A change in the way we place TransitionElementKinds in the tree.

src/elements-kind.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 118 matching lines @@
     case FAST_ELEMENTS:
       return to_kind == FAST_HOLEY_ELEMENTS;
     case FAST_HOLEY_ELEMENTS:
       return false;
     default:
       return false;
   }
 }
 
 
+ElementsKind GetUnifiedFastElementsKind(ElementsKind e1, ElementsKind e2) {
+  ASSERT(IsFastElementsKind(e1));
+  ASSERT(IsFastElementsKind(e2));  

[danno, 2012/11/14 15:28:18]

I think you can simplify this code:

int i1 = GetSequenceIndexFromFastElementsKind(e1);
int i2 = GetSequenceIndexFromFastElementsKind(e2);

ElementsKind result = GetFastElementsKindFromSequenceIndex(max(i1, i2);
return ((IsFastHoleyElementKind(e1) != IsFastHoleyElementsKind(e2))
 ? GetHoleyElementsKind(result)
 : result;

[mvstanton, 2012/11/16 15:15:06]

Done.

+  if (e1 == e2) {
+    return e1;
+  }
+  
+  int i1 = GetSequenceIndexFromFastElementsKind(e1);
+  int i2 = GetSequenceIndexFromFastElementsKind(e2);
+  ASSERT(i1 != i2);
+  int max = i1 > i2 ? i1 : i2;
+  int min = i1 < i2 ? i1 : i2;
+  // The only reason not to take the max as the result is if the max is packed and the
+  // min is holey
+  ElementsKind eMax = GetFastElementsKindFromSequenceIndex(max);
+  ElementsKind eMin = GetFastElementsKindFromSequenceIndex(min);
+  if (IsFastPackedElementsKind(eMax) && !IsFastPackedElementsKind(eMin)) {
+    return GetNextMoreGeneralFastElementsKind(eMin, false);
+  }
+  return eMax;
+}
+
+
 } }  // namespace v8::internal