Better single stepping in VM debugger

runtime/vm/code_generator.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/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/bigint_operations.h"
 #include "vm/code_patcher.h"
@@ skipping 855 matching lines @@
 
 // Gets called from debug stub when code reaches a breakpoint.
 DEFINE_RUNTIME_ENTRY(BreakpointDynamicHandler, 0) {
   ASSERT(arguments.ArgCount() ==
      kBreakpointDynamicHandlerRuntimeEntry.argument_count());
   ASSERT(isolate->debugger() != NULL);
   isolate->debugger()->SignalBpReached();
 }
 
 
+DEFINE_RUNTIME_ENTRY(SingleStepHandler, 0) {
+  ASSERT(arguments.ArgCount() ==
+         kSingleStepHandlerRuntimeEntry.argument_count());
+  ASSERT(isolate->debugger() != NULL);
+  isolate->debugger()->SingleStepCallback();
+}
+
+
 static RawFunction* InlineCacheMissHandler(
     const GrowableArray<const Instance*>& args,
     const ICData& ic_data,
     const Array& args_descriptor_array) {
   const Instance& receiver = *args[0];
   const Code& target_code =
       Code::Handle(ResolveCompileInstanceCallTarget(receiver, ic_data));
   if (target_code.IsNull()) {
     // Let the megamorphic stub handle special cases: NoSuchMethod,
     // closure calls.
@@ skipping 399 matching lines @@
                                              args_descriptor);
     }
   }
   CheckResultError(result);
   arguments.SetReturn(result);
 }
 
 
 static bool CanOptimizeFunction(const Function& function, Isolate* isolate) {
   const intptr_t kLowInvocationCount = -100000000;
-  if (isolate->debugger()->HasBreakpoint(function)) {
-    // We cannot set breakpoints in optimized code, so do not optimize
-    // the function.
+  if (isolate->debugger()->IsStepping() ||
+      isolate->debugger()->HasBreakpoint(function)) {
+    // We cannot set breakpoints and single step in optimized code,
+    // so do not optimize the function.
     function.set_usage_counter(0);
     return false;
   }
   if (function.deoptimization_counter() >=
       FLAG_deoptimization_counter_threshold) {
     if (FLAG_trace_failed_optimization_attempts ||
         FLAG_stop_on_excessive_deoptimization) {
       OS::PrintErr("Too Many Deoptimizations: %s\n",
           function.ToFullyQualifiedCString());
       if (FLAG_stop_on_excessive_deoptimization) {
@@ skipping 567 matching lines @@
 //   Arg1: Value that is being stored.
 DEFINE_RUNTIME_ENTRY(UpdateFieldCid, 2) {
   ASSERT(arguments.ArgCount() == kUpdateFieldCidRuntimeEntry.argument_count());
   const Field& field = Field::CheckedHandle(arguments.ArgAt(0));
   const Object& value = Object::Handle(arguments.ArgAt(1));
 
   field.UpdateCid(value.GetClassId());
 }
 
 }  // namespace dart