tint/transform: Refactor BuiltinPolyfill transform

Move the bulk of the logic into the State class.
Reduces deep indentation, and likely improves performance by reducing the number of variable that require lambda capture.

Change-Id: I85c87298157f34645d0ae064439bb640f7af7c80
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/123200
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@chromium.org>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>
This commit is contained in:
Ben Clayton 2023-03-08 19:40:09 +00:00 committed by Dawn LUCI CQ
parent 9eff4810c6
commit ce2578bc99
1 changed files with 230 additions and 213 deletions

View File

@ -40,17 +40,100 @@ using BinaryOpSignature = std::tuple<ast::BinaryOp, const type::Type*, const typ
/// PIMPL state for the transform
struct BuiltinPolyfill::State {
/// Constructor
/// @param c the CloneContext
/// @param p the builtins to polyfill
State(CloneContext& c, Builtins p) : ctx(c), polyfill(p) {
/// @param program the source program
/// @param config the transform config
State(const Program* program, const Config& config) : src(program), cfg(config) {
has_full_ptr_params = false;
for (auto* enable : c.src->AST().Enables()) {
for (auto* enable : src->AST().Enables()) {
if (enable->extension == builtin::Extension::kChromiumExperimentalFullPtrParameters) {
has_full_ptr_params = true;
}
}
}
/// Runs the transform
/// @returns the new program or SkipTransform if the transform is not required
Transform::ApplyResult Run() {
for (auto* node : src->ASTNodes().Objects()) {
Switch(
node, //
[&](const ast::CallExpression* expr) { Call(expr); },
[&](const ast::BinaryExpression* bin_op) {
if (auto* s = src->Sem().Get(bin_op);
!s || s->Stage() == sem::EvaluationStage::kConstant ||
s->Stage() == sem::EvaluationStage::kNotEvaluated) {
return; // Don't polyfill @const expressions
}
switch (bin_op->op) {
case ast::BinaryOp::kShiftLeft:
case ast::BinaryOp::kShiftRight: {
if (cfg.builtins.bitshift_modulo) {
ctx.Replace(bin_op,
[this, bin_op] { return BitshiftModulo(bin_op); });
made_changes = true;
}
break;
}
case ast::BinaryOp::kDivide: {
if (cfg.builtins.int_div_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_integer_scalar_or_vector()) {
ctx.Replace(bin_op,
[this, bin_op] { return IntDivMod(bin_op); });
made_changes = true;
}
}
break;
}
case ast::BinaryOp::kModulo: {
if (cfg.builtins.int_div_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_integer_scalar_or_vector()) {
ctx.Replace(bin_op,
[this, bin_op] { return IntDivMod(bin_op); });
made_changes = true;
}
}
if (cfg.builtins.precise_float_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_float_scalar_or_vector()) {
ctx.Replace(bin_op,
[this, bin_op] { return PreciseFloatMod(bin_op); });
made_changes = true;
}
}
break;
}
default:
break;
}
},
[&](const ast::Expression* expr) {
if (cfg.builtins.bgra8unorm) {
if (auto* ty_expr = src->Sem().Get<sem::TypeExpression>(expr)) {
if (auto* tex = ty_expr->Type()->As<type::StorageTexture>()) {
if (tex->texel_format() == builtin::TexelFormat::kBgra8Unorm) {
ctx.Replace(expr, [this, tex] {
return ctx.dst->Expr(ctx.dst->ty.storage_texture(
tex->dim(), builtin::TexelFormat::kRgba8Unorm,
tex->access()));
});
made_changes = true;
}
}
}
}
});
}
if (!made_changes) {
return SkipTransform;
}
ctx.Clone();
return Program(std::move(b));
}
////////////////////////////////////////////////////////////////////////////
// Function polyfills
////////////////////////////////////////////////////////////////////////////
@ -71,7 +154,7 @@ struct BuiltinPolyfill::State {
};
utils::Vector<const ast::Statement*, 4> body;
switch (polyfill.acosh) {
switch (cfg.builtins.acosh) {
case Level::kFull:
// return log(x + sqrt(x*x - 1));
body.Push(b.Return(
@ -85,7 +168,7 @@ struct BuiltinPolyfill::State {
}
default:
TINT_ICE(Transform, b.Diagnostics())
<< "unhandled polyfill level: " << static_cast<int>(polyfill.acosh);
<< "unhandled polyfill level: " << static_cast<int>(cfg.builtins.acosh);
return {};
}
@ -125,7 +208,7 @@ struct BuiltinPolyfill::State {
};
utils::Vector<const ast::Statement*, 1> body;
switch (polyfill.atanh) {
switch (cfg.builtins.atanh) {
case Level::kFull:
// return log((1+x) / (1-x)) * 0.5
body.Push(
@ -138,7 +221,7 @@ struct BuiltinPolyfill::State {
break;
default:
TINT_ICE(Transform, b.Diagnostics())
<< "unhandled polyfill level: " << static_cast<int>(polyfill.acosh);
<< "unhandled polyfill level: " << static_cast<int>(cfg.builtins.acosh);
return {};
}
@ -306,7 +389,7 @@ struct BuiltinPolyfill::State {
b.Decl(b.Let("e", b.Call("min", u32(W), b.Add("s", "count")))),
};
switch (polyfill.extract_bits) {
switch (cfg.builtins.extract_bits) {
case Level::kFull:
body.Push(b.Decl(b.Let("shl", b.Sub(u32(W), "e"))));
body.Push(b.Decl(b.Let("shr", b.Add("shl", "s"))));
@ -328,7 +411,7 @@ struct BuiltinPolyfill::State {
break;
default:
TINT_ICE(Transform, b.Diagnostics())
<< "unhandled polyfill level: " << static_cast<int>(polyfill.extract_bits);
<< "unhandled polyfill level: " << static_cast<int>(cfg.builtins.extract_bits);
return {};
}
@ -532,7 +615,7 @@ struct BuiltinPolyfill::State {
utils::Vector<const ast::Statement*, 8> body;
switch (polyfill.insert_bits) {
switch (cfg.builtins.insert_bits) {
case Level::kFull:
// let e = offset + count;
body.Push(b.Decl(b.Let("e", b.Add("offset", "count"))));
@ -566,7 +649,7 @@ struct BuiltinPolyfill::State {
break;
default:
TINT_ICE(Transform, b.Diagnostics())
<< "unhandled polyfill level: " << static_cast<int>(polyfill.insert_bits);
<< "unhandled polyfill level: " << static_cast<int>(cfg.builtins.insert_bits);
return {};
}
@ -727,8 +810,8 @@ struct BuiltinPolyfill::State {
/// @param bin_op the original BinaryExpression
/// @return the polyfill value for bitshift operation
const ast::Expression* BitshiftModulo(const ast::BinaryExpression* bin_op) {
auto* lhs_ty = ctx.src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = ctx.src->TypeOf(bin_op->rhs)->UnwrapRef();
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = src->TypeOf(bin_op->rhs)->UnwrapRef();
auto* lhs_el_ty = type::Type::DeepestElementOf(lhs_ty);
const ast::Expression* mask = b.Expr(AInt(lhs_el_ty->Size() * 8 - 1));
if (rhs_ty->Is<type::Vector>()) {
@ -744,8 +827,8 @@ struct BuiltinPolyfill::State {
/// @param bin_op the original BinaryExpression
/// @return the polyfill divide or modulo
const ast::Expression* IntDivMod(const ast::BinaryExpression* bin_op) {
auto* lhs_ty = ctx.src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = ctx.src->TypeOf(bin_op->rhs)->UnwrapRef();
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = src->TypeOf(bin_op->rhs)->UnwrapRef();
BinaryOpSignature sig{bin_op->op, lhs_ty, rhs_ty};
auto fn = binary_op_polyfills.GetOrCreate(sig, [&] {
const bool is_div = bin_op->op == ast::BinaryOp::kDivide;
@ -839,8 +922,8 @@ struct BuiltinPolyfill::State {
/// @param bin_op the original BinaryExpression
/// @return the polyfill divide or modulo
const ast::Expression* PreciseFloatMod(const ast::BinaryExpression* bin_op) {
auto* lhs_ty = ctx.src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = ctx.src->TypeOf(bin_op->rhs)->UnwrapRef();
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
auto* rhs_ty = src->TypeOf(bin_op->rhs)->UnwrapRef();
BinaryOpSignature sig{bin_op->op, lhs_ty, rhs_ty};
auto fn = binary_op_polyfills.GetOrCreate(sig, [&] {
uint32_t lhs_width = 1;
@ -888,23 +971,27 @@ struct BuiltinPolyfill::State {
}
private:
/// The clone context
CloneContext& ctx;
/// The builtins to polyfill
Builtins polyfill;
/// The source program
Program const* const src;
/// The transform config
const Config& cfg;
/// The destination program builder
ProgramBuilder& b = *ctx.dst;
ProgramBuilder b;
/// The clone context
CloneContext ctx{&b, src};
/// The source clone context
const sem::Info& sem = ctx.src->Sem();
// Polyfill functions for binary operators.
const sem::Info& sem = src->Sem();
/// Polyfill functions for binary operators.
utils::Hashmap<BinaryOpSignature, Symbol, 8> binary_op_polyfills;
/// Polyfill builtins.
utils::Hashmap<const sem::Builtin*, Symbol, 8> builtin_polyfills;
// Tracks whether the chromium_experimental_full_ptr_parameters extension has been enabled.
bool has_full_ptr_params;
bool has_full_ptr_params = false;
/// True if the transform has made changes (i.e. the program needs cloning)
bool made_changes = false;
/// @returns the AST type for the given sem type
ast::Type T(const type::Type* ty) const { return CreateASTTypeFor(ctx, ty); }
ast::Type T(const type::Type* ty) { return CreateASTTypeFor(ctx, ty); }
/// @returns 1 if `ty` is not a vector, otherwise the vector width
uint32_t WidthOf(const type::Type* ty) const {
@ -917,7 +1004,7 @@ struct BuiltinPolyfill::State {
/// @returns a scalar or vector with the given width, with each element with
/// the given value.
template <typename T>
const ast::Expression* ScalarOrVector(uint32_t width, T value) const {
const ast::Expression* ScalarOrVector(uint32_t width, T value) {
if (width == 1) {
return b.Expr(value);
}
@ -931,158 +1018,144 @@ struct BuiltinPolyfill::State {
}
return b.Call(b.ty.vec<To>(width), e);
}
};
BuiltinPolyfill::BuiltinPolyfill() = default;
BuiltinPolyfill::~BuiltinPolyfill() = default;
Transform::ApplyResult BuiltinPolyfill::Apply(const Program* src,
const DataMap& data,
DataMap&) const {
auto* cfg = data.Get<Config>();
if (!cfg) {
return SkipTransform;
}
auto& polyfill = cfg->builtins;
utils::Hashmap<const sem::Builtin*, Symbol, 8> builtin_polyfills;
ProgramBuilder b;
CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
State s{ctx, polyfill};
bool made_changes = false;
for (auto* node : src->ASTNodes().Objects()) {
Switch(
node,
[&](const ast::CallExpression* expr) {
auto* call = src->Sem().Get(expr)->UnwrapMaterialize()->As<sem::Call>();
if (!call || call->Stage() == sem::EvaluationStage::kConstant ||
call->Stage() == sem::EvaluationStage::kNotEvaluated) {
return; // Don't polyfill @const expressions
}
auto* builtin = call->Target()->As<sem::Builtin>();
if (!builtin) {
return;
}
Symbol fn;
/// Examines the call expression @p expr, applying any necessary polyfill transforms
void Call(const ast::CallExpression* expr) {
auto* call = src->Sem().Get(expr)->UnwrapMaterialize()->As<sem::Call>();
if (!call || call->Stage() == sem::EvaluationStage::kConstant ||
call->Stage() == sem::EvaluationStage::kNotEvaluated) {
return; // Don't polyfill @const expressions
}
Symbol fn = Switch(
call->Target(), //
[&](const sem::Builtin* builtin) {
switch (builtin->Type()) {
case sem::BuiltinType::kAcosh:
if (polyfill.acosh != Level::kNone) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.acosh(builtin->ReturnType()); });
if (cfg.builtins.acosh != Level::kNone) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return acosh(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kAsinh:
if (polyfill.asinh) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.asinh(builtin->ReturnType()); });
if (cfg.builtins.asinh) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return asinh(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kAtanh:
if (polyfill.atanh != Level::kNone) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.atanh(builtin->ReturnType()); });
if (cfg.builtins.atanh != Level::kNone) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return atanh(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kClamp:
if (polyfill.clamp_int) {
if (cfg.builtins.clamp_int) {
auto& sig = builtin->Signature();
if (sig.parameters[0]->Type()->is_integer_scalar_or_vector()) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.clampInteger(builtin->ReturnType()); });
return builtin_polyfills.GetOrCreate(
builtin, [&] { return clampInteger(builtin->ReturnType()); });
}
}
break;
return Symbol{};
case sem::BuiltinType::kCountLeadingZeros:
if (polyfill.count_leading_zeros) {
fn = builtin_polyfills.GetOrCreate(builtin, [&] {
return s.countLeadingZeros(builtin->ReturnType());
});
if (cfg.builtins.count_leading_zeros) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return countLeadingZeros(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kCountTrailingZeros:
if (polyfill.count_trailing_zeros) {
fn = builtin_polyfills.GetOrCreate(builtin, [&] {
return s.countTrailingZeros(builtin->ReturnType());
});
if (cfg.builtins.count_trailing_zeros) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return countTrailingZeros(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kExtractBits:
if (polyfill.extract_bits != Level::kNone) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.extractBits(builtin->ReturnType()); });
if (cfg.builtins.extract_bits != Level::kNone) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return extractBits(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kFirstLeadingBit:
if (polyfill.first_leading_bit) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.firstLeadingBit(builtin->ReturnType()); });
if (cfg.builtins.first_leading_bit) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return firstLeadingBit(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kFirstTrailingBit:
if (polyfill.first_trailing_bit) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.firstTrailingBit(builtin->ReturnType()); });
if (cfg.builtins.first_trailing_bit) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return firstTrailingBit(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kInsertBits:
if (polyfill.insert_bits != Level::kNone) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.insertBits(builtin->ReturnType()); });
if (cfg.builtins.insert_bits != Level::kNone) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return insertBits(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kReflect:
// Only polyfill for vec2<f32>. See https://crbug.com/tint/1798 for more
// details.
if (polyfill.reflect_vec2_f32) {
// Only polyfill for vec2<f32>. See https://crbug.com/tint/1798 for
// more details.
if (cfg.builtins.reflect_vec2_f32) {
auto& sig = builtin->Signature();
auto* vec = sig.return_type->As<type::Vector>();
if (vec && vec->Width() == 2 && vec->type()->Is<type::F32>()) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.reflect(builtin->ReturnType()); });
return builtin_polyfills.GetOrCreate(
builtin, [&] { return reflect(builtin->ReturnType()); });
}
}
break;
return Symbol{};
case sem::BuiltinType::kSaturate:
if (polyfill.saturate) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.saturate(builtin->ReturnType()); });
if (cfg.builtins.saturate) {
return builtin_polyfills.GetOrCreate(
builtin, [&] { return saturate(builtin->ReturnType()); });
}
break;
return Symbol{};
case sem::BuiltinType::kSign:
if (polyfill.sign_int) {
if (cfg.builtins.sign_int) {
auto* ty = builtin->ReturnType();
if (ty->is_signed_integer_scalar_or_vector()) {
fn = builtin_polyfills.GetOrCreate(builtin,
[&] { return s.sign_int(ty); });
return builtin_polyfills.GetOrCreate(builtin,
[&] { return sign_int(ty); });
}
}
break;
return Symbol{};
case sem::BuiltinType::kTextureSampleBaseClampToEdge:
if (polyfill.texture_sample_base_clamp_to_edge_2d_f32) {
if (cfg.builtins.texture_sample_base_clamp_to_edge_2d_f32) {
auto& sig = builtin->Signature();
auto* tex = sig.Parameter(sem::ParameterUsage::kTexture);
if (auto* stex = tex->Type()->As<type::SampledTexture>()) {
if (stex->type()->Is<type::F32>()) {
fn = builtin_polyfills.GetOrCreate(builtin, [&] {
return s.textureSampleBaseClampToEdge_2d_f32();
return builtin_polyfills.GetOrCreate(builtin, [&] {
return textureSampleBaseClampToEdge_2d_f32();
});
}
}
}
break;
return Symbol{};
case sem::BuiltinType::kTextureStore:
if (polyfill.bgra8unorm) {
if (cfg.builtins.bgra8unorm) {
auto& sig = builtin->Signature();
auto* tex = sig.Parameter(sem::ParameterUsage::kTexture);
if (auto* stex = tex->Type()->As<type::StorageTexture>()) {
if (stex->texel_format() == builtin::TexelFormat::kBgra8Unorm) {
size_t value_idx = static_cast<size_t>(
sig.IndexOf(sem::ParameterUsage::kValue));
ctx.Replace(expr, [&ctx, expr, value_idx] {
ctx.Replace(expr, [this, expr, value_idx] {
utils::Vector<const ast::Expression*, 3> args;
for (auto* arg : expr->args) {
arg = ctx.Clone(arg);
@ -1099,106 +1172,50 @@ Transform::ApplyResult BuiltinPolyfill::Apply(const Program* src,
}
}
}
break;
return Symbol{};
case sem::BuiltinType::kQuantizeToF16:
if (polyfill.quantize_to_vec_f16) {
if (cfg.builtins.quantize_to_vec_f16) {
if (auto* vec = builtin->ReturnType()->As<type::Vector>()) {
fn = builtin_polyfills.GetOrCreate(
builtin, [&] { return s.quantizeToF16(vec); });
return builtin_polyfills.GetOrCreate(
builtin, [&] { return quantizeToF16(vec); });
}
}
break;
return Symbol{};
case sem::BuiltinType::kWorkgroupUniformLoad:
if (polyfill.workgroup_uniform_load) {
fn = builtin_polyfills.GetOrCreate(builtin, [&] {
return s.workgroupUniformLoad(builtin->ReturnType());
if (cfg.builtins.workgroup_uniform_load) {
return builtin_polyfills.GetOrCreate(builtin, [&] {
return workgroupUniformLoad(builtin->ReturnType());
});
}
break;
return Symbol{};
default:
break;
}
if (fn.IsValid()) {
ctx.Replace(call->Declaration(), [&ctx, fn, expr] {
return ctx.dst->Call(fn, ctx.Clone(expr->args));
});
made_changes = true;
}
},
[&](const ast::BinaryExpression* bin_op) {
if (auto* sem = src->Sem().Get(bin_op);
!sem || sem->Stage() == sem::EvaluationStage::kConstant ||
sem->Stage() == sem::EvaluationStage::kNotEvaluated) {
return; // Don't polyfill @const expressions
}
switch (bin_op->op) {
case ast::BinaryOp::kShiftLeft:
case ast::BinaryOp::kShiftRight: {
if (polyfill.bitshift_modulo) {
ctx.Replace(bin_op, [bin_op, &s] { return s.BitshiftModulo(bin_op); });
made_changes = true;
}
break;
}
case ast::BinaryOp::kDivide: {
if (polyfill.int_div_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_integer_scalar_or_vector()) {
ctx.Replace(bin_op, [bin_op, &s] { return s.IntDivMod(bin_op); });
made_changes = true;
}
}
break;
}
case ast::BinaryOp::kModulo: {
if (polyfill.int_div_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_integer_scalar_or_vector()) {
ctx.Replace(bin_op, [bin_op, &s] { return s.IntDivMod(bin_op); });
made_changes = true;
}
}
if (polyfill.precise_float_mod) {
auto* lhs_ty = src->TypeOf(bin_op->lhs)->UnwrapRef();
if (lhs_ty->is_float_scalar_or_vector()) {
ctx.Replace(bin_op,
[bin_op, &s] { return s.PreciseFloatMod(bin_op); });
made_changes = true;
}
}
break;
}
default:
break;
}
},
[&](const ast::Expression* expr) {
if (polyfill.bgra8unorm) {
if (auto* ty_expr = src->Sem().Get<sem::TypeExpression>(expr)) {
if (auto* tex = ty_expr->Type()->As<type::StorageTexture>()) {
if (tex->texel_format() == builtin::TexelFormat::kBgra8Unorm) {
ctx.Replace(expr, [&ctx, tex] {
return ctx.dst->Expr(ctx.dst->ty.storage_texture(
tex->dim(), builtin::TexelFormat::kRgba8Unorm,
tex->access()));
});
made_changes = true;
}
}
}
return Symbol{};
}
});
}
if (!made_changes) {
if (fn.IsValid()) {
ctx.Replace(call->Declaration(),
[this, fn, expr] { return ctx.dst->Call(fn, ctx.Clone(expr->args)); });
made_changes = true;
}
}
};
BuiltinPolyfill::BuiltinPolyfill() = default;
BuiltinPolyfill::~BuiltinPolyfill() = default;
Transform::ApplyResult BuiltinPolyfill::Apply(const Program* src,
const DataMap& data,
DataMap&) const {
auto* cfg = data.Get<Config>();
if (!cfg) {
return SkipTransform;
}
ctx.Clone();
return Program(std::move(b));
return State{src, *cfg}.Run();
}
BuiltinPolyfill::Config::Config(const Builtins& b) : builtins(b) {}