[turbofan] add more comments to compiler/graph-visualizer.cc.

src/compiler/graph-visualizer.cc

 // Copyright 2013 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/graph-visualizer.h"
 
 #include <sstream>
 #include <string>
 
 #include "src/code-stubs.h"
@@ skipping 600 matching lines @@
   return os;
 }
 
 const int kUnvisited = 0;
 const int kOnStack = 1;
 const int kVisited = 2;
 
 std::ostream& operator<<(std::ostream& os, const AsRPO& ar) {
   base::AccountingAllocator allocator;
   Zone local_zone(&allocator);
+
+  // Do a post-order depth-first search on the RPO graph. For every node,
+  // print:
+  //
+  //   - the node id
+  //   - the operator mnemonic
+  //   - in square brackets its parameter (if present)
+  //   - in parentheses the list of argument ids and their mnemonics
+  //   - the node type (if it is typed)
+
+  // Post-order guarantees that all inputs of a node will be printed before
+  // the node itself.

[Jarin, 2016/06/07 19:35:31]

Maybe you should hedge with "(if possible, cycles are broken arbitrarily)"

[bgeron, 2016/06/08 12:04:56]

Done.

+
   ZoneVector<byte> state(ar.graph.NodeCount(), kUnvisited, &local_zone);
   ZoneStack<Node*> stack(&local_zone);
 
   stack.push(ar.graph.end());
   state[ar.graph.end()->id()] = kOnStack;
   while (!stack.empty()) {
     Node* n = stack.top();
     bool pop = true;
     for (Node* const i : n->inputs()) {
       if (state[i->id()] == kUnvisited) {
         state[i->id()] = kOnStack;
         stack.push(i);
         pop = false;
         break;
       }
     }
     if (pop) {
       state[n->id()] = kVisited;
       stack.pop();
       os << "#" << n->id() << ":" << *n->op() << "(";
+      // Print the arguments

[Jarin, 2016/06/07 19:35:31]

arguments -> inputs.

Please end sentences in comments with dots (here and below).

[bgeron, 2016/06/08 12:04:56]

Done.

       int j = 0;
       for (Node* const i : n->inputs()) {
         if (j++ > 0) os << ", ";
         os << "#" << SafeId(i) << ":" << SafeMnemonic(i);
       }
       os << ")";
+      // Print the node type, if any
       if (NodeProperties::IsTyped(n)) {
         os << "  [Type: ";
         NodeProperties::GetType(n)->PrintTo(os);
         os << "]";
       }
       os << std::endl;
     }
   }
   return os;
 }
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8