1 /*
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 24 
 25 #ifndef SHARE_OOPS_ACCESSDECORATORS_HPP
 26 #define SHARE_OOPS_ACCESSDECORATORS_HPP
 27 
 28 #include "gc/shared/barrierSetConfig.hpp"
 29 #include "memory/allocation.hpp"
 30 #include "metaprogramming/integralConstant.hpp"
 31 #include "utilities/globalDefinitions.hpp"
 32 
 33 // A decorator is an attribute or property that affects the way a memory access is performed in some way.
 34 // There are different groups of decorators. Some have to do with memory ordering, others to do with,
 35 // e.g. strength of references, strength of GC barriers, or whether compression should be applied or not.
 36 // Some decorators are set at buildtime, such as whether primitives require GC barriers or not, others
 37 // at callsites such as whether an access is in the heap or not, and others are resolved at runtime
 38 // such as GC-specific barriers and encoding/decoding compressed oops.
 39 typedef uint64_t DecoratorSet;
 40 
 41 // The HasDecorator trait can help at compile-time determining whether a decorator set
 42 // has an intersection with a certain other decorator set
 43 template <DecoratorSet decorators, DecoratorSet decorator>
 44 struct HasDecorator: public IntegralConstant<bool, (decorators & decorator) != 0> {};
 45 
 46 // == Internal Decorators - do not use ==
 47 // * INTERNAL_EMPTY: This is the name for the empty decorator set (in absence of other decorators).
 48 // * INTERNAL_CONVERT_COMPRESSED_OOPS: This is an oop access that will require converting an oop
 49 //   to a narrowOop or vice versa, if UseCompressedOops is known to be set.
 50 // * INTERNAL_VALUE_IS_OOP: Remember that the involved access is on oop rather than primitive.
 51 const DecoratorSet INTERNAL_EMPTY                    = UCONST64(0);
 52 const DecoratorSet INTERNAL_CONVERT_COMPRESSED_OOP   = UCONST64(1) << 1;
 53 const DecoratorSet INTERNAL_VALUE_IS_OOP             = UCONST64(1) << 2;
 54 
 55 // == Internal build-time Decorators ==
 56 // * INTERNAL_BT_BARRIER_ON_PRIMITIVES: This is set in the barrierSetConfig.hpp file.
 57 // * INTERNAL_BT_TO_SPACE_INVARIANT: This is set in the barrierSetConfig.hpp file iff
 58 //   no GC is bundled in the build that is to-space invariant.
 59 const DecoratorSet INTERNAL_BT_BARRIER_ON_PRIMITIVES = UCONST64(1) << 3;
 60 const DecoratorSet INTERNAL_BT_TO_SPACE_INVARIANT    = UCONST64(1) << 4;
 61 
 62 // == Internal run-time Decorators ==
 63 // * INTERNAL_RT_USE_COMPRESSED_OOPS: This decorator will be set in runtime resolved
 64 //   access backends iff UseCompressedOops is true.
 65 const DecoratorSet INTERNAL_RT_USE_COMPRESSED_OOPS   = UCONST64(1) << 5;
 66 
 67 const DecoratorSet INTERNAL_DECORATOR_MASK           = INTERNAL_CONVERT_COMPRESSED_OOP | INTERNAL_VALUE_IS_OOP |
 68                                                        INTERNAL_BT_BARRIER_ON_PRIMITIVES | INTERNAL_RT_USE_COMPRESSED_OOPS;
 69 
 70 // == Memory Ordering Decorators ==
 71 // The memory ordering decorators can be described in the following way:
 72 // === Decorator Rules ===
 73 // The different types of memory ordering guarantees have a strict order of strength.
 74 // Explicitly specifying the stronger ordering implies that the guarantees of the weaker
 75 // property holds too. The names come from the C++11 atomic operations, and typically
 76 // have a JMM equivalent property.
 77 // The equivalence may be viewed like this:
 78 // MO_UNORDERED is equivalent to JMM plain.
 79 // MO_VOLATILE has no equivalence in JMM, because it's a C++ thing.
 80 // MO_RELAXED is equivalent to JMM opaque.
 81 // MO_ACQUIRE is equivalent to JMM acquire.
 82 // MO_RELEASE is equivalent to JMM release.
 83 // MO_SEQ_CST is equivalent to JMM volatile.
 84 //
 85 // === Stores ===
 86 //  * MO_UNORDERED (Default): No guarantees.
 87 //    - The compiler and hardware are free to reorder aggressively. And they will.
 88 //  * MO_VOLATILE: Volatile stores (in the C++ sense).
 89 //    - The stores are not reordered by the compiler (but possibly the HW) w.r.t. other
 90 //      volatile accesses in program order (but possibly non-volatile accesses).
 91 //  * MO_RELAXED: Relaxed atomic stores.
 92 //    - The stores are atomic.
 93 //    - Guarantees from volatile stores hold.
 94 //  * MO_RELEASE: Releasing stores.
 95 //    - The releasing store will make its preceding memory accesses observable to memory accesses
 96 //      subsequent to an acquiring load observing this releasing store.
 97 //    - Guarantees from relaxed stores hold.
 98 //  * MO_SEQ_CST: Sequentially consistent stores.
 99 //    - The stores are observed in the same order by MO_SEQ_CST loads on other processors
100 //    - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
101 //    - Guarantees from releasing stores hold.
102 // === Loads ===
103 //  * MO_UNORDERED (Default): No guarantees
104 //    - The compiler and hardware are free to reorder aggressively. And they will.
105 //  * MO_VOLATILE: Volatile loads (in the C++ sense).
106 //    - The loads are not reordered by the compiler (but possibly the HW) w.r.t. other
107 //      volatile accesses in program order (but possibly non-volatile accesses).
108 //  * MO_RELAXED: Relaxed atomic loads.
109 //    - The loads are atomic.
110 //    - Guarantees from volatile loads hold.
111 //  * MO_ACQUIRE: Acquiring loads.
112 //    - An acquiring load will make subsequent memory accesses observe the memory accesses
113 //      preceding the releasing store that the acquiring load observed.
114 //    - Guarantees from relaxed loads hold.
115 //  * MO_SEQ_CST: Sequentially consistent loads.
116 //    - These loads observe MO_SEQ_CST stores in the same order on other processors
117 //    - Preceding loads and stores in program order are not reordered with subsequent loads and stores in program order.
118 //    - Guarantees from acquiring loads hold.
119 // === Atomic Cmpxchg ===
120 //  * MO_RELAXED: Atomic but relaxed cmpxchg.
121 //    - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold unconditionally.
122 //  * MO_SEQ_CST: Sequentially consistent cmpxchg.
123 //    - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold unconditionally.
124 // === Atomic Xchg ===
125 //  * MO_RELAXED: Atomic but relaxed atomic xchg.
126 //    - Guarantees from MO_RELAXED loads and MO_RELAXED stores hold.
127 //  * MO_SEQ_CST: Sequentially consistent xchg.
128 //    - Guarantees from MO_SEQ_CST loads and MO_SEQ_CST stores hold.
129 const DecoratorSet MO_UNORDERED      = UCONST64(1) << 6;
130 const DecoratorSet MO_VOLATILE       = UCONST64(1) << 7;
131 const DecoratorSet MO_RELAXED        = UCONST64(1) << 8;
132 const DecoratorSet MO_ACQUIRE        = UCONST64(1) << 9;
133 const DecoratorSet MO_RELEASE        = UCONST64(1) << 10;
134 const DecoratorSet MO_SEQ_CST        = UCONST64(1) << 11;
135 const DecoratorSet MO_DECORATOR_MASK = MO_UNORDERED | MO_VOLATILE | MO_RELAXED |
136                                        MO_ACQUIRE | MO_RELEASE | MO_SEQ_CST;
137 
138 // === Barrier Strength Decorators ===
139 // * AS_RAW: The access will translate into a raw memory access, hence ignoring all semantic concerns
140 //   except memory ordering and compressed oops. This will bypass runtime function pointer dispatching
141 //   in the pipeline and hardwire to raw accesses without going trough the GC access barriers.
142 //  - Accesses on oop* translate to raw memory accesses without runtime checks
143 //  - Accesses on narrowOop* translate to encoded/decoded memory accesses without runtime checks
144 //  - Accesses on HeapWord* translate to a runtime check choosing one of the above
145 //  - Accesses on other types translate to raw memory accesses without runtime checks
146 // * AS_DEST_NOT_INITIALIZED: This property can be important to e.g. SATB barriers by
147 //   marking that the previous value is uninitialized nonsense rather than a real value.
148 // * AS_NO_KEEPALIVE: The barrier is used only on oop references and will not keep any involved objects
149 //   alive, regardless of the type of reference being accessed. It will however perform the memory access
150 //   in a consistent way w.r.t. e.g. concurrent compaction, so that the right field is being accessed,
151 //   or maintain, e.g. intergenerational or interregional pointers if applicable. This should be used with
152 //   extreme caution in isolated scopes.
153 // * AS_NORMAL: The accesses will be resolved to an accessor on the BarrierSet class, giving the
154 //   responsibility of performing the access and what barriers to be performed to the GC. This is the default.
155 //   Note that primitive accesses will only be resolved on the barrier set if the appropriate build-time
156 //   decorator for enabling primitive barriers is enabled for the build.
157 const DecoratorSet AS_RAW                  = UCONST64(1) << 12;
158 const DecoratorSet AS_DEST_NOT_INITIALIZED = UCONST64(1) << 13;
159 const DecoratorSet AS_NO_KEEPALIVE         = UCONST64(1) << 14;
160 const DecoratorSet AS_NORMAL               = UCONST64(1) << 15;
161 const DecoratorSet AS_DECORATOR_MASK       = AS_RAW | AS_DEST_NOT_INITIALIZED |
162                                              AS_NO_KEEPALIVE | AS_NORMAL;
163 
164 // === Reference Strength Decorators ===
165 // These decorators only apply to accesses on oop-like types (oop/narrowOop).
166 // * ON_STRONG_OOP_REF: Memory access is performed on a strongly reachable reference.
167 // * ON_WEAK_OOP_REF: The memory access is performed on a weakly reachable reference.
168 // * ON_PHANTOM_OOP_REF: The memory access is performed on a phantomly reachable reference.
169 //   This is the same ring of strength as jweak and weak oops in the VM.
170 // * ON_UNKNOWN_OOP_REF: The memory access is performed on a reference of unknown strength.
171 //   This could for example come from the unsafe API.
172 // * Default (no explicit reference strength specified): ON_STRONG_OOP_REF
173 const DecoratorSet ON_STRONG_OOP_REF  = UCONST64(1) << 16;
174 const DecoratorSet ON_WEAK_OOP_REF    = UCONST64(1) << 17;
175 const DecoratorSet ON_PHANTOM_OOP_REF = UCONST64(1) << 18;
176 const DecoratorSet ON_UNKNOWN_OOP_REF = UCONST64(1) << 19;
177 const DecoratorSet ON_DECORATOR_MASK  = ON_STRONG_OOP_REF | ON_WEAK_OOP_REF |
178                                         ON_PHANTOM_OOP_REF | ON_UNKNOWN_OOP_REF;
179 
180 // === Access Location ===
181 // Accesses can take place in, e.g. the heap, old or young generation and different native roots.
182 // The location is important to the GC as it may imply different actions. The following decorators are used:
183 // * IN_HEAP: The access is performed in the heap. Many barriers such as card marking will
184 //   be omitted if this decorator is not set.
185 // * IN_HEAP_ARRAY: The access is performed on a heap allocated array. This is sometimes a special case
186 //   for some GCs, and implies that it is an IN_HEAP.
187 // * IN_ROOT: The access is performed in an off-heap data structure pointing into the Java heap.
188 // * IN_CONCURRENT_ROOT: The access is performed in an off-heap data structure pointing into the Java heap,
189 //   but is notably not scanned during safepoints. This is sometimes a special case for some GCs and
190 //   implies that it is also an IN_ROOT.
191 const DecoratorSet IN_HEAP            = UCONST64(1) << 20;
192 const DecoratorSet IN_HEAP_ARRAY      = UCONST64(1) << 21;
193 const DecoratorSet IN_ROOT            = UCONST64(1) << 22;
194 const DecoratorSet IN_CONCURRENT_ROOT = UCONST64(1) << 23;
195 const DecoratorSet IN_ARCHIVE_ROOT    = UCONST64(1) << 24;
196 const DecoratorSet IN_DECORATOR_MASK  = IN_HEAP | IN_HEAP_ARRAY |
197                                         IN_ROOT | IN_CONCURRENT_ROOT |
198                                         IN_ARCHIVE_ROOT;
199 
200 // == Value Decorators ==
201 // * OOP_NOT_NULL: This property can make certain barriers faster such as compressing oops.
202 const DecoratorSet OOP_NOT_NULL       = UCONST64(1) << 25;
203 const DecoratorSet OOP_DECORATOR_MASK = OOP_NOT_NULL;
204 
205 // == Arraycopy Decorators ==
206 // * ARRAYCOPY_CHECKCAST: This property means that the class of the objects in source
207 //   are not guaranteed to be subclasses of the class of the destination array. This requires
208 //   a check-cast barrier during the copying operation. If this is not set, it is assumed
209 //   that the array is covariant: (the source array type is-a destination array type)
210 // * ARRAYCOPY_DISJOINT: This property means that it is known that the two array ranges
211 //   are disjoint.
212 // * ARRAYCOPY_ARRAYOF: The copy is in the arrayof form.
213 // * ARRAYCOPY_ATOMIC: The accesses have to be atomic over the size of its elements.
214 // * ARRAYCOPY_ALIGNED: The accesses have to be aligned on a HeapWord.
215 const DecoratorSet ARRAYCOPY_CHECKCAST            = UCONST64(1) << 26;
216 const DecoratorSet ARRAYCOPY_DISJOINT             = UCONST64(1) << 27;
217 const DecoratorSet ARRAYCOPY_ARRAYOF              = UCONST64(1) << 28;
218 const DecoratorSet ARRAYCOPY_ATOMIC               = UCONST64(1) << 29;
219 const DecoratorSet ARRAYCOPY_ALIGNED              = UCONST64(1) << 30;
220 const DecoratorSet ARRAYCOPY_DECORATOR_MASK       = ARRAYCOPY_CHECKCAST | ARRAYCOPY_DISJOINT |
221                                                     ARRAYCOPY_DISJOINT | ARRAYCOPY_ARRAYOF |
222                                                     ARRAYCOPY_ATOMIC | ARRAYCOPY_ALIGNED;
223 
224 // Keep track of the last decorator.
225 const DecoratorSet DECORATOR_LAST = UCONST64(1) << 30;
226 
227 namespace AccessInternal {
228   // This class adds implied decorators that follow according to decorator rules.
229   // For example adding default reference strength and default memory ordering
230   // semantics.
231   template <DecoratorSet input_decorators>
232   struct DecoratorFixup: AllStatic {
233     // If no reference strength has been picked, then strong will be picked
234     static const DecoratorSet ref_strength_default = input_decorators |
235       (((ON_DECORATOR_MASK & input_decorators) == 0 && (INTERNAL_VALUE_IS_OOP & input_decorators) != 0) ?
236        ON_STRONG_OOP_REF : INTERNAL_EMPTY);
237     // If no memory ordering has been picked, unordered will be picked
238     static const DecoratorSet memory_ordering_default = ref_strength_default |
239       ((MO_DECORATOR_MASK & ref_strength_default) == 0 ? MO_UNORDERED : INTERNAL_EMPTY);
240     // If no barrier strength has been picked, normal will be used
241     static const DecoratorSet barrier_strength_default = memory_ordering_default |
242       ((AS_DECORATOR_MASK & memory_ordering_default) == 0 ? AS_NORMAL : INTERNAL_EMPTY);
243     // Heap array accesses imply it is a heap access
244     static const DecoratorSet heap_array_is_in_heap = barrier_strength_default |
245       ((IN_HEAP_ARRAY & barrier_strength_default) != 0 ? IN_HEAP : INTERNAL_EMPTY);
246     static const DecoratorSet conc_root_is_root = heap_array_is_in_heap |
247       ((IN_CONCURRENT_ROOT & heap_array_is_in_heap) != 0 ? IN_ROOT : INTERNAL_EMPTY);
248     static const DecoratorSet archive_root_is_root = conc_root_is_root |
249       ((IN_ARCHIVE_ROOT & conc_root_is_root) != 0 ? IN_ROOT : INTERNAL_EMPTY);
250     static const DecoratorSet value = archive_root_is_root | BT_BUILDTIME_DECORATORS;
251   };
252 
253   // This function implements the above DecoratorFixup rules, but without meta
254   // programming for code generation that does not use templates.
255   inline DecoratorSet decorator_fixup(DecoratorSet input_decorators) {
256     // If no reference strength has been picked, then strong will be picked
257     DecoratorSet ref_strength_default = input_decorators |
258       (((ON_DECORATOR_MASK & input_decorators) == 0 && (INTERNAL_VALUE_IS_OOP & input_decorators) != 0) ?
259        ON_STRONG_OOP_REF : INTERNAL_EMPTY);
260     // If no memory ordering has been picked, unordered will be picked
261     DecoratorSet memory_ordering_default = ref_strength_default |
262       ((MO_DECORATOR_MASK & ref_strength_default) == 0 ? MO_UNORDERED : INTERNAL_EMPTY);
263     // If no barrier strength has been picked, normal will be used
264     DecoratorSet barrier_strength_default = memory_ordering_default |
265       ((AS_DECORATOR_MASK & memory_ordering_default) == 0 ? AS_NORMAL : INTERNAL_EMPTY);
266     // Heap array accesses imply it is a heap access
267     DecoratorSet heap_array_is_in_heap = barrier_strength_default |
268       ((IN_HEAP_ARRAY & barrier_strength_default) != 0 ? IN_HEAP : INTERNAL_EMPTY);
269     DecoratorSet conc_root_is_root = heap_array_is_in_heap |
270       ((IN_CONCURRENT_ROOT & heap_array_is_in_heap) != 0 ? IN_ROOT : INTERNAL_EMPTY);
271     DecoratorSet archive_root_is_root = conc_root_is_root |
272       ((IN_ARCHIVE_ROOT & conc_root_is_root) != 0 ? IN_ROOT : INTERNAL_EMPTY);
273     DecoratorSet value = archive_root_is_root | BT_BUILDTIME_DECORATORS;
274     return value;
275   }
276 }
277 
278 #endif // SHARE_OOPS_ACCESSDECORATORS_HPP