Tests for GuardField length check along with bug fixes

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 137eb9d02f3af8898714e60c7d0b491a368d0bcf..4c363b30055dd37e2243adc515bf5440faf32c92 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -5351,7 +5351,11 @@ RawField* Field::New(const String& name,
   result.set_has_initializer(false);
   result.set_guarded_cid(kIllegalCid);
   result.set_is_nullable(false);

[srdjan, 2013/08/28 16:00:55]

Maybe add comment that list length guard is implemented for final variables
only, at the moment.

[Cutch, 2013/08/29 08:27:17]

Done.

-  result.set_guarded_list_length(Field::kUnknownFixedLength);
+  if (is_final) {
+    result.set_guarded_list_length(Field::kUnknownFixedLength);
+  } else {
+    result.set_guarded_list_length(Field::kNoFixedLength);
+  }
   result.set_dependent_code(Object::null_array());
   return result.raw();
 }
@@ -5379,6 +5383,16 @@ RawString* Field::UserVisibleName() const {
 }
 
 
+intptr_t Field::guarded_list_length() const {
+  return Smi::Value(raw_ptr()->guarded_list_length_);
+}
+
+
+void Field::set_guarded_list_length(intptr_t list_length) const {
+  raw_ptr()->guarded_list_length_ = Smi::New(list_length);
+}
+
+
 const char* Field::ToCString() const {
   if (IsNull()) {
     return "Field::null";
@@ -5571,7 +5585,6 @@ void Field::UpdateLength(intptr_t list_length) const {
     // List length unchanged.
     return;
   }
-
   // Multiple list lengths assigned here, stop tracking length.
   set_guarded_list_length(Field::kNoFixedLength);
   DeoptimizeDependentCode();