Precompilation: drop Field objects unless they are an entry point or referenced from a constant poo…

runtime/vm/snapshot.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/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
 #include "vm/dart.h"
@@ skipping 10 matching lines @@
 #include "vm/verified_memory.h"
 #include "vm/version.h"
 
 // We currently only expect the Dart mutator to read snapshots.
 #define ASSERT_NO_SAFEPOINT_SCOPE()                            \
     isolate()->AssertCurrentThreadIsMutator();                 \
     ASSERT(thread()->no_safepoint_scope_depth() != 0)
 
 namespace dart {
 
+DECLARE_FLAG(bool, use_field_guards);
+
+
 static const int kNumVmIsolateSnapshotReferences = 32 * KB;
 static const int kNumInitialReferencesInFullSnapshot = 160 * KB;
 static const int kNumInitialReferences = 64;
 
 
 static bool IsSingletonClassId(intptr_t class_id) {
   // Check if this is a singleton object class which is shared by all isolates.
   return ((class_id >= kClassCid && class_id <= kUnwindErrorCid) ||
           (class_id >= kNullCid && class_id <= kVoidCid));
 }
@@ skipping 462 matching lines @@
     ASSERT(next_field_offset > 0);
     // Instance::NextFieldOffset() returns the offset of the first field in
     // a Dart object.
     bool read_as_reference = RawObject::IsCanonical(tags) ? false : true;
     intptr_t offset = Instance::NextFieldOffset();
     intptr_t result_cid = result->GetClassId();
     while (offset < next_field_offset) {
       pobj_ = ReadObjectImpl(read_as_reference);
       result->SetFieldAtOffset(offset, pobj_);
       if ((offset != type_argument_field_offset) &&
-          (kind_ == Snapshot::kMessage)) {
+          (kind_ == Snapshot::kMessage) &&
+          FLAG_use_field_guards) {
         // TODO(fschneider): Consider hoisting these lookups out of the loop.
         // This would involve creating a handle, since cls_ can't be reused
         // across the call to ReadObjectImpl.
         cls_ = isolate()->class_table()->At(result_cid);
         array_ = cls_.OffsetToFieldMap();
         field_ ^= array_.At(offset >> kWordSizeLog2);
         ASSERT(!field_.IsNull());
         ASSERT(field_.Offset() == offset);
         obj_ = pobj_.raw();
         field_.RecordStore(obj_);
@@ skipping 2062 matching lines @@
   if (setjmp(*jump.Set()) == 0) {
     NoSafepointScope no_safepoint;
     WriteObject(obj.raw());
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart