Add flag —enable-debugger (default true) in order to disable debugger single stepping code.

runtime/vm/block_scheduler.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/block_scheduler.h"
 
 #include "vm/allocation.h"
 #include "vm/code_patcher.h"
 #include "vm/flow_graph.h"
 
 namespace dart {
 
+DEFINE_FLAG(bool, emit_edge_counters, true, "Emit edge counters at targets.");
+
 // Compute the edge count at the deopt id of a TargetEntry or Goto.
 static intptr_t ComputeEdgeCount(const Code& unoptimized_code,
                                  intptr_t deopt_id) {
   ASSERT(deopt_id != Isolate::kNoDeoptId);
 
+  if (!FLAG_emit_edge_counters) {
+    // Assume everything was visited once.
+    return 1;
+  }
   uword pc = unoptimized_code.GetPcForDeoptId(deopt_id, PcDescriptors::kDeopt);
   Array& array = Array::Handle();
   array ^= CodePatcher::GetEdgeCounterAt(pc, unoptimized_code);
   ASSERT(!array.IsNull());
   return Smi::Value(Smi::RawCast(array.At(0)));
 }
 
 
 // There is an edge from instruction->successor.  Set its weight (edge count
 // per function entry).
@@ skipping 169 matching lines @@
   for (intptr_t i = block_count - 1; i >= 0; --i) {
     if (chains[i]->first->block == flow_graph()->postorder()[i]) {
       for (Link* link = chains[i]->first; link != NULL; link = link->next) {
         flow_graph()->CodegenBlockOrder(true)->Add(link->block);
       }
     }
   }
 }
 
 }  // namespace dart