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// Copyright 2021 The Tint Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 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/ast/transform/remove_phonies.h"
#include <memory>
#include <unordered_map>
#include <utility>
#include <vector>
#include "src/tint/ast/traverse_expressions.h"
#include "src/tint/program_builder.h"
#include "src/tint/sem/block_statement.h"
#include "src/tint/sem/function.h"
#include "src/tint/sem/statement.h"
#include "src/tint/sem/variable.h"
#include "src/tint/utils/map.h"
#include "src/tint/utils/scoped_assignment.h"
TINT_INSTANTIATE_TYPEINFO(tint::ast::transform::RemovePhonies);
namespace tint::ast::transform {
namespace {
using SinkSignature = std::vector<const type::Type*>;
} // namespace
RemovePhonies::RemovePhonies() = default;
RemovePhonies::~RemovePhonies() = default;
Transform::ApplyResult RemovePhonies::Apply(const Program* src, const DataMap&, DataMap&) const {
ProgramBuilder b;
CloneContext ctx{&b, src, /* auto_clone_symbols */ true};
auto& sem = src->Sem();
utils::Hashmap<SinkSignature, Symbol, 8, utils::Hasher<SinkSignature>> sinks;
bool made_changes = false;
for (auto* node : src->ASTNodes().Objects()) {
Switch(
node,
[&](const AssignmentStatement* stmt) {
if (stmt->lhs->Is<PhonyExpression>()) {
made_changes = true;
std::vector<const Expression*> side_effects;
if (!TraverseExpressions(
stmt->rhs, b.Diagnostics(), [&](const CallExpression* expr) {
// CallExpression may map to a function or builtin call
// (both may have side-effects), or a value constructor or value
// conversion (both do not have side effects).
auto* call = sem.Get<sem::Call>(expr);
if (!call) {
// Semantic node must be a Materialize, in which case the
// expression was creation-time (compile time), so could not
// have side effects. Just skip.
return TraverseAction::Skip;
}
if (call->Target()->IsAnyOf<sem::Function, sem::Builtin>() &&
call->HasSideEffects()) {
side_effects.push_back(expr);
return TraverseAction::Skip;
}
return TraverseAction::Descend;
})) {
return;
}
if (side_effects.empty()) {
// Phony assignment with no side effects.
// Just remove it.
RemoveStatement(ctx, stmt);
return;
}
if (side_effects.size() == 1) {
if (auto* call_expr = side_effects[0]->As<CallExpression>()) {
// Phony assignment with single call side effect.
auto* call = sem.Get(call_expr)->Unwrap()->As<sem::Call>();
if (call->Target()->MustUse()) {
// Replace phony assignment assignment to uniquely named let.
ctx.Replace<Statement>(stmt, [&, call_expr] { //
auto name = b.Symbols().New("tint_phony");
auto* rhs = ctx.Clone(call_expr);
return b.Decl(b.Let(name, rhs));
});
} else {
// Replace phony assignment with call statement.
ctx.Replace(stmt, [&, call_expr] { //
return b.CallStmt(ctx.Clone(call_expr));
});
}
return;
}
}
// Phony assignment with multiple side effects.
// Generate a call to a placeholder function with the side
// effects as arguments.
ctx.Replace(stmt, [&, side_effects] {
SinkSignature sig;
for (auto* arg : side_effects) {
sig.push_back(sem.GetVal(arg)->Type()->UnwrapRef());
}
auto sink = sinks.GetOrCreate(sig, [&] {
auto name = b.Symbols().New("phony_sink");
utils::Vector<const Parameter*, 8> params;
for (auto* ty : sig) {
auto ast_ty = CreateASTTypeFor(ctx, ty);
params.Push(b.Param("p" + std::to_string(params.Length()), ast_ty));
}
b.Func(name, params, b.ty.void_(), {});
return name;
});
utils::Vector<const Expression*, 8> args;
for (auto* arg : side_effects) {
args.Push(ctx.Clone(arg));
}
return b.CallStmt(b.Call(sink, args));
});
}
},
[&](const CallStatement* stmt) {
// Remove call statements to const value-returning functions.
// TODO(crbug.com/tint/1637): Remove if `stmt->expr` has no side-effects.
auto* sem_expr = sem.Get(stmt->expr);
if ((sem_expr->ConstantValue() != nullptr) && !sem_expr->HasSideEffects()) {
made_changes = true;
ctx.Remove(sem.Get(stmt)->Block()->Declaration()->statements, stmt);
}
});
}
if (!made_changes) {
return SkipTransform;
}
ctx.Clone();
return Program(std::move(b));
}
} // namespace tint::ast::transform