8330585: Refactor/rename forwardee handling

Reviewed-by: stefank, ayang

Author: rkennke

src/hotspot/share/gc/g1/g1OopClosures.inline.hpp

@@ -227,8 +227,8 @@ void G1ParCopyClosure<barrier, should_mark>::do_oop_work(T* p) {
   if (state.is_in_cset()) {
     oop forwardee;
     markWord m = obj->mark();
-    if (m.is_marked()) {
-      forwardee = cast_to_oop(m.decode_pointer());
+    if (m.is_forwarded()) {
+      forwardee = m.forwardee();
     } else {
       forwardee = _par_scan_state->copy_to_survivor_space(state, obj, m);
     }

src/hotspot/share/gc/g1/g1ParScanThreadState.cpp

@@ -211,8 +211,8 @@ void G1ParScanThreadState::do_oop_evac(T* p) {
   }
 
   markWord m = obj->mark();
-  if (m.is_marked()) {
-    obj = cast_to_oop(m.decode_pointer());
+  if (m.is_forwarded()) {
+    obj = m.forwardee();
   } else {
     obj = do_copy_to_survivor_space(region_attr, obj, m);
   }

src/hotspot/share/gc/parallel/psPromotionManager.inline.hpp

@@ -145,15 +145,15 @@ inline oop PSPromotionManager::copy_to_survivor_space(oop o) {
   // in o. There may be multiple threads racing on it, and it may be forwarded
   // at any time.
   markWord m = o->mark();
-  if (!m.is_marked()) {
+  if (!m.is_forwarded()) {
     return copy_unmarked_to_survivor_space<promote_immediately>(o, m);
   } else {
     // Ensure any loads from the forwardee follow all changes that precede
     // the release-cmpxchg that performed the forwarding, possibly in some
     // other thread.
     OrderAccess::acquire();
     // Return the already installed forwardee.
-    return cast_to_oop(m.decode_pointer());
+    return m.forwardee();
   }
 }
 

src/hotspot/share/gc/shared/preservedMarks.inline.hpp

@@ -43,7 +43,7 @@ inline void PreservedMarks::push_if_necessary(oop obj, markWord m) {
 }
 
 inline void PreservedMarks::push_always(oop obj, markWord m) {
-  assert(!m.is_marked(), "precondition");
+  assert(!m.is_forwarded(), "precondition");
   PreservedMark elem(obj, m);
   _stack.push(elem);
 }

src/hotspot/share/oops/markWord.hpp

@@ -143,6 +143,9 @@ class markWord {
   bool is_marked()   const {
     return (mask_bits(value(), lock_mask_in_place) == marked_value);
   }
+  bool is_forwarded()   const {
+    return (mask_bits(value(), lock_mask_in_place) == marked_value);
+  }
   bool is_neutral()  const {  // Not locked, or marked - a "clean" neutral state
     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
   }
@@ -225,7 +228,7 @@ class markWord {
   }
 
   // used to encode pointers during GC
-  markWord clear_lock_bits() { return markWord(value() & ~lock_mask_in_place); }
+  markWord clear_lock_bits() const { return markWord(value() & ~lock_mask_in_place); }
 
   // age operations
   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
@@ -259,7 +262,11 @@ class markWord {
   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }
 
   // Recover address of oop from encoded form used in mark
-  inline void* decode_pointer() { return (void*)clear_lock_bits().value(); }
+  inline void* decode_pointer() const { return (void*)clear_lock_bits().value(); }
+
+  inline oop forwardee() const {
+    return cast_to_oop(decode_pointer());
+  }
 };
 
 // Support atomic operations.

src/hotspot/share/oops/oop.inline.hpp

@@ -262,9 +262,7 @@ bool oopDesc::is_gc_marked() const {
 
 // Used by scavengers
 bool oopDesc::is_forwarded() const {
-  // The extra heap check is needed since the obj might be locked, in which case the
-  // mark would point to a stack location and have the sentinel bit cleared
-  return mark().is_marked();
+  return mark().is_forwarded();
 }
 
 // Used by scavengers
@@ -289,8 +287,7 @@ oop oopDesc::forward_to_atomic(oop p, markWord compare, atomic_memory_order orde
 // The forwardee is used when copying during scavenge and mark-sweep.
 // It does need to clear the low two locking- and GC-related bits.
 oop oopDesc::forwardee() const {
-  assert(is_forwarded(), "only decode when actually forwarded");
-  return cast_to_oop(mark().decode_pointer());
+  return mark().forwardee();
 }
 
 // The following method needs to be MT safe.