fix(graph.cc): fix topo_sort

src/core/graph.cc

@@ -87,48 +87,33 @@ string GraphObj::toString() const {
 }
 
 bool GraphObj::topo_sort() {
-    if (this->sorted)
+    if (this->sorted) {
         return true;
-
-    // std::unordered_set<Tensor> inputs;
-    std::unordered_set<Operator> waiting(this->ops.begin(), this->ops.end());
+    }
     std::vector<Operator> sorted;
-
-    while (!waiting.empty()) {
+    std::unordered_set<OperatorObj *> flags;
+    sorted.reserve(ops.size());
+    flags.reserve(ops.size());
+    while (sorted.size() < ops.size()) {
         // Any node is move to sorted in this loop.
         auto modified = false;
-        // Find head nodes.
-        for (auto it = waiting.begin(); it != waiting.end();) {
-            const auto &this_inputs = (*it)->getInputs();
-            // If none of the input tensors is in waiting list,
-            // this node is a head node.
-            const auto is_head = std::all_of(
-                this_inputs.begin(), this_inputs.end(), [&](const auto &input) {
-                    auto src = input->getSource();
-                    return src // If the source node is in the waiting
-                               // list, means that this node is not the
-                               // head node.
-                               ? waiting.find(src) == waiting.end()
-                               // This tensor has no source node,
-                               // it must be a input tensor.
-                               : (/*inputs.insert(input),*/ true);
-                });
-            // Moves head node to sorted.
-            if (is_head) {
+        for (auto const &op : ops) {
+            if (auto const &inputs = op->getInputs();
+                flags.find(op.get()) == flags.end() &&
+                std::all_of(inputs.begin(), inputs.end(),
+                            [&flags](auto const &input) {
+                                auto ptr = input->getSource().get();
+                                return !ptr || flags.find(ptr) != flags.end();
+                            })) {
                 modified = true;
-                sorted.emplace_back(std::move(*it));
-                it = waiting.erase(it);
-            } else {
-                ++it;
+                sorted.emplace_back(op);
+                flags.insert(op.get());
             }
         }
-        // Waiting list never modifies during a pass,
-        // sorting fails.
         if (!modified) {
             return false;
         }
     }
-    // Done.
     this->ops = std::move(sorted);
     return this->sorted = true;
 }