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