Add flag --support_debugger, controls emitting single stepping checks. Disable in --noopt, 6% gain.

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/bit_vector.h"
 #include "vm/cha.h"
@@ skipping 36 matching lines @@
 DECLARE_FLAG(bool, disassemble_optimized);
 DECLARE_FLAG(bool, emit_edge_counters);
 DECLARE_FLAG(bool, enable_type_checks);
 DECLARE_FLAG(bool, intrinsify);
 DECLARE_FLAG(int, optimization_counter_threshold);
 DECLARE_FLAG(bool, propagate_ic_data);
 DECLARE_FLAG(int, regexp_optimization_counter_threshold);
 DECLARE_FLAG(int, reoptimization_counter_threshold);
 DECLARE_FLAG(int, stacktrace_every);
 DECLARE_FLAG(charp, stacktrace_filter);
+DECLARE_FLAG(bool, support_debugger);
 DECLARE_FLAG(bool, use_cha);
 DECLARE_FLAG(bool, use_field_guards);
 DECLARE_FLAG(bool, use_osr);
 DECLARE_FLAG(bool, warn_on_javascript_compatibility);
 
 static void NooptModeHandler(bool value) {
   if (value) {
     FLAG_always_megamorphic_calls = value;
     FLAG_optimization_counter_threshold = -1;
     FLAG_use_field_guards = false;
     FLAG_use_osr = false;
     FLAG_emit_edge_counters = false;
+    FLAG_support_debugger = false;
   }
 }
 
 
 // --noopt disables optimizer and tunes unoptimized code to run as fast
 // as possible.
 DEFINE_FLAG_HANDLER(NooptModeHandler,
                     noopt,
                     "Run fast unoptimized code only.");
 
@@ skipping 1637 matching lines @@
 
 
 void FlowGraphCompiler::FrameStateClear() {
   ASSERT(!is_optimizing());
   frame_state_.TruncateTo(0);
 }
 #endif
 
 
 }  // namespace dart