Investigate & fix issues around usage_count and deoptimization_count

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 0942260d56cc401155ddb08d7594c8034e9a841b..27bd84c533fee0f6710b90a7f76f86da3ceb7165 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -2797,9 +2797,10 @@ static bool IsMutatorOrAtSafepoint() {
 }
 #endif
 
+
 void Class::RegisterCHACode(const Code& code) {
   if (FLAG_trace_cha) {
-    THR_Print("RegisterCHACode %s class %s\n",
+    THR_Print("RegisterCHACode '%s' depends on class '%s'\n",
         Function::Handle(code.function()).ToQualifiedCString(), ToCString());
   }
   DEBUG_ASSERT(IsMutatorOrAtSafepoint());
@@ -2809,10 +2810,15 @@ void Class::RegisterCHACode(const Code& code) {
 }
 
 
-void Class::DisableCHAOptimizedCode() {
+void Class::DisableCHAOptimizedCode(const Class& subclass) {
   ASSERT(Thread::Current()->IsMutatorThread());
   CHACodeArray a(*this);
-  a.DisableCode();

[Florian Schneider, 2016/01/04 11:31:38]

What about the other call-sites of DisableCode()? Also check HasCodes there?

+  if (a.HasCodes()) {

[Florian Schneider, 2016/01/04 11:31:38]

If you always check HasCodes before calling DisableCode, maybe add an ASSERT
inside DisableCode()

ASSERT(HasCodes())

and remove the check for a null code array there.

[srdjan, 2016/01/04 18:29:53]

What I really meant to do (and changed it to):

  CHACodeArray a(*this);
  if (FLAG_trace_deoptimization && a.HasCodes()) {
    THR_Print("Adding subclass %s\n", subclass.ToCString());
  }
  a.DisableCode();

No need to guard calling 'DisableCode', let it handle it itself (more robust).

+    if (FLAG_trace_deoptimization) {
+      THR_Print("Adding subclass %s\n", subclass.ToCString());
+    }
+    a.DisableCode();
+  }
 }
 
 
@@ -5820,7 +5826,7 @@ bool Function::IsOptimizable() const {
       ((end_token_pos() - token_pos()) < FLAG_huge_method_cutoff_in_tokens)) {
     // Additional check needed for implicit getters.
     return (unoptimized_code() == Object::null()) ||
-           (Code::Handle(unoptimized_code()).Size() <
+        (Code::Handle(unoptimized_code()).Size() <
             FLAG_huge_method_cutoff_in_code_size);
   }
   return false;
@@ -5837,6 +5843,7 @@ void Function::SetIsOptimizable(bool value) const {
   set_is_optimizable(value);
   if (!value) {
     set_is_inlinable(false);
+    set_usage_counter(INT_MIN);
   }
 }