[wasm] Int64Lowering: changing to DFS.

src/compiler/int64-lowering.cc

Index: src/compiler/int64-lowering.cc
diff --git a/src/compiler/int64-lowering.cc b/src/compiler/int64-lowering.cc
index 4e592c1256f4fd3062ef0c0d3249b5b7c0fa5aba..71eb7d7d5ecd6c1d951460048b56f1ab776cef41 100644
--- a/src/compiler/int64-lowering.cc
+++ b/src/compiler/int64-lowering.cc
@@ -24,7 +24,7 @@ Int64Lowering::Int64Lowering(Graph* graph, MachineOperatorBuilder* machine,
       graph_(graph),
       machine_(machine),
       common_(common),
-      state_(graph, 4),
+      state_(graph, 3),
       stack_(zone),
       replacements_(zone->NewArray<Replacement>(graph->NodeCount())),
       signature_(signature) {
@@ -35,25 +35,26 @@ void Int64Lowering::LowerGraph() {
   if (!machine()->Is32()) {
     return;
   }
-  stack_.push(graph()->end());
+  stack_.push({graph()->end(), 0});
   state_.Set(graph()->end(), State::kOnStack);
 
   while (!stack_.empty()) {
-    Node* top = stack_.top();
-    if (state_.Get(top) == State::kInputsPushed) {
-      stack_.pop();
-      state_.Set(top, State::kVisited);
+    NodeState top = stack_.top();
+    stack_.pop();

[titzer, 2016/03/14 14:14:13]

You can move the pop into the true branch and drop the re-pushing in the false
branch.

[ahaas, 2016/03/14 14:25:18]

Done.

+    if (top.input_index == top.node->InputCount()) {
+      // if (state_.Get(top) == State::kInputsPushed) {
+      state_.Set(top.node, State::kVisited);
       // All inputs of top have already been reduced, now reduce top.
-      LowerNode(top);
+      LowerNode(top.node);
     } else {
       // Push all children onto the stack.

[titzer, 2016/03/14 14:14:13]

Update comment.

[ahaas, 2016/03/14 14:25:18]

Done.

-      for (Node* input : top->inputs()) {
-        if (state_.Get(input) == State::kUnvisited) {
-          stack_.push(input);
-          state_.Set(input, State::kOnStack);
-        }
+      Node* input = top.node->InputAt(top.input_index);

[titzer, 2016/03/14 14:14:13]

It's ok to through the ++ inside here, too.

[ahaas, 2016/03/14 14:25:18]

Done.

+      top.input_index++;
+      stack_.push(top);
+      if (state_.Get(input) == State::kUnvisited) {
+        stack_.push({input, 0});
+        state_.Set(input, State::kOnStack);
       }
-      state_.Set(top, State::kInputsPushed);
     }
   }
 }