VM: Allow configuring use_field_guards on the per-isolate basis and include it into snapshot featur…

runtime/vm/object.cc

 // Copyright (c) 2012, 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/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 7637 matching lines @@
   result.set_has_initializer(false);
   result.set_is_unboxing_candidate(true);
   result.set_kernel_field(NULL);
   Isolate* isolate = Isolate::Current();
 
   // Use field guards if they are enabled and the isolate has never reloaded.
   // TODO(johnmccutchan): The reload case assumes the worst case (everything is
   // dynamic and possibly null). Attempt to relax this later.
   const bool use_guarded_cid =
       FLAG_precompiled_mode ||
-      (FLAG_use_field_guards && !isolate->HasAttemptedReload());
+      (isolate->use_field_guards() && !isolate->HasAttemptedReload());
   result.set_guarded_cid(use_guarded_cid ? kIllegalCid : kDynamicCid);
   result.set_is_nullable(use_guarded_cid ? false : true);
   result.set_guarded_list_length_in_object_offset(Field::kUnknownLengthOffset);
   // Presently, we only attempt to remember the list length for final fields.
   if (is_final && use_guarded_cid) {
     result.set_guarded_list_length(Field::kUnknownFixedLength);
   } else {
     result.set_guarded_list_length(Field::kNoFixedLength);
   }
 }
@@ skipping 490 matching lines @@
     set_guarded_list_length_in_object_offset(Field::kUnknownLengthOffset);
   }
 
   // Expected class id or nullability of the field changed.
   return true;
 }
 
 
 void Field::RecordStore(const Object& value) const {
   ASSERT(IsOriginal());
-  if (!FLAG_use_field_guards) {
+  if (!Isolate::Current()->use_field_guards()) {
     return;
   }
 
   if (FLAG_trace_field_guards) {
     THR_Print("Store %s %s <- %s\n", ToCString(), GuardedPropertiesAsCString(),
               value.ToCString());
   }
 
   if (UpdateGuardedCidAndLength(value)) {
     if (FLAG_trace_field_guards) {
@@ skipping 14747 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart