src/transform/array_length_from_uniform.h

// Copyright 2021 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_TRANSFORM_ARRAY_LENGTH_FROM_UNIFORM_H_
#define SRC_TRANSFORM_ARRAY_LENGTH_FROM_UNIFORM_H_

#include <unordered_map>
#include <unordered_set>

#include "src/sem/binding_point.h"
#include "src/transform/transform.h"

namespace tint {

// Forward declarations
class CloneContext;

namespace transform {

/// ArrayLengthFromUniform is a transform that implements calls to arrayLength()
/// by calculating the length from the total size of the storage buffer, which
/// is received via a uniform buffer.
///
/// The generated uniform buffer will have the form:
/// ```
/// struct buffer_size_struct {
///  buffer_size : array<u32, 8>;
/// };
///
/// [[group(0), binding(30)]]
/// var<uniform> buffer_size_ubo : buffer_size_struct;
/// ```
/// The binding group and number used for this uniform buffer is provided via
/// the `Config` transform input. The `Config` struct also defines the mapping
/// from a storage buffer's `BindingPoint` to the array index that will be used
/// to get the size of that buffer.
///
/// This transform assumes that the `SimplifyPointers`
/// transforms have been run before it so that arguments to the arrayLength
/// builtin always have the form `&resource.array`.
class ArrayLengthFromUniform
    : public Castable<ArrayLengthFromUniform, Transform> {
 public:
  /// Constructor
  ArrayLengthFromUniform();
  /// Destructor
  ~ArrayLengthFromUniform() override;

  /// Configuration options for the ArrayLengthFromUniform transform.
  struct Config : public Castable<Data, transform::Data> {
    /// Constructor
    /// @param ubo_bp the binding point to use for the generated uniform buffer.
    explicit Config(sem::BindingPoint ubo_bp);

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

    /// Copy assignment
    /// @return this Config
    Config& operator=(const Config&);

    /// Destructor
    ~Config() override;

    /// The binding point to use for the generated uniform buffer.
    sem::BindingPoint ubo_binding;

    /// The mapping from binding point to the index for the buffer size lookup.
    std::unordered_map<sem::BindingPoint, uint32_t> bindpoint_to_size_index;
  };

  /// Information produced about what the transform did.
  struct Result : public Castable<Result, transform::Data> {
    /// Constructor
    /// @param used_size_indices Indices into the UBO that are statically used.
    explicit Result(std::unordered_set<uint32_t> used_size_indices);

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

    /// Destructor
    ~Result() override;

    /// Indices into the UBO that are statically used.
    const std::unordered_set<uint32_t> used_size_indices;
  };

 protected:
  /// 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) override;
};

}  // namespace transform
}  // namespace tint

#endif  // SRC_TRANSFORM_ARRAY_LENGTH_FROM_UNIFORM_H_