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/expression.h"
#include "src/utils/get_or_create.h"

namespace tint {
namespace transform {

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

WrapArraysInStructs::WrapArraysInStructs() = default;

WrapArraysInStructs::~WrapArraysInStructs() = default;

Output WrapArraysInStructs::Run(const Program* in, const DataMap&) {
  ProgramBuilder out;
  CloneContext ctx(&out, in);

  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([&](ast::Type* ast_type) -> 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 array accessors so `a[1]` becomes `a.arr[1]`
  ctx.ReplaceAll([&](ast::ArrayAccessorExpression* accessor)
                     -> ast::ArrayAccessorExpression* {
    if (auto* array =
            As<sem::Array>(sem.Get(accessor->array())->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->array());
        auto* idx = ctx.Clone(accessor->idx_expr());
        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([&](ast::TypeConstructorExpression* ctor) -> ast::Expression* {
    if (auto* array = As<sem::Array>(sem.Get(ctor)->Type()->UnwrapRef())) {
      if (auto w = wrapper(array)) {
        // Wrap the array type constructor with another constructor for
        // the wrapper
        auto* wrapped_array_ty = ctx.Clone(ctor->type());
        auto* array_ty = w.array_type(ctx);
        auto* arr_ctor =
            ctx.dst->Construct(array_ty, ctx.Clone(ctor->values()));
        return ctx.dst->Construct(wrapped_array_ty, arr_ctor);
      }
    }
    return nullptr;
  });

  ctx.Clone();

  return Output(Program(std::move(out)));
}

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<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->create<ast::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