mfbt/AtomicBitfields.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef mozilla_AtomicBitfields_h
   8 #define mozilla_AtomicBitfields_h
   9
  10 #include "mozilla/Assertions.h"
  11 #include "mozilla/MacroArgs.h"
  12 #include "mozilla/MacroForEach.h"
  13
  14 #include <atomic>
  15 #include <limits>
  16 #include <stdint.h>
  17 #include <type_traits>
  18
  19 namespace mozilla {
  20
  21 // Creates a series of atomic bitfields.
  22 //
  23 // |aBitfields| is the name of the underlying storage for the bitfields.
  24 // |aBitFieldsSize| is the size of the underlying storage (8, 16, 32, or 64).
  25 //
  26 // Bitfields are specified as a triplet of (type, name, size), which mirrors
  27 // the way you declare native C++ bitfields (bool mMyField1: 1). Trailing
  28 // commas are not supported in the list of bitfields.
  29 //
  30 // Signed integer types are not supported by this Macro to avoid dealing with
  31 // packing/unpacking the sign bit and C++'s general messiness around signed
  32 // integer representations not being fully defined.
  33 //
  34 // You cannot request a single field that's the
  35 // size of the the entire bitfield storage. Just use a normal atomic integer!
  36 //
  37 //
  38 // ========================== SEMANTICS AND SAFETY ============================
  39 //
  40 // All fields are default-initialized to 0.
  41 //
  42 // In debug builds, storing a value to a bitfield that's larger than its bits
  43 // can fit will trigger an assertion. In release builds, the value will just be
  44 // masked off.
  45 //
  46 // If you request anything unsupported by this macro it should result in
  47 // a compile-time error (either a static assert or just weird macro errors).
  48 // For instance, this macro will statically prevent using more bits than
  49 // |aBitFieldsSize|, so specifying the size is just to prevent accidentally
  50 // making the storage bigger.
  51 //
  52 // Each field will get a Load$NAME and Store$Name method which will atomically
  53 // load and store the requested value with a Sequentially Consistent memory
  54 // order (to be on the safe side). Storing a field requires a compare-exchange,
  55 // so a thread may get stalled if there's a lot of contention on the bitfields.
  56 //
  57 //
  58 // ============================== MOTIVATION ==================================
  59 //
  60 // You might be wondering: why would I need atomic bitfields? Well as it turns
  61 // out, bitfields and concurrency mess a lot of people up!
  62 //
  63 // CPUs don't have operations to write to a handful of bits -- they generally
  64 // only have the precision of a byte. So when you use C++'s native bitfields,
  65 // the compiler generates code to mask and shift the values in for you. This
  66 // means writing to a single field will actually overwrite all the other
  67 // bitfields that are packed in with it!
  68 //
  69 // In single-threaded code this is fine; the old values are loaded and written
  70 // back by the compiler's generated code. But in concurrent code, it means
  71 // that accessing two different fields can be an unexpected Data Race (which is
  72 // Undefined Behavior!).
  73 //
  74 // By using MOZ_ATOMIC_BITFIELDS, you protect yourself from these Data Races,
  75 // and don't have to worry about writes getting lost.
  76 //
  77 //
  78 // ================================ EXAMPLE ===================================
  79 //
  80 //   #include "mozilla/AtomicBitfields.h"
  81 //   #include <stdint.h>
  82 //
  83 //
  84 //   struct MyType {
  85 //     MOZ_ATOMIC_BITFIELDS(mAtomicFields, 8, (
  86 //      (bool, IsDownloaded, 1),
  87 //      (uint32_t, SomeData, 2),
  88 //      (uint8_t, OtherData, 5)
  89 //     ))
  90 //
  91 //     int32_t aNormalInteger;
  92 //
  93 //     explicit MyType(uint32_t aSomeData): aNormalInteger(7) {
  94 //       StoreSomeData(aSomeData);
  95 //       // Other bitfields were already default initialized to 0/false
  96 //     }
  97 //   };
  98 //
  99 //
 100 //   int main() {
 101 //     MyType val(3);
 102 //
 103 //     if (!val.LoadIsDownloaded()) {
 104 //       val.StoreOtherData(2);
 105 //       val.StoreIsDownloaded(true);
 106 //     }
 107 //   }
 108 //
 109 //
 110 // ============================== GENERATED ===================================
 111 //
 112 // This macro is a real mess to read because, well, it's a macro. So for the
 113 // sake of anyone who has to review or modify its internals, here's a rough
 114 // sketch of what the above example would expand to:
 115 //
 116 //   struct MyType {
 117 //     // The actual storage of the bitfields, initialized to 0.
 118 //     std::atomic_uint8_t mAtomicFields{0};
 119 //
 120 //     // How many bits were actually used (in this case, all of them).
 121 //     static const size_t mAtomicFields_USED_BITS = 8;
 122 //
 123 //     // The offset values for each field.
 124 //     static const size_t mAtomicFieldsIsDownloaded = 0;
 125 //     static const size_t mAtomicFieldsSomeData = 1;
 126 //     static const size_t mAtomicFieldsOtherData = 3;
 127 //
 128 //     // Quick safety guard to prevent capacity overflow.
 129 //     static_assert(mAtomicFields_USED_BITS <= 8);
 130 //
 131 //     // Asserts that fields are reasonable.
 132 //     static_assert(8>1, "mAtomicFields: MOZ_ATOMIC_BITFIELDS field too big");
 133 //     static_assert(std::is_unsigned<bool>(), "mAtomicFields:
 134 //     MOZ_ATOMIC_BITFIELDS doesn't support signed payloads");
 135 //     // ...and so on
 136 //
 137 //     // Load/Store methods for all the fields.
 138 //
 139 //     bool LoadIsDownloaded() { ... }
 140 //     void StoreIsDownloaded(bool aValue) { ... }
 141 //
 142 //     uint32_t LoadSomeData() { ... }
 143 //     void StoreSomeData(uint32_t aValue) { ... }
 144 //
 145 //     uint8_t LoadOtherData() { ... }
 146 //     void StoreOtherData(uint8_t aValue) { ... }
 147 //
 148 //
 149 //     // Remainder of the struct body continues normally.
 150 //     int32_t aNormalInteger;
 151 //     explicit MyType(uint32_t aSomeData): aNormalInteger(7) {
 152 //       StoreSomeData(aSomeData);
 153 //       // Other bitfields were already default initialized to 0/false.
 154 //     }
 155 //   }
 156 //
 157 // Also if you're wondering why there's so many MOZ_CONCAT's -- it's because
 158 // the preprocessor sometimes gets confused if we use ## on certain arguments.
 159 // MOZ_CONCAT reliably kept the preprocessor happy, sorry it's so ugly!
 160 //
 161 //
 162 // ==================== FIXMES / FUTURE WORK ==================================
 163 //
 164 // * It would be nice if LoadField could be IsField for booleans.
 165 //
 166 // * For the case of setting something to all 1's or 0's, we can use
 167 //   |fetch_or| or |fetch_and| instead of |compare_exchange_weak|. Is this
 168 //   worth providing? (Possibly for 1-bit boolean fields?)
 169 //
 170 // * Try harder to hide the atomic/enum/array internals from
 171 //   the outer struct?
 172 //
 173 #define MOZ_ATOMIC_BITFIELDS(aBitfields, aBitfieldsSize, aFields)             \
 174   std::atomic_uint##aBitfieldsSize##_t aBitfields{0};                         \
 175                                                                               \
 176   static const size_t MOZ_CONCAT(aBitfields, _USED_BITS) =                    \
 177       MOZ_FOR_EACH_SEPARATED(MOZ_ATOMIC_BITFIELDS_FIELD_SIZE, (+), (),        \
 178                              aFields);                                        \
 179                                                                               \
 180   MOZ_ROLL_EACH(MOZ_ATOMIC_BITFIELDS_OFFSET_HELPER1, (aBitfields, ), aFields) \
 181                                                                               \
 182   static_assert(MOZ_CONCAT(aBitfields, _USED_BITS) <= aBitfieldsSize,         \
 183                 #aBitfields ": Maximum bits (" #aBitfieldsSize                \
 184                             ") exceeded for MOZ_ATOMIC_BITFIELDS instance");  \
 185                                                                               \
 186   MOZ_FOR_EACH(MOZ_ATOMIC_BITFIELDS_FIELD_HELPER,                             \
 187                (aBitfields, aBitfieldsSize, ), aFields)
 188
 189 // Just a helper to unpack the head of the list.
 190 #define MOZ_ATOMIC_BITFIELDS_OFFSET_HELPER1(aBitfields, aFields) \
 191   MOZ_ATOMIC_BITFIELDS_OFFSET_HELPER2(aBitfields, MOZ_ARG_1 aFields, aFields);
 192
 193 // Just a helper to unpack the name and call the real function.
 194 #define MOZ_ATOMIC_BITFIELDS_OFFSET_HELPER2(aBitfields, aField, aFields) \
 195   MOZ_ATOMIC_BITFIELDS_OFFSET(aBitfields, MOZ_ARG_2 aField, aFields)
 196
 197 // To compute the offset of a field, why sum up all the offsets after it
 198 // (inclusive) and subtract that from the total sum itself. We do this to swap
 199 // the rolling sum that |MOZ_ROLL_EACH| gets us from descending to ascending.
 200 #define MOZ_ATOMIC_BITFIELDS_OFFSET(aBitfields, aFieldName, aFields)    \
 201   static const size_t MOZ_CONCAT(aBitfields, aFieldName) =              \
 202       MOZ_CONCAT(aBitfields, _USED_BITS) -                              \
 203       (MOZ_FOR_EACH_SEPARATED(MOZ_ATOMIC_BITFIELDS_FIELD_SIZE, (+), (), \
 204                               aFields));
 205
 206 // Just a more clearly named way of unpacking the size.
 207 #define MOZ_ATOMIC_BITFIELDS_FIELD_SIZE(aArgs) MOZ_ARG_3 aArgs
 208
 209 // Just a helper to unpack the tuple and call the real function.
 210 #define MOZ_ATOMIC_BITFIELDS_FIELD_HELPER(aBitfields, aBitfieldsSize, aArgs) \
 211   MOZ_ATOMIC_BITFIELDS_FIELD(aBitfields, aBitfieldsSize, MOZ_ARG_1 aArgs,    \
 212                              MOZ_ARG_2 aArgs, MOZ_ARG_3 aArgs)
 213
 214 // We need to disable this with coverity because it doesn't like checking that
 215 // booleans are < 2 (because they always are).
 216 #ifdef __COVERITY__
 217 #  define MOZ_ATOMIC_BITFIELDS_STORE_GUARD(aValue, aFieldSize)
 218 #else
 219 #  define MOZ_ATOMIC_BITFIELDS_STORE_GUARD(aValue, aFieldSize) \
 220     MOZ_ASSERT(((uint64_t)aValue) < (1ull << aFieldSize),      \
 221                "Stored value exceeded capacity of bitfield!")
 222 #endif
 223
 224 // Generates the Load and Store methods for each field.
 225 //
 226 // Some comments here because inline macro comments are a pain in the neck:
 227 //
 228 // Most of the locals are forward declared to minimize messy macroified
 229 // type declaration. Also a lot of locals are used to try to make things
 230 // a little more clear, while also avoiding integer promotion issues.
 231 // This is why some locals are literally just copying a value we already have:
 232 // to force it to the right size.
 233 //
 234 // There's an annoying overflow case where a bitfields instance has a field
 235 // that is the same size as the bitfields. Rather than trying to handle that,
 236 // we just static_assert against it.
 237 //
 238 //
 239 // BITMATH EXPLAINED:
 240 //
 241 // For |Load$Name|:
 242 //
 243 //    mask = ((1 << fieldSize) - 1) << offset
 244 //
 245 // If you subtract 1 from a value with 1 bit set you get all 1's below that bit.
 246 // This is perfect for ANDing out |fieldSize| bits. We shift by |offset| to get
 247 // it in the right place.
 248 //
 249 //    value = (aBitfields.load() & mask) >> offset
 250 //
 251 // This sets every bit we're not interested in to 0. Shifting the result by
 252 // |offset| converts the value back to its native format, ready to be cast
 253 // up to an integer type.
 254 //
 255 //
 256 // For |Store$Name|:
 257 //
 258 //    packedValue = (resizedValue << offset) & mask
 259 //
 260 // This converts a native value to the packed format. If the value is in bounds,
 261 // the AND will do nothing. If it's out of bounds (not checked in release),
 262 // then it will cause the value to wrap around by modulo 2^aFieldSize, just like
 263 // a normal uint.
 264 //
 265 //    clearedValue = oldValue & ~mask;
 266 //
 267 // This clears the bits where our field is stored on our bitfield storage by
 268 // ANDing it with an inverted (NOTed) mask.
 269 //
 270 //    newValue = clearedValue | packedValue;
 271 //
 272 // Once we have |packedValue| and |clearedValue| they just need to be ORed
 273 // together to merge the new field value with the old values of all the other
 274 // fields.
 275 //
 276 // This last step is done in a while loop because someone else can modify
 277 // the bits before we have a chance to. If we didn't guard against this,
 278 // our write would undo the write the other thread did. |compare_exchange_weak|
 279 // is specifically designed to handle this. We give it what we expect the
 280 // current value to be, and what we want it to be. If someone else modifies
 281 // the bitfields before us, then we will reload the value and try again.
 282 //
 283 // Note that |compare_exchange_weak| writes back the actual value to the
 284 // "expected" argument (it's passed by-reference), so we don't need to do
 285 // another load in the body of the loop when we fail to write our result.
 286 #define MOZ_ATOMIC_BITFIELDS_FIELD(aBitfields, aBitfieldsSize, aFieldType, \
 287                                    aFieldName, aFieldSize)                 \
 288   static_assert(aBitfieldsSize > aFieldSize,                               \
 289                 #aBitfields ": MOZ_ATOMIC_BITFIELDS field too big");       \
 290   static_assert(std::is_unsigned<aFieldType>(), #aBitfields                \
 291                 ": MOZ_ATOMIC_BITFIELDS doesn't support signed payloads"); \
 292                                                                            \
 293   aFieldType MOZ_CONCAT(Load, aFieldName)() const {                        \
 294     uint##aBitfieldsSize##_t fieldSize, mask, masked, value;               \
 295     size_t offset = MOZ_CONCAT(aBitfields, aFieldName);                    \
 296     fieldSize = aFieldSize;                                                \
 297     mask = ((1ull << fieldSize) - 1ull) << offset;                         \
 298     masked = aBitfields.load() & mask;                                     \
 299     value = (masked >> offset);                                            \
 300     return value;                                                          \
 301   }                                                                        \
 302                                                                            \
 303   void MOZ_CONCAT(Store, aFieldName)(aFieldType aValue) {                  \
 304     MOZ_ATOMIC_BITFIELDS_STORE_GUARD(aValue, aFieldSize);                  \
 305     uint##aBitfieldsSize##_t fieldSize, mask, resizedValue, packedValue,   \
 306         oldValue, clearedValue, newValue;                                  \
 307     size_t offset = MOZ_CONCAT(aBitfields, aFieldName);                    \
 308     fieldSize = aFieldSize;                                                \
 309     mask = ((1ull << fieldSize) - 1ull) << offset;                         \
 310     resizedValue = aValue;                                                 \
 311     packedValue = (resizedValue << offset) & mask;                         \
 312     oldValue = aBitfields.load();                                          \
 313     do {                                                                   \
 314       clearedValue = oldValue & ~mask;                                     \
 315       newValue = clearedValue | packedValue;                               \
 316     } while (!aBitfields.compare_exchange_weak(oldValue, newValue));       \
 317   }
 318
 319 // OK SO THIS IS A GROSS HACK. GCC 10.2 (and below) has a bug[1] where it
 320 // doesn't allow a static array to reference itself in its initializer, so we
 321 // need to create a hacky way to produce a rolling sum of all the offsets.
 322 //
 323 // To do this, we make a tweaked version of |MOZ_FOR_EACH| which instead of
 324 // passing just one argument to |aMacro| it passes the remaining values of
 325 // |aArgs|.
 326 //
 327 // This allows us to expand an input (a, b, c, d) quadratically to:
 328 //
 329 // int sum1 = a + b + c + d;
 330 // int sum2 = b + c + d;
 331 // int sum3 = c + d;
 332 // int sum4 = d;
 333 //
 334 // So all of this is a copy-paste of |MOZ_FOR_EACH| except the definition
 335 // of |MOZ_FOR_EACH_HELPER| no longer extracts an argument with |MOZ_ARG_1|.
 336 // Also this is restricted to 32 arguments just to reduce footprint a little.
 337 //
 338 // If the GCC bug is ever fixed, then this hack can be removed, and we can
 339 // use the non-quadratic version that was originally written[2]. In case
 340 // that link dies, a brief summary of that implementation:
 341 //
 342 // * Associate each field with an index by creating an `enum class` with
 343 //   entries for each field (an existing gecko patten).
 344 //
 345 // * Calculate offsets with a constexpr static array whose initializer
 346 //   self-referentially adds the contents of the previous index to the
 347 //   compute the current one.
 348 //
 349 // * Index into this array with the enum.
 350 //
 351 // [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97234
 352 // [2]: https://phabricator.services.mozilla.com/D91622?id=346499
 353 #define MOZ_ROLL_EACH_EXPAND_HELPER(...) __VA_ARGS__
 354 #define MOZ_ROLL_EACH_GLUE(a, b) a b
 355 #define MOZ_ROLL_EACH_SEPARATED(aMacro, aSeparator, aFixedArgs, aArgs)       \
 356   MOZ_ROLL_EACH_GLUE(MOZ_PASTE_PREFIX_AND_ARG_COUNT(                         \
 357                          MOZ_ROLL_EACH_, MOZ_ROLL_EACH_EXPAND_HELPER aArgs), \
 358                      (aMacro, aSeparator, aFixedArgs, aArgs))
 359 #define MOZ_ROLL_EACH(aMacro, aFixedArgs, aArgs) \
 360   MOZ_ROLL_EACH_SEPARATED(aMacro, (), aFixedArgs, aArgs)
 361
 362 #define MOZ_ROLL_EACH_HELPER_GLUE(a, b) a b
 363 #define MOZ_ROLL_EACH_HELPER(aMacro, aFixedArgs, aArgs) \
 364   MOZ_ROLL_EACH_HELPER_GLUE(aMacro,                     \
 365                             (MOZ_ROLL_EACH_EXPAND_HELPER aFixedArgs aArgs))
 366
 367 #define MOZ_ROLL_EACH_0(m, s, fa, a)
 368 #define MOZ_ROLL_EACH_1(m, s, fa, a) MOZ_ROLL_EACH_HELPER(m, fa, a)
 369 #define MOZ_ROLL_EACH_2(m, s, fa, a) \
 370   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 371   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_1(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 372 #define MOZ_ROLL_EACH_3(m, s, fa, a) \
 373   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 374   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_2(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 375 #define MOZ_ROLL_EACH_4(m, s, fa, a) \
 376   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 377   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_3(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 378 #define MOZ_ROLL_EACH_5(m, s, fa, a) \
 379   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 380   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_4(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 381 #define MOZ_ROLL_EACH_6(m, s, fa, a) \
 382   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 383   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_5(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 384 #define MOZ_ROLL_EACH_7(m, s, fa, a) \
 385   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 386   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_6(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 387 #define MOZ_ROLL_EACH_8(m, s, fa, a) \
 388   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 389   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_7(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 390 #define MOZ_ROLL_EACH_9(m, s, fa, a) \
 391   MOZ_ROLL_EACH_HELPER(m, fa, a)     \
 392   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_8(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 393 #define MOZ_ROLL_EACH_10(m, s, fa, a) \
 394   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 395   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_9(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 396 #define MOZ_ROLL_EACH_11(m, s, fa, a) \
 397   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 398   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_10(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 399 #define MOZ_ROLL_EACH_12(m, s, fa, a) \
 400   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 401   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_11(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 402 #define MOZ_ROLL_EACH_13(m, s, fa, a) \
 403   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 404   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_12(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 405 #define MOZ_ROLL_EACH_14(m, s, fa, a) \
 406   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 407   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_13(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 408 #define MOZ_ROLL_EACH_15(m, s, fa, a) \
 409   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 410   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_14(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 411 #define MOZ_ROLL_EACH_16(m, s, fa, a) \
 412   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 413   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_15(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 414 #define MOZ_ROLL_EACH_17(m, s, fa, a) \
 415   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 416   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_16(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 417 #define MOZ_ROLL_EACH_18(m, s, fa, a) \
 418   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 419   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_17(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 420 #define MOZ_ROLL_EACH_19(m, s, fa, a) \
 421   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 422   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_18(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 423 #define MOZ_ROLL_EACH_20(m, s, fa, a) \
 424   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 425   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_19(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 426 #define MOZ_ROLL_EACH_21(m, s, fa, a) \
 427   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 428   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_20(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 429 #define MOZ_ROLL_EACH_22(m, s, fa, a) \
 430   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 431   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_21(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 432 #define MOZ_ROLL_EACH_23(m, s, fa, a) \
 433   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 434   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_22(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 435 #define MOZ_ROLL_EACH_24(m, s, fa, a) \
 436   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 437   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_23(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 438 #define MOZ_ROLL_EACH_25(m, s, fa, a) \
 439   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 440   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_24(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 441 #define MOZ_ROLL_EACH_26(m, s, fa, a) \
 442   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 443   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_25(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 444 #define MOZ_ROLL_EACH_27(m, s, fa, a) \
 445   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 446   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_26(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 447 #define MOZ_ROLL_EACH_28(m, s, fa, a) \
 448   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 449   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_27(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 450 #define MOZ_ROLL_EACH_29(m, s, fa, a) \
 451   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 452   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_28(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 453 #define MOZ_ROLL_EACH_30(m, s, fa, a) \
 454   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 455   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_29(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 456 #define MOZ_ROLL_EACH_31(m, s, fa, a) \
 457   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 458   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_30(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 459 #define MOZ_ROLL_EACH_32(m, s, fa, a) \
 460   MOZ_ROLL_EACH_HELPER(m, fa, a)      \
 461   MOZ_ROLL_EACH_EXPAND_HELPER s MOZ_ROLL_EACH_31(m, s, fa, (MOZ_ARGS_AFTER_1 a))
 462 }  // namespace mozilla
 463 #endif /* mozilla_AtomicBitfields_h */