include/llvm/Support/Alignment.h

   1 //===-- llvm/Support/Alignment.h - Useful alignment functions ---*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file contains types to represent alignments.
  10 // They are instrumented to guarantee some invariants are preserved and prevent
  11 // invalid manipulations.
  12 //
  13 // - Align represents an alignment in bytes, it is always set and always a valid
  14 // power of two, its minimum value is 1 which means no alignment requirements.
  15 //
  16 // - MaybeAlign is an optional type, it may be undefined or set. When it's set
  17 // you can get the underlying Align type by using the getValue() method.
  18 //
  19 //===----------------------------------------------------------------------===//
  20
  21 #ifndef LLVM_SUPPORT_ALIGNMENT_H_
  22 #define LLVM_SUPPORT_ALIGNMENT_H_
  23
  24 #include "llvm/ADT/Optional.h"
  25 #include "llvm/Support/Compiler.h"
  26 #include "llvm/Support/MathExtras.h"
  27 #include <cassert>
  28 #include <limits>
  29
  30 namespace llvm {
  31
  32 #define ALIGN_CHECK_ISPOSITIVE(decl)                                           \
  33   assert(decl > 0 && (#decl " should be defined"))
  34 #define ALIGN_CHECK_ISSET(decl)                                                \
  35   assert(decl.hasValue() && (#decl " should be defined"))
  36
  37 /// This struct is a compact representation of a valid (non-zero power of two)
  38 /// alignment.
  39 /// It is suitable for use as static global constants.
  40 struct Align {
  41 private:
  42   uint8_t ShiftValue = 0; /// The log2 of the required alignment.
  43                           /// ShiftValue is less than 64 by construction.
  44
  45   friend struct MaybeAlign;
  46   friend unsigned Log2(Align);
  47   friend bool operator==(Align Lhs, Align Rhs);
  48   friend bool operator!=(Align Lhs, Align Rhs);
  49   friend bool operator<=(Align Lhs, Align Rhs);
  50   friend bool operator>=(Align Lhs, Align Rhs);
  51   friend bool operator<(Align Lhs, Align Rhs);
  52   friend bool operator>(Align Lhs, Align Rhs);
  53   friend unsigned encode(struct MaybeAlign A);
  54   friend struct MaybeAlign decodeMaybeAlign(unsigned Value);
  55
  56   /// A trivial type to allow construction of constexpr Align.
  57   /// This is currently needed to workaround a bug in GCC 5.3 which prevents
  58   /// definition of constexpr assign operators.
  59   /// https://stackoverflow.com/questions/46756288/explicitly-defaulted-function-cannot-be-declared-as-constexpr-because-the-implic
  60   /// FIXME: Remove this, make all assign operators constexpr and introduce user
  61   /// defined literals when we don't have to support GCC 5.3 anymore.
  62   /// https://llvm.org/docs/GettingStarted.html#getting-a-modern-host-c-toolchain
  63   struct LogValue {
  64     uint8_t Log;
  65   };
  66
  67 public:
  68   /// Default is byte-aligned.
  69   constexpr Align() = default;
  70   /// Do not perform checks in case of copy/move construct/assign, because the
  71   /// checks have been performed when building `Other`.
  72   constexpr Align(const Align &Other) = default;
  73   constexpr Align(Align &&Other) = default;
  74   Align &operator=(const Align &Other) = default;
  75   Align &operator=(Align &&Other) = default;
  76
  77   explicit Align(uint64_t Value) {
  78     assert(Value > 0 && "Value must not be 0");
  79     assert(llvm::isPowerOf2_64(Value) && "Alignment is not a power of 2");
  80     ShiftValue = Log2_64(Value);
  81     assert(ShiftValue < 64 && "Broken invariant");
  82   }
  83
  84   /// This is a hole in the type system and should not be abused.
  85   /// Needed to interact with C for instance.
  86   uint64_t value() const { return uint64_t(1) << ShiftValue; }
  87
  88   /// Returns a default constructed Align which corresponds to no alignment.
  89   /// This is useful to test for unalignment as it conveys clear semantic.
  90   /// `if (A != Align::None())`
  91   /// would be better than
  92   /// `if (A > Align(1))`
  93   constexpr static const Align None() { return Align(); }
  94
  95   /// Allow constructions of constexpr Align.
  96   template <size_t kValue> constexpr static LogValue Constant() {
  97     return LogValue{static_cast<uint8_t>(CTLog2<kValue>())};
  98   }
  99
 100   /// Allow constructions of constexpr Align from types.
 101   /// Compile time equivalent to Align(alignof(T)).
 102   template <typename T> constexpr static LogValue Of() {
 103     return Constant<std::alignment_of<T>::value>();
 104   }
 105
 106   /// Constexpr constructor from LogValue type.
 107   constexpr Align(LogValue CA) : ShiftValue(CA.Log) {}
 108 };
 109
 110 /// Treats the value 0 as a 1, so Align is always at least 1.
 111 inline Align assumeAligned(uint64_t Value) {
 112   return Value ? Align(Value) : Align();
 113 }
 114
 115 /// This struct is a compact representation of a valid (power of two) or
 116 /// undefined (0) alignment.
 117 struct MaybeAlign : public llvm::Optional<Align> {
 118 private:
 119   using UP = llvm::Optional<Align>;
 120
 121 public:
 122   /// Default is undefined.
 123   MaybeAlign() = default;
 124   /// Do not perform checks in case of copy/move construct/assign, because the
 125   /// checks have been performed when building `Other`.
 126   MaybeAlign(const MaybeAlign &Other) = default;
 127   MaybeAlign &operator=(const MaybeAlign &Other) = default;
 128   MaybeAlign(MaybeAlign &&Other) = default;
 129   MaybeAlign &operator=(MaybeAlign &&Other) = default;
 130
 131   /// Use llvm::Optional<Align> constructor.
 132   using UP::UP;
 133
 134   explicit MaybeAlign(uint64_t Value) {
 135     assert((Value == 0 || llvm::isPowerOf2_64(Value)) &&
 136            "Alignment is neither 0 nor a power of 2");
 137     if (Value)
 138       emplace(Value);
 139   }
 140
 141   /// For convenience, returns a valid alignment or 1 if undefined.
 142   Align valueOrOne() const { return hasValue() ? getValue() : Align(); }
 143 };
 144
 145 /// Checks that SizeInBytes is a multiple of the alignment.
 146 inline bool isAligned(Align Lhs, uint64_t SizeInBytes) {
 147   return SizeInBytes % Lhs.value() == 0;
 148 }
 149
 150 /// Checks that SizeInBytes is a multiple of the alignment.
 151 /// Returns false if the alignment is undefined.
 152 inline bool isAligned(MaybeAlign Lhs, uint64_t SizeInBytes) {
 153   ALIGN_CHECK_ISSET(Lhs);
 154   return SizeInBytes % (*Lhs).value() == 0;
 155 }
 156
 157 /// Checks that Addr is a multiple of the alignment.
 158 inline bool isAddrAligned(Align Lhs, const void *Addr) {
 159   return isAligned(Lhs, reinterpret_cast<uintptr_t>(Addr));
 160 }
 161
 162 /// Returns a multiple of A needed to store `Size` bytes.
 163 inline uint64_t alignTo(uint64_t Size, Align A) {
 164   return (Size + A.value() - 1) / A.value() * A.value();
 165 }
 166
 167 /// Returns a multiple of A needed to store `Size` bytes.
 168 /// Returns `Size` if current alignment is undefined.
 169 inline uint64_t alignTo(uint64_t Size, MaybeAlign A) {
 170   return A ? alignTo(Size, A.getValue()) : Size;
 171 }
 172
 173 /// Aligns `Addr` to `Alignment` bytes, rounding up.
 174 inline uintptr_t alignAddr(const void *Addr, Align Alignment) {
 175   uintptr_t ArithAddr = reinterpret_cast<uintptr_t>(Addr);
 176   assert(ArithAddr + Alignment.value() - 1 >= ArithAddr && "Overflow");
 177   return alignTo(ArithAddr, Alignment);
 178 }
 179
 180 /// Returns the offset to the next integer (mod 2**64) that is greater than
 181 /// or equal to \p Value and is a multiple of \p Align.
 182 inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) {
 183   return alignTo(Value, Alignment) - Value;
 184 }
 185
 186 /// Returns the necessary adjustment for aligning `Addr` to `Alignment`
 187 /// bytes, rounding up.
 188 inline uint64_t offsetToAlignedAddr(const void *Addr, Align Alignment) {
 189   return offsetToAlignment(reinterpret_cast<uintptr_t>(Addr), Alignment);
 190 }
 191
 192 /// Returns the log2 of the alignment.
 193 inline unsigned Log2(Align A) { return A.ShiftValue; }
 194
 195 /// Returns the log2 of the alignment.
 196 /// \pre A must be defined.
 197 inline unsigned Log2(MaybeAlign A) {
 198   ALIGN_CHECK_ISSET(A);
 199   return Log2(A.getValue());
 200 }
 201
 202 /// Returns the alignment that satisfies both alignments.
 203 /// Same semantic as MinAlign.
 204 inline Align commonAlignment(Align A, Align B) { return std::min(A, B); }
 205
 206 /// Returns the alignment that satisfies both alignments.
 207 /// Same semantic as MinAlign.
 208 inline Align commonAlignment(Align A, uint64_t Offset) {
 209   return Align(MinAlign(A.value(), Offset));
 210 }
 211
 212 /// Returns the alignment that satisfies both alignments.
 213 /// Same semantic as MinAlign.
 214 inline MaybeAlign commonAlignment(MaybeAlign A, MaybeAlign B) {
 215   return A && B ? commonAlignment(*A, *B) : A ? A : B;
 216 }
 217
 218 /// Returns the alignment that satisfies both alignments.
 219 /// Same semantic as MinAlign.
 220 inline MaybeAlign commonAlignment(MaybeAlign A, uint64_t Offset) {
 221   return MaybeAlign(MinAlign((*A).value(), Offset));
 222 }
 223
 224 /// Returns a representation of the alignment that encodes undefined as 0.
 225 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; }
 226
 227 /// Dual operation of the encode function above.
 228 inline MaybeAlign decodeMaybeAlign(unsigned Value) {
 229   if (Value == 0)
 230     return MaybeAlign();
 231   Align Out;
 232   Out.ShiftValue = Value - 1;
 233   return Out;
 234 }
 235
 236 /// Returns a representation of the alignment, the encoded value is positive by
 237 /// definition.
 238 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); }
 239
 240 /// Comparisons between Align and scalars. Rhs must be positive.
 241 inline bool operator==(Align Lhs, uint64_t Rhs) {
 242   ALIGN_CHECK_ISPOSITIVE(Rhs);
 243   return Lhs.value() == Rhs;
 244 }
 245 inline bool operator!=(Align Lhs, uint64_t Rhs) {
 246   ALIGN_CHECK_ISPOSITIVE(Rhs);
 247   return Lhs.value() != Rhs;
 248 }
 249 inline bool operator<=(Align Lhs, uint64_t Rhs) {
 250   ALIGN_CHECK_ISPOSITIVE(Rhs);
 251   return Lhs.value() <= Rhs;
 252 }
 253 inline bool operator>=(Align Lhs, uint64_t Rhs) {
 254   ALIGN_CHECK_ISPOSITIVE(Rhs);
 255   return Lhs.value() >= Rhs;
 256 }
 257 inline bool operator<(Align Lhs, uint64_t Rhs) {
 258   ALIGN_CHECK_ISPOSITIVE(Rhs);
 259   return Lhs.value() < Rhs;
 260 }
 261 inline bool operator>(Align Lhs, uint64_t Rhs) {
 262   ALIGN_CHECK_ISPOSITIVE(Rhs);
 263   return Lhs.value() > Rhs;
 264 }
 265
 266 /// Comparisons between MaybeAlign and scalars.
 267 inline bool operator==(MaybeAlign Lhs, uint64_t Rhs) {
 268   return Lhs ? (*Lhs).value() == Rhs : Rhs == 0;
 269 }
 270 inline bool operator!=(MaybeAlign Lhs, uint64_t Rhs) {
 271   return Lhs ? (*Lhs).value() != Rhs : Rhs != 0;
 272 }
 273 inline bool operator<=(MaybeAlign Lhs, uint64_t Rhs) {
 274   ALIGN_CHECK_ISSET(Lhs);
 275   ALIGN_CHECK_ISPOSITIVE(Rhs);
 276   return (*Lhs).value() <= Rhs;
 277 }
 278 inline bool operator>=(MaybeAlign Lhs, uint64_t Rhs) {
 279   ALIGN_CHECK_ISSET(Lhs);
 280   ALIGN_CHECK_ISPOSITIVE(Rhs);
 281   return (*Lhs).value() >= Rhs;
 282 }
 283 inline bool operator<(MaybeAlign Lhs, uint64_t Rhs) {
 284   ALIGN_CHECK_ISSET(Lhs);
 285   ALIGN_CHECK_ISPOSITIVE(Rhs);
 286   return (*Lhs).value() < Rhs;
 287 }
 288 inline bool operator>(MaybeAlign Lhs, uint64_t Rhs) {
 289   ALIGN_CHECK_ISSET(Lhs);
 290   ALIGN_CHECK_ISPOSITIVE(Rhs);
 291   return (*Lhs).value() > Rhs;
 292 }
 293
 294 /// Comparisons operators between Align.
 295 inline bool operator==(Align Lhs, Align Rhs) {
 296   return Lhs.ShiftValue == Rhs.ShiftValue;
 297 }
 298 inline bool operator!=(Align Lhs, Align Rhs) {
 299   return Lhs.ShiftValue != Rhs.ShiftValue;
 300 }
 301 inline bool operator<=(Align Lhs, Align Rhs) {
 302   return Lhs.ShiftValue <= Rhs.ShiftValue;
 303 }
 304 inline bool operator>=(Align Lhs, Align Rhs) {
 305   return Lhs.ShiftValue >= Rhs.ShiftValue;
 306 }
 307 inline bool operator<(Align Lhs, Align Rhs) {
 308   return Lhs.ShiftValue < Rhs.ShiftValue;
 309 }
 310 inline bool operator>(Align Lhs, Align Rhs) {
 311   return Lhs.ShiftValue > Rhs.ShiftValue;
 312 }
 313
 314 /// Comparisons operators between Align and MaybeAlign.
 315 inline bool operator==(Align Lhs, MaybeAlign Rhs) {
 316   ALIGN_CHECK_ISSET(Rhs);
 317   return Lhs.value() == (*Rhs).value();
 318 }
 319 inline bool operator!=(Align Lhs, MaybeAlign Rhs) {
 320   ALIGN_CHECK_ISSET(Rhs);
 321   return Lhs.value() != (*Rhs).value();
 322 }
 323 inline bool operator<=(Align Lhs, MaybeAlign Rhs) {
 324   ALIGN_CHECK_ISSET(Rhs);
 325   return Lhs.value() <= (*Rhs).value();
 326 }
 327 inline bool operator>=(Align Lhs, MaybeAlign Rhs) {
 328   ALIGN_CHECK_ISSET(Rhs);
 329   return Lhs.value() >= (*Rhs).value();
 330 }
 331 inline bool operator<(Align Lhs, MaybeAlign Rhs) {
 332   ALIGN_CHECK_ISSET(Rhs);
 333   return Lhs.value() < (*Rhs).value();
 334 }
 335 inline bool operator>(Align Lhs, MaybeAlign Rhs) {
 336   ALIGN_CHECK_ISSET(Rhs);
 337   return Lhs.value() > (*Rhs).value();
 338 }
 339
 340 /// Comparisons operators between MaybeAlign and Align.
 341 inline bool operator==(MaybeAlign Lhs, Align Rhs) {
 342   ALIGN_CHECK_ISSET(Lhs);
 343   return Lhs && (*Lhs).value() == Rhs.value();
 344 }
 345 inline bool operator!=(MaybeAlign Lhs, Align Rhs) {
 346   ALIGN_CHECK_ISSET(Lhs);
 347   return Lhs && (*Lhs).value() != Rhs.value();
 348 }
 349 inline bool operator<=(MaybeAlign Lhs, Align Rhs) {
 350   ALIGN_CHECK_ISSET(Lhs);
 351   return Lhs && (*Lhs).value() <= Rhs.value();
 352 }
 353 inline bool operator>=(MaybeAlign Lhs, Align Rhs) {
 354   ALIGN_CHECK_ISSET(Lhs);
 355   return Lhs && (*Lhs).value() >= Rhs.value();
 356 }
 357 inline bool operator<(MaybeAlign Lhs, Align Rhs) {
 358   ALIGN_CHECK_ISSET(Lhs);
 359   return Lhs && (*Lhs).value() < Rhs.value();
 360 }
 361 inline bool operator>(MaybeAlign Lhs, Align Rhs) {
 362   ALIGN_CHECK_ISSET(Lhs);
 363   return Lhs && (*Lhs).value() > Rhs.value();
 364 }
 365
 366 inline Align operator/(Align Lhs, uint64_t Divisor) {
 367   assert(llvm::isPowerOf2_64(Divisor) &&
 368          "Divisor must be positive and a power of 2");
 369   assert(Lhs != 1 && "Can't halve byte alignment");
 370   return Align(Lhs.value() / Divisor);
 371 }
 372
 373 inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) {
 374   assert(llvm::isPowerOf2_64(Divisor) &&
 375          "Divisor must be positive and a power of 2");
 376   return Lhs ? Lhs.getValue() / Divisor : MaybeAlign();
 377 }
 378
 379 inline Align max(MaybeAlign Lhs, Align Rhs) {
 380   return Lhs && *Lhs > Rhs ? *Lhs : Rhs;
 381 }
 382
 383 inline Align max(Align Lhs, MaybeAlign Rhs) {
 384   return Rhs && *Rhs > Lhs ? *Rhs : Lhs;
 385 }
 386
 387 #undef ALIGN_CHECK_ISPOSITIVE
 388 #undef ALIGN_CHECK_ISSET
 389
 390 } // namespace llvm
 391
 392 #endif // LLVM_SUPPORT_ALIGNMENT_H_