Allocate fewer empty arrays.

Allocate fewer empty arrays.

Use VM isolate's canonical, untyped, empty array when possible.

Takes Dart2JS benchmark from ~9000 empty arrays to ~200.

R=asiva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=38435

[siva, 2014-07-09 20:08:03]

LGTM with some comments.

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/flow_graph_co...
File runtime/vm/flow_graph_compiler.cc (right):

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/flow_graph_co...
runtime/vm/flow_graph_compiler.cc:750: code.set_object_table(object_array);
I think it would be preferable to write this code as:

intptr_t deopt_info_length = DeoptTable::SizeFor(deopt_infos_.length();
if (deopt_info_length == 0) {
   code.set_deopt_info_array(Object::empty_array());
   code.set_object_table(Object::empty_array());
} else {
   const Array& array = Array::Handle(...);
   ....
   ....
}

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.cc
File runtime/vm/object.cc (right):

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.cc#new...
runtime/vm/object.cc:6477: }
Similarly here we could go with
if (count == 0) {
  set_ic_data_array(Object::empty_array());
} else {
  const Array& a = Array::Handle(Array::New(...));
  ...
  ...
}

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.cc#new...
runtime/vm/object.cc:10598: result.raw_ptr()->names_ = names.raw();
ditto here too, avoids the handle creation.

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.cc#new...
runtime/vm/object.cc:10699: Array::Handle(Array::NewOrEmpty(num_handlers));
Ditto.

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.h
File runtime/vm/object.h (right):

https://codereview.chromium.org/381483002/diff/20001/runtime/vm/object.h#newc...
runtime/vm/object.h:6034: }
may not need this if you do the explicit checks in the call locations.

[koda, 2014-07-21 16:41:09]

Committed patchset #3 manually as r38435 (presubmit successful).