src/transform/module_scope_var_to_entry_point_param.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_MODULE_SCOPE_VAR_TO_ENTRY_POINT_PARAM_H_
#define SRC_TRANSFORM_MODULE_SCOPE_VAR_TO_ENTRY_POINT_PARAM_H_

#include "src/transform/transform.h"

namespace tint {
namespace transform {

/// Move module-scope variables into the entry point as parameters.
///
/// MSL does not allow module-scope variables to have any address space other
/// than `constant`. This transform moves all module-scope declarations into the
/// entry point function (either as parameters or function-scope variables) and
/// then passes them as pointer parameters to any function that references them.
///
/// Since WGSL does not allow entry point parameters or function-scope variables
/// to have these storage classes, we annotate the new variable declarations
/// with an attribute that bypasses that validation rule.
///
/// Before:
/// ```
/// [[block]]
/// struct S {
///   f : f32;
/// };
/// [[binding(0), group(0)]]
/// var<storage, read> s : S;
/// var<private> p : f32 = 2.0;
///
/// fn foo() {
///   p = p + f;
/// }
///
/// [[stage(compute), workgroup_size(1)]]
/// fn main() {
///   foo();
/// }
/// ```
///
/// After:
/// ```
/// fn foo(p : ptr<private, f32>, sptr : ptr<storage, S, read>) {
///   *p = *p + (*sptr).f;
/// }
///
/// [[stage(compute), workgroup_size(1)]]
/// fn main(sptr : ptr<storage, S, read>) {
///   var<private> p : f32 = 2.0;
///   foo(&p, sptr);
/// }
/// ```
class ModuleScopeVarToEntryPointParam
    : public Castable<ModuleScopeVarToEntryPointParam, Transform> {
 public:
  /// Constructor
  ModuleScopeVarToEntryPointParam();
  /// Destructor
  ~ModuleScopeVarToEntryPointParam() override;

 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;

  struct State;
};

}  // namespace transform
}  // namespace tint

#endif  // SRC_TRANSFORM_MODULE_SCOPE_VAR_TO_ENTRY_POINT_PARAM_H_