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// Copyright 2022 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/transform/preserve_padding.h"
#include <unordered_set>
#include <utility>
#include "src/tint/program_builder.h"
#include "src/tint/sem/struct.h"
#include "src/tint/type/reference.h"
#include "src/tint/utils/map.h"
#include "src/tint/utils/vector.h"
TINT_INSTANTIATE_TYPEINFO(tint::transform::PreservePadding);
using namespace tint::number_suffixes; // NOLINT
namespace tint::transform {
PreservePadding::PreservePadding() = default;
PreservePadding::~PreservePadding() = default;
/// The PIMPL state for the PreservePadding transform
struct PreservePadding::State {
/// Constructor
/// @param src the source Program
explicit State(const Program* src) : ctx{&b, src, /* auto_clone_symbols */ true} {}
/// The main function for the transform.
/// @returns the ApplyResult
ApplyResult Run() {
// Gather a list of assignments that need to be transformed.
std::unordered_set<const ast::AssignmentStatement*> assignments_to_transform;
for (auto* node : ctx.src->ASTNodes().Objects()) {
Switch(
node, //
[&](const ast::AssignmentStatement* assign) {
auto* ty = sem.Get(assign->lhs)->Type();
if (assign->lhs->Is<ast::PhonyExpression>()) {
// Ignore phony assignment.
return;
}
if (ty->As<type::Reference>()->AddressSpace() != ast::AddressSpace::kStorage) {
// We only care about assignments that write to variables in the storage
// address space, as nothing else is host-visible.
return;
}
if (HasPadding(ty->UnwrapRef())) {
// The assigned type has padding bytes, so we need to decompose the writes.
assignments_to_transform.insert(assign);
}
},
[&](const ast::Enable* enable) {
// Check if the full pointer parameters extension is already enabled.
if (enable->extension ==
ast::Extension::kChromiumExperimentalFullPtrParameters) {
ext_enabled = true;
}
});
}
if (assignments_to_transform.empty()) {
return SkipTransform;
}
// Replace all assignments that include padding with decomposed versions.
ctx.ReplaceAll([&](const ast::AssignmentStatement* assign) -> const ast::Statement* {
if (!assignments_to_transform.count(assign)) {
return nullptr;
}
auto* ty = sem.Get(assign->lhs)->Type()->UnwrapRef();
return MakeAssignment(ty, ctx.Clone(assign->lhs), ctx.Clone(assign->rhs));
});
ctx.Clone();
return Program(std::move(b));
}
/// Create a statement that will perform the assignment `lhs = rhs`, creating and using helper
/// functions to decompose the assignment into element-wise copies if needed.
/// @param ty the type of the assignment
/// @param lhs the lhs expression (in the destination program)
/// @param rhs the rhs expression (in the destination program)
/// @returns the statement that performs the assignment
const ast::Statement* MakeAssignment(const type::Type* ty,
const ast::Expression* lhs,
const ast::Expression* rhs) {
if (!HasPadding(ty)) {
// No padding - use a regular assignment.
return b.Assign(lhs, rhs);
}
// Call (and create if necessary) a helper function that assigns a composite using the
// statements in `body`. The helper will have the form:
// fn assign_helper_T(dest : ptr<storage, T, read_write>, value : T) {
// <body>
// }
// It will be called by passing a pointer to the original LHS:
// assign_helper_T(&lhs, rhs);
//
// Since this requires passing pointers to the storage address space, this will also enable
// the chromium_experimental_full_ptr_parameters extension.
constexpr const char* kDestParamName = "dest";
constexpr const char* kValueParamName = "value";
auto call_helper = [&](auto&& body) {
EnableExtension();
auto helper = helpers.GetOrCreate(ty, [&]() {
auto helper_name = b.Symbols().New("assign_and_preserve_padding");
utils::Vector<const ast::Parameter*, 2> params = {
b.Param(kDestParamName,
b.ty.pointer(CreateASTTypeFor(ctx, ty), ast::AddressSpace::kStorage,
ast::Access::kReadWrite)),
b.Param(kValueParamName, CreateASTTypeFor(ctx, ty)),
};
b.Func(helper_name, params, b.ty.void_(), body());
return helper_name;
});
return b.CallStmt(b.Call(helper, b.AddressOf(lhs), rhs));
};
return Switch(
ty, //
[&](const type::Array* arr) {
// Call a helper function that uses a loop to assigns each element separately.
return call_helper([&]() {
utils::Vector<const ast::Statement*, 8> body;
auto* idx = b.Var("i", b.Expr(0_u));
body.Push(
b.For(b.Decl(idx), b.LessThan(idx, u32(arr->ConstantCount().value())),
b.Assign(idx, b.Add(idx, 1_u)),
b.Block(MakeAssignment(arr->ElemType(),
b.IndexAccessor(b.Deref(kDestParamName), idx),
b.IndexAccessor(kValueParamName, idx)))));
return body;
});
},
[&](const sem::Struct* str) {
// Call a helper function that assigns each member separately.
return call_helper([&]() {
utils::Vector<const ast::Statement*, 8> body;
for (auto member : str->Members()) {
auto name = sym.NameFor(member->Declaration()->symbol);
body.Push(MakeAssignment(member->Type(),
b.MemberAccessor(b.Deref(kDestParamName), name),
b.MemberAccessor(kValueParamName, name)));
}
return body;
});
},
[&](Default) {
TINT_ICE(Transform, b.Diagnostics()) << "unhandled type with padding";
return nullptr;
});
}
/// Checks if a type contains padding bytes.
/// @param ty the type to check
/// @returns true if `ty` (or any of its contained types) have padding bytes
bool HasPadding(const type::Type* ty) {
return Switch(
ty, //
[&](const type::Array* arr) {
auto* elem_ty = arr->ElemType();
if (elem_ty->Size() % elem_ty->Align() > 0) {
return true;
}
return HasPadding(elem_ty);
},
[&](const sem::Struct* str) {
uint32_t current_offset = 0;
for (auto* member : str->Members()) {
if (member->Offset() > current_offset) {
return true;
}
if (HasPadding(member->Type())) {
return true;
}
current_offset += member->Type()->Size();
}
return (current_offset < str->Size());
},
[&](Default) { return false; });
}
/// Enable the full pointer parameters extension, if we have not already done so.
void EnableExtension() {
if (!ext_enabled) {
b.Enable(ast::Extension::kChromiumExperimentalFullPtrParameters);
ext_enabled = true;
}
}
private:
/// The program builder
ProgramBuilder b;
/// The clone context
CloneContext ctx;
/// Alias to the semantic info in ctx.src
const sem::Info& sem = ctx.src->Sem();
/// Alias to the symbols in ctx.src
const SymbolTable& sym = ctx.src->Symbols();
/// Flag to track whether we have already enabled the full pointer parameters extension.
bool ext_enabled = false;
/// Map of semantic types to their assignment helper functions.
utils::Hashmap<const type::Type*, Symbol, 8> helpers;
};
Transform::ApplyResult PreservePadding::Apply(const Program* program,
const DataMap&,
DataMap&) const {
return State(program).Run();
}
} // namespace tint::transform