Add FLAG_trace_maps

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 9333e9edc4003e2dd7a9f4bb7884eb6645ed2d6e..cb7b351d6dfd2f031ac867451dd094d09e547ce8 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2049,7 +2049,8 @@ class JSObject: public JSReceiver {
   // an initial capacity for holding these properties.
   static void NormalizeProperties(Handle<JSObject> object,
                                   PropertyNormalizationMode mode,
-                                  int expected_additional_properties);
+                                  int expected_additional_properties,
+                                  const char* reason);
 
   // Convert and update the elements backing store to be a
   // SeededNumberDictionary dictionary.  Returns the backing after conversion.
@@ -2058,7 +2059,7 @@ class JSObject: public JSReceiver {
 
   // Transform slow named properties to fast variants.
   static void MigrateSlowToFast(Handle<JSObject> object,
-                                int unused_property_fields);
+                                int unused_property_fields, const char* reason);
 
   // Access fast-case object properties at index.
   static Handle<Object> FastPropertyAt(Handle<JSObject> object,
@@ -5878,7 +5879,8 @@ class Map: public HeapObject {
                                             int descriptor_number,
                                             Handle<Object> value);
 
-  static Handle<Map> Normalize(Handle<Map> map, PropertyNormalizationMode mode);
+  static Handle<Map> Normalize(Handle<Map> map, PropertyNormalizationMode mode,
+                               const char* reason);
 
   // Returns the constructor name (the name (possibly, inferred name) of the
   // function that was used to instantiate the object).
@@ -6087,7 +6089,7 @@ class Map: public HeapObject {
 
   // Returns a copy of the map, with all transitions dropped from the
   // instance descriptors.
-  static Handle<Map> Copy(Handle<Map> map);
+  static Handle<Map> Copy(Handle<Map> map, const char* reason);
   static Handle<Map> Create(Isolate* isolate, int inobject_properties);
 
   // Returns the next free property index (only valid for FAST MODE).
@@ -6315,6 +6317,11 @@ class Map: public HeapObject {
   // The "shared" flags of both this map and |other| are ignored.
   bool EquivalentToForNormalization(Map* other, PropertyNormalizationMode mode);
 
+#if TRACE_MAPS
+  static void TraceTransition(const char* what, Map* from, Map* to, Name* name);
+  static void TraceAllTransitions(Map* map);
+#endif
+
  private:
   static void ConnectElementsTransition(Handle<Map> parent, Handle<Map> child);
   static void ConnectTransition(Handle<Map> parent, Handle<Map> child,
@@ -6336,6 +6343,7 @@ class Map: public HeapObject {
                                             Handle<DescriptorArray> descriptors,
                                             TransitionFlag flag,
                                             MaybeHandle<Name> maybe_name,
+                                            const char* reason,
                                             SimpleTransitionFlag simple_flag);
   static Handle<Map> CopyReplaceDescriptor(Handle<Map> map,
                                            Handle<DescriptorArray> descriptors,
@@ -6709,6 +6717,13 @@ class SharedFunctionInfo: public HeapObject {
   // available.
   DECL_ACCESSORS(feedback_vector, TypeFeedbackVector)
 
+#if TRACE_MAPS
+  // [unique_id] - For --trace-maps purposes, an identifier that's persistent
+  // even if the GC moves this SharedFunctionInfo.
+  inline int unique_id() const;
+  inline void set_unique_id(int value);
+#endif
+
   // [instance class name]: class name for instances.
   DECL_ACCESSORS(instance_class_name, Object)
 
@@ -6955,10 +6970,16 @@ class SharedFunctionInfo: public HeapObject {
   static const int kInferredNameOffset = kDebugInfoOffset + kPointerSize;
   static const int kFeedbackVectorOffset =
       kInferredNameOffset + kPointerSize;
+#if TRACE_MAPS
+  static const int kUniqueIdOffset = kFeedbackVectorOffset + kPointerSize;
+  static const int kLastPointerFieldOffset = kUniqueIdOffset;
+#else
+  static const int kLastPointerFieldOffset = kFeedbackVectorOffset;
+#endif
+
 #if V8_HOST_ARCH_32_BIT
   // Smi fields.
-  static const int kLengthOffset =
-      kFeedbackVectorOffset + kPointerSize;
+  static const int kLengthOffset = kLastPointerFieldOffset + kPointerSize;
   static const int kFormalParameterCountOffset = kLengthOffset + kPointerSize;
   static const int kExpectedNofPropertiesOffset =
       kFormalParameterCountOffset + kPointerSize;
@@ -6994,8 +7015,7 @@ class SharedFunctionInfo: public HeapObject {
 // word is not set and thus this word cannot be treated as pointer
 // to HeapObject during old space traversal.
 #if V8_TARGET_LITTLE_ENDIAN
-  static const int kLengthOffset =
-      kFeedbackVectorOffset + kPointerSize;
+  static const int kLengthOffset = kLastPointerFieldOffset + kPointerSize;
   static const int kFormalParameterCountOffset =
       kLengthOffset + kIntSize;
 
@@ -7029,7 +7049,7 @@ class SharedFunctionInfo: public HeapObject {
 
 #elif V8_TARGET_BIG_ENDIAN
   static const int kFormalParameterCountOffset =
-      kFeedbackVectorOffset + kPointerSize;
+      kLastPointerFieldOffset + kPointerSize;
   static const int kLengthOffset = kFormalParameterCountOffset + kIntSize;
 
   static const int kNumLiteralsOffset = kLengthOffset + kIntSize;
@@ -7062,7 +7082,7 @@ class SharedFunctionInfo: public HeapObject {
   static const int kAlignedSize = POINTER_SIZE_ALIGN(kSize);
 
   typedef FixedBodyDescriptor<kNameOffset,
-                              kFeedbackVectorOffset + kPointerSize,
+                              kLastPointerFieldOffset + kPointerSize,
                               kSize> BodyDescriptor;
 
   // Bit positions in start_position_and_type.
@@ -8578,6 +8598,10 @@ class Name: public HeapObject {
   DECLARE_CAST(Name)
 
   DECLARE_PRINTER(Name)
+#if TRACE_MAPS
+  void NameShortPrint();
+  int NameShortPrint(Vector<char> str);
+#endif
 
   // Layout description.
   static const int kHashFieldSlot = HeapObject::kHeaderSize;
@@ -8680,6 +8704,10 @@ class Symbol: public Name {
 
   const char* PrivateSymbolToName() const;
 
+#if TRACE_MAPS
+  friend class Name;  // For PrivateSymbolToName.
+#endif
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Symbol);
 };