From 839efa2e268e6f47de953f067c967aa03cdd178e Mon Sep 17 00:00:00 2001
From: verwaest <verwaest@chromium.org>
Date: Tue, 17 Feb 2015 00:57:54 -0800
Subject: [PATCH] Reduce field type tracking to a single stable map per field.

BUG=

Review URL: https://codereview.chromium.org/930983003

Cr-Commit-Position: refs/heads/master@{#26679}
---
 src/objects.cc                 | 10 ----------
 src/types.cc                   |  5 +----
 test/cctest/test-migrations.cc |  4 ++--
 3 files changed, 3 insertions(+), 16 deletions(-)

diff --git a/src/objects.cc b/src/objects.cc
index 775a66479b..74f8d52bda 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2326,18 +2326,8 @@ void Map::UpdateFieldType(int descriptor, Handle<Name> name,
 Handle<HeapType> Map::GeneralizeFieldType(Handle<HeapType> type1,
                                           Handle<HeapType> type2,
                                           Isolate* isolate) {
-  static const int kMaxClassesPerFieldType = 5;
   if (type1->NowIs(type2)) return type2;
   if (type2->NowIs(type1)) return type1;
-  if (type1->NowStable() && type2->NowStable()) {
-    Handle<HeapType> type = HeapType::Union(type1, type2, isolate);
-    if (type->NumClasses() <= kMaxClassesPerFieldType) {
-      DCHECK(type->NowStable());
-      DCHECK(type1->NowIs(type));
-      DCHECK(type2->NowIs(type));
-      return type;
-    }
-  }
   return HeapType::Any(isolate);
 }
 
diff --git a/src/types.cc b/src/types.cc
index c1225f396e..37386cd82f 100644
--- a/src/types.cc
+++ b/src/types.cc
@@ -575,10 +575,7 @@ bool TypeImpl<Config>::NowIs(TypeImpl* that) {
 template<class Config>
 bool TypeImpl<Config>::NowStable() {
   DisallowHeapAllocation no_allocation;
-  for (Iterator<i::Map> it = this->Classes(); !it.Done(); it.Advance()) {
-    if (!it.Current()->is_stable()) return false;
-  }
-  return true;
+  return !this->IsClass() || this->AsClass()->Map()->is_stable();
 }
 
 
diff --git a/test/cctest/test-migrations.cc b/test/cctest/test-migrations.cc
index db03901c3d..2f7ff8703c 100644
--- a/test/cctest/test-migrations.cc
+++ b/test/cctest/test-migrations.cc
@@ -694,7 +694,7 @@ TEST(GeneralizeRepresentationHeapObjectToHeapObject) {
   Isolate* isolate = CcTest::i_isolate();
   Handle<HeapType> any_type = HeapType::Any(isolate);
 
-  const int kMaxClassesPerFieldType = 5;
+  const int kMaxClassesPerFieldType = 1;
   Handle<HeapType> current_type =
       HeapType::Class(Map::Create(isolate, 0), isolate);
 
@@ -1070,7 +1070,7 @@ TEST(ReconfigureDataFieldAttribute_GeneralizeRepresentationHeapObjToHeapObj) {
   Isolate* isolate = CcTest::i_isolate();
   Handle<HeapType> any_type = HeapType::Any(isolate);
 
-  const int kMaxClassesPerFieldType = 5;
+  const int kMaxClassesPerFieldType = 1;
   Handle<HeapType> current_type =
       HeapType::Class(Map::Create(isolate, 0), isolate);