Reload length of retained_maps array after GC.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index f7d0fd5b65fc5fa923c7dfbccf9cda42128a6795..14217aac7c315092c7a2907d1c789d14a421a024 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -8277,9 +8277,14 @@ Handle<WeakFixedArray> WeakFixedArray::Allocate(
 }
 
 
-Handle<ArrayList> ArrayList::Add(Handle<ArrayList> array, Handle<Object> obj) {
+Handle<ArrayList> ArrayList::Add(Handle<ArrayList> array, Handle<Object> obj,
+                                 AddMode mode) {
   int length = array->Length();
   array = EnsureSpace(array, length + 1);
+  if (mode == kReloadLengthAfterAllocation) {
+    DCHECK(array->Length() <= length);
+    length = array->Length();
+  }
   array->Set(length, *obj);
   array->SetLength(length + 1);
   return array;
@@ -8287,9 +8292,12 @@ Handle<ArrayList> ArrayList::Add(Handle<ArrayList> array, Handle<Object> obj) {
 
 
 Handle<ArrayList> ArrayList::Add(Handle<ArrayList> array, Handle<Object> obj1,
-                                 Handle<Object> obj2) {
+                                 Handle<Object> obj2, AddMode mode) {
   int length = array->Length();
   array = EnsureSpace(array, length + 2);
+  if (mode == kReloadLengthAfterAllocation) {
+    length = array->Length();

[Erik Corry, 2015/03/25 09:53:07]

Missing DCHECK from the single-argument version.

Did you try just doing this unconditionally, and was it too slow?  It looks a
bit like a trap for the unwary now.

+  }
   array->Set(length, *obj1);
   array->Set(length + 1, *obj2);
   array->SetLength(length + 2);
@@ -8299,10 +8307,12 @@ Handle<ArrayList> ArrayList::Add(Handle<ArrayList> array, Handle<Object> obj1,
 
 Handle<ArrayList> ArrayList::EnsureSpace(Handle<ArrayList> array, int length) {
   int capacity = array->length();

[Erik Corry, 2015/03/25 09:53:07]

// This is the length of the FixedArray

+  bool empty = (capacity == 0);
   if (capacity < kFirstIndex + length) {
     capacity = kFirstIndex + length;
     capacity = capacity + Max(capacity / 2, 2);

[Erik Corry, 2015/03/25 09:53:07]

Division by 2 of a signed value can be an expensive operation.  Consider either
making it unsigned or using shift.

     array = Handle<ArrayList>::cast(FixedArray::CopySize(array, capacity));
+    if (empty) array->SetLength(0);

[Erik Corry, 2015/03/25 09:53:06]

// This sets the length of the ArrayList, using the first entry in the fixed
array

   }
   return array;
 }