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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// -*- mode: C++ -*-
//
// Copyright 2022-2023 Google LLC
//
// Licensed under the Apache License v2.0 with LLVM Exceptions (the
// "License"); you may not use this file except in compliance with the
// License. You may obtain a copy of the License at
//
// https://llvm.org/LICENSE.txt
//
// 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.
//
// Author: Giuliano Procida
#ifndef STG_UNIFICATION_H_
#define STG_UNIFICATION_H_
#include <exception>
#include <unordered_map>
#include <unordered_set>
#include "graph.h"
#include "metrics.h"
#include "substitution.h"
namespace stg {
// Keep track of which nodes are pending substitution and rewrite the graph on
// destruction.
class Unification {
public:
Unification(Graph& graph, Id start, Metrics& metrics)
: graph_(graph),
start_(start),
mapping_(start),
metrics_(metrics),
find_query_(metrics, "unification.find_query"),
find_halved_(metrics, "unification.find_halved"),
union_known_(metrics, "unification.union_known"),
union_unknown_(metrics, "unification.union_unknown") {}
~Unification() {
if (std::uncaught_exceptions() > 0) {
// abort unification
return;
}
// apply substitutions to the entire graph
const Time time(metrics_, "unification.rewrite");
Counter removed(metrics_, "unification.removed");
Counter retained(metrics_, "unification.retained");
auto remap = [&](Id& id) {
Update(id);
};
::stg::Substitute substitute(graph_, remap);
graph_.ForEach(start_, graph_.Limit(), [&](Id id) {
if (Find(id) != id) {
graph_.Remove(id);
++removed;
} else {
substitute(id);
++retained;
}
});
}
void Reserve(Id limit) {
mapping_.Reserve(limit);
}
bool Unify(Id id1, Id id2);
Id Find(Id id) {
++find_query_;
// path halving - tiny performance gain
while (true) {
// note: safe to take references as mapping cannot grow after this
auto& parent = mapping_[id];
if (parent == id) {
return id;
}
auto& parent_parent = mapping_[parent];
if (parent_parent == parent) {
return parent;
}
id = parent = parent_parent;
++find_halved_;
}
}
void Union(Id id1, Id id2) {
// id2 will always be preferred as a parent node; interpreted as a
// substitution, id1 will be replaced by id2
const Id fid1 = Find(id1);
const Id fid2 = Find(id2);
if (fid1 == fid2) {
++union_known_;
return;
}
mapping_[fid1] = fid2;
++union_unknown_;
}
// update id to representative id
void Update(Id& id) {
const Id fid = Find(id);
// avoid silent stores
if (fid != id) {
id = fid;
}
}
private:
Graph& graph_;
Id start_;
DenseIdMapping mapping_;
Metrics& metrics_;
Counter find_query_;
Counter find_halved_;
Counter union_known_;
Counter union_unknown_;
};
} // namespace stg
#endif // STG_UNIFICATION_H_
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