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/*
* Copyright (c) 2019 Samsung Electronics Co., Ltd. All Rights Reserved
*
* 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 "loco/IR/Algorithm.h"
#include <cassert>
#include <set>
#include <stack>
namespace
{
class Frame final
{
public:
Frame(loco::Node *ptr) : _ptr{ptr}, _pos{-1}
{
// DO NOTHING
}
public:
loco::Node *ptr(void) const { return _ptr; }
int64_t pos(void) const { return _pos; }
loco::Node &node(void) const { return *_ptr; }
void advance(void) { _pos += 1; }
private:
loco::Node *_ptr = nullptr;
int64_t _pos = -1;
};
} // namespace
namespace loco
{
// TODO Support cyclic graphs
std::vector<loco::Node *> postorder_traversal(const std::vector<loco::Node *> &roots)
{
std::vector<loco::Node *> res;
std::set<loco::Node *> visited_nodes;
std::stack<Frame> frames;
auto visited = [&visited_nodes](loco::Node *node) {
return visited_nodes.find(node) != visited_nodes.end();
};
// NOTE There is not much difference between "auto" and "auto &" as node is of "loco::Node *"
// type.
for (auto node : roots)
{
assert((node != nullptr) && "root is invalid");
frames.push(Frame{node});
}
while (!frames.empty())
{
auto &top_frame = frames.top();
if (top_frame.pos() == -1)
{
if (visited(top_frame.ptr()))
{
frames.pop();
continue;
}
visited_nodes.insert(top_frame.ptr());
}
top_frame.advance();
assert(top_frame.pos() >= 0);
if (top_frame.pos() < static_cast<int64_t>(top_frame.node().arity()))
{
// Let's visit the next argument
//
// NOTE "next" may be nullptr if a graph is under construction.
if (auto next = top_frame.node().arg(top_frame.pos()))
{
frames.push(Frame{next});
}
}
else
{
// Let's visit the current argument (all the arguments are already visited)
auto curr = top_frame.ptr();
res.emplace_back(curr);
frames.pop();
}
}
return res;
}
std::set<loco::Node *> active_nodes(const std::vector<loco::Node *> &roots)
{
// This implementation works but may be inefficient
//
// TODO Use efficient implementation if necessary
auto nodes = postorder_traversal(roots);
return std::set<loco::Node *>{nodes.begin(), nodes.end()};
}
} // namespace loco
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