Nonvirtual pointer visitor in GCs

runtime/vm/raw_object.h

 // 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.
 
 #ifndef RUNTIME_VM_RAW_OBJECT_H_
 #define RUNTIME_VM_RAW_OBJECT_H_
 
 #include "platform/assert.h"
 #include "vm/atomic.h"
 #include "vm/exceptions.h"
@@ skipping 435 matching lines @@
     return result;
   }
 
   bool Contains(uword addr) const {
     intptr_t this_size = Size();
     uword this_addr = RawObject::ToAddr(this);
     return (addr >= this_addr) && (addr < (this_addr + this_size));
   }
 
   void Validate(Isolate* isolate) const;
-  intptr_t VisitPointers(ObjectPointerVisitor* visitor);
   bool FindObject(FindObjectVisitor* visitor);
 
+  intptr_t VisitPointers(ObjectPointerVisitor* visitor) {

[erikcorry, 2017/05/31 10:40:42]

I think instead of duplicating the code you can just call
VisitPointersNonvirtual(visitor) here.  In that case perhaps you should move
this to a .cc file to stop the inliner getting overly eager for things where it
does not matter.

+    // Fall back to virtual variant for predefined classes
+    intptr_t class_id = GetClassId();
+    if (class_id < kNumPredefinedCids) {
+      return VisitPointersPredefined(visitor, class_id);
+    }
+
+    // Calculate the first and last raw object pointer fields.
+    intptr_t instance_size = Size();
+    uword obj_addr = ToAddr(this);
+    uword from = obj_addr + sizeof(RawObject);
+    uword to = obj_addr + instance_size - kWordSize;
+
+    // Call visitor function non-virtually
+    visitor->VisitPointers(reinterpret_cast<RawObject**>(from),
+                           reinterpret_cast<RawObject**>(to));
+
+    return instance_size;
+  }
+
+  template <class V>

[erikcorry, 2017/05/31 10:40:42]

template <class V, bool call_virtually = false>

This way you can avoid the code duplication.

+  intptr_t VisitPointersNonvirtual(V* visitor) {

[erikcorry, 2017/05/31 10:40:42]

Perhaps it should be called VisitPointersTemplatized if it is also used for the
virtual version.

+    // Fall back to virtual variant for predefined classes
+    intptr_t class_id = GetClassId();
+    if (class_id < kNumPredefinedCids) {
+      return VisitPointersPredefined(visitor, class_id);
+    }
+
+    // Calculate the first and last raw object pointer fields.
+    intptr_t instance_size = Size();
+    uword obj_addr = ToAddr(this);
+    uword from = obj_addr + sizeof(RawObject);
+    uword to = obj_addr + instance_size - kWordSize;
+
+    // Call visitor function non-virtually
+    visitor->V::VisitPointers(reinterpret_cast<RawObject**>(from),
+                              reinterpret_cast<RawObject**>(to));
+
+    return instance_size;
+  }
+
   static RawObject* FromAddr(uword addr) {
     // We expect the untagged address here.
     ASSERT((addr & kSmiTagMask) != kHeapObjectTag);
     return reinterpret_cast<RawObject*>(addr + kHeapObjectTag);
   }
 
   static uword ToAddr(const RawObject* raw_obj) {
     return reinterpret_cast<uword>(raw_obj->ptr());
   }
 
@@ skipping 37 matching lines @@
   class ReservedBits
       : public BitField<uword, intptr_t, kReservedTagPos, kReservedTagSize> {};
 
   // TODO(koda): After handling tags_, return const*, like Object::raw_ptr().
   RawObject* ptr() const {
     ASSERT(IsHeapObject());
     return reinterpret_cast<RawObject*>(reinterpret_cast<uword>(this) -
                                         kHeapObjectTag);
   }
 
+  intptr_t VisitPointersPredefined(ObjectPointerVisitor* visitor,
+                                   intptr_t class_id);
+
   intptr_t SizeFromClass() const;
 
   intptr_t GetClassId() const {
     uword tags = ptr()->tags_;
     return ClassIdTag::decode(tags);
   }
 
   void SetClassId(intptr_t new_cid) {
     uword tags = ptr()->tags_;
     ptr()->tags_ = ClassIdTag::update(new_cid, tags);
@@ skipping 1925 matching lines @@
                  kTypedDataInt8ArrayViewCid + 15);
   COMPILE_ASSERT(kByteBufferCid == kExternalTypedDataInt8ArrayCid + 14);
   COMPILE_ASSERT(kNullCid == kByteBufferCid + 1);
   return (kNullCid - kTypedDataInt8ArrayCid);
 }
 
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_RAW_OBJECT_H_