Replace C++ bitfields with our own BitFields

src/heap-snapshot-generator.h

 // 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.
 
 #ifndef V8_HEAP_SNAPSHOT_GENERATOR_H_
 #define V8_HEAP_SNAPSHOT_GENERATOR_H_
 
 #include "src/profile-generator-inl.h"
 
 namespace v8 {
@@ skipping 10 matching lines @@
   enum Type {
     kContextVariable = v8::HeapGraphEdge::kContextVariable,
     kElement = v8::HeapGraphEdge::kElement,
     kProperty = v8::HeapGraphEdge::kProperty,
     kInternal = v8::HeapGraphEdge::kInternal,
     kHidden = v8::HeapGraphEdge::kHidden,
     kShortcut = v8::HeapGraphEdge::kShortcut,
     kWeak = v8::HeapGraphEdge::kWeak
   };
 
-  HeapGraphEdge() { }
   HeapGraphEdge(Type type, const char* name, int from, int to);
   HeapGraphEdge(Type type, int index, int from, int to);
   void ReplaceToIndexWithEntry(HeapSnapshot* snapshot);
 
-  Type type() const { return static_cast<Type>(type_); }
+  Type type() const { return TypeField::decode(bit_field_); }
   int index() const {
-    DCHECK(type_ == kElement || type_ == kHidden);
+    DCHECK(type() == kElement || type() == kHidden);
     return index_;
   }
   const char* name() const {
-    DCHECK(type_ == kContextVariable
-        || type_ == kProperty
-        || type_ == kInternal
-        || type_ == kShortcut
-        || type_ == kWeak);
+    DCHECK(type() == kContextVariable || type() == kProperty ||
+           type() == kInternal || type() == kShortcut || type() == kWeak);
     return name_;
   }
   INLINE(HeapEntry* from() const);
   HeapEntry* to() const { return to_entry_; }
 
  private:
   INLINE(HeapSnapshot* snapshot() const);
+  int from_index() const { return FromIndexField::decode(bit_field_); }
 
-  unsigned type_ : 3;
-  int from_index_ : 29;

[brucedawson, 2014/11/05 01:33:17]

FWIW, I believe that this usage of bit fields is portable. Certainly VC++
handles it fine.

+  class TypeField : public BitField<Type, 0, 3> {};
+  class FromIndexField : public BitField<int, 3, 29> {};
+  uint32_t bit_field_;
   union {
     // During entries population |to_index_| is used for storing the index,
     // afterwards it is replaced with a pointer to the entry.
     int to_index_;
     HeapEntry* to_entry_;
   };
   union {
     int index_;
     const char* name_;
   };
@@ skipping 534 matching lines @@
   friend class HeapSnapshotJSONSerializerEnumerator;
   friend class HeapSnapshotJSONSerializerIterator;
 
   DISALLOW_COPY_AND_ASSIGN(HeapSnapshotJSONSerializer);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_SNAPSHOT_GENERATOR_H_