPoint guard(node);
        // Any Value whose type is None should be replaced with a Constant
        // This can occur if a module has an optional attribute, and it is
        // initialized as None.
        for (Value* output : node->outputs()) {
          if (output->type()->cast<NoneType>()) {
            output->replaceAllUsesWith(graph_->insertConstant(IValue()));
            changed = true;
          }
        }
      }
      // XXX: remember that if you want to simplify an expression by combining
      // multiple nodes into a different one, then you need to check that they
      // all belong to the given block
      // TODO: this doesn't work with Scalar-Tensor ops! We should
      // canonicalize those
      if (node->kind() == prim::If) {
        IfView n(node);
        // this handles redundant short circuits like "x and True" or "x or
        // False"
        for (const auto i : c10::irange(n.outputs().size())) {
          if (n.outputs().at(i)->type() != BoolType::get()) {
            continue;
          }
          bool true_val =
              constant_as<bool>(n.thenOutputs().at(i)).value_or(false);
          bool false_val =
              constant_as<bool>(n.elseOutputs().at(i)).value_or(true);
          // if an if node's output equals its condition replace output with
          // condition
          if (true_val && !false_val) {
            GRAPH_UPDATE(
                "Replacing ",
                n.outputs().at(i)->debugName(),
                " (True or False) with ",
                n.cond()->debugName());
            n.outputs().at(i)->replaceAllUsesWith(n.cond());
            changed = true;
          }
        }

        // check for types that can be refined
        for (size_t i = 0; i < n.outputs().size(); ++i) {
          // common case of optional for now
          bool inputs_non_optional =
              !n.thenOutputs().at(i)->type()->cast<OptionalType>() &&
              !n.elseOutputs().at(i)->type()->cast<OptionalType>();
          auto output_optional =
              n.outputs().at(i)->type()->cast<OptionalType>();
          if (inputs_non_optional && output_optional) {
            if (auto unif = unifyTypes(
                    n.thenOutputs().at(i)->type(),
                    n.elseOutputs().at(i)->type())) {
              n.outputs().at(i)->setType(*unif);
              changed = true;
            }
          }
        }
      } else if (
          node->kind() == aten::__is__ || node->kind() == aten::__isnot__) {
        // if we are comparing a None value with a value that can't be None
        // replace the output with true if node is __isnot__ or false if node is
        // __is__
        AT_ASSERT(node->inputs().size() == 2);
        for (size_t check_none_index : {0, 1}) {
          bool input_must_be_none =
              node->inputs().at(check_none_index)->mustBeNone();
          bool other_must_not_be_none =
              node->inputs().at(1 - check_none_index)->mustNotBeNone();
          if (input_must_be_none && other_must_not_be_none) {
            WithInsertPoint guard(node);
            auto output = node->owningGraph()->insertConstant(
                node->kind() == aten::__isnot__);
            GRAPH_UPDATE(
                "Folding ", getHeader(node), " to ", output->debugName());
            node->output()->replaceAllUsesWith(output);
            changed = true;
          }
        }
      } else if (
          node->kind() == prim::unchecked_unwrap_optional ||
          node->kind() == aten::_unwrap_optional) {
        // we are unwrapping an input that can't be None, remove the unwrap
        auto input = node->input();
        if (input->mustNotBeNone()) {
          GRAPH_UPDATE(
              "Unwrapping ",
              getHeader(node),
              " as ",
              node->input(),
              " can't be optional");
          node->output()->replaceAllUsesWith(node->input());
          changed = true;
        }
      } else if (node->kind() == prim::unchecked_cast) {
        // unchecked_cast is not generated for tensor properties, so we are not
        // losing anything by calling unshapedType here
        auto input_type = unshapedType(node->input()->type());
        auto output_type = unshapedType(node->output()->type());
        if (input_type->isSubtypeOf(*output_type)) {
          GRAPH_UPDATE(
              "Removing ",
              getHeader(node),
              " as input type subtypes output type");
          node->output()->replaceAllUsesWith(node->input());
          changed = true;
        }
      } else if (
          (node->kind() == aten::Int || node->kind() == aten::ceil) &&
          node->inputs().size() == 1 &&
          node->input()->type()->cast<IntType>()) {
        GRAPH_UPDATE(
            "Removing ", getHeader(node), " as input is already an integer");
        node->output()->replaceAllUsesWith(node->input());
        changed = true;
      } else if (node->kind() == aten::ne || node->kind() == aten::eq) {
        if (node->inputs().size() != 2 ||
            node->inputs().at(0) != node->inputs().at(1)) {
          continue;
        }
        auto inp_type = node->inputs().at(0)->type();
        // only handling common immutable types here because other types like
        // Tensor or list of Tensor might throw on aten::eq
        auto immut_type = [&](const TypePtr& type) {
          auto kind = type->kind();
          static const std::vector<TypeKind> handled_immutable_types = {
              TypeKind::BoolType,
              TypeKind::IntType,
              TypeKind::FloatType,
              TypeKind::NoneType};
          return (
              std::find(
                  handled_immutable_types.begin(),
                  handled_immutable_types.end(),
                  kind) != handled_immutable_types.end());
        };
        bool non_throwing_type = false;
        if (auto li_type = inp_type->cast<ListType>()) {
          non_throwing_type = immut_type(li_type->getElementType());
        } else if (auto di_type = inp_type->cast<DictType>()) {
          non_throwing_type =
              (immut_type(di_type->getKeyType()) &&
               immut_type(di_type->getValueType()));
        } else {
          non_throwing_type = immut_type(inp_type);
        }
        if (non_throwing_type) {
          WithInsertPoint guard(node);
          node->output()->replaceAllUsesWith(
              graph_->insertConstant(node->kind() == aten::eq));
          changed = true;
        }
      } else if (
          node->kind() == aten::mul || node->kind() == aten::floordiv ||
          node->kind() == aten::div) {
        changed |= trySimplifyMulOrDiv(*node);
      } else if (node->kind() == aten::add || node->kind() == aten::sub) {
        changed |= trySimplifyAddOrSub(*node);
      }
    }
    return changed;
  }

 private:
  std::shared_ptr<Graph> graph_;
};

bool PeepholeOptimizeNonTensor(const std::shared_ptr<Graph>& graph) {
  PeepholeOptimizeNonTensorImpl peephole(graph);
  bool changed = peephole.run();
  GRAPH_DUMP("After PeepholeOptimize: ", graph);
  return changed;
}

} // namespace jit
} // namespace torch