1 files changed, 121 insertions, 0 deletions
diff --git a/compiler/loco/src/IR/Algorithm.cpp b/compiler/loco/src/IR/Algorithm.cpp
new file mode 100644
index 000000000..712e29975
--- /dev/null
+++ b/compiler/loco/src/IR/Algorithm.cpp
@@ -0,0 +1,121 @@
+/*
+ * 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