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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/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::transform::RemovePhonies);
namespace tint::transform {
namespace {
using SinkSignature = std::vector<const sem::Type*>;
} // namespace
RemovePhonies::RemovePhonies() = default;
RemovePhonies::~RemovePhonies() = default;
bool RemovePhonies::ShouldRun(const Program* program, const DataMap&) const {
for (auto* node : program->ASTNodes().Objects()) {
if (node->Is<ast::PhonyExpression>()) {
return true;
}
if (auto* stmt = node->As<ast::CallStatement>()) {
if (program->Sem().Get(stmt->expr)->ConstantValue() != nullptr) {
return true;
}
}
}
return false;
}
void RemovePhonies::Run(CloneContext& ctx, const DataMap&, DataMap&) const {
auto& sem = ctx.src->Sem();
std::unordered_map<SinkSignature, Symbol, utils::Hasher<SinkSignature>> sinks;
for (auto* node : ctx.src->ASTNodes().Objects()) {
Switch(
node,
[&](const ast::AssignmentStatement* stmt) {
if (stmt->lhs->Is<ast::PhonyExpression>()) {
std::vector<const ast::Expression*> side_effects;
if (!ast::TraverseExpressions(
stmt->rhs, ctx.dst->Diagnostics(),
[&](const ast::CallExpression* expr) {
// ast::CallExpression may map to a function or builtin call
// (both may have side-effects), or a type constructor or
// type 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 ast::TraverseAction::Skip;
}
if (call->Target()->IsAnyOf<sem::Function, sem::Builtin>() &&
call->HasSideEffects()) {
side_effects.push_back(expr);
return ast::TraverseAction::Skip;
}
return ast::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 = side_effects[0]->As<ast::CallExpression>()) {
// Phony assignment with single call side effect.
// Replace phony assignment with call.
ctx.Replace(stmt,
[&, call] { return ctx.dst->CallStmt(ctx.Clone(call)); });
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.Get(arg)->Type()->UnwrapRef());
}
auto sink = utils::GetOrCreate(sinks, sig, [&] {
auto name = ctx.dst->Symbols().New("phony_sink");
utils::Vector<const ast::Parameter*, 8> params;
for (auto* ty : sig) {
auto* ast_ty = CreateASTTypeFor(ctx, ty);
params.Push(
ctx.dst->Param("p" + std::to_string(params.Length()), ast_ty));
}
ctx.dst->Func(name, params, ctx.dst->ty.void_(), {});
return name;
});
utils::Vector<const ast::Expression*, 8> args;
for (auto* arg : side_effects) {
args.Push(ctx.Clone(arg));
}
return ctx.dst->CallStmt(ctx.dst->Call(sink, args));
});
}
},
[&](const ast::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()) {
ctx.Remove(sem.Get(stmt)->Block()->Declaration()->statements, stmt);
}
});
}
ctx.Clone();
}
} // namespace tint::transform