Allocate fewer empty arrays.

runtime/vm/flow_graph_compiler.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_XXX.
 
 #include "vm/flow_graph_compiler.h"
 
 #include "vm/cha.h"
 #include "vm/dart_entry.h"
@@ skipping 713 matching lines @@
 
 
 void FlowGraphCompiler::FinalizeDeoptInfo(const Code& code) {
   // For functions with optional arguments, all incoming arguments are copied
   // to spill slots. The deoptimization environment does not track them.
   const Function& function = parsed_function().function();
   const intptr_t incoming_arg_count =
       function.HasOptionalParameters() ? 0 : function.num_fixed_parameters();
   DeoptInfoBuilder builder(isolate(), incoming_arg_count);
 
-  const Array& array =
-      Array::Handle(Array::New(DeoptTable::SizeFor(deopt_infos_.length()),
-                               Heap::kOld));
+  const Array& array = Array::Handle(Array::NewOrEmpty(
+      DeoptTable::SizeFor(deopt_infos_.length()),
+      Heap::kOld));
   Smi& offset = Smi::Handle();
   DeoptInfo& info = DeoptInfo::Handle();
   Smi& reason = Smi::Handle();
   for (intptr_t i = 0; i < deopt_infos_.length(); i++) {
     offset = Smi::New(deopt_infos_[i]->pc_offset());
     info = deopt_infos_[i]->CreateDeoptInfo(this, &builder, array);
     reason = Smi::New(deopt_infos_[i]->reason());
     DeoptTable::SetEntry(array, i, offset, info, reason);
   }
   code.set_deopt_info_array(array);
   const Array& object_array =
       Array::Handle(Array::MakeArray(builder.object_table()));
   ASSERT(code.object_table() == Array::null());
   code.set_object_table(object_array);

[siva, 2014/07/09 20:08:02]

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(...);
   ....
   ....
}

 }
 
 
 void FlowGraphCompiler::FinalizeStackmaps(const Code& code) {
   if (stackmap_table_builder_ == NULL) {
     // The unoptimizing compiler has no stack maps.
     code.set_stackmaps(Object::null_array());
   } else {
     // Finalize the stack map array and add it to the code object.
     ASSERT(is_optimizing());
@@ skipping 629 matching lines @@
   }
   const ICData& ic_data = ICData::ZoneHandle(isolate(), ICData::New(
       parsed_function().function(), String::Handle(isolate(), target.name()),
       arguments_descriptor, deopt_id, num_args_tested));
   ic_data.AddTarget(target);
   (*deopt_id_to_ic_data_)[deopt_id] = &ic_data;
   return &ic_data;
 }
 
 }  // namespace dart