/// 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/tint/writer/glsl/generator_impl.h"

#include <algorithm>
#include <cmath>
#include <iomanip>
#include <set>
#include <utility>
#include <vector>

#include "src/tint/ast/call_statement.h"
#include "src/tint/ast/fallthrough_statement.h"
#include "src/tint/ast/id_attribute.h"
#include "src/tint/ast/internal_attribute.h"
#include "src/tint/ast/interpolate_attribute.h"
#include "src/tint/ast/variable_decl_statement.h"
#include "src/tint/debug.h"
#include "src/tint/sem/array.h"
#include "src/tint/sem/atomic.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/call.h"
#include "src/tint/sem/constant.h"
#include "src/tint/sem/depth_multisampled_texture.h"
#include "src/tint/sem/depth_texture.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/member_accessor_expression.h"
#include "src/tint/sem/module.h"
#include "src/tint/sem/multisampled_texture.h"
#include "src/tint/sem/sampled_texture.h"
#include "src/tint/sem/statement.h"
#include "src/tint/sem/storage_texture.h"
#include "src/tint/sem/struct.h"
#include "src/tint/sem/type_constructor.h"
#include "src/tint/sem/type_conversion.h"
#include "src/tint/sem/variable.h"
#include "src/tint/transform/add_empty_entry_point.h"
#include "src/tint/transform/add_spirv_block_attribute.h"
#include "src/tint/transform/binding_remapper.h"
#include "src/tint/transform/builtin_polyfill.h"
#include "src/tint/transform/canonicalize_entry_point_io.h"
#include "src/tint/transform/combine_samplers.h"
#include "src/tint/transform/decompose_memory_access.h"
#include "src/tint/transform/disable_uniformity_analysis.h"
#include "src/tint/transform/expand_compound_assignment.h"
#include "src/tint/transform/fold_trivial_single_use_lets.h"
#include "src/tint/transform/loop_to_for_loop.h"
#include "src/tint/transform/manager.h"
#include "src/tint/transform/promote_initializers_to_let.h"
#include "src/tint/transform/promote_side_effects_to_decl.h"
#include "src/tint/transform/remove_phonies.h"
#include "src/tint/transform/renamer.h"
#include "src/tint/transform/simplify_pointers.h"
#include "src/tint/transform/single_entry_point.h"
#include "src/tint/transform/unshadow.h"
#include "src/tint/transform/unwind_discard_functions.h"
#include "src/tint/transform/zero_init_workgroup_memory.h"
#include "src/tint/utils/defer.h"
#include "src/tint/utils/map.h"
#include "src/tint/utils/scoped_assignment.h"
#include "src/tint/writer/append_vector.h"
#include "src/tint/writer/float_to_string.h"
#include "src/tint/writer/generate_external_texture_bindings.h"

using namespace tint::number_suffixes;  // NOLINT

namespace {

bool IsRelational(tint::ast::BinaryOp op) {
    return op == tint::ast::BinaryOp::kEqual || op == tint::ast::BinaryOp::kNotEqual ||
           op == tint::ast::BinaryOp::kLessThan || op == tint::ast::BinaryOp::kGreaterThan ||
           op == tint::ast::BinaryOp::kLessThanEqual ||
           op == tint::ast::BinaryOp::kGreaterThanEqual;
}

bool RequiresOESSampleVariables(tint::ast::Builtin builtin) {
    switch (builtin) {
        case tint::ast::Builtin::kSampleIndex:
        case tint::ast::Builtin::kSampleMask:
            return true;
        default:
            return false;
    }
}

}  // namespace

namespace tint::writer::glsl {
namespace {

const char kTempNamePrefix[] = "tint_tmp";
const char kSpecConstantPrefix[] = "WGSL_SPEC_CONSTANT_";

bool last_is_break_or_fallthrough(const ast::BlockStatement* stmts) {
    return IsAnyOf<ast::BreakStatement, ast::FallthroughStatement>(stmts->Last());
}

const char* convert_texel_format_to_glsl(const ast::TexelFormat format) {
    switch (format) {
        case ast::TexelFormat::kR32Uint:
            return "r32ui";
        case ast::TexelFormat::kR32Sint:
            return "r32i";
        case ast::TexelFormat::kR32Float:
            return "r32f";
        case ast::TexelFormat::kRgba8Unorm:
            return "rgba8";
        case ast::TexelFormat::kRgba8Snorm:
            return "rgba8_snorm";
        case ast::TexelFormat::kRgba8Uint:
            return "rgba8ui";
        case ast::TexelFormat::kRgba8Sint:
            return "rgba8i";
        case ast::TexelFormat::kRg32Uint:
            return "rg32ui";
        case ast::TexelFormat::kRg32Sint:
            return "rg32i";
        case ast::TexelFormat::kRg32Float:
            return "rg32f";
        case ast::TexelFormat::kRgba16Uint:
            return "rgba16ui";
        case ast::TexelFormat::kRgba16Sint:
            return "rgba16i";
        case ast::TexelFormat::kRgba16Float:
            return "rgba16f";
        case ast::TexelFormat::kRgba32Uint:
            return "rgba32ui";
        case ast::TexelFormat::kRgba32Sint:
            return "rgba32i";
        case ast::TexelFormat::kRgba32Float:
            return "rgba32f";
        case ast::TexelFormat::kNone:
            return "unknown";
    }
    return "unknown";
}

void PrintF32(std::ostream& out, float value) {
    // Note: Currently inf and nan should not be constructable, but this is implemented for the day
    // we support them.
    if (std::isinf(value)) {
        out << (value >= 0 ? "uintBitsToFloat(0x7f800000u)" : "uintBitsToFloat(0xff800000u)");
    } else if (std::isnan(value)) {
        out << "uintBitsToFloat(0x7fc00000u)";
    } else {
        out << FloatToString(value) << "f";
    }
}

}  // namespace

SanitizedResult::SanitizedResult() = default;
SanitizedResult::~SanitizedResult() = default;
SanitizedResult::SanitizedResult(SanitizedResult&&) = default;

SanitizedResult Sanitize(const Program* in,
                         const Options& options,
                         const std::string& entry_point) {
    transform::Manager manager;
    transform::DataMap data;

    manager.Add<transform::DisableUniformityAnalysis>();

    {  // Builtin polyfills
        transform::BuiltinPolyfill::Builtins polyfills;
        polyfills.acosh = transform::BuiltinPolyfill::Level::kRangeCheck;
        polyfills.atanh = transform::BuiltinPolyfill::Level::kRangeCheck;
        polyfills.count_leading_zeros = true;
        polyfills.count_trailing_zeros = true;
        polyfills.extract_bits = transform::BuiltinPolyfill::Level::kClampParameters;
        polyfills.first_leading_bit = true;
        polyfills.first_trailing_bit = true;
        polyfills.insert_bits = transform::BuiltinPolyfill::Level::kClampParameters;
        data.Add<transform::BuiltinPolyfill::Config>(polyfills);
        manager.Add<transform::BuiltinPolyfill>();
    }

    if (!entry_point.empty()) {
        manager.Add<transform::SingleEntryPoint>();
        data.Add<transform::SingleEntryPoint::Config>(entry_point);
    }
    manager.Add<transform::Renamer>();
    data.Add<transform::Renamer::Config>(transform::Renamer::Target::kGlslKeywords,
                                         /* preserve_unicode */ false);
    manager.Add<transform::Unshadow>();

    // Attempt to convert `loop`s into for-loops. This is to try and massage the
    // output into something that will not cause FXC to choke or misbehave.
    manager.Add<transform::FoldTrivialSingleUseLets>();
    manager.Add<transform::LoopToForLoop>();

    if (!options.disable_workgroup_init) {
        // ZeroInitWorkgroupMemory must come before CanonicalizeEntryPointIO as
        // ZeroInitWorkgroupMemory may inject new builtin parameters.
        manager.Add<transform::ZeroInitWorkgroupMemory>();
    }
    manager.Add<transform::CanonicalizeEntryPointIO>();
    manager.Add<transform::ExpandCompoundAssignment>();
    manager.Add<transform::PromoteSideEffectsToDecl>();
    manager.Add<transform::UnwindDiscardFunctions>();
    manager.Add<transform::SimplifyPointers>();

    manager.Add<transform::RemovePhonies>();

    if (options.generate_external_texture_bindings) {
        auto new_bindings_map = writer::GenerateExternalTextureBindings(in);
        data.Add<transform::MultiplanarExternalTexture::NewBindingPoints>(new_bindings_map);
    }
    manager.Add<transform::MultiplanarExternalTexture>();

    data.Add<transform::CombineSamplers::BindingInfo>(options.binding_map,
                                                      options.placeholder_binding_point);
    manager.Add<transform::CombineSamplers>();

    data.Add<transform::BindingRemapper::Remappings>(
        options.binding_points, options.access_controls, options.allow_collisions);
    manager.Add<transform::BindingRemapper>();

    manager.Add<transform::PromoteInitializersToLet>();
    manager.Add<transform::AddEmptyEntryPoint>();
    manager.Add<transform::AddSpirvBlockAttribute>();
    data.Add<transform::CanonicalizeEntryPointIO::Config>(
        transform::CanonicalizeEntryPointIO::ShaderStyle::kGlsl);

    auto out = manager.Run(in, data);

    SanitizedResult result;
    result.program = std::move(out.program);
    return result;
}

GeneratorImpl::GeneratorImpl(const Program* program, const Version& version)
    : TextGenerator(program), version_(version) {}

GeneratorImpl::~GeneratorImpl() = default;

bool GeneratorImpl::Generate() {
    {
        auto out = line();
        out << "#version " << version_.major_version << version_.minor_version << "0";
        if (version_.IsES()) {
            out << " es";
        }
    }

    auto helpers_insertion_point = current_buffer_->lines.size();

    line();

    auto* mod = builder_.Sem().Module();
    for (auto* decl : mod->DependencyOrderedDeclarations()) {
        if (decl->Is<ast::Alias>()) {
            continue;  // Ignore aliases.
        }

        if (auto* global = decl->As<ast::Variable>()) {
            if (!EmitGlobalVariable(global)) {
                return false;
            }
        } else if (auto* str = decl->As<ast::Struct>()) {
            // Skip emission if the struct contains a runtime-sized array, since its
            // only use will be as the store-type of a buffer and we emit those
            // elsewhere.
            // TODO(crbug.com/tint/1339): We could also avoid emitting any other
            // struct that is only used as a buffer store type.
            const sem::Struct* sem_str = builder_.Sem().Get(str);
            const auto& members = sem_str->Members();
            TINT_ASSERT(Writer, members.size() > 0);
            auto* last_member = members[members.size() - 1];
            auto* arr = last_member->Type()->As<sem::Array>();
            if (!arr || !arr->IsRuntimeSized()) {
                if (!EmitStructType(current_buffer_, sem_str)) {
                    return false;
                }
            }
        } else if (auto* func = decl->As<ast::Function>()) {
            if (func->IsEntryPoint()) {
                if (!EmitEntryPointFunction(func)) {
                    return false;
                }
            } else {
                if (!EmitFunction(func)) {
                    return false;
                }
            }
        } else if (auto* ext = decl->As<ast::Enable>()) {
            // Record the required extension for generating extension directive later
            if (!RecordExtension(ext)) {
                return false;
            }
        } else {
            TINT_ICE(Writer, diagnostics_)
                << "unhandled module-scope declaration: " << decl->TypeInfo().name;
            return false;
        }
    }

    TextBuffer extensions;

    if (version_.IsES() && requires_oes_sample_variables_) {
        extensions.Append("#extension GL_OES_sample_variables : require");
    }

    auto indent = current_buffer_->current_indent;

    if (!extensions.lines.empty()) {
        current_buffer_->Insert(extensions, helpers_insertion_point, indent);
        helpers_insertion_point += extensions.lines.size();
    }

    if (version_.IsES() && requires_default_precision_qualifier_) {
        current_buffer_->Insert("precision mediump float;", helpers_insertion_point++, indent);
    }

    if (!helpers_.lines.empty()) {
        current_buffer_->Insert("", helpers_insertion_point++, indent);
        current_buffer_->Insert(helpers_, helpers_insertion_point, indent);
        helpers_insertion_point += helpers_.lines.size();
    }

    return true;
}

bool GeneratorImpl::RecordExtension(const ast::Enable*) {
    /*
    Deal with extension node here, recording it within the generator for
    later emition.
    For example:
    ```
      if (ext->kind == ast::Enable::ExtensionKind::kF16) {
      require_fp16_ = true;
      }
    ```
    */

    return true;
}

bool GeneratorImpl::EmitIndexAccessor(std::ostream& out, const ast::IndexAccessorExpression* expr) {
    if (!EmitExpression(out, expr->object)) {
        return false;
    }
    out << "[";

    if (!EmitExpression(out, expr->index)) {
        return false;
    }
    out << "]";

    return true;
}

bool GeneratorImpl::EmitBitcast(std::ostream& out, const ast::BitcastExpression* expr) {
    auto* src_type = TypeOf(expr->expr)->UnwrapRef();
    auto* dst_type = TypeOf(expr)->UnwrapRef();

    if (!dst_type->is_integer_scalar_or_vector() && !dst_type->is_float_scalar_or_vector()) {
        diagnostics_.add_error(
            diag::System::Writer,
            "Unable to do bitcast to type " + dst_type->FriendlyName(builder_.Symbols()));
        return false;
    }

    if (src_type == dst_type) {
        return EmitExpression(out, expr->expr);
    }

    if (src_type->is_float_scalar_or_vector() && dst_type->is_signed_scalar_or_vector()) {
        out << "floatBitsToInt";
    } else if (src_type->is_float_scalar_or_vector() && dst_type->is_unsigned_scalar_or_vector()) {
        out << "floatBitsToUint";
    } else if (src_type->is_signed_scalar_or_vector() && dst_type->is_float_scalar_or_vector()) {
        out << "intBitsToFloat";
    } else if (src_type->is_unsigned_scalar_or_vector() && dst_type->is_float_scalar_or_vector()) {
        out << "uintBitsToFloat";
    } else {
        if (!EmitType(out, dst_type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
            return false;
        }
    }
    ScopedParen sp(out);
    if (!EmitExpression(out, expr->expr)) {
        return false;
    }
    return true;
}

bool GeneratorImpl::EmitAssign(const ast::AssignmentStatement* stmt) {
    auto out = line();
    if (!EmitExpression(out, stmt->lhs)) {
        return false;
    }
    out << " = ";
    if (!EmitExpression(out, stmt->rhs)) {
        return false;
    }
    out << ";";
    return true;
}

bool GeneratorImpl::EmitVectorRelational(std::ostream& out, const ast::BinaryExpression* expr) {
    switch (expr->op) {
        case ast::BinaryOp::kEqual:
            out << "equal";
            break;
        case ast::BinaryOp::kNotEqual:
            out << "notEqual";
            break;
        case ast::BinaryOp::kLessThan:
            out << "lessThan";
            break;
        case ast::BinaryOp::kGreaterThan:
            out << "greaterThan";
            break;
        case ast::BinaryOp::kLessThanEqual:
            out << "lessThanEqual";
            break;
        case ast::BinaryOp::kGreaterThanEqual:
            out << "greaterThanEqual";
            break;
        default:
            break;
    }
    ScopedParen sp(out);
    if (!EmitExpression(out, expr->lhs)) {
        return false;
    }
    out << ", ";
    if (!EmitExpression(out, expr->rhs)) {
        return false;
    }
    return true;
}

bool GeneratorImpl::EmitBitwiseBoolOp(std::ostream& out, const ast::BinaryExpression* expr) {
    auto* bool_type = TypeOf(expr->lhs)->UnwrapRef();
    auto* uint_type = BoolTypeToUint(bool_type);

    // Cast result to bool scalar or vector type.
    if (!EmitType(out, bool_type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
        return false;
    }
    ScopedParen outerCastParen(out);
    // Cast LHS to uint scalar or vector type.
    if (!EmitType(out, uint_type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
        return false;
    }
    {
        ScopedParen innerCastParen(out);
        // Emit LHS.
        if (!EmitExpression(out, expr->lhs)) {
            return false;
        }
    }
    // Emit operator.
    if (expr->op == ast::BinaryOp::kAnd) {
        out << " & ";
    } else if (expr->op == ast::BinaryOp::kOr) {
        out << " | ";
    } else {
        TINT_ICE(Writer, diagnostics_) << "unexpected binary op: " << FriendlyName(expr->op);
        return false;
    }
    // Cast RHS to uint scalar or vector type.
    if (!EmitType(out, uint_type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
        return false;
    }
    {
        ScopedParen innerCastParen(out);
        // Emit RHS.
        if (!EmitExpression(out, expr->rhs)) {
            return false;
        }
    }
    return true;
}

bool GeneratorImpl::EmitFloatModulo(std::ostream& out, const ast::BinaryExpression* expr) {
    std::string fn;
    auto* ret_ty = TypeOf(expr)->UnwrapRef();
    fn = utils::GetOrCreate(float_modulo_funcs_, ret_ty, [&]() -> std::string {
        TextBuffer b;
        TINT_DEFER(helpers_.Append(b));

        auto fn_name = UniqueIdentifier("tint_float_modulo");
        std::vector<std::string> parameter_names;
        {
            auto decl = line(&b);
            if (!EmitTypeAndName(decl, ret_ty, ast::StorageClass::kNone, ast::Access::kUndefined,
                                 fn_name)) {
                return "";
            }
            {
                ScopedParen sp(decl);
                const auto* ty = TypeOf(expr->lhs)->UnwrapRef();
                if (!EmitTypeAndName(decl, ty, ast::StorageClass::kNone, ast::Access::kUndefined,
                                     "lhs")) {
                    return "";
                }
                decl << ", ";
                ty = TypeOf(expr->rhs)->UnwrapRef();
                if (!EmitTypeAndName(decl, ty, ast::StorageClass::kNone, ast::Access::kUndefined,
                                     "rhs")) {
                    return "";
                }
            }
            decl << " {";
        }
        {
            ScopedIndent si(&b);
            line(&b) << "return (lhs - rhs * trunc(lhs / rhs));";
        }
        line(&b) << "}";
        line(&b);
        return fn_name;
    });

    if (fn.empty()) {
        return false;
    }

    // Call the helper
    out << fn;
    {
        ScopedParen sp(out);
        if (!EmitExpression(out, expr->lhs)) {
            return false;
        }
        out << ", ";
        if (!EmitExpression(out, expr->rhs)) {
            return false;
        }
    }
    return true;
}

bool GeneratorImpl::EmitBinary(std::ostream& out, const ast::BinaryExpression* expr) {
    if (IsRelational(expr->op) && !TypeOf(expr->lhs)->UnwrapRef()->is_scalar()) {
        return EmitVectorRelational(out, expr);
    }
    if (expr->op == ast::BinaryOp::kLogicalAnd || expr->op == ast::BinaryOp::kLogicalOr) {
        auto name = UniqueIdentifier(kTempNamePrefix);

        {
            auto pre = line();
            pre << "bool " << name << " = ";
            if (!EmitExpression(pre, expr->lhs)) {
                return false;
            }
            pre << ";";
        }

        if (expr->op == ast::BinaryOp::kLogicalOr) {
            line() << "if (!" << name << ") {";
        } else {
            line() << "if (" << name << ") {";
        }

        {
            ScopedIndent si(this);
            auto pre = line();
            pre << name << " = ";
            if (!EmitExpression(pre, expr->rhs)) {
                return false;
            }
            pre << ";";
        }

        line() << "}";

        out << "(" << name << ")";
        return true;
    }
    if ((expr->op == ast::BinaryOp::kAnd || expr->op == ast::BinaryOp::kOr) &&
        TypeOf(expr->lhs)->UnwrapRef()->is_bool_scalar_or_vector()) {
        return EmitBitwiseBoolOp(out, expr);
    }

    if (expr->op == ast::BinaryOp::kModulo &&
        (TypeOf(expr->lhs)->UnwrapRef()->is_float_scalar_or_vector() ||
         TypeOf(expr->rhs)->UnwrapRef()->is_float_scalar_or_vector())) {
        return EmitFloatModulo(out, expr);
    }

    ScopedParen sp(out);
    if (!EmitExpression(out, expr->lhs)) {
        return false;
    }
    out << " ";

    switch (expr->op) {
        case ast::BinaryOp::kAnd:
            out << "&";
            break;
        case ast::BinaryOp::kOr:
            out << "|";
            break;
        case ast::BinaryOp::kXor:
            out << "^";
            break;
        case ast::BinaryOp::kLogicalAnd:
        case ast::BinaryOp::kLogicalOr: {
            // These are both handled above.
            TINT_UNREACHABLE(Writer, diagnostics_);
            return false;
        }
        case ast::BinaryOp::kEqual:
            out << "==";
            break;
        case ast::BinaryOp::kNotEqual:
            out << "!=";
            break;
        case ast::BinaryOp::kLessThan:
            out << "<";
            break;
        case ast::BinaryOp::kGreaterThan:
            out << ">";
            break;
        case ast::BinaryOp::kLessThanEqual:
            out << "<=";
            break;
        case ast::BinaryOp::kGreaterThanEqual:
            out << ">=";
            break;
        case ast::BinaryOp::kShiftLeft:
            out << "<<";
            break;
        case ast::BinaryOp::kShiftRight:
            // TODO(dsinclair): MSL is based on C++14, and >> in C++14 has
            // implementation-defined behaviour for negative LHS.  We may have to
            // generate extra code to implement WGSL-specified behaviour for negative
            // LHS.
            out << R"(>>)";
            break;

        case ast::BinaryOp::kAdd:
            out << "+";
            break;
        case ast::BinaryOp::kSubtract:
            out << "-";
            break;
        case ast::BinaryOp::kMultiply:
            out << "*";
            break;
        case ast::BinaryOp::kDivide:
            out << "/";
            break;
        case ast::BinaryOp::kModulo:
            out << "%";
            break;
        case ast::BinaryOp::kNone:
            diagnostics_.add_error(diag::System::Writer, "missing binary operation type");
            return false;
    }
    out << " ";

    if (!EmitExpression(out, expr->rhs)) {
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitStatements(const ast::StatementList& stmts) {
    for (auto* s : stmts) {
        if (!EmitStatement(s)) {
            return false;
        }
    }
    return true;
}

bool GeneratorImpl::EmitStatementsWithIndent(const ast::StatementList& stmts) {
    ScopedIndent si(this);
    return EmitStatements(stmts);
}

bool GeneratorImpl::EmitBlock(const ast::BlockStatement* stmt) {
    line() << "{";
    if (!EmitStatementsWithIndent(stmt->statements)) {
        return false;
    }
    line() << "}";
    return true;
}

bool GeneratorImpl::EmitBreak(const ast::BreakStatement*) {
    line() << "break;";
    return true;
}

bool GeneratorImpl::EmitCall(std::ostream& out, const ast::CallExpression* expr) {
    auto* call = builder_.Sem().Get<sem::Call>(expr);
    auto* target = call->Target();

    if (target->Is<sem::Function>()) {
        return EmitFunctionCall(out, call);
    }
    if (auto* builtin = target->As<sem::Builtin>()) {
        return EmitBuiltinCall(out, call, builtin);
    }
    if (auto* cast = target->As<sem::TypeConversion>()) {
        return EmitTypeConversion(out, call, cast);
    }
    if (auto* ctor = target->As<sem::TypeConstructor>()) {
        return EmitTypeConstructor(out, call, ctor);
    }
    TINT_ICE(Writer, diagnostics_) << "unhandled call target: " << target->TypeInfo().name;
    return false;
}

bool GeneratorImpl::EmitFunctionCall(std::ostream& out, const sem::Call* call) {
    const auto& args = call->Arguments();
    auto* decl = call->Declaration();
    auto* ident = decl->target.name;

    auto name = builder_.Symbols().NameFor(ident->symbol);
    auto caller_sym = ident->symbol;

    out << name;
    ScopedParen sp(out);

    bool first = true;
    for (auto* arg : args) {
        if (!first) {
            out << ", ";
        }
        first = false;

        if (!EmitExpression(out, arg->Declaration())) {
            return false;
        }
    }

    return true;
}

bool GeneratorImpl::EmitBuiltinCall(std::ostream& out,
                                    const sem::Call* call,
                                    const sem::Builtin* builtin) {
    auto* expr = call->Declaration();
    if (builtin->IsTexture()) {
        return EmitTextureCall(out, call, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kCountOneBits) {
        return EmitCountOneBitsCall(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kSelect) {
        return EmitSelectCall(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kDot) {
        return EmitDotCall(out, expr, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kModf) {
        return EmitModfCall(out, expr, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kFrexp) {
        return EmitFrexpCall(out, expr, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kDegrees) {
        return EmitDegreesCall(out, expr, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kRadians) {
        return EmitRadiansCall(out, expr, builtin);
    }
    if (builtin->Type() == sem::BuiltinType::kArrayLength) {
        return EmitArrayLength(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kExtractBits) {
        return EmitExtractBits(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kInsertBits) {
        return EmitInsertBits(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kFma && version_.IsES()) {
        return EmitEmulatedFMA(out, expr);
    }
    if (builtin->Type() == sem::BuiltinType::kAbs &&
        TypeOf(expr->args[0])->UnwrapRef()->is_unsigned_scalar_or_vector()) {
        // GLSL does not support abs() on unsigned arguments. However, it's a no-op.
        return EmitExpression(out, expr->args[0]);
    }
    if ((builtin->Type() == sem::BuiltinType::kAny || builtin->Type() == sem::BuiltinType::kAll) &&
        TypeOf(expr->args[0])->UnwrapRef()->is_scalar()) {
        // GLSL does not support any() or all() on scalar arguments. It's a no-op.
        return EmitExpression(out, expr->args[0]);
    }
    if (builtin->IsBarrier()) {
        return EmitBarrierCall(out, builtin);
    }
    if (builtin->IsAtomic()) {
        return EmitWorkgroupAtomicCall(out, expr, builtin);
    }
    auto name = generate_builtin_name(builtin);
    if (name.empty()) {
        return false;
    }

    out << name;
    ScopedParen sp(out);

    bool first = true;
    for (auto* arg : call->Arguments()) {
        if (!first) {
            out << ", ";
        }
        first = false;

        if (!EmitExpression(out, arg->Declaration())) {
            return false;
        }
    }

    return true;
}

bool GeneratorImpl::EmitTypeConversion(std::ostream& out,
                                       const sem::Call* call,
                                       const sem::TypeConversion* conv) {
    if (!EmitType(out, conv->Target(), ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
        return false;
    }
    ScopedParen sp(out);

    if (!EmitExpression(out, call->Arguments()[0]->Declaration())) {
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitTypeConstructor(std::ostream& out,
                                        const sem::Call* call,
                                        const sem::TypeConstructor* ctor) {
    auto* type = ctor->ReturnType();

    // If the type constructor is empty then we need to construct with the zero
    // value for all components.
    if (call->Arguments().empty()) {
        return EmitZeroValue(out, type);
    }

    auto it = structure_builders_.find(As<sem::Struct>(type));
    if (it != structure_builders_.end()) {
        out << it->second << "(";
    } else {
        if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
            return false;
        }
        out << "(";
    }

    bool first = true;
    for (auto* arg : call->Arguments()) {
        if (!first) {
            out << ", ";
        }
        first = false;

        if (!EmitExpression(out, arg->Declaration())) {
            return false;
        }
    }

    out << ")";
    return true;
}

bool GeneratorImpl::EmitWorkgroupAtomicCall(std::ostream& out,
                                            const ast::CallExpression* expr,
                                            const sem::Builtin* builtin) {
    auto call = [&](const char* name) {
        out << name;
        {
            ScopedParen sp(out);
            for (size_t i = 0; i < expr->args.size(); i++) {
                auto* arg = expr->args[i];
                if (i > 0) {
                    out << ", ";
                }
                if (!EmitExpression(out, arg)) {
                    return false;
                }
            }
        }
        return true;
    };

    switch (builtin->Type()) {
        case sem::BuiltinType::kAtomicLoad: {
            // GLSL does not have an atomicLoad, so we emulate it with
            // atomicOr using 0 as the OR value
            out << "atomicOr";
            {
                ScopedParen sp(out);
                if (!EmitExpression(out, expr->args[0])) {
                    return false;
                }
                out << ", 0";
                if (builtin->ReturnType()->Is<sem::U32>()) {
                    out << "u";
                }
            }
            return true;
        }
        case sem::BuiltinType::kAtomicCompareExchangeWeak: {
            // Emit the builtin return type unique to this overload. This does not
            // exist in the AST, so it will not be generated in Generate().
            if (!EmitStructTypeOnce(&helpers_, builtin->ReturnType()->As<sem::Struct>())) {
                return false;
            }

            auto* dest = expr->args[0];
            auto* compare_value = expr->args[1];
            auto* value = expr->args[2];

            std::string result = UniqueIdentifier("atomic_compare_result");

            {
                auto pre = line();
                if (!EmitTypeAndName(pre, builtin->ReturnType(), ast::StorageClass::kNone,
                                     ast::Access::kUndefined, result)) {
                    return false;
                }
                pre << ";";
            }
            {
                auto pre = line();
                pre << result << ".old_value = atomicCompSwap";
                {
                    ScopedParen sp(pre);
                    if (!EmitExpression(pre, dest)) {
                        return false;
                    }
                    pre << ", ";
                    if (!EmitExpression(pre, compare_value)) {
                        return false;
                    }
                    pre << ", ";
                    if (!EmitExpression(pre, value)) {
                        return false;
                    }
                }
                pre << ";";
            }
            {
                auto pre = line();
                pre << result << ".exchanged = " << result << ".old_value == ";
                if (!EmitExpression(pre, compare_value)) {
                    return false;
                }
                pre << ";";
            }

            out << result;
            return true;
        }

        case sem::BuiltinType::kAtomicAdd:
        case sem::BuiltinType::kAtomicSub:
            return call("atomicAdd");

        case sem::BuiltinType::kAtomicMax:
            return call("atomicMax");

        case sem::BuiltinType::kAtomicMin:
            return call("atomicMin");

        case sem::BuiltinType::kAtomicAnd:
            return call("atomicAnd");

        case sem::BuiltinType::kAtomicOr:
            return call("atomicOr");

        case sem::BuiltinType::kAtomicXor:
            return call("atomicXor");

        case sem::BuiltinType::kAtomicExchange:
        case sem::BuiltinType::kAtomicStore:
            // GLSL does not have an atomicStore, so we emulate it with
            // atomicExchange.
            return call("atomicExchange");

        default:
            break;
    }

    TINT_UNREACHABLE(Writer, diagnostics_) << "unsupported atomic builtin: " << builtin->Type();
    return false;
}

bool GeneratorImpl::EmitArrayLength(std::ostream& out, const ast::CallExpression* expr) {
    out << "uint(";
    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ".length())";
    return true;
}

bool GeneratorImpl::EmitExtractBits(std::ostream& out, const ast::CallExpression* expr) {
    out << "bitfieldExtract(";
    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ", int(";
    if (!EmitExpression(out, expr->args[1])) {
        return false;
    }
    out << "), int(";
    if (!EmitExpression(out, expr->args[2])) {
        return false;
    }
    out << "))";
    return true;
}

bool GeneratorImpl::EmitInsertBits(std::ostream& out, const ast::CallExpression* expr) {
    out << "bitfieldInsert(";
    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ", ";
    if (!EmitExpression(out, expr->args[1])) {
        return false;
    }
    out << ", int(";
    if (!EmitExpression(out, expr->args[2])) {
        return false;
    }
    out << "), int(";
    if (!EmitExpression(out, expr->args[3])) {
        return false;
    }
    out << "))";
    return true;
}

bool GeneratorImpl::EmitEmulatedFMA(std::ostream& out, const ast::CallExpression* expr) {
    out << "((";
    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ") * (";
    if (!EmitExpression(out, expr->args[1])) {
        return false;
    }
    out << ") + (";
    if (!EmitExpression(out, expr->args[2])) {
        return false;
    }
    out << "))";
    return true;
}

bool GeneratorImpl::EmitCountOneBitsCall(std::ostream& out, const ast::CallExpression* expr) {
    // GLSL's bitCount returns an integer type, so cast it to the appropriate
    // unsigned type.
    if (!EmitType(out, TypeOf(expr)->UnwrapRef(), ast::StorageClass::kNone, ast::Access::kReadWrite,
                  "")) {
        return false;
    }
    out << "(bitCount(";

    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << "))";
    return true;
}

bool GeneratorImpl::EmitSelectCall(std::ostream& out, const ast::CallExpression* expr) {
    auto* expr_false = expr->args[0];
    auto* expr_true = expr->args[1];
    auto* expr_cond = expr->args[2];
    // GLSL does not support ternary expressions with a bool vector conditional,
    // but it does support mix() with same.
    if (TypeOf(expr_cond)->UnwrapRef()->is_bool_vector()) {
        out << "mix(";
        if (!EmitExpression(out, expr_false)) {
            return false;
        }
        out << ", ";
        if (!EmitExpression(out, expr_true)) {
            return false;
        }
        out << ", ";
        if (!EmitExpression(out, expr_cond)) {
            return false;
        }
        out << ")";
        return true;
    }
    ScopedParen paren(out);
    if (!EmitExpression(out, expr_cond)) {
        return false;
    }

    out << " ? ";

    if (!EmitExpression(out, expr_true)) {
        return false;
    }

    out << " : ";

    if (!EmitExpression(out, expr_false)) {
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitDotCall(std::ostream& out,
                                const ast::CallExpression* expr,
                                const sem::Builtin* builtin) {
    auto* vec_ty = builtin->Parameters()[0]->Type()->As<sem::Vector>();
    std::string fn = "dot";
    if (vec_ty->type()->is_integer_scalar()) {
        // GLSL does not have a builtin for dot() with integer vector types.
        // Generate the helper function if it hasn't been created already
        fn = utils::GetOrCreate(int_dot_funcs_, vec_ty, [&]() -> std::string {
            TextBuffer b;
            TINT_DEFER(helpers_.Append(b));

            auto fn_name = UniqueIdentifier("tint_int_dot");

            std::string v;
            {
                std::stringstream s;
                if (!EmitType(s, vec_ty->type(), ast::StorageClass::kNone, ast::Access::kRead,
                              "")) {
                    return "";
                }
                v = s.str();
            }
            {  // (u)int tint_int_dot([i|u]vecN a, [i|u]vecN b) {
                auto l = line(&b);
                if (!EmitType(l, vec_ty->type(), ast::StorageClass::kNone, ast::Access::kRead,
                              "")) {
                    return "";
                }
                l << " " << fn_name << "(";
                if (!EmitType(l, vec_ty, ast::StorageClass::kNone, ast::Access::kRead, "")) {
                    return "";
                }
                l << " a, ";
                if (!EmitType(l, vec_ty, ast::StorageClass::kNone, ast::Access::kRead, "")) {
                    return "";
                }
                l << " b) {";
            }
            {
                auto l = line(&b);
                l << "  return ";
                for (uint32_t i = 0; i < vec_ty->Width(); i++) {
                    if (i > 0) {
                        l << " + ";
                    }
                    l << "a[" << i << "]*b[" << i << "]";
                }
                l << ";";
            }
            line(&b) << "}";
            return fn_name;
        });
        if (fn.empty()) {
            return false;
        }
    }

    out << fn;
    ScopedParen sp(out);

    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ", ";
    if (!EmitExpression(out, expr->args[1])) {
        return false;
    }
    return true;
}

bool GeneratorImpl::EmitModfCall(std::ostream& out,
                                 const ast::CallExpression* expr,
                                 const sem::Builtin* builtin) {
    if (expr->args.size() == 1) {
        return CallBuiltinHelper(
            out, expr, builtin, [&](TextBuffer* b, const std::vector<std::string>& params) {
                // Emit the builtin return type unique to this overload. This does not
                // exist in the AST, so it will not be generated in Generate().
                if (!EmitStructType(&helpers_, builtin->ReturnType()->As<sem::Struct>())) {
                    return false;
                }

                {
                    auto l = line(b);
                    if (!EmitType(l, builtin->ReturnType(), ast::StorageClass::kNone,
                                  ast::Access::kUndefined, "")) {
                        return false;
                    }
                    l << " result;";
                }
                line(b) << "result.fract = modf(" << params[0] << ", result.whole);";
                line(b) << "return result;";
                return true;
            });
    }

    // DEPRECATED
    out << "modf";
    ScopedParen sp(out);
    if (!EmitExpression(out, expr->args[0])) {
        return false;
    }
    out << ", ";
    if (!EmitExpression(out, expr->args[1])) {
        return false;
    }
    return true;
}

bool GeneratorImpl::EmitFrexpCall(std::ostream& out,
                                  const ast::CallExpression* expr,
                                  const sem::Builtin* builtin) {
    if (expr->args.size() == 1) {
        return CallBuiltinHelper(
            out, expr, builtin, [&](TextBuffer* b, const std::vector<std::string>& params) {
                // Emit the builtin return type unique to this overload. This does not
                // exist in the AST, so it will not be generated in Generate().
                if (!EmitStructType(&helpers_, builtin->ReturnType()->As<sem::Struct>())) {
                    return false;
                }

                {
                    auto l = line(b);
                    if (!EmitType(l, builtin->ReturnType(), ast::StorageClass::kNone,
                                  ast::Access::kUndefined, "")) {
                        return false;
                    }
                    l << " result;";
                }
                line(b) << "result.sig = frexp(" << params[0] << ", result.exp);";
                line(b) << "return result;";
                return true;
            });
    }
    // DEPRECATED
    // Exponent is an integer in WGSL, but HLSL wants a float.
    // We need to make the call with a temporary float, and then cast.
    return CallBuiltinHelper(
        out, expr, builtin, [&](TextBuffer* b, const std::vector<std::string>& params) {
            auto* significand_ty = builtin->Parameters()[0]->Type();
            auto significand = params[0];
            auto* exponent_ty = builtin->Parameters()[1]->Type();
            auto exponent = params[1];

            std::string width;
            if (auto* vec = significand_ty->As<sem::Vector>()) {
                width = std::to_string(vec->Width());
            }

            // Exponent is an integer, which HLSL does not have an overload for.
            // We need to cast from a float.
            line(b) << "float" << width << " float_exp;";
            line(b) << "float" << width << " significand = frexp(" << significand
                    << ", float_exp);";
            {
                auto l = line(b);
                l << exponent << " = ";
                if (!EmitType(l, exponent_ty->UnwrapPtr(), ast::StorageClass::kNone,
                              ast::Access::kUndefined, "")) {
                    return false;
                }
                l << "(float_exp);";
            }
            line(b) << "return significand;";
            return true;
        });
}

bool GeneratorImpl::EmitDegreesCall(std::ostream& out,
                                    const ast::CallExpression* expr,
                                    const sem::Builtin* builtin) {
    return CallBuiltinHelper(out, expr, builtin,
                             [&](TextBuffer* b, const std::vector<std::string>& params) {
                                 line(b) << "return " << params[0] << " * " << std::setprecision(20)
                                         << sem::kRadToDeg << ";";
                                 return true;
                             });
}

bool GeneratorImpl::EmitRadiansCall(std::ostream& out,
                                    const ast::CallExpression* expr,
                                    const sem::Builtin* builtin) {
    return CallBuiltinHelper(out, expr, builtin,
                             [&](TextBuffer* b, const std::vector<std::string>& params) {
                                 line(b) << "return " << params[0] << " * " << std::setprecision(20)
                                         << sem::kDegToRad << ";";
                                 return true;
                             });
}

bool GeneratorImpl::EmitBarrierCall(std::ostream& out, const sem::Builtin* builtin) {
    // TODO(crbug.com/tint/661): Combine sequential barriers to a single
    // instruction.
    if (builtin->Type() == sem::BuiltinType::kWorkgroupBarrier) {
        out << "barrier()";
    } else if (builtin->Type() == sem::BuiltinType::kStorageBarrier) {
        out << "{ barrier(); memoryBarrierBuffer(); }";
    } else {
        TINT_UNREACHABLE(Writer, diagnostics_)
            << "unexpected barrier builtin type " << sem::str(builtin->Type());
        return false;
    }
    return true;
}

const ast::Expression* GeneratorImpl::CreateF32Zero(const sem::Statement* stmt) {
    auto* zero = builder_.Expr(0_f);
    auto* f32 = builder_.create<sem::F32>();
    auto* sem_zero = builder_.create<sem::Expression>(zero, f32, stmt, sem::Constant{},
                                                      /* has_side_effects */ false);
    builder_.Sem().Add(zero, sem_zero);
    return zero;
}

bool GeneratorImpl::EmitTextureCall(std::ostream& out,
                                    const sem::Call* call,
                                    const sem::Builtin* builtin) {
    using Usage = sem::ParameterUsage;

    auto& signature = builtin->Signature();
    auto* expr = call->Declaration();
    auto arguments = expr->args;

    // Returns the argument with the given usage
    auto arg = [&](Usage usage) {
        auto idx = signature.IndexOf(usage);
        return (idx >= 0) ? arguments[static_cast<size_t>(idx)] : nullptr;
    };

    auto* texture = arg(Usage::kTexture);
    if (!texture) {
        TINT_ICE(Writer, diagnostics_) << "missing texture argument";
        return false;
    }

    auto* texture_type = TypeOf(texture)->UnwrapRef()->As<sem::Texture>();

    switch (builtin->Type()) {
        case sem::BuiltinType::kTextureDimensions: {
            if (texture_type->Is<sem::StorageTexture>()) {
                out << "imageSize(";
            } else {
                out << "textureSize(";
            }
            if (!EmitExpression(out, texture)) {
                return false;
            }

            // The LOD parameter is mandatory on textureSize() for non-multisampled
            // textures.
            if (!texture_type->Is<sem::StorageTexture>() &&
                !texture_type->Is<sem::MultisampledTexture>() &&
                !texture_type->Is<sem::DepthMultisampledTexture>()) {
                out << ", ";
                if (auto* level_arg = arg(Usage::kLevel)) {
                    if (!EmitExpression(out, level_arg)) {
                        return false;
                    }
                } else {
                    out << "0";
                }
            }
            out << ")";
            // textureSize() on array samplers returns the array size in the
            // final component, so strip it out.
            if (texture_type->dim() == ast::TextureDimension::k2dArray ||
                texture_type->dim() == ast::TextureDimension::kCubeArray) {
                out << ".xy";
            }
            return true;
        }
        case sem::BuiltinType::kTextureNumLayers: {
            if (texture_type->Is<sem::StorageTexture>()) {
                out << "imageSize(";
            } else {
                out << "textureSize(";
            }
            // textureSize() on sampler2dArray returns the array size in the
            // final component, so return it
            if (!EmitExpression(out, texture)) {
                return false;
            }
            // The LOD parameter is mandatory on textureSize() for non-multisampled
            // textures.
            if (!texture_type->Is<sem::StorageTexture>() &&
                !texture_type->Is<sem::MultisampledTexture>() &&
                !texture_type->Is<sem::DepthMultisampledTexture>()) {
                out << ", ";
                if (auto* level_arg = arg(Usage::kLevel)) {
                    if (!EmitExpression(out, level_arg)) {
                        return false;
                    }
                } else {
                    out << "0";
                }
            }
            out << ").z";
            return true;
        }
        case sem::BuiltinType::kTextureNumLevels: {
            out << "textureQueryLevels(";
            if (!EmitExpression(out, texture)) {
                return false;
            }
            out << ")";
            return true;
        }
        case sem::BuiltinType::kTextureNumSamples: {
            out << "textureSamples(";
            if (!EmitExpression(out, texture)) {
                return false;
            }
            out << ")";
            return true;
        }
        default:
            break;
    }

    uint32_t glsl_ret_width = 4u;
    bool append_depth_ref_to_coords = true;
    bool is_depth = texture_type->Is<sem::DepthTexture>();

    switch (builtin->Type()) {
        case sem::BuiltinType::kTextureSample:
        case sem::BuiltinType::kTextureSampleBias:
            out << "texture";
            if (is_depth) {
                glsl_ret_width = 1u;
            }
            break;
        case sem::BuiltinType::kTextureSampleLevel:
            out << "textureLod";
            if (is_depth) {
                glsl_ret_width = 1u;
            }
            break;
        case sem::BuiltinType::kTextureGather:
        case sem::BuiltinType::kTextureGatherCompare:
            out << "textureGather";
            append_depth_ref_to_coords = false;
            break;
        case sem::BuiltinType::kTextureSampleGrad:
            out << "textureGrad";
            break;
        case sem::BuiltinType::kTextureSampleCompare:
        case sem::BuiltinType::kTextureSampleCompareLevel:
            out << "texture";
            glsl_ret_width = 1;
            break;
        case sem::BuiltinType::kTextureLoad:
            out << "texelFetch";
            break;
        case sem::BuiltinType::kTextureStore:
            out << "imageStore";
            break;
        default:
            diagnostics_.add_error(diag::System::Writer,
                                   "Internal compiler error: Unhandled texture builtin '" +
                                       std::string(builtin->str()) + "'");
            return false;
    }

    if (builtin->Signature().IndexOf(sem::ParameterUsage::kOffset) >= 0) {
        out << "Offset";
    }

    out << "(";

    if (!EmitExpression(out, texture)) {
        return false;
    }

    out << ", ";

    auto* param_coords = arg(Usage::kCoords);
    if (!param_coords) {
        TINT_ICE(Writer, diagnostics_) << "missing coords argument";
        return false;
    }

    if (auto* array_index = arg(Usage::kArrayIndex)) {
        // Array index needs to be appended to the coordinates.
        param_coords = AppendVector(&builder_, param_coords, array_index)->Declaration();
    }

    // GLSL requires Dref to be appended to the coordinates, *unless* it's
    // samplerCubeArrayShadow, in which case it will be handled as a separate
    // parameter.
    if (texture_type->dim() == ast::TextureDimension::kCubeArray) {
        append_depth_ref_to_coords = false;
    }

    if (is_depth && append_depth_ref_to_coords) {
        auto* depth_ref = arg(Usage::kDepthRef);
        if (!depth_ref) {
            // Sampling a depth texture in GLSL always requires a depth reference, so
            // append zero here.
            depth_ref = CreateF32Zero(builder_.Sem().Get(param_coords)->Stmt());
        }
        param_coords = AppendVector(&builder_, param_coords, depth_ref)->Declaration();
    }

    if (!EmitExpression(out, param_coords)) {
        return false;
    }

    for (auto usage :
         {Usage::kLevel, Usage::kDdx, Usage::kDdy, Usage::kSampleIndex, Usage::kValue}) {
        if (auto* e = arg(usage)) {
            out << ", ";
            if (usage == Usage::kLevel && is_depth) {
                // WGSL's textureSampleLevel() "level" param is i32 for depth textures,
                // whereas GLSL's textureLod() "lod" param is always float, so cast it.
                out << "float(";
                if (!EmitExpression(out, e)) {
                    return false;
                }
                out << ")";
            } else if (!EmitExpression(out, e)) {
                return false;
            }
        }
    }

    // GLSL's textureGather always requires a refZ parameter.
    if (is_depth && builtin->Type() == sem::BuiltinType::kTextureGather) {
        out << ", 0.0";
    }

    // [1] samplerCubeArrayShadow requires a separate depthRef parameter
    if (is_depth && !append_depth_ref_to_coords) {
        if (auto* e = arg(Usage::kDepthRef)) {
            out << ", ";
            if (!EmitExpression(out, e)) {
                return false;
            }
        } else if (builtin->Type() == sem::BuiltinType::kTextureSample) {
            out << ", 0.0f";
        }
    }

    for (auto usage : {Usage::kOffset, Usage::kComponent, Usage::kBias}) {
        if (auto* e = arg(usage)) {
            out << ", ";
            if (!EmitExpression(out, e)) {
                return false;
            }
        }
    }

    out << ")";

    if (builtin->ReturnType()->Is<sem::Void>()) {
        return true;
    }
    // If the builtin return type does not match the number of elements of the
    // GLSL builtin, we need to swizzle the expression to generate the correct
    // number of components.
    uint32_t wgsl_ret_width = 1;
    if (auto* vec = builtin->ReturnType()->As<sem::Vector>()) {
        wgsl_ret_width = vec->Width();
    }
    if (wgsl_ret_width < glsl_ret_width) {
        out << ".";
        for (uint32_t i = 0; i < wgsl_ret_width; i++) {
            out << "xyz"[i];
        }
    }
    if (wgsl_ret_width > glsl_ret_width) {
        TINT_ICE(Writer, diagnostics_)
            << "WGSL return width (" << wgsl_ret_width << ") is wider than GLSL return width ("
            << glsl_ret_width << ") for " << builtin->Type();
        return false;
    }

    return true;
}

std::string GeneratorImpl::generate_builtin_name(const sem::Builtin* builtin) {
    switch (builtin->Type()) {
        case sem::BuiltinType::kAbs:
        case sem::BuiltinType::kAcos:
        case sem::BuiltinType::kAcosh:
        case sem::BuiltinType::kAll:
        case sem::BuiltinType::kAny:
        case sem::BuiltinType::kAsin:
        case sem::BuiltinType::kAsinh:
        case sem::BuiltinType::kAtan:
        case sem::BuiltinType::kAtanh:
        case sem::BuiltinType::kCeil:
        case sem::BuiltinType::kClamp:
        case sem::BuiltinType::kCos:
        case sem::BuiltinType::kCosh:
        case sem::BuiltinType::kCross:
        case sem::BuiltinType::kDeterminant:
        case sem::BuiltinType::kDistance:
        case sem::BuiltinType::kDot:
        case sem::BuiltinType::kExp:
        case sem::BuiltinType::kExp2:
        case sem::BuiltinType::kFloor:
        case sem::BuiltinType::kFrexp:
        case sem::BuiltinType::kLdexp:
        case sem::BuiltinType::kLength:
        case sem::BuiltinType::kLog:
        case sem::BuiltinType::kLog2:
        case sem::BuiltinType::kMax:
        case sem::BuiltinType::kMin:
        case sem::BuiltinType::kModf:
        case sem::BuiltinType::kNormalize:
        case sem::BuiltinType::kPow:
        case sem::BuiltinType::kReflect:
        case sem::BuiltinType::kRefract:
        case sem::BuiltinType::kRound:
        case sem::BuiltinType::kSign:
        case sem::BuiltinType::kSin:
        case sem::BuiltinType::kSinh:
        case sem::BuiltinType::kSqrt:
        case sem::BuiltinType::kStep:
        case sem::BuiltinType::kTan:
        case sem::BuiltinType::kTanh:
        case sem::BuiltinType::kTranspose:
        case sem::BuiltinType::kTrunc:
            return builtin->str();
        case sem::BuiltinType::kAtan2:
            return "atan";
        case sem::BuiltinType::kCountOneBits:
            return "bitCount";
        case sem::BuiltinType::kDpdx:
            return "dFdx";
        case sem::BuiltinType::kDpdxCoarse:
            if (version_.IsES()) {
                return "dFdx";
            }
            return "dFdxCoarse";
        case sem::BuiltinType::kDpdxFine:
            if (version_.IsES()) {
                return "dFdx";
            }
            return "dFdxFine";
        case sem::BuiltinType::kDpdy:
            return "dFdy";
        case sem::BuiltinType::kDpdyCoarse:
            if (version_.IsES()) {
                return "dFdy";
            }
            return "dFdyCoarse";
        case sem::BuiltinType::kDpdyFine:
            if (version_.IsES()) {
                return "dFdy";
            }
            return "dFdyFine";
        case sem::BuiltinType::kFaceForward:
            return "faceforward";
        case sem::BuiltinType::kFract:
            return "fract";
        case sem::BuiltinType::kFma:
            return "fma";
        case sem::BuiltinType::kFwidth:
        case sem::BuiltinType::kFwidthCoarse:
        case sem::BuiltinType::kFwidthFine:
            return "fwidth";
        case sem::BuiltinType::kInverseSqrt:
            return "inversesqrt";
        case sem::BuiltinType::kMix:
            return "mix";
        case sem::BuiltinType::kPack2x16float:
            return "packHalf2x16";
        case sem::BuiltinType::kPack2x16snorm:
            return "packSnorm2x16";
        case sem::BuiltinType::kPack2x16unorm:
            return "packUnorm2x16";
        case sem::BuiltinType::kPack4x8snorm:
            return "packSnorm4x8";
        case sem::BuiltinType::kPack4x8unorm:
            return "packUnorm4x8";
        case sem::BuiltinType::kReverseBits:
            return "bitfieldReverse";
        case sem::BuiltinType::kSmoothstep:
            return "smoothstep";
        case sem::BuiltinType::kUnpack2x16float:
            return "unpackHalf2x16";
        case sem::BuiltinType::kUnpack2x16snorm:
            return "unpackSnorm2x16";
        case sem::BuiltinType::kUnpack2x16unorm:
            return "unpackUnorm2x16";
        case sem::BuiltinType::kUnpack4x8snorm:
            return "unpackSnorm4x8";
        case sem::BuiltinType::kUnpack4x8unorm:
            return "unpackUnorm4x8";
        default:
            diagnostics_.add_error(diag::System::Writer,
                                   "Unknown builtin method: " + std::string(builtin->str()));
    }

    return "";
}

bool GeneratorImpl::EmitCase(const ast::CaseStatement* stmt) {
    if (stmt->IsDefault()) {
        line() << "default: {";
    } else {
        for (auto* selector : stmt->selectors) {
            auto out = line();
            out << "case ";
            if (!EmitLiteral(out, selector)) {
                return false;
            }
            out << ":";
            if (selector == stmt->selectors.back()) {
                out << " {";
            }
        }
    }

    {
        ScopedIndent si(this);
        if (!EmitStatements(stmt->body->statements)) {
            return false;
        }
        if (!last_is_break_or_fallthrough(stmt->body)) {
            line() << "break;";
        }
    }

    line() << "}";

    return true;
}

bool GeneratorImpl::EmitContinue(const ast::ContinueStatement*) {
    if (!emit_continuing_ || !emit_continuing_()) {
        return false;
    }
    line() << "continue;";
    return true;
}

bool GeneratorImpl::EmitDiscard(const ast::DiscardStatement*) {
    // TODO(dsinclair): Verify this is correct when the discard semantics are
    // defined for WGSL (https://github.com/gpuweb/gpuweb/issues/361)
    line() << "discard;";
    return true;
}

bool GeneratorImpl::EmitExpression(std::ostream& out, const ast::Expression* expr) {
    if (auto* sem = builder_.Sem().Get(expr)) {
        if (auto constant = sem->ConstantValue()) {
            return EmitConstant(out, constant);
        }
    }
    return Switch(
        expr,
        [&](const ast::IndexAccessorExpression* a) {  //
            return EmitIndexAccessor(out, a);
        },
        [&](const ast::BinaryExpression* b) {  //
            return EmitBinary(out, b);
        },
        [&](const ast::BitcastExpression* b) {  //
            return EmitBitcast(out, b);
        },
        [&](const ast::CallExpression* c) {  //
            return EmitCall(out, c);
        },
        [&](const ast::IdentifierExpression* i) {  //
            return EmitIdentifier(out, i);
        },
        [&](const ast::LiteralExpression* l) {  //
            return EmitLiteral(out, l);
        },
        [&](const ast::MemberAccessorExpression* m) {  //
            return EmitMemberAccessor(out, m);
        },
        [&](const ast::UnaryOpExpression* u) {  //
            return EmitUnaryOp(out, u);
        },
        [&](Default) {  //
            diagnostics_.add_error(diag::System::Writer, "unknown expression type: " +
                                                             std::string(expr->TypeInfo().name));
            return false;
        });
}

bool GeneratorImpl::EmitIdentifier(std::ostream& out, const ast::IdentifierExpression* expr) {
    out << builder_.Symbols().NameFor(expr->symbol);
    return true;
}

bool GeneratorImpl::EmitIf(const ast::IfStatement* stmt) {
    {
        auto out = line();
        out << "if (";
        if (!EmitExpression(out, stmt->condition)) {
            return false;
        }
        out << ") {";
    }

    if (!EmitStatementsWithIndent(stmt->body->statements)) {
        return false;
    }

    if (stmt->else_statement) {
        line() << "} else {";
        if (auto* block = stmt->else_statement->As<ast::BlockStatement>()) {
            if (!EmitStatementsWithIndent(block->statements)) {
                return false;
            }
        } else {
            if (!EmitStatementsWithIndent({stmt->else_statement})) {
                return false;
            }
        }
    }
    line() << "}";

    return true;
}

bool GeneratorImpl::EmitFunction(const ast::Function* func) {
    auto* sem = builder_.Sem().Get(func);

    if (ast::HasAttribute<ast::InternalAttribute>(func->attributes)) {
        // An internal function. Do not emit.
        return true;
    }

    {
        auto out = line();
        auto name = builder_.Symbols().NameFor(func->symbol);
        if (!EmitType(out, sem->ReturnType(), ast::StorageClass::kNone, ast::Access::kReadWrite,
                      "")) {
            return false;
        }

        out << " " << name << "(";

        bool first = true;

        for (auto* v : sem->Parameters()) {
            if (!first) {
                out << ", ";
            }
            first = false;

            auto const* type = v->Type();

            if (auto* ptr = type->As<sem::Pointer>()) {
                // Transform pointer parameters in to `inout` parameters.
                // The WGSL spec is highly restrictive in what can be passed in pointer
                // parameters, which allows for this transformation. See:
                // https://gpuweb.github.io/gpuweb/wgsl/#function-restriction
                out << "inout ";
                type = ptr->StoreType();
            }

            // Note: WGSL only allows for StorageClass::kNone on parameters, however
            // the sanitizer transforms generates load / store functions for storage
            // or uniform buffers. These functions have a buffer parameter with
            // StorageClass::kStorage or StorageClass::kUniform. This is required to
            // correctly translate the parameter to a [RW]ByteAddressBuffer for
            // storage buffers and a uint4[N] for uniform buffers.
            if (!EmitTypeAndName(out, type, v->StorageClass(), v->Access(),
                                 builder_.Symbols().NameFor(v->Declaration()->symbol))) {
                return false;
            }
        }
        out << ") {";
    }

    if (!EmitStatementsWithIndent(func->body->statements)) {
        return false;
    }

    line() << "}";
    line();

    return true;
}

bool GeneratorImpl::EmitGlobalVariable(const ast::Variable* global) {
    return Switch(
        global,  //
        [&](const ast::Var* var) {
            auto* sem = builder_.Sem().Get(global);
            switch (sem->StorageClass()) {
                case ast::StorageClass::kUniform:
                    return EmitUniformVariable(var, sem);
                case ast::StorageClass::kStorage:
                    return EmitStorageVariable(var, sem);
                case ast::StorageClass::kHandle:
                    return EmitHandleVariable(var, sem);
                case ast::StorageClass::kPrivate:
                    return EmitPrivateVariable(sem);
                case ast::StorageClass::kWorkgroup:
                    return EmitWorkgroupVariable(sem);
                case ast::StorageClass::kInput:
                case ast::StorageClass::kOutput:
                    return EmitIOVariable(sem);
                default:
                    TINT_ICE(Writer, diagnostics_)
                        << "unhandled storage class " << sem->StorageClass();
                    return false;
            }
        },
        [&](const ast::Let* let) { return EmitProgramConstVariable(let); },
        [&](const ast::Override* override) { return EmitOverride(override); },
        [&](const ast::Const*) {
            return true;  // Constants are embedded at their use
        },
        [&](Default) {
            TINT_ICE(Writer, diagnostics_)
                << "unhandled global variable type " << global->TypeInfo().name;
            return false;
        });
}

bool GeneratorImpl::EmitUniformVariable(const ast::Var* var, const sem::Variable* sem) {
    auto* type = sem->Type()->UnwrapRef();
    auto* str = type->As<sem::Struct>();
    if (!str) {
        TINT_ICE(Writer, builder_.Diagnostics()) << "storage variable must be of struct type";
        return false;
    }
    ast::VariableBindingPoint bp = var->BindingPoint();
    {
        auto out = line();
        out << "layout(binding = " << bp.binding->value;
        if (version_.IsDesktop()) {
            out << ", std140";
        }
        out << ") uniform " << UniqueIdentifier(StructName(str)) << " {";
    }
    EmitStructMembers(current_buffer_, str, /* emit_offsets */ true);
    auto name = builder_.Symbols().NameFor(var->symbol);
    line() << "} " << name << ";";
    line();

    return true;
}

bool GeneratorImpl::EmitStorageVariable(const ast::Var* var, const sem::Variable* sem) {
    auto* type = sem->Type()->UnwrapRef();
    auto* str = type->As<sem::Struct>();
    if (!str) {
        TINT_ICE(Writer, builder_.Diagnostics()) << "storage variable must be of struct type";
        return false;
    }
    ast::VariableBindingPoint bp = var->BindingPoint();
    line() << "layout(binding = " << bp.binding->value << ", std430) buffer "
           << UniqueIdentifier(StructName(str)) << " {";
    EmitStructMembers(current_buffer_, str, /* emit_offsets */ true);
    auto name = builder_.Symbols().NameFor(var->symbol);
    line() << "} " << name << ";";
    return true;
}

bool GeneratorImpl::EmitHandleVariable(const ast::Var* var, const sem::Variable* sem) {
    auto out = line();

    auto name = builder_.Symbols().NameFor(var->symbol);
    auto* type = sem->Type()->UnwrapRef();
    if (type->Is<sem::Sampler>()) {
        // GLSL ignores Sampler variables.
        return true;
    }
    if (auto* storage = type->As<sem::StorageTexture>()) {
        out << "layout(" << convert_texel_format_to_glsl(storage->texel_format()) << ") ";
    }
    if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(), name)) {
        return false;
    }

    out << ";";
    return true;
}

bool GeneratorImpl::EmitPrivateVariable(const sem::Variable* var) {
    auto* decl = var->Declaration();
    auto out = line();

    auto name = builder_.Symbols().NameFor(decl->symbol);
    auto* type = var->Type()->UnwrapRef();
    if (!EmitTypeAndName(out, type, var->StorageClass(), var->Access(), name)) {
        return false;
    }

    out << " = ";
    if (auto* constructor = decl->constructor) {
        if (!EmitExpression(out, constructor)) {
            return false;
        }
    } else {
        if (!EmitZeroValue(out, var->Type()->UnwrapRef())) {
            return false;
        }
    }

    out << ";";
    return true;
}

bool GeneratorImpl::EmitWorkgroupVariable(const sem::Variable* var) {
    auto* decl = var->Declaration();
    auto out = line();

    out << "shared ";

    auto name = builder_.Symbols().NameFor(decl->symbol);
    auto* type = var->Type()->UnwrapRef();
    if (!EmitTypeAndName(out, type, var->StorageClass(), var->Access(), name)) {
        return false;
    }

    if (auto* constructor = decl->constructor) {
        out << " = ";
        if (!EmitExpression(out, constructor)) {
            return false;
        }
    }

    out << ";";
    return true;
}

bool GeneratorImpl::EmitIOVariable(const sem::Variable* var) {
    auto* decl = var->Declaration();

    if (auto* b = ast::GetAttribute<ast::BuiltinAttribute>(decl->attributes)) {
        // Use of gl_SampleID requires the GL_OES_sample_variables extension
        if (RequiresOESSampleVariables(b->builtin)) {
            requires_oes_sample_variables_ = true;
        }
        // Do not emit builtin (gl_) variables.
        return true;
    }

    auto out = line();
    EmitAttributes(out, decl->attributes);
    EmitInterpolationQualifiers(out, decl->attributes);

    auto name = builder_.Symbols().NameFor(decl->symbol);
    auto* type = var->Type()->UnwrapRef();
    if (!EmitTypeAndName(out, type, var->StorageClass(), var->Access(), name)) {
        return false;
    }

    if (auto* constructor = decl->constructor) {
        out << " = ";
        if (!EmitExpression(out, constructor)) {
            return false;
        }
    }

    out << ";";
    return true;
}

void GeneratorImpl::EmitInterpolationQualifiers(std::ostream& out,
                                                const ast::AttributeList& attributes) {
    for (auto* attr : attributes) {
        if (auto* interpolate = attr->As<ast::InterpolateAttribute>()) {
            switch (interpolate->type) {
                case ast::InterpolationType::kPerspective:
                case ast::InterpolationType::kLinear:
                    break;
                case ast::InterpolationType::kFlat:
                    out << "flat ";
                    break;
            }
            switch (interpolate->sampling) {
                case ast::InterpolationSampling::kCentroid:
                    out << "centroid ";
                    break;
                case ast::InterpolationSampling::kSample:
                case ast::InterpolationSampling::kCenter:
                case ast::InterpolationSampling::kNone:
                    break;
            }
        }
    }
}

bool GeneratorImpl::EmitAttributes(std::ostream& out, const ast::AttributeList& attributes) {
    if (attributes.empty()) {
        return true;
    }
    bool first = true;
    for (auto* attr : attributes) {
        if (auto* location = attr->As<ast::LocationAttribute>()) {
            out << (first ? "layout(" : ", ");
            out << "location = " << std::to_string(location->value);
            first = false;
        }
    }
    if (!first) {
        out << ") ";
    }
    return true;
}

bool GeneratorImpl::EmitEntryPointFunction(const ast::Function* func) {
    auto* func_sem = builder_.Sem().Get(func);

    if (func->PipelineStage() == ast::PipelineStage::kFragment) {
        requires_default_precision_qualifier_ = true;
    }

    if (func->PipelineStage() == ast::PipelineStage::kCompute) {
        auto out = line();
        // Emit the layout(local_size) attributes.
        auto wgsize = func_sem->WorkgroupSize();
        out << "layout(";
        for (size_t i = 0; i < 3; i++) {
            if (i > 0) {
                out << ", ";
            }
            out << "local_size_" << (i == 0 ? "x" : i == 1 ? "y" : "z") << " = ";

            if (wgsize[i].overridable_const) {
                auto* global = builder_.Sem().Get<sem::GlobalVariable>(wgsize[i].overridable_const);
                if (!global->Declaration()->Is<ast::Override>()) {
                    TINT_ICE(Writer, builder_.Diagnostics())
                        << "expected a pipeline-overridable constant";
                }
                out << kSpecConstantPrefix << global->ConstantId();
            } else {
                out << std::to_string(wgsize[i].value);
            }
        }
        out << ") in;";
    }

    // Emit original entry point signature
    {
        auto out = line();
        out << func->return_type->FriendlyName(builder_.Symbols()) << " "
            << builder_.Symbols().NameFor(func->symbol) << "(";

        bool first = true;

        // Emit entry point parameters.
        for (auto* var : func->params) {
            auto* sem = builder_.Sem().Get(var);
            auto* type = sem->Type();
            if (!type->Is<sem::Struct>()) {
                // ICE likely indicates that the CanonicalizeEntryPointIO transform was
                // not run, or a builtin parameter was added after it was run.
                TINT_ICE(Writer, diagnostics_) << "Unsupported non-struct entry point parameter";
            }

            if (!first) {
                out << ", ";
            }
            first = false;

            if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
                                 builder_.Symbols().NameFor(var->symbol))) {
                return false;
            }
        }

        out << ") {";
    }

    // Emit original entry point function body
    {
        ScopedIndent si(this);
        if (func->PipelineStage() == ast::PipelineStage::kVertex) {
            line() << "gl_PointSize = 1.0;";
        }

        if (!EmitStatements(func->body->statements)) {
            return false;
        }

        if (!Is<ast::ReturnStatement>(func->body->Last())) {
            ast::ReturnStatement ret(ProgramID(), Source{});
            if (!EmitStatement(&ret)) {
                return false;
            }
        }
    }

    line() << "}";

    return true;
}

bool GeneratorImpl::EmitConstant(std::ostream& out, const sem::Constant& constant) {
    return EmitConstantRange(out, constant, constant.Type(), 0, constant.ElementCount());
}

bool GeneratorImpl::EmitConstantRange(std::ostream& out,
                                      const sem::Constant& constant,
                                      const sem::Type* range_ty,
                                      size_t start,
                                      size_t end) {
    return Switch(
        range_ty,  //
        [&](const sem::Bool*) {
            out << (constant.Element<AInt>(start) ? "true" : "false");
            return true;
        },
        [&](const sem::F32*) {
            PrintF32(out, static_cast<float>(constant.Element<AFloat>(start)));
            return true;
        },
        [&](const sem::I32*) {
            out << constant.Element<AInt>(start).value;
            return true;
        },
        [&](const sem::U32*) {
            out << constant.Element<AInt>(start).value << "u";
            return true;
        },
        [&](const sem::Vector* v) {
            if (!EmitType(out, v, ast::StorageClass::kNone, ast::Access::kUndefined, "")) {
                return false;
            }

            ScopedParen sp(out);

            if (constant.AllEqual(start, end)) {
                return EmitConstantRange(out, constant, v->type(), start, start + 1);
            }

            for (size_t i = start; i < end; i++) {
                if (i > start) {
                    out << ", ";
                }
                if (!EmitConstantRange(out, constant, v->type(), i, i + 1u)) {
                    return false;
                }
            }
            return true;
        },
        [&](const sem::Matrix* m) {
            if (!EmitType(out, m, ast::StorageClass::kNone, ast::Access::kUndefined, "")) {
                return false;
            }

            ScopedParen sp(out);

            for (size_t column_idx = 0; column_idx < m->columns(); column_idx++) {
                if (column_idx > 0) {
                    out << ", ";
                }
                size_t col_start = m->rows() * column_idx;
                size_t col_end = col_start + m->rows();
                if (!EmitConstantRange(out, constant, m->ColumnType(), col_start, col_end)) {
                    return false;
                }
            }
            return true;
        },
        [&](const sem::Array* a) {
            if (!EmitType(out, a, ast::StorageClass::kNone, ast::Access::kUndefined, "")) {
                return false;
            }

            ScopedParen sp(out);

            auto* el_ty = a->ElemType();

            uint32_t step = 0;
            sem::Type::DeepestElementOf(el_ty, &step);
            for (size_t i = start; i < end; i += step) {
                if (i > start) {
                    out << ", ";
                }
                if (!EmitConstantRange(out, constant, el_ty, i, i + step)) {
                    return false;
                }
            }

            return true;
        },
        [&](Default) {
            diagnostics_.add_error(
                diag::System::Writer,
                "unhandled constant type: " + builder_.FriendlyName(constant.Type()));
            return false;
        });
}

bool GeneratorImpl::EmitLiteral(std::ostream& out, const ast::LiteralExpression* lit) {
    return Switch(
        lit,
        [&](const ast::BoolLiteralExpression* l) {
            out << (l->value ? "true" : "false");
            return true;
        },
        [&](const ast::FloatLiteralExpression* l) {
            PrintF32(out, static_cast<float>(l->value));
            return true;
        },
        [&](const ast::IntLiteralExpression* l) {
            out << l->value;
            if (l->suffix == ast::IntLiteralExpression::Suffix::kU) {
                out << "u";
            }
            return true;
        },
        [&](Default) {
            diagnostics_.add_error(diag::System::Writer, "unknown literal type");
            return false;
        });
}

bool GeneratorImpl::EmitZeroValue(std::ostream& out, const sem::Type* type) {
    if (type->Is<sem::Bool>()) {
        out << "false";
    } else if (type->Is<sem::F32>()) {
        out << "0.0f";
    } else if (type->Is<sem::I32>()) {
        out << "0";
    } else if (type->Is<sem::U32>()) {
        out << "0u";
    } else if (auto* vec = type->As<sem::Vector>()) {
        if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
            return false;
        }
        ScopedParen sp(out);
        for (uint32_t i = 0; i < vec->Width(); i++) {
            if (i != 0) {
                out << ", ";
            }
            if (!EmitZeroValue(out, vec->type())) {
                return false;
            }
        }
    } else if (auto* mat = type->As<sem::Matrix>()) {
        if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kReadWrite, "")) {
            return false;
        }
        ScopedParen sp(out);
        for (uint32_t i = 0; i < (mat->rows() * mat->columns()); i++) {
            if (i != 0) {
                out << ", ";
            }
            if (!EmitZeroValue(out, mat->type())) {
                return false;
            }
        }
    } else if (auto* str = type->As<sem::Struct>()) {
        if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kUndefined, "")) {
            return false;
        }
        bool first = true;
        ScopedParen sp(out);
        for (auto* member : str->Members()) {
            if (!first) {
                out << ", ";
            } else {
                first = false;
            }
            EmitZeroValue(out, member->Type());
        }
    } else if (auto* array = type->As<sem::Array>()) {
        if (!EmitType(out, type, ast::StorageClass::kNone, ast::Access::kUndefined, "")) {
            return false;
        }
        ScopedParen sp(out);
        for (uint32_t i = 0; i < array->Count(); i++) {
            if (i != 0) {
                out << ", ";
            }
            EmitZeroValue(out, array->ElemType());
        }
    } else {
        diagnostics_.add_error(diag::System::Writer, "Invalid type for zero emission: " +
                                                         type->FriendlyName(builder_.Symbols()));
        return false;
    }
    return true;
}

bool GeneratorImpl::EmitLoop(const ast::LoopStatement* stmt) {
    auto emit_continuing = [this, stmt]() {
        if (stmt->continuing && !stmt->continuing->Empty()) {
            if (!EmitBlock(stmt->continuing)) {
                return false;
            }
        }
        return true;
    };

    TINT_SCOPED_ASSIGNMENT(emit_continuing_, emit_continuing);
    line() << "while (true) {";
    {
        ScopedIndent si(this);
        if (!EmitStatements(stmt->body->statements)) {
            return false;
        }
        if (!emit_continuing_()) {
            return false;
        }
    }
    line() << "}";

    return true;
}

bool GeneratorImpl::EmitForLoop(const ast::ForLoopStatement* stmt) {
    // Nest a for loop with a new block. In HLSL the initializer scope is not
    // nested by the for-loop, so we may get variable redefinitions.
    line() << "{";
    increment_indent();
    TINT_DEFER({
        decrement_indent();
        line() << "}";
    });

    TextBuffer init_buf;
    if (auto* init = stmt->initializer) {
        TINT_SCOPED_ASSIGNMENT(current_buffer_, &init_buf);
        if (!EmitStatement(init)) {
            return false;
        }
    }

    TextBuffer cond_pre;
    std::stringstream cond_buf;
    if (auto* cond = stmt->condition) {
        TINT_SCOPED_ASSIGNMENT(current_buffer_, &cond_pre);
        if (!EmitExpression(cond_buf, cond)) {
            return false;
        }
    }

    TextBuffer cont_buf;
    if (auto* cont = stmt->continuing) {
        TINT_SCOPED_ASSIGNMENT(current_buffer_, &cont_buf);
        if (!EmitStatement(cont)) {
            return false;
        }
    }

    // If the for-loop has a multi-statement conditional and / or continuing, then
    // we cannot emit this as a regular for-loop in HLSL. Instead we need to
    // generate a `while(true)` loop.
    bool emit_as_loop = cond_pre.lines.size() > 0 || cont_buf.lines.size() > 1;

    // If the for-loop has multi-statement initializer, or is going to be emitted
    // as a `while(true)` loop, then declare the initializer statement(s) before
    // the loop.
    if (init_buf.lines.size() > 1 || (stmt->initializer && emit_as_loop)) {
        current_buffer_->Append(init_buf);
        init_buf.lines.clear();  // Don't emit the initializer again in the 'for'
    }

    if (emit_as_loop) {
        auto emit_continuing = [&]() {
            current_buffer_->Append(cont_buf);
            return true;
        };

        TINT_SCOPED_ASSIGNMENT(emit_continuing_, emit_continuing);
        line() << "while (true) {";
        increment_indent();
        TINT_DEFER({
            decrement_indent();
            line() << "}";
        });

        if (stmt->condition) {
            current_buffer_->Append(cond_pre);
            line() << "if (!(" << cond_buf.str() << ")) { break; }";
        }

        if (!EmitStatements(stmt->body->statements)) {
            return false;
        }

        if (!emit_continuing_()) {
            return false;
        }
    } else {
        // For-loop can be generated.
        {
            auto out = line();
            out << "for";
            {
                ScopedParen sp(out);

                if (!init_buf.lines.empty()) {
                    out << init_buf.lines[0].content << " ";
                } else {
                    out << "; ";
                }

                out << cond_buf.str() << "; ";

                if (!cont_buf.lines.empty()) {
                    out << TrimSuffix(cont_buf.lines[0].content, ";");
                }
            }
            out << " {";
        }
        {
            auto emit_continuing = [] { return true; };
            TINT_SCOPED_ASSIGNMENT(emit_continuing_, emit_continuing);
            if (!EmitStatementsWithIndent(stmt->body->statements)) {
                return false;
            }
        }
        line() << "}";
    }

    return true;
}

bool GeneratorImpl::EmitWhile(const ast::WhileStatement* stmt) {
    TextBuffer cond_pre;
    std::stringstream cond_buf;
    {
        auto* cond = stmt->condition;
        TINT_SCOPED_ASSIGNMENT(current_buffer_, &cond_pre);
        if (!EmitExpression(cond_buf, cond)) {
            return false;
        }
    }

    auto emit_continuing = [&]() { return true; };
    TINT_SCOPED_ASSIGNMENT(emit_continuing_, emit_continuing);

    // If the whilehas a multi-statement conditional, then we cannot emit this
    // as a regular while in GLSL. Instead we need to generate a `while(true)` loop.
    bool emit_as_loop = cond_pre.lines.size() > 0;
    if (emit_as_loop) {
        line() << "while (true) {";
        increment_indent();
        TINT_DEFER({
            decrement_indent();
            line() << "}";
        });

        current_buffer_->Append(cond_pre);
        line() << "if (!(" << cond_buf.str() << ")) { break; }";

        if (!EmitStatements(stmt->body->statements)) {
            return false;
        }
    } else {
        // While can be generated.
        {
            auto out = line();
            out << "while";
            {
                ScopedParen sp(out);
                out << cond_buf.str();
            }
            out << " {";
        }
        if (!EmitStatementsWithIndent(stmt->body->statements)) {
            return false;
        }
        line() << "}";
    }

    return true;
}

bool GeneratorImpl::EmitMemberAccessor(std::ostream& out,
                                       const ast::MemberAccessorExpression* expr) {
    if (!EmitExpression(out, expr->structure)) {
        return false;
    }
    out << ".";

    // Swizzles output the name directly
    if (builder_.Sem().Get(expr)->Is<sem::Swizzle>()) {
        out << builder_.Symbols().NameFor(expr->member->symbol);
    } else if (!EmitExpression(out, expr->member)) {
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitReturn(const ast::ReturnStatement* stmt) {
    if (stmt->value) {
        auto out = line();
        out << "return ";
        if (!EmitExpression(out, stmt->value)) {
            return false;
        }
        out << ";";
    } else {
        line() << "return;";
    }
    return true;
}

bool GeneratorImpl::EmitStatement(const ast::Statement* stmt) {
    if (auto* a = stmt->As<ast::AssignmentStatement>()) {
        return EmitAssign(a);
    }
    if (auto* b = stmt->As<ast::BlockStatement>()) {
        return EmitBlock(b);
    }
    if (auto* b = stmt->As<ast::BreakStatement>()) {
        return EmitBreak(b);
    }
    if (auto* c = stmt->As<ast::CallStatement>()) {
        auto out = line();
        if (!EmitCall(out, c->expr)) {
            return false;
        }
        out << ";";
        return true;
    }
    if (auto* c = stmt->As<ast::ContinueStatement>()) {
        return EmitContinue(c);
    }
    if (auto* d = stmt->As<ast::DiscardStatement>()) {
        return EmitDiscard(d);
    }
    if (stmt->As<ast::FallthroughStatement>()) {
        line() << "/* fallthrough */";
        return true;
    }
    if (auto* i = stmt->As<ast::IfStatement>()) {
        return EmitIf(i);
    }
    if (auto* l = stmt->As<ast::LoopStatement>()) {
        return EmitLoop(l);
    }
    if (auto* l = stmt->As<ast::ForLoopStatement>()) {
        return EmitForLoop(l);
    }
    if (auto* l = stmt->As<ast::WhileStatement>()) {
        return EmitWhile(l);
    }
    if (auto* r = stmt->As<ast::ReturnStatement>()) {
        return EmitReturn(r);
    }
    if (auto* s = stmt->As<ast::SwitchStatement>()) {
        return EmitSwitch(s);
    }
    if (auto* v = stmt->As<ast::VariableDeclStatement>()) {
        return Switch(
            v->variable,  //
            [&](const ast::Var* var) { return EmitVar(var); },
            [&](const ast::Let* let) { return EmitLet(let); },
            [&](const ast::Const*) {
                return true;  // Constants are embedded at their use
            },
            [&](Default) {  //
                TINT_ICE(Writer, diagnostics_)
                    << "unknown variable type: " << v->variable->TypeInfo().name;
                return false;
            });
    }

    diagnostics_.add_error(diag::System::Writer,
                           "unknown statement type: " + std::string(stmt->TypeInfo().name));
    return false;
}

bool GeneratorImpl::EmitSwitch(const ast::SwitchStatement* stmt) {
    {  // switch(expr) {
        auto out = line();
        out << "switch(";
        if (!EmitExpression(out, stmt->condition)) {
            return false;
        }
        out << ") {";
    }

    {
        ScopedIndent si(this);
        for (auto* s : stmt->body) {
            if (!EmitCase(s)) {
                return false;
            }
        }
    }

    line() << "}";

    return true;
}

bool GeneratorImpl::EmitType(std::ostream& out,
                             const sem::Type* type,
                             ast::StorageClass storage_class,
                             ast::Access access,
                             const std::string& name,
                             bool* name_printed /* = nullptr */) {
    if (name_printed) {
        *name_printed = false;
    }
    switch (storage_class) {
        case ast::StorageClass::kInput: {
            out << "in ";
            break;
        }
        case ast::StorageClass::kOutput: {
            out << "out ";
            break;
        }
        case ast::StorageClass::kUniform:
        case ast::StorageClass::kHandle: {
            out << "uniform ";
            break;
        }
        default:
            break;
    }

    if (auto* ary = type->As<sem::Array>()) {
        const sem::Type* base_type = ary;
        std::vector<uint32_t> sizes;
        while (auto* arr = base_type->As<sem::Array>()) {
            sizes.push_back(arr->Count());
            base_type = arr->ElemType();
        }
        if (!EmitType(out, base_type, storage_class, access, "")) {
            return false;
        }
        if (!name.empty()) {
            out << " " << name;
            if (name_printed) {
                *name_printed = true;
            }
        }
        for (uint32_t size : sizes) {
            if (size > 0) {
                out << "[" << size << "]";
            } else {
                out << "[]";
            }
        }
    } else if (type->Is<sem::Bool>()) {
        out << "bool";
    } else if (type->Is<sem::F32>()) {
        out << "float";
    } else if (type->Is<sem::F16>()) {
        diagnostics_.add_error(diag::System::Writer, "Type f16 is not completely implemented yet.");
        return false;
    } else if (type->Is<sem::I32>()) {
        out << "int";
    } else if (auto* mat = type->As<sem::Matrix>()) {
        TINT_ASSERT(Writer, mat->type()->Is<sem::F32>());
        out << "mat" << mat->columns();
        if (mat->rows() != mat->columns()) {
            out << "x" << mat->rows();
        }
    } else if (type->Is<sem::Pointer>()) {
        TINT_ICE(Writer, diagnostics_)
            << "Attempting to emit pointer type. These should have been removed "
               "with the InlinePointerLets transform";
        return false;
    } else if (type->Is<sem::Sampler>()) {
        return false;
    } else if (auto* str = type->As<sem::Struct>()) {
        out << StructName(str);
    } else if (auto* tex = type->As<sem::Texture>()) {
        if (tex->Is<sem::ExternalTexture>()) {
            TINT_ICE(Writer, diagnostics_) << "Multiplanar external texture transform was not run.";
            return false;
        }

        auto* storage = tex->As<sem::StorageTexture>();
        auto* ms = tex->As<sem::MultisampledTexture>();
        auto* depth_ms = tex->As<sem::DepthMultisampledTexture>();
        auto* sampled = tex->As<sem::SampledTexture>();

        out << "highp ";

        if (storage && storage->access() != ast::Access::kRead) {
            out << "writeonly ";
        }
        auto* subtype = sampled   ? sampled->type()
                        : storage ? storage->type()
                        : ms      ? ms->type()
                                  : nullptr;
        if (!subtype || subtype->Is<sem::F32>()) {
        } else if (subtype->Is<sem::I32>()) {
            out << "i";
        } else if (subtype->Is<sem::U32>()) {
            out << "u";
        } else {
            TINT_ICE(Writer, diagnostics_) << "Unsupported texture type";
            return false;
        }

        out << (storage ? "image" : "sampler");

        switch (tex->dim()) {
            case ast::TextureDimension::k1d:
                out << "1D";
                break;
            case ast::TextureDimension::k2d:
                out << ((ms || depth_ms) ? "2DMS" : "2D");
                break;
            case ast::TextureDimension::k2dArray:
                out << ((ms || depth_ms) ? "2DMSArray" : "2DArray");
                break;
            case ast::TextureDimension::k3d:
                out << "3D";
                break;
            case ast::TextureDimension::kCube:
                out << "Cube";
                break;
            case ast::TextureDimension::kCubeArray:
                out << "CubeArray";
                break;
            default:
                TINT_UNREACHABLE(Writer, diagnostics_)
                    << "unexpected TextureDimension " << tex->dim();
                return false;
        }
        if (tex->Is<sem::DepthTexture>()) {
            out << "Shadow";
        }
    } else if (type->Is<sem::U32>()) {
        out << "uint";
    } else if (auto* vec = type->As<sem::Vector>()) {
        auto width = vec->Width();
        if (vec->type()->Is<sem::F32>() && width >= 1 && width <= 4) {
            out << "vec" << width;
        } else if (vec->type()->Is<sem::I32>() && width >= 1 && width <= 4) {
            out << "ivec" << width;
        } else if (vec->type()->Is<sem::U32>() && width >= 1 && width <= 4) {
            out << "uvec" << width;
        } else if (vec->type()->Is<sem::Bool>() && width >= 1 && width <= 4) {
            out << "bvec" << width;
        } else {
            out << "vector<";
            if (!EmitType(out, vec->type(), storage_class, access, "")) {
                return false;
            }
            out << ", " << width << ">";
        }
    } else if (auto* atomic = type->As<sem::Atomic>()) {
        if (!EmitType(out, atomic->Type(), storage_class, access, name)) {
            return false;
        }
    } else if (type->Is<sem::Void>()) {
        out << "void";
    } else {
        diagnostics_.add_error(diag::System::Writer, "unknown type in EmitType");
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitTypeAndName(std::ostream& out,
                                    const sem::Type* type,
                                    ast::StorageClass storage_class,
                                    ast::Access access,
                                    const std::string& name) {
    bool printed_name = false;
    if (!EmitType(out, type, storage_class, access, name, &printed_name)) {
        return false;
    }
    if (!name.empty() && !printed_name) {
        out << " " << name;
    }
    return true;
}

bool GeneratorImpl::EmitStructType(TextBuffer* b, const sem::Struct* str) {
    auto storage_class_uses = str->StorageClassUsage();
    line(b) << "struct " << StructName(str) << " {";
    EmitStructMembers(b, str, false);
    line(b) << "};";
    line(b);

    return true;
}

bool GeneratorImpl::EmitStructTypeOnce(TextBuffer* buffer, const sem::Struct* str) {
    auto it = emitted_structs_.emplace(str);
    if (!it.second) {
        return true;
    }
    return EmitStructType(buffer, str);
}

bool GeneratorImpl::EmitStructMembers(TextBuffer* b, const sem::Struct* str, bool emit_offsets) {
    ScopedIndent si(b);
    for (auto* mem : str->Members()) {
        auto name = builder_.Symbols().NameFor(mem->Name());

        auto* ty = mem->Type();

        auto out = line(b);

        // Note: offsets are unsupported on GLSL ES.
        if (emit_offsets && version_.IsDesktop() && mem->Offset() != 0) {
            out << "layout(offset=" << mem->Offset() << ") ";
        }
        if (!EmitTypeAndName(out, ty, ast::StorageClass::kNone, ast::Access::kReadWrite, name)) {
            return false;
        }
        out << ";";
    }
    return true;
}

bool GeneratorImpl::EmitUnaryOp(std::ostream& out, const ast::UnaryOpExpression* expr) {
    switch (expr->op) {
        case ast::UnaryOp::kIndirection:
        case ast::UnaryOp::kAddressOf:
            return EmitExpression(out, expr->expr);
        case ast::UnaryOp::kComplement:
            out << "~";
            break;
        case ast::UnaryOp::kNot:
            if (TypeOf(expr)->UnwrapRef()->is_scalar()) {
                out << "!";
            } else {
                out << "not";
            }
            break;
        case ast::UnaryOp::kNegation:
            out << "-";
            break;
    }

    ScopedParen sp(out);
    if (!EmitExpression(out, expr->expr)) {
        return false;
    }

    return true;
}

bool GeneratorImpl::EmitVar(const ast::Var* var) {
    auto* sem = builder_.Sem().Get(var);
    auto* type = sem->Type()->UnwrapRef();

    auto out = line();
    if (!EmitTypeAndName(out, type, sem->StorageClass(), sem->Access(),
                         builder_.Symbols().NameFor(var->symbol))) {
        return false;
    }

    out << " = ";

    if (var->constructor) {
        if (!EmitExpression(out, var->constructor)) {
            return false;
        }
    } else {
        if (!EmitZeroValue(out, type)) {
            return false;
        }
    }
    out << ";";

    return true;
}

bool GeneratorImpl::EmitLet(const ast::Let* let) {
    auto* sem = builder_.Sem().Get(let);
    auto* type = sem->Type()->UnwrapRef();

    auto out = line();
    // TODO(senorblanco): handle const
    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
                         builder_.Symbols().NameFor(let->symbol))) {
        return false;
    }

    out << " = ";

    if (!EmitExpression(out, let->constructor)) {
        return false;
    }

    out << ";";

    return true;
}

bool GeneratorImpl::EmitProgramConstVariable(const ast::Variable* var) {
    auto* sem = builder_.Sem().Get(var);
    auto* type = sem->Type();

    auto out = line();
    out << "const ";
    if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
                         builder_.Symbols().NameFor(var->symbol))) {
        return false;
    }
    out << " = ";
    if (!EmitExpression(out, var->constructor)) {
        return false;
    }
    out << ";";

    return true;
}

bool GeneratorImpl::EmitOverride(const ast::Override* override) {
    auto* sem = builder_.Sem().Get(override);
    auto* type = sem->Type();

    auto* global = sem->As<sem::GlobalVariable>();
    auto const_id = global->ConstantId();

    line() << "#ifndef " << kSpecConstantPrefix << const_id;

    if (override->constructor != nullptr) {
        auto out = line();
        out << "#define " << kSpecConstantPrefix << const_id << " ";
        if (!EmitExpression(out, override->constructor)) {
            return false;
        }
    } else {
        line() << "#error spec constant required for constant id " << const_id;
    }
    line() << "#endif";
    {
        auto out = line();
        out << "const ";
        if (!EmitTypeAndName(out, type, ast::StorageClass::kNone, ast::Access::kUndefined,
                             builder_.Symbols().NameFor(override->symbol))) {
            return false;
        }
        out << " = " << kSpecConstantPrefix << const_id << ";";
    }

    return true;
}

template <typename F>
bool GeneratorImpl::CallBuiltinHelper(std::ostream& out,
                                      const ast::CallExpression* call,
                                      const sem::Builtin* builtin,
                                      F&& build) {
    // Generate the helper function if it hasn't been created already
    auto fn = utils::GetOrCreate(builtins_, builtin, [&]() -> std::string {
        TextBuffer b;
        TINT_DEFER(helpers_.Append(b));

        auto fn_name = UniqueIdentifier(std::string("tint_") + sem::str(builtin->Type()));
        std::vector<std::string> parameter_names;
        {
            auto decl = line(&b);
            if (!EmitTypeAndName(decl, builtin->ReturnType(), ast::StorageClass::kNone,
                                 ast::Access::kUndefined, fn_name)) {
                return "";
            }
            {
                ScopedParen sp(decl);
                for (auto* param : builtin->Parameters()) {
                    if (!parameter_names.empty()) {
                        decl << ", ";
                    }
                    auto param_name = "param_" + std::to_string(parameter_names.size());
                    const auto* ty = param->Type();
                    if (auto* ptr = ty->As<sem::Pointer>()) {
                        decl << "inout ";
                        ty = ptr->StoreType();
                    }
                    if (!EmitTypeAndName(decl, ty, ast::StorageClass::kNone,
                                         ast::Access::kUndefined, param_name)) {
                        return "";
                    }
                    parameter_names.emplace_back(std::move(param_name));
                }
            }
            decl << " {";
        }
        {
            ScopedIndent si(&b);
            if (!build(&b, parameter_names)) {
                return "";
            }
        }
        line(&b) << "}";
        line(&b);
        return fn_name;
    });

    if (fn.empty()) {
        return false;
    }

    // Call the helper
    out << fn;
    {
        ScopedParen sp(out);
        bool first = true;
        for (auto* arg : call->args) {
            if (!first) {
                out << ", ";
            }
            first = false;
            if (!EmitExpression(out, arg)) {
                return false;
            }
        }
    }
    return true;
}

sem::Type* GeneratorImpl::BoolTypeToUint(const sem::Type* type) {
    auto* u32 = builder_.create<sem::U32>();
    if (type->Is<sem::Bool>()) {
        return u32;
    } else if (auto* vec = type->As<sem::Vector>()) {
        return builder_.create<sem::Vector>(u32, vec->Width());
    } else {
        return nullptr;
    }
}

}  // namespace tint::writer::glsl