From 40d4674d611928314d7471b03a651b179481550b Mon Sep 17 00:00:00 2001
From: ishell <ishell@chromium.org>
Date: Wed, 19 Nov 2014 10:10:12 -0800
Subject: [PATCH] Removed unnecessary generalization of all fields in
 Map::GeneralizeRepresentation() (introduced in r25082).

This generalization caused unnecessary map deprecation when the transition tree of the split map is full.

BUG=chromium:431807
LOG=N

Review URL: https://codereview.chromium.org/736953003

Cr-Commit-Position: refs/heads/master@{#25427}
---
 src/objects.cc | 25 +++++++++++++++++--------
 src/objects.h  |  2 +-
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/src/objects.cc b/src/objects.cc
index cdd6718736..a6a716a3bc 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2259,18 +2259,21 @@ void Map::DeprecateTransitionTree() {
 // Invalidates a transition target at |key|, and installs |new_descriptors| over
 // the current instance_descriptors to ensure proper sharing of descriptor
 // arrays.
-void Map::DeprecateTarget(Name* key, DescriptorArray* new_descriptors,
+// Returns true if the transition target at given key was deprecated.
+bool Map::DeprecateTarget(Name* key, DescriptorArray* new_descriptors,
                           LayoutDescriptor* new_layout_descriptor) {
+  bool transition_target_deprecated = false;
   if (HasTransitionArray()) {
     TransitionArray* transitions = this->transitions();
     int transition = transitions->Search(key);
     if (transition != TransitionArray::kNotFound) {
       transitions->GetTarget(transition)->DeprecateTransitionTree();
+      transition_target_deprecated = true;
     }
   }
 
   // Don't overwrite the empty descriptor array.
-  if (NumberOfOwnDescriptors() == 0) return;
+  if (NumberOfOwnDescriptors() == 0) return transition_target_deprecated;
 
   DescriptorArray* to_replace = instance_descriptors();
   Map* current = this;
@@ -2284,6 +2287,7 @@ void Map::DeprecateTarget(Name* key, DescriptorArray* new_descriptors,
   }
 
   set_owns_descriptors(false);
+  return transition_target_deprecated;
 }
 
 
@@ -2731,8 +2735,17 @@ Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
 
   Handle<LayoutDescriptor> new_layout_descriptor =
       LayoutDescriptor::New(split_map, new_descriptors, old_nof);
-  split_map->DeprecateTarget(old_descriptors->GetKey(split_nof),
-                             *new_descriptors, *new_layout_descriptor);
+  bool transition_target_deprecated =
+      split_map->DeprecateTarget(old_descriptors->GetKey(split_nof),
+                                 *new_descriptors, *new_layout_descriptor);
+
+  // If |transition_target_deprecated| is true then the transition array
+  // already contains entry for given descriptor. This means that the transition
+  // could be inserted regardless of whether transitions array is full or not.
+  if (!transition_target_deprecated && !split_map->CanHaveMoreTransitions()) {
+    return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
+                                            "GenAll_CantHaveMoreTransitions");
+  }
 
   if (FLAG_trace_generalization) {
     PropertyDetails old_details = old_descriptors->GetDetails(modify_index);
@@ -2755,10 +2768,6 @@ Handle<Map> Map::GeneralizeRepresentation(Handle<Map> old_map,
   // Add missing transitions.
   Handle<Map> new_map = split_map;
   for (int i = split_nof; i < old_nof; ++i) {
-    if (!new_map->CanHaveMoreTransitions()) {
-      return CopyGeneralizeAllRepresentations(old_map, modify_index, store_mode,
-                                              "can't have more transitions");
-    }
     new_map = CopyInstallDescriptors(new_map, i, new_descriptors,
                                      new_layout_descriptor);
   }
diff --git a/src/objects.h b/src/objects.h
index 0c2d22f42d..678dcb2ed5 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -6364,7 +6364,7 @@ class Map: public HeapObject {
   void ZapTransitions();
 
   void DeprecateTransitionTree();
-  void DeprecateTarget(Name* key, DescriptorArray* new_descriptors,
+  bool DeprecateTarget(Name* key, DescriptorArray* new_descriptors,
                        LayoutDescriptor* new_layout_descriptor);
 
   Map* FindLastMatchMap(int verbatim, int length, DescriptorArray* descriptors);