1 /* 2 * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved. 3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. 4 * 5 * This code is free software; you can redistribute it and/or modify it 6 * under the terms of the GNU General Public License version 2 only, as 7 * published by the Free Software Foundation. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 * 23 */ 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 --- EOF ---