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// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
#include "src/transform/pad_array_elements.h"
#include <unordered_map>
#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 {
namespace {
using ArrayBuilder = std::function<const ast::Array*()>;
/// PadArray returns a function that constructs a new array in `ctx.dst` with
/// the element type padded to account for the explicit stride. PadArray will
/// recursively pad arrays-of-arrays. The new array element type will be added
/// to module-scope type declarations of `ctx.dst`.
/// @param ctx the CloneContext
/// @param create_ast_type_for Transform::CreateASTTypeFor()
/// @param padded_arrays a map of src array type to the new array name
/// @param array the array type
/// @return the new AST array
template <typename CREATE_AST_TYPE_FOR>
ArrayBuilder PadArray(
CloneContext& ctx,
CREATE_AST_TYPE_FOR&& create_ast_type_for,
std::unordered_map<const sem::Array*, ArrayBuilder>& padded_arrays,
const sem::Array* array) {
if (array->IsStrideImplicit()) {
// We don't want to wrap arrays that have an implicit stride
return nullptr;
return utils::GetOrCreate(padded_arrays, array, [&] {
// Generate a unique name for the array element type
auto name = ctx.dst->Symbols().New("tint_padded_array_element");
// Examine the element type. Is it also an array?
const ast::Type* el_ty = nullptr;
if (auto* el_array = array->ElemType()->As<sem::Array>()) {
// Array of array - call PadArray() on the element type
if (auto p =
PadArray(ctx, create_ast_type_for, padded_arrays, el_array)) {
el_ty = p();
// If the element wasn't a padded array, just create the typical AST type
// for it
if (el_ty == nullptr) {
el_ty = create_ast_type_for(ctx, array->ElemType());
// 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->Member("el", el_ty, {ctx.dst->MemberSize(array->Stride())})});
auto* dst = ctx.dst;
return [=] {
if (array->IsRuntimeSized()) {
return dst->ty.array(dst->create<ast::TypeName>(name));
} else {
return dst->ty.array(dst->create<ast::TypeName>(name), array->Count());
} // namespace
PadArrayElements::PadArrayElements() = default;
PadArrayElements::~PadArrayElements() = default;
void PadArrayElements::Run(CloneContext& ctx, const DataMap&, DataMap&) {
auto& sem = ctx.src->Sem();
std::unordered_map<const sem::Array*, ArrayBuilder> padded_arrays;
auto pad = [&](const sem::Array* array) {
return PadArray(ctx, CreateASTTypeFor, padded_arrays, array);
// Replace all array types with their corresponding padded array type
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>()) {
if (auto p = pad(array)) {
return p();
return nullptr;
// Fix up array accessors so `a[1]` becomes `a[1].el`
ctx.ReplaceAll([&](const ast::ArrayAccessorExpression* accessor)
-> const ast::Expression* {
if (auto* array = tint::As<sem::Array>(
sem.Get(accessor->array)->Type()->UnwrapRef())) {
if (pad(array)) {
// Array element is wrapped in a structure. Emit a member accessor
// to get to the actual array element.
auto* idx = ctx.CloneWithoutTransform(accessor);
return ctx.dst->MemberAccessor(idx, "el");
return nullptr;
// Fix up array constructors so `A(1,2)` becomes
// `A(padded(1), padded(2))`
ctx.ReplaceAll([&](const ast::TypeConstructorExpression* ctor)
-> const ast::Expression* {
if (auto* array =
tint::As<sem::Array>(sem.Get(ctor)->Type()->UnwrapRef())) {
if (auto p = pad(array)) {
auto* arr_ty = p();
auto el_typename = arr_ty->type->As<ast::TypeName>()->name;
ast::ExpressionList args;
for (auto* arg : ctor->values) {
ctx.dst->create<ast::TypeName>(el_typename), ctx.Clone(arg)));
return ctx.dst->Construct(arr_ty, args);
return nullptr;
} // namespace transform
} // namespace tint