function.h

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

/*!
 * \file tvm/ir/function.h
 * \brief Function nodes.
 */
#ifndef TVM_IR_FUNCTION_H_
#define TVM_IR_FUNCTION_H_

#include <tvm/ir/attrs.h>
#include <tvm/ir/expr.h>
#include <tvm/runtime/container.h>

#include <string>
#include <type_traits>

namespace tvm {

/*!
 * \brief Possible Calling conventions.
 *
 *  NOTE: The calling convention also implies
 *  the way we implement the function during lowering.
 */
enum class CallingConv : int {
  /*!
   * \brief Default calling convetion.
   *
   * - Uses the native calling convention of the target.
   * - Implementation: specified by the native target.
   */
  kDefault = 0,
  /*!
   * \brief PackedFunc that exposes a CPackedFunc signature.
   *
   * - Calling by PackedFunc calling convention.
   * - Implementation: Expose a function with the CPackedFunc signature.
   */
  kCPackedFunc = 1,
  /*!
   * \brief Device kernel launch
   *
   * - Call by PackedFunc calling convention.
   * - Implementation: defined by device runtime(e.g. runtime/cuda)
   */
  kDeviceKernelLaunch = 2,
};

/*!
 * \brief Base node of all functions.
 *
 * We support several variants of functions throughout the stack.
 * All of the functions share the same type system(via checked_type)
 * to support cross variant calls.
 *
 * \sa BaseFunc
 */
class BaseFuncNode : public RelayExprNode {
 public:
  /*! \brief Additional attributes storing the meta-data */
  DictAttrs attrs;

  /*!
   * \brief Get a function attribute.
   *
   * \param attr_key The attribute key.
   * \param default_value The default value if the key does not exist, defaults to nullptr.
   *
   * \return The result
   *
   * \tparam TOBjectRef the expected object type.
   * \throw Error if the key exists but the value does not match TObjectRef
   *
   * \code
   *
   *  void GetAttrExample(const BaseFunc& f) {
   *    auto value = f->GetAttr<Integer>("AttrKey", 0);
   *  }
   *
   * \endcode
   */
  template <typename TObjectRef>
  Optional<TObjectRef> GetAttr(
      const std::string& attr_key,
      Optional<TObjectRef> default_value = Optional<TObjectRef>(nullptr)) const {
    static_assert(std::is_base_of<ObjectRef, TObjectRef>::value,
                  "Can only call GetAttr with ObjectRef types.");
    if (!attrs.defined()) return default_value;
    auto it = attrs->dict.find(attr_key);
    if (it != attrs->dict.end()) {
      return Downcast<Optional<TObjectRef>>((*it).second);
    } else {
      return default_value;
    }
  }
  // variant that uses TObjectRef to enable implicit conversion to default value.
  template <typename TObjectRef>
  Optional<TObjectRef> GetAttr(const std::string& attr_key, TObjectRef default_value) const {
    return GetAttr<TObjectRef>(attr_key, Optional<TObjectRef>(default_value));
  }
  /*!
   * \brief Check whether the function has an non-zero integer attr.
   *
   * This function can be used to check whether an optional
   * attribute mark(e.g. inline) exists.
   *
   * \param attr_key The key to the attribute.
   * \return The check result.
   *
   * \code
   *
   *  void HasNonzeroAttrExample(const BaseFunc& f) {
   *    if (f->HasNonzeroAttr(attr::kInline)) {
   *      // inline the function.
   *    }
   *  }
   *
   * \endcode
   */
  bool HasNonzeroAttr(const std::string& attr_key) const {
    return GetAttr<Integer>(attr_key, 0) != 0;
  }

  static constexpr const char* _type_key = "BaseFunc";
  static constexpr const uint32_t _type_child_slots = 2;
  TVM_DECLARE_BASE_OBJECT_INFO(BaseFuncNode, RelayExprNode);
};

/*!
 * \brief Managed reference to BaseFuncNode.
 * \sa BaseFuncNode
 */
class BaseFunc : public RelayExpr {
 public:
  TVM_DEFINE_OBJECT_REF_METHODS(BaseFunc, RelayExpr, BaseFuncNode);
};

/*!
 * \brief Create a new function that copies func, but overrides
 *        the attribute value key with the value.
 *
 * \param func The input function.
 * \param attr_key The attribute key.
 * \param attr_value The value attribute value.
 *
 * \tparam TFunc The corresponding function type.
 *
 * \returns The new function with updated attributes.
 *
 * \note This function performs copy on write optimization for func.
 *       If we move a uniquely referenced func into WithAttr,
 *       then no additional copy will be performed.
 *
 *       This is also why we make it as a function instead of a member function
 *       and why we pass by value in the first argument.
 *
 * \code
 *
 *  // Recommended way to trigger copy on write
 *  func = WithAttr(std::move(func), "key1", value1);
 *  func = WithAttr(std::move(func), "key2", value2);
 *
 * \endcode
 */
template <typename TFunc,
          typename = typename std::enable_if<std::is_base_of<BaseFunc, TFunc>::value>::type>
inline TFunc WithAttr(TFunc func, const std::string& attr_key, ObjectRef attr_value) {
  using TNode = typename TFunc::ContainerType;
  static_assert(TNode::_type_final, "Can only operate on the leaf nodes");
  TNode* node = func.CopyOnWrite();
  if (node->attrs.defined()) {
    node->attrs.CopyOnWrite()->dict.Set(attr_key, attr_value);
  } else {
    Map<String, ObjectRef> dict = {{attr_key, attr_value}};
    node->attrs = DictAttrs(dict);
  }
  return func;
}

/*!
 * \brief Generic attribute names that can be attached to any function.
 *
 * \sa tvm::tir::attr, tvm::relay::attr
 */
namespace attr {
/*!
 * \brief Indicates the special calling convention.
 *
 * Type: Integer
 *
 * \sa tvm::CallingConv
 */
constexpr const char* kCallingConv = "calling_conv";

/*!
 * \brief Compilation target of the function.
 *
 * Type: Target
 *
 * \sa tvm::Target
 */
constexpr const char* kTarget = "target";

/*!
 * \brief Global linker symbol of the function in generated code.
 *
 *  This option forces the code generator to name the
 *  function with the given.
 *
 *  For example, we could set a global_symbol of a function
 *  early to make sure that we can always refer to it by
 *  the symbol name in the generated DLL.
 *
 *  We should not set the attribute for local functions,
 *  so that the compiler can freely rename them.
 *
 *  A unique global symbol will be automatically assigned
 *  to each function in the module before the target code
 *  generation phase.
 *
 * Type: String
 */
constexpr const char* kGlobalSymbol = "global_symbol";
}  // namespace attr
}  // namespace tvm
#endif  // TVM_IR_FUNCTION_H_