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src/hotspot/share/oops/access.hpp

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 40 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
 41 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
 42 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
 43 // such as GC-specific barriers and encoding/decoding compressed oops. For more information about what
 44 // decorators are available, cf. oops/accessDecorators.hpp.
 45 // By pipelining handling of these decorators, the design of the Access API allows separation of concern
 46 // over the different orthogonal concerns of decorators, while providing a powerful way of
 47 // expressing these orthogonal semantic properties in a unified way.
 48 //
 49 // == OPERATIONS ==
 50 // * load: Load a value from an address.
 51 // * load_at: Load a value from an internal pointer relative to a base object.
 52 // * store: Store a value at an address.
 53 // * store_at: Store a value in an internal pointer relative to a base object.
 54 // * atomic_cmpxchg: Atomically compare-and-swap a new value at an address if previous value matched the compared value.
 55 // * atomic_cmpxchg_at: Atomically compare-and-swap a new value at an internal pointer address if previous value matched the compared value.
 56 // * atomic_xchg: Atomically swap a new value at an address if previous value matched the compared value.
 57 // * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
 58 // * arraycopy: Copy data from one heap array to another heap array. The ArrayAccess class has convenience functions for this.
 59 // * clone: Clone the contents of an object to a newly allocated object.

 60 //
 61 // == IMPLEMENTATION ==
 62 // Each access goes through the following steps in a template pipeline.
 63 // There are essentially 5 steps for each access:
 64 // * Step 1:   Set default decorators and decay types. This step gets rid of CV qualifiers
 65 //             and sets default decorators to sensible values.
 66 // * Step 2:   Reduce types. This step makes sure there is only a single T type and not
 67 //             multiple types. The P type of the address and T type of the value must
 68 //             match.
 69 // * Step 3:   Pre-runtime dispatch. This step checks whether a runtime call can be
 70 //             avoided, and in that case avoids it (calling raw accesses or
 71 //             primitive accesses in a build that does not require primitive GC barriers)
 72 // * Step 4:   Runtime-dispatch. This step performs a runtime dispatch to the corresponding
 73 //             BarrierSet::AccessBarrier accessor that attaches GC-required barriers
 74 //             to the access.
 75 // * Step 5.a: Barrier resolution. This step is invoked the first time a runtime-dispatch
 76 //             happens for an access. The appropriate BarrierSet::AccessBarrier accessor
 77 //             is resolved, then the function pointer is updated to that accessor for
 78 //             future invocations.
 79 // * Step 5.b: Post-runtime dispatch. This step now casts previously unknown types such
 80 //             as the address type of an oop on the heap (is it oop* or narrowOop*) to
 81 //             the appropriate type. It also splits sufficiently orthogonal accesses into
 82 //             different functions, such as whether the access involves oops or primitives
 83 //             and whether the access is performed on the heap or outside. Then the
 84 //             appropriate BarrierSet::AccessBarrier is called to perform the access.
 85 //
 86 // The implementation of step 1-4 resides in in accessBackend.hpp, to allow selected
 87 // accesses to be accessible from only access.hpp, as opposed to access.inline.hpp.
 88 // Steps 5.a and 5.b require knowledge about the GC backends, and therefore needs to
 89 // include the various GC backend .inline.hpp headers. Their implementation resides in
 90 // access.inline.hpp. The accesses that are allowed through the access.hpp file
 91 // must be instantiated in access.cpp using the INSTANTIATE_HPP_ACCESS macro.
 92 


 93 template <DecoratorSet decorators = DECORATORS_NONE>
 94 class Access: public AllStatic {
 95   // This function asserts that if an access gets passed in a decorator outside
 96   // of the expected_decorators, then something is wrong. It additionally checks
 97   // the consistency of the decorators so that supposedly disjoint decorators are indeed
 98   // disjoint. For example, an access can not be both in heap and on root at the
 99   // same time.
100   template <DecoratorSet expected_decorators>
101   static void verify_decorators();
102 
103   template <DecoratorSet expected_mo_decorators>
104   static void verify_primitive_decorators() {
105     const DecoratorSet primitive_decorators = (AS_DECORATOR_MASK ^ AS_NO_KEEPALIVE) |
106                                               IN_HEAP | IS_ARRAY;
107     verify_decorators<expected_mo_decorators | primitive_decorators>();
108   }
109 
110   template <DecoratorSet expected_mo_decorators>
111   static void verify_oop_decorators() {
112     const DecoratorSet oop_decorators = AS_DECORATOR_MASK | IN_DECORATOR_MASK |
113                                         (ON_DECORATOR_MASK ^ ON_UNKNOWN_OOP_REF) | // no unknown oop refs outside of the heap
114                                         IS_ARRAY | IS_NOT_NULL | IS_DEST_UNINITIALIZED;
115     verify_decorators<expected_mo_decorators | oop_decorators>();
116   }
117 
118   template <DecoratorSet expected_mo_decorators>
119   static void verify_heap_oop_decorators() {
120     const DecoratorSet heap_oop_decorators = AS_DECORATOR_MASK | ON_DECORATOR_MASK |
121                                              IN_HEAP | IS_ARRAY | IS_NOT_NULL;
122     verify_decorators<expected_mo_decorators | heap_oop_decorators>();
123   }
124 






125   static const DecoratorSet load_mo_decorators = MO_UNORDERED | MO_RELAXED | MO_ACQUIRE | MO_SEQ_CST;
126   static const DecoratorSet store_mo_decorators = MO_UNORDERED | MO_RELAXED | MO_RELEASE | MO_SEQ_CST;
127   static const DecoratorSet atomic_xchg_mo_decorators = MO_SEQ_CST;
128   static const DecoratorSet atomic_cmpxchg_mo_decorators = MO_RELAXED | MO_SEQ_CST;
129 
130 protected:
131   template <typename T>
132   static inline bool oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
133                                    arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
134                                    size_t length) {
135     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
136                       AS_DECORATOR_MASK | IS_ARRAY | IS_DEST_UNINITIALIZED>();
137     return AccessInternal::arraycopy<decorators | INTERNAL_VALUE_IS_OOP>(src_obj, src_offset_in_bytes, src_raw,
138                                                                          dst_obj, dst_offset_in_bytes, dst_raw,
139                                                                          length);
140   }
141 
142   template <typename T>
143   static inline void arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
144                                arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
145                                size_t length) {
146     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
147                       AS_DECORATOR_MASK | IS_ARRAY>();
148     AccessInternal::arraycopy<decorators>(src_obj, src_offset_in_bytes, src_raw,
149                                           dst_obj, dst_offset_in_bytes, dst_raw,
150                                           length);
151   }
152 
153 public:
154   // Primitive heap accesses
155   static inline AccessInternal::LoadAtProxy<decorators> load_at(oop base, ptrdiff_t offset) {
156     verify_primitive_decorators<load_mo_decorators>();
157     return AccessInternal::LoadAtProxy<decorators>(base, offset);
158   }
159 

195     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
196     OopType new_oop_value = new_value;
197     OopType compare_oop_value = compare_value;
198     return AccessInternal::atomic_cmpxchg_at<decorators | INTERNAL_VALUE_IS_OOP>(base, offset, compare_oop_value, new_oop_value);
199   }
200 
201   template <typename T>
202   static inline T oop_atomic_xchg_at(oop base, ptrdiff_t offset, T new_value) {
203     verify_heap_oop_decorators<atomic_xchg_mo_decorators>();
204     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
205     OopType new_oop_value = new_value;
206     return AccessInternal::atomic_xchg_at<decorators | INTERNAL_VALUE_IS_OOP>(base, offset, new_oop_value);
207   }
208 
209   // Clone an object from src to dst
210   static inline void clone(oop src, oop dst, size_t size) {
211     verify_decorators<IN_HEAP>();
212     AccessInternal::clone<decorators>(src, dst, size);
213   }
214 








215   // Primitive accesses
216   template <typename P>
217   static inline P load(P* addr) {
218     verify_primitive_decorators<load_mo_decorators>();
219     return AccessInternal::load<decorators, P, P>(addr);
220   }
221 
222   template <typename P, typename T>
223   static inline void store(P* addr, T value) {
224     verify_primitive_decorators<store_mo_decorators>();
225     AccessInternal::store<decorators>(addr, value);
226   }
227 
228   template <typename P, typename T>
229   static inline T atomic_cmpxchg(P* addr, T compare_value, T new_value) {
230     verify_primitive_decorators<atomic_cmpxchg_mo_decorators>();
231     return AccessInternal::atomic_cmpxchg<decorators>(addr, compare_value, new_value);
232   }
233 
234   template <typename P, typename T>

300   }
301 
302   template <typename T>
303   static inline void arraycopy_to_native(arrayOop src_obj, size_t src_offset_in_bytes,
304                                          T* dst,
305                                          size_t length) {
306     AccessT::arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const T*>(NULL),
307                        NULL, 0, dst,
308                        length);
309   }
310 
311   template <typename T>
312   static inline void arraycopy_from_native(const T* src,
313                                            arrayOop dst_obj, size_t dst_offset_in_bytes,
314                                            size_t length) {
315     AccessT::arraycopy(NULL, 0, src,
316                        dst_obj, dst_offset_in_bytes, reinterpret_cast<T*>(NULL),
317                        length);
318   }
319 
320   static inline bool oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes,
321                                    arrayOop dst_obj, size_t dst_offset_in_bytes,
322                                    size_t length) {
323     return AccessT::oop_arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const HeapWord*>(NULL),
324                                   dst_obj, dst_offset_in_bytes, reinterpret_cast<HeapWord*>(NULL),
325                                   length);
326   }
327 
328   template <typename T>
329   static inline bool oop_arraycopy_raw(T* src, T* dst, size_t length) {
330     return AccessT::oop_arraycopy(NULL, 0, src,
331                                   NULL, 0, dst,
332                                   length);
333   }
334 
335 };
336 
337 template <DecoratorSet decorators>
338 template <DecoratorSet expected_decorators>
339 void Access<decorators>::verify_decorators() {
340   STATIC_ASSERT((~expected_decorators & decorators) == 0); // unexpected decorator used
341   const DecoratorSet barrier_strength_decorators = decorators & AS_DECORATOR_MASK;
342   STATIC_ASSERT(barrier_strength_decorators == 0 || ( // make sure barrier strength decorators are disjoint if set
343     (barrier_strength_decorators ^ AS_NO_KEEPALIVE) == 0 ||
344     (barrier_strength_decorators ^ AS_RAW) == 0 ||
345     (barrier_strength_decorators ^ AS_NORMAL) == 0
346   ));
347   const DecoratorSet ref_strength_decorators = decorators & ON_DECORATOR_MASK;
348   STATIC_ASSERT(ref_strength_decorators == 0 || ( // make sure ref strength decorators are disjoint if set
349     (ref_strength_decorators ^ ON_STRONG_OOP_REF) == 0 ||
350     (ref_strength_decorators ^ ON_WEAK_OOP_REF) == 0 ||
351     (ref_strength_decorators ^ ON_PHANTOM_OOP_REF) == 0 ||
352     (ref_strength_decorators ^ ON_UNKNOWN_OOP_REF) == 0

 40 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
 41 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
 42 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
 43 // such as GC-specific barriers and encoding/decoding compressed oops. For more information about what
 44 // decorators are available, cf. oops/accessDecorators.hpp.
 45 // By pipelining handling of these decorators, the design of the Access API allows separation of concern
 46 // over the different orthogonal concerns of decorators, while providing a powerful way of
 47 // expressing these orthogonal semantic properties in a unified way.
 48 //
 49 // == OPERATIONS ==
 50 // * load: Load a value from an address.
 51 // * load_at: Load a value from an internal pointer relative to a base object.
 52 // * store: Store a value at an address.
 53 // * store_at: Store a value in an internal pointer relative to a base object.
 54 // * atomic_cmpxchg: Atomically compare-and-swap a new value at an address if previous value matched the compared value.
 55 // * atomic_cmpxchg_at: Atomically compare-and-swap a new value at an internal pointer address if previous value matched the compared value.
 56 // * atomic_xchg: Atomically swap a new value at an address if previous value matched the compared value.
 57 // * atomic_xchg_at: Atomically swap a new value at an internal pointer address if previous value matched the compared value.
 58 // * arraycopy: Copy data from one heap array to another heap array. The ArrayAccess class has convenience functions for this.
 59 // * clone: Clone the contents of an object to a newly allocated object.
 60 // * value_copy: Copy the contents of a value type from one heap address to another
 61 //
 62 // == IMPLEMENTATION ==
 63 // Each access goes through the following steps in a template pipeline.
 64 // There are essentially 5 steps for each access:
 65 // * Step 1:   Set default decorators and decay types. This step gets rid of CV qualifiers
 66 //             and sets default decorators to sensible values.
 67 // * Step 2:   Reduce types. This step makes sure there is only a single T type and not
 68 //             multiple types. The P type of the address and T type of the value must
 69 //             match.
 70 // * Step 3:   Pre-runtime dispatch. This step checks whether a runtime call can be
 71 //             avoided, and in that case avoids it (calling raw accesses or
 72 //             primitive accesses in a build that does not require primitive GC barriers)
 73 // * Step 4:   Runtime-dispatch. This step performs a runtime dispatch to the corresponding
 74 //             BarrierSet::AccessBarrier accessor that attaches GC-required barriers
 75 //             to the access.
 76 // * Step 5.a: Barrier resolution. This step is invoked the first time a runtime-dispatch
 77 //             happens for an access. The appropriate BarrierSet::AccessBarrier accessor
 78 //             is resolved, then the function pointer is updated to that accessor for
 79 //             future invocations.
 80 // * Step 5.b: Post-runtime dispatch. This step now casts previously unknown types such
 81 //             as the address type of an oop on the heap (is it oop* or narrowOop*) to
 82 //             the appropriate type. It also splits sufficiently orthogonal accesses into
 83 //             different functions, such as whether the access involves oops or primitives
 84 //             and whether the access is performed on the heap or outside. Then the
 85 //             appropriate BarrierSet::AccessBarrier is called to perform the access.
 86 //
 87 // The implementation of step 1-4 resides in in accessBackend.hpp, to allow selected
 88 // accesses to be accessible from only access.hpp, as opposed to access.inline.hpp.
 89 // Steps 5.a and 5.b require knowledge about the GC backends, and therefore needs to
 90 // include the various GC backend .inline.hpp headers. Their implementation resides in
 91 // access.inline.hpp. The accesses that are allowed through the access.hpp file
 92 // must be instantiated in access.cpp using the INSTANTIATE_HPP_ACCESS macro.
 93 
 94 class InlineKlass;
 95 
 96 template <DecoratorSet decorators = DECORATORS_NONE>
 97 class Access: public AllStatic {
 98   // This function asserts that if an access gets passed in a decorator outside
 99   // of the expected_decorators, then something is wrong. It additionally checks
100   // the consistency of the decorators so that supposedly disjoint decorators are indeed
101   // disjoint. For example, an access can not be both in heap and on root at the
102   // same time.
103   template <DecoratorSet expected_decorators>
104   static void verify_decorators();
105 
106   template <DecoratorSet expected_mo_decorators>
107   static void verify_primitive_decorators() {
108     const DecoratorSet primitive_decorators = (AS_DECORATOR_MASK ^ AS_NO_KEEPALIVE) |
109                                               IN_HEAP | IS_ARRAY;
110     verify_decorators<expected_mo_decorators | primitive_decorators>();
111   }
112 
113   template <DecoratorSet expected_mo_decorators>
114   static void verify_oop_decorators() {
115     const DecoratorSet oop_decorators = AS_DECORATOR_MASK | IN_DECORATOR_MASK |
116                                         (ON_DECORATOR_MASK ^ ON_UNKNOWN_OOP_REF) | // no unknown oop refs outside of the heap
117                                         IS_ARRAY | IS_NOT_NULL | IS_DEST_UNINITIALIZED;
118     verify_decorators<expected_mo_decorators | oop_decorators>();
119   }
120 
121   template <DecoratorSet expected_mo_decorators>
122   static void verify_heap_oop_decorators() {
123     const DecoratorSet heap_oop_decorators = AS_DECORATOR_MASK | ON_DECORATOR_MASK |
124                                              IN_HEAP | IS_ARRAY | IS_NOT_NULL;
125     verify_decorators<expected_mo_decorators | heap_oop_decorators>();
126   }
127 
128   template <DecoratorSet expected_mo_decorators>
129   static void verify_heap_value_decorators() {
130     const DecoratorSet heap_value_decorators = IN_HEAP | IS_DEST_UNINITIALIZED;
131     verify_decorators<expected_mo_decorators | heap_value_decorators>();
132   }
133 
134   static const DecoratorSet load_mo_decorators = MO_UNORDERED | MO_RELAXED | MO_ACQUIRE | MO_SEQ_CST;
135   static const DecoratorSet store_mo_decorators = MO_UNORDERED | MO_RELAXED | MO_RELEASE | MO_SEQ_CST;
136   static const DecoratorSet atomic_xchg_mo_decorators = MO_SEQ_CST;
137   static const DecoratorSet atomic_cmpxchg_mo_decorators = MO_RELAXED | MO_SEQ_CST;
138 
139 protected:
140   template <typename T>
141   static inline void oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
142                                    arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
143                                    size_t length) {
144     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
145                       AS_DECORATOR_MASK | IS_ARRAY | IS_DEST_UNINITIALIZED>();
146     AccessInternal::arraycopy<decorators | INTERNAL_VALUE_IS_OOP>(src_obj, src_offset_in_bytes, src_raw,
147                                                                   dst_obj, dst_offset_in_bytes, dst_raw,
148                                                                   length);
149   }
150 
151   template <typename T>
152   static inline void arraycopy(arrayOop src_obj, size_t src_offset_in_bytes, const T* src_raw,
153                                arrayOop dst_obj, size_t dst_offset_in_bytes, T* dst_raw,
154                                size_t length) {
155     verify_decorators<ARRAYCOPY_DECORATOR_MASK | IN_HEAP |
156                       AS_DECORATOR_MASK | IS_ARRAY>();
157     AccessInternal::arraycopy<decorators>(src_obj, src_offset_in_bytes, src_raw,
158                                           dst_obj, dst_offset_in_bytes, dst_raw,
159                                           length);
160   }
161 
162 public:
163   // Primitive heap accesses
164   static inline AccessInternal::LoadAtProxy<decorators> load_at(oop base, ptrdiff_t offset) {
165     verify_primitive_decorators<load_mo_decorators>();
166     return AccessInternal::LoadAtProxy<decorators>(base, offset);
167   }
168 

204     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
205     OopType new_oop_value = new_value;
206     OopType compare_oop_value = compare_value;
207     return AccessInternal::atomic_cmpxchg_at<decorators | INTERNAL_VALUE_IS_OOP>(base, offset, compare_oop_value, new_oop_value);
208   }
209 
210   template <typename T>
211   static inline T oop_atomic_xchg_at(oop base, ptrdiff_t offset, T new_value) {
212     verify_heap_oop_decorators<atomic_xchg_mo_decorators>();
213     typedef typename AccessInternal::OopOrNarrowOop<T>::type OopType;
214     OopType new_oop_value = new_value;
215     return AccessInternal::atomic_xchg_at<decorators | INTERNAL_VALUE_IS_OOP>(base, offset, new_oop_value);
216   }
217 
218   // Clone an object from src to dst
219   static inline void clone(oop src, oop dst, size_t size) {
220     verify_decorators<IN_HEAP>();
221     AccessInternal::clone<decorators>(src, dst, size);
222   }
223 
224   // inline type heap access (when inlined)...
225 
226   // Copy value type data from src to dst
227   static inline void value_copy(void* src, void* dst, InlineKlass* md) {
228     verify_heap_value_decorators<IN_HEAP>();
229     AccessInternal::value_copy<decorators>(src, dst, md);
230   }
231 
232   // Primitive accesses
233   template <typename P>
234   static inline P load(P* addr) {
235     verify_primitive_decorators<load_mo_decorators>();
236     return AccessInternal::load<decorators, P, P>(addr);
237   }
238 
239   template <typename P, typename T>
240   static inline void store(P* addr, T value) {
241     verify_primitive_decorators<store_mo_decorators>();
242     AccessInternal::store<decorators>(addr, value);
243   }
244 
245   template <typename P, typename T>
246   static inline T atomic_cmpxchg(P* addr, T compare_value, T new_value) {
247     verify_primitive_decorators<atomic_cmpxchg_mo_decorators>();
248     return AccessInternal::atomic_cmpxchg<decorators>(addr, compare_value, new_value);
249   }
250 
251   template <typename P, typename T>

317   }
318 
319   template <typename T>
320   static inline void arraycopy_to_native(arrayOop src_obj, size_t src_offset_in_bytes,
321                                          T* dst,
322                                          size_t length) {
323     AccessT::arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const T*>(NULL),
324                        NULL, 0, dst,
325                        length);
326   }
327 
328   template <typename T>
329   static inline void arraycopy_from_native(const T* src,
330                                            arrayOop dst_obj, size_t dst_offset_in_bytes,
331                                            size_t length) {
332     AccessT::arraycopy(NULL, 0, src,
333                        dst_obj, dst_offset_in_bytes, reinterpret_cast<T*>(NULL),
334                        length);
335   }
336 
337   static inline void oop_arraycopy(arrayOop src_obj, size_t src_offset_in_bytes,
338                                    arrayOop dst_obj, size_t dst_offset_in_bytes,
339                                    size_t length) {
340     AccessT::oop_arraycopy(src_obj, src_offset_in_bytes, reinterpret_cast<const HeapWord*>(NULL),
341                            dst_obj, dst_offset_in_bytes, reinterpret_cast<HeapWord*>(NULL),
342                            length);
343   }
344 
345   template <typename T>
346   static inline void oop_arraycopy_raw(T* src, T* dst, size_t length) {
347     AccessT::oop_arraycopy(NULL, 0, src,
348                            NULL, 0, dst,
349                            length);
350   }
351 
352 };
353 
354 template <DecoratorSet decorators>
355 template <DecoratorSet expected_decorators>
356 void Access<decorators>::verify_decorators() {
357   STATIC_ASSERT((~expected_decorators & decorators) == 0); // unexpected decorator used
358   const DecoratorSet barrier_strength_decorators = decorators & AS_DECORATOR_MASK;
359   STATIC_ASSERT(barrier_strength_decorators == 0 || ( // make sure barrier strength decorators are disjoint if set
360     (barrier_strength_decorators ^ AS_NO_KEEPALIVE) == 0 ||
361     (barrier_strength_decorators ^ AS_RAW) == 0 ||
362     (barrier_strength_decorators ^ AS_NORMAL) == 0
363   ));
364   const DecoratorSet ref_strength_decorators = decorators & ON_DECORATOR_MASK;
365   STATIC_ASSERT(ref_strength_decorators == 0 || ( // make sure ref strength decorators are disjoint if set
366     (ref_strength_decorators ^ ON_STRONG_OOP_REF) == 0 ||
367     (ref_strength_decorators ^ ON_WEAK_OOP_REF) == 0 ||
368     (ref_strength_decorators ^ ON_PHANTOM_OOP_REF) == 0 ||
369     (ref_strength_decorators ^ ON_UNKNOWN_OOP_REF) == 0
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