Some optimizations for packer.js.

src/objects-inl.h

Index: src/objects-inl.h
===================================================================
--- src/objects-inl.h	(revision 3335)
+++ src/objects-inl.h	(working copy)
@@ -3103,8 +3103,18 @@
 
 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);
+    }
+  }
 }