[wasm] Int64Lowering: changing to DFS.

src/compiler/int64-lowering.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/int64-lowering.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node-properties.h"
 
 #include "src/compiler/node.h"
 #include "src/wasm/wasm-module.h"
 #include "src/zone.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 Int64Lowering::Int64Lowering(Graph* graph, MachineOperatorBuilder* machine,
                              CommonOperatorBuilder* common, Zone* zone,
                              Signature<MachineRepresentation>* signature)
     : zone_(zone),
       graph_(graph),
       machine_(machine),
       common_(common),
-      state_(graph, 4),
+      state_(graph, 3),
       stack_(zone),
       replacements_(zone->NewArray<Replacement>(graph->NodeCount())),
       signature_(signature) {
   memset(replacements_, 0, sizeof(Replacement) * graph->NodeCount());
 }
 
 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);
     }
   }
 }
 
 static int GetParameterIndexAfterLowering(
     Signature<MachineRepresentation>* signature, int old_index) {
   int result = old_index;
   for (int i = 0; i < old_index; i++) {
     if (signature->GetParam(i) == MachineRepresentation::kWord64) {
       result++;
@@ skipping 426 matching lines @@
 }
 
 Node* Int64Lowering::GetReplacementHigh(Node* node) {
   Node* result = replacements_[node->id()].high;
   DCHECK(result);
   return result;
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8