[serializer] encode recent long-encoded root list items as hot objects.

src/snapshot/serializer.cc

 // Copyright 2016 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/snapshot/serializer.h"
 
 #include "src/macro-assembler.h"
 #include "src/snapshot/natives.h"
 
 namespace v8 {
@@ skipping 122 matching lines @@
            reference.large_object_index() < seen_large_objects_index_;
   } else if (chunk_index == completed_chunks_[space].length()) {
     return reference.chunk_offset() < pending_chunk_[space];
   } else {
     return chunk_index < completed_chunks_[space].length() &&
            reference.chunk_offset() < completed_chunks_[space][chunk_index];
   }
 }
 #endif  // DEBUG
 
-bool Serializer::SerializeKnownObject(HeapObject* obj, HowToCode how_to_code,
-                                      WhereToPoint where_to_point, int skip) {
+bool Serializer::SerializeHotObject(HeapObject* obj, HowToCode how_to_code,
+                                    WhereToPoint where_to_point, int skip) {
   if (how_to_code == kPlain && where_to_point == kStartOfObject) {

[vogelheim, 2016/06/23 13:39:14]

[Feel free to ignore, since this is not even about your CL... :) ]

I was trying to parse the logic here, and stumbled a bit over the control flow.
For methods like these (SerializeHotObject + SerializeBackReference below),
where we effectively have an 'does this even apply?' condition plus the core
work of the method, I find it somewhat easier to read to handle all of the
conditions as early-out conditions at the top.

That's totally a matter of taste, though, and as said, it's not even about your
change... :-/

E.g. SerializeHotObject:
if (! ...how_to_code + where_to_point...)
  return false;
int index = ...
if (index == ...)
  return false;

[work being done]
return true;

[Yang, 2016/06/24 06:00:58]

Done.

     // Encode a reference to a hot object by its index in the working set.
     int index = hot_objects_.Find(obj);
     if (index != HotObjectsList::kNotFound) {
       DCHECK(index >= 0 && index < kNumberOfHotObjects);
       if (FLAG_trace_serializer) {
         PrintF(" Encoding hot object %d:", index);
         obj->ShortPrint();
         PrintF("\n");
       }
       if (skip != 0) {
         sink_.Put(kHotObjectWithSkip + index, "HotObjectWithSkip");
         sink_.PutInt(skip, "HotObjectSkipDistance");
       } else {
         sink_.Put(kHotObject + index, "HotObject");
       }
       return true;
     }
   }
+  return false;
+}
+
+bool Serializer::SerializeBackReference(HeapObject* obj, HowToCode how_to_code,
+                                        WhereToPoint where_to_point, int skip) {
   SerializerReference reference = reference_map_.Lookup(obj);
   if (reference.is_valid()) {
     // Encode the location of an already deserialized object in order to write
     // its location into a later object.  We can encode the location as an
     // offset fromthe start of the deserialized objects or as an offset
     // backwards from thecurrent allocation pointer.
     if (reference.is_attached_reference()) {
       FlushSkip(skip);
       if (FLAG_trace_serializer) {
         PrintF(" Encoding attached reference %d\n",
@@ skipping 40 matching lines @@
     if (skip == 0) {
       sink_.Put(kRootArrayConstants + root_index, "RootConstant");
     } else {
       sink_.Put(kRootArrayConstantsWithSkip + root_index, "RootConstant");
       sink_.PutInt(skip, "SkipInPutRoot");
     }
   } else {
     FlushSkip(skip);
     sink_.Put(kRootArray + how_to_code + where_to_point, "RootSerialization");
     sink_.PutInt(root_index, "root_index");
+    hot_objects_.Add(object);
   }
 }
 
 void Serializer::PutSmi(Smi* smi) {
   sink_.Put(kOnePointerRawData, "Smi");
   byte* bytes = reinterpret_cast<byte*>(&smi);
   for (int i = 0; i < kPointerSize; i++) sink_.Put(bytes[i], "Byte");
 }
 
 void Serializer::PutBackReference(HeapObject* object,
@@ skipping 540 matching lines @@
   if (to_skip != 0 && return_skip == kIgnoringReturn) {
     sink_->Put(kSkip, "Skip");
     sink_->PutInt(to_skip, "SkipDistance");
     to_skip = 0;
   }
   return to_skip;
 }
 
 }  // namespace internal
 }  // namespace v8