src/transform/wrap_arrays_in_structs.cc

// 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.

#include "src/transform/wrap_arrays_in_structs.h"

#include <utility>

#include "src/program_builder.h"
#include "src/sem/array.h"
#include "src/sem/call.h"
#include "src/sem/expression.h"
#include "src/sem/type_constructor.h"
#include "src/utils/map.h"
#include "src/utils/transform.h"

TINT_INSTANTIATE_TYPEINFO(tint::transform::WrapArraysInStructs);

namespace tint {
namespace transform {

WrapArraysInStructs::WrappedArrayInfo::WrappedArrayInfo() = default;
WrapArraysInStructs::WrappedArrayInfo::WrappedArrayInfo(
    const WrappedArrayInfo&) = default;
WrapArraysInStructs::WrappedArrayInfo::~WrappedArrayInfo() = default;

WrapArraysInStructs::WrapArraysInStructs() = default;

WrapArraysInStructs::~WrapArraysInStructs() = default;

void WrapArraysInStructs::Run(CloneContext& ctx, const DataMap&, DataMap&) {
  auto& sem = ctx.src->Sem();

  std::unordered_map<const sem::Array*, WrappedArrayInfo> wrapped_arrays;
  auto wrapper = [&](const sem::Array* array) {
    return WrapArray(ctx, wrapped_arrays, array);
  };
  auto wrapper_typename = [&](const sem::Array* arr) -> ast::TypeName* {
    auto info = wrapper(arr);
    return info ? ctx.dst->create<ast::TypeName>(info.wrapper_name) : nullptr;
  };

  // Replace all array types with their corresponding wrapper
  ctx.ReplaceAll([&](const ast::Type* ast_type) -> const ast::Type* {
    auto* type = ctx.src->TypeOf(ast_type);
    if (auto* array = type->UnwrapRef()->As<sem::Array>()) {
      return wrapper_typename(array);
    }
    return nullptr;
  });

  // Fix up index accessors so `a[1]` becomes `a.arr[1]`
  ctx.ReplaceAll([&](const ast::IndexAccessorExpression* accessor)
                     -> const ast::IndexAccessorExpression* {
    if (auto* array = ::tint::As<sem::Array>(
            sem.Get(accessor->object)->Type()->UnwrapRef())) {
      if (wrapper(array)) {
        // Array is wrapped in a structure. Emit a member accessor to get
        // to the actual array.
        auto* arr = ctx.Clone(accessor->object);
        auto* idx = ctx.Clone(accessor->index);
        auto* unwrapped = ctx.dst->MemberAccessor(arr, "arr");
        return ctx.dst->IndexAccessor(accessor->source, unwrapped, idx);
      }
    }
    return nullptr;
  });

  // Fix up array constructors so `A(1,2)` becomes `tint_array_wrapper(A(1,2))`
  ctx.ReplaceAll(
      [&](const ast::CallExpression* expr) -> const ast::Expression* {
        if (auto* call = sem.Get(expr)) {
          if (auto* ctor = call->Target()->As<sem::TypeConstructor>()) {
            if (auto* array = ctor->ReturnType()->As<sem::Array>()) {
              if (auto w = wrapper(array)) {
                // Wrap the array type constructor with another constructor for
                // the wrapper
                auto* wrapped_array_ty = ctx.dst->ty.type_name(w.wrapper_name);
                auto* array_ty = w.array_type(ctx);
                auto args = utils::Transform(
                    call->Arguments(), [&](const tint::sem::Expression* s) {
                      return ctx.Clone(s->Declaration());
                    });
                auto* arr_ctor = ctx.dst->Construct(array_ty, args);
                return ctx.dst->Construct(wrapped_array_ty, arr_ctor);
              }
            }
          }
        }
        return nullptr;
      });

  ctx.Clone();
}

WrapArraysInStructs::WrappedArrayInfo WrapArraysInStructs::WrapArray(
    CloneContext& ctx,
    std::unordered_map<const sem::Array*, WrappedArrayInfo>& wrapped_arrays,
    const sem::Array* array) const {
  if (array->IsRuntimeSized()) {
    return {};  // We don't want to wrap runtime sized arrays
  }

  return utils::GetOrCreate(wrapped_arrays, array, [&] {
    WrappedArrayInfo info;

    // Generate a unique name for the array wrapper
    info.wrapper_name = ctx.dst->Symbols().New("tint_array_wrapper");

    // Examine the element type. Is it also an array?
    std::function<const ast::Type*(CloneContext&)> el_type;
    if (auto* el_array = array->ElemType()->As<sem::Array>()) {
      // Array of array - call WrapArray() on the element type
      if (auto el = WrapArray(ctx, wrapped_arrays, el_array)) {
        el_type = [=](CloneContext& c) {
          return c.dst->create<ast::TypeName>(el.wrapper_name);
        };
      }
    }

    // If the element wasn't an array, just create the typical AST type for it
    if (!el_type) {
      el_type = [=](CloneContext& c) {
        return CreateASTTypeFor(c, array->ElemType());
      };
    }

    // Construct the single structure field type
    info.array_type = [=](CloneContext& c) {
      ast::DecorationList decos;
      if (!array->IsStrideImplicit()) {
        decos.emplace_back(
            c.dst->create<ast::StrideDecoration>(array->Stride()));
      }
      return c.dst->ty.array(el_type(c), array->Count(), std::move(decos));
    };

    // Structure() will create and append the ast::Struct to the
    // global declarations of `ctx.dst`. As we haven't finished building the
    // current module-scope statement or function, this will be placed
    // immediately before the usage.
    ctx.dst->Structure(info.wrapper_name,
                       {ctx.dst->Member("arr", info.array_type(ctx))});
    return info;
  });
}

}  // namespace transform
}  // namespace tint