Some optimizations for packer.js.

src/objects-inl.h

 // Copyright 2006-2008 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 3085 matching lines @@
   // No write barrier is needed since empty_fixed_array is not in new space.
   // Please note this function is used during marking:
   //  - MarkCompactCollector::MarkUnmarkedObject
   ASSERT(!Heap::InNewSpace(Heap::raw_unchecked_empty_fixed_array()));
   WRITE_FIELD(this, kCodeCacheOffset, Heap::raw_unchecked_empty_fixed_array());
 }
 
 
 void JSArray::EnsureSize(int required_size) {
   ASSERT(HasFastElements());
-  if (elements()->length() >= required_size) return;
-  Expand(required_size);
+  Array* elts = elements();
+  if (elts->length() < required_size) {
+    // Doubling in size would be overkill, but leave some slack to avoid
+    // constantly growing.
+    Expand(required_size + (required_size >> 3));
+  } else if (!Heap::new_space()->Contains(elts)) {
+    // It's a performance benefit to keep a frequently used array in new-space.
+    const int kArraySizeThatFitsComfortablyInNewSpace = 128;

[Søren Thygesen Gjesse, 2009/11/19 21:42:57]

This does not take the calculation required_size + (required_size >> 3) in
Expand into account...

[Erik Corry, 2009/11/20 10:12:46]

Since it's a number I pulled out of my backside I don't think that matters.

+    if (required_size < kArraySizeThatFitsComfortablyInNewSpace) {

[Søren Thygesen Gjesse, 2009/11/19 21:42:57]

Maybe combine these two if's into one if condition. Also make a note that
"Expand" will always allocate a new backing store even if it is not expanding.

[Erik Corry, 2009/11/20 10:12:46]

Done.

+      Expand(required_size);
+    }
+  }
 }
 
 
 void JSArray::SetContent(FixedArray* storage) {
   set_length(Smi::FromInt(storage->length()), SKIP_WRITE_BARRIER);
   set_elements(storage);
 }
 
 
 Object* FixedArray::Copy() {
@@ skipping 19 matching lines @@
 #undef WRITE_INT_FIELD
 #undef READ_SHORT_FIELD
 #undef WRITE_SHORT_FIELD
 #undef READ_BYTE_FIELD
 #undef WRITE_BYTE_FIELD
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_INL_H_