src/tint/transform/builtin_polyfill.h

// Copyright 2022 The Tint Authors.
//
// Licensed 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.

#ifndef SRC_TINT_TRANSFORM_BUILTIN_POLYFILL_H_
#define SRC_TINT_TRANSFORM_BUILTIN_POLYFILL_H_

#include "src/tint/transform/transform.h"

namespace tint::transform {

/// Implements builtins for backends that do not have a native implementation.
class BuiltinPolyfill final : public Castable<BuiltinPolyfill, Transform> {
 public:
  /// Constructor
  BuiltinPolyfill();
  /// Destructor
  ~BuiltinPolyfill() override;

  /// Enumerator of polyfill levels
  enum class Level {
    /// No polyfill needed, supported by the backend.
    kNone,
    /// Clamp the parameters to the inner implementation.
    kClampParameters,
    /// Polyfill the entire function
    kFull,
  };

  /// Specifies the builtins that should be polyfilled by the transform.
  struct Builtins {
    /// Should `countLeadingZeros()` be polyfilled?
    bool count_leading_zeros = false;
    /// Should `countTrailingZeros()` be polyfilled?
    bool count_trailing_zeros = false;
    /// What level should `extractBits()` be polyfilled?
    Level extract_bits = Level::kNone;
    /// Should `firstLeadingBit()` be polyfilled?
    bool first_leading_bit = false;
    /// Should `firstTrailingBit()` be polyfilled?
    bool first_trailing_bit = false;
    /// Should `insertBits()` be polyfilled?
    Level insert_bits = Level::kNone;
  };

  /// Config is consumed by the BuiltinPolyfill transform.
  /// Config specifies the builtins that should be polyfilled.
  struct Config final : public Castable<Data, transform::Data> {
    /// Constructor
    /// @param b the list of builtins to polyfill
    explicit Config(const Builtins& b);

    /// Copy constructor
    Config(const Config&);

    /// Destructor
    ~Config() override;

    /// The builtins to polyfill
    const Builtins builtins;
  };

  /// @param program the program to inspect
  /// @param data optional extra transform-specific input data
  /// @returns true if this transform should be run for the given program
  bool ShouldRun(const Program* program,
                 const DataMap& data = {}) const override;

 protected:
  struct State;

  /// Runs the transform using the CloneContext built for transforming a
  /// program. Run() is responsible for calling Clone() on the CloneContext.
  /// @param ctx the CloneContext primed with the input program and
  /// ProgramBuilder
  /// @param inputs optional extra transform-specific input data
  /// @param outputs optional extra transform-specific output data
  void Run(CloneContext& ctx,
           const DataMap& inputs,
           DataMap& outputs) const override;
};

}  // namespace tint::transform

#endif  // SRC_TINT_TRANSFORM_BUILTIN_POLYFILL_H_