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{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 /// Returns a multiple of A needed to store `Size` bytes.
 158 inline uint64_t alignTo(uint64_t Size, Align A) {
 159   return (Size + A.value() - 1) / A.value() * A.value();
 160 }
 161
 162 /// Returns a multiple of A needed to store `Size` bytes.
 163 /// Returns `Size` if current alignment is undefined.
 164 inline uint64_t alignTo(uint64_t Size, MaybeAlign A) {
 165   return A ? alignTo(Size, A.getValue()) : Size;
 166 }
 167
 168 /// Returns the offset to the next integer (mod 2**64) that is greater than
 169 /// or equal to \p Value and is a multiple of \p Align.
 170 inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) {
 171   return alignTo(Value, Alignment) - Value;
 172 }
 173
 174 /// Returns the log2 of the alignment.
 175 inline unsigned Log2(Align A) { return A.ShiftValue; }
 176
 177 /// Returns the log2 of the alignment.
 178 /// \pre A must be defined.
 179 inline unsigned Log2(MaybeAlign A) {
 180   ALIGN_CHECK_ISSET(A);
 181   return Log2(A.getValue());
 182 }
 183
 184 /// Returns the alignment that satisfies both alignments.
 185 /// Same semantic as MinAlign.
 186 inline Align commonAlignment(Align A, Align B) { return std::min(A, B); }
 187
 188 /// Returns the alignment that satisfies both alignments.
 189 /// Same semantic as MinAlign.
 190 inline Align commonAlignment(Align A, uint64_t Offset) {
 191   return Align(MinAlign(A.value(), Offset));
 192 }
 193
 194 /// Returns the alignment that satisfies both alignments.
 195 /// Same semantic as MinAlign.
 196 inline MaybeAlign commonAlignment(MaybeAlign A, MaybeAlign B) {
 197   return A && B ? commonAlignment(*A, *B) : A ? A : B;
 198 }
 199
 200 /// Returns the alignment that satisfies both alignments.
 201 /// Same semantic as MinAlign.
 202 inline MaybeAlign commonAlignment(MaybeAlign A, uint64_t Offset) {
 203   return MaybeAlign(MinAlign((*A).value(), Offset));
 204 }
 205
 206 /// Returns a representation of the alignment that encodes undefined as 0.
 207 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; }
 208
 209 /// Dual operation of the encode function above.
 210 inline MaybeAlign decodeMaybeAlign(unsigned Value) {
 211   if (Value == 0)
 212     return MaybeAlign();
 213   Align Out;
 214   Out.ShiftValue = Value - 1;
 215   return Out;
 216 }
 217
 218 /// Returns a representation of the alignment, the encoded value is positive by
 219 /// definition.
 220 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); }
 221
 222 /// Comparisons between Align and scalars. Rhs must be positive.
 223 inline bool operator==(Align Lhs, uint64_t Rhs) {
 224   ALIGN_CHECK_ISPOSITIVE(Rhs);
 225   return Lhs.value() == Rhs;
 226 }
 227 inline bool operator!=(Align Lhs, uint64_t Rhs) {
 228   ALIGN_CHECK_ISPOSITIVE(Rhs);
 229   return Lhs.value() != Rhs;
 230 }
 231 inline bool operator<=(Align Lhs, uint64_t Rhs) {
 232   ALIGN_CHECK_ISPOSITIVE(Rhs);
 233   return Lhs.value() <= Rhs;
 234 }
 235 inline bool operator>=(Align Lhs, uint64_t Rhs) {
 236   ALIGN_CHECK_ISPOSITIVE(Rhs);
 237   return Lhs.value() >= Rhs;
 238 }
 239 inline bool operator<(Align Lhs, uint64_t Rhs) {
 240   ALIGN_CHECK_ISPOSITIVE(Rhs);
 241   return Lhs.value() < Rhs;
 242 }
 243 inline bool operator>(Align Lhs, uint64_t Rhs) {
 244   ALIGN_CHECK_ISPOSITIVE(Rhs);
 245   return Lhs.value() > Rhs;
 246 }
 247
 248 /// Comparisons between MaybeAlign and scalars.
 249 inline bool operator==(MaybeAlign Lhs, uint64_t Rhs) {
 250   return Lhs ? (*Lhs).value() == Rhs : Rhs == 0;
 251 }
 252 inline bool operator!=(MaybeAlign Lhs, uint64_t Rhs) {
 253   return Lhs ? (*Lhs).value() != Rhs : Rhs != 0;
 254 }
 255 inline bool operator<=(MaybeAlign Lhs, uint64_t Rhs) {
 256   ALIGN_CHECK_ISSET(Lhs);
 257   ALIGN_CHECK_ISPOSITIVE(Rhs);
 258   return (*Lhs).value() <= Rhs;
 259 }
 260 inline bool operator>=(MaybeAlign Lhs, uint64_t Rhs) {
 261   ALIGN_CHECK_ISSET(Lhs);
 262   ALIGN_CHECK_ISPOSITIVE(Rhs);
 263   return (*Lhs).value() >= Rhs;
 264 }
 265 inline bool operator<(MaybeAlign Lhs, uint64_t Rhs) {
 266   ALIGN_CHECK_ISSET(Lhs);
 267   ALIGN_CHECK_ISPOSITIVE(Rhs);
 268   return (*Lhs).value() < Rhs;
 269 }
 270 inline bool operator>(MaybeAlign Lhs, uint64_t Rhs) {
 271   ALIGN_CHECK_ISSET(Lhs);
 272   ALIGN_CHECK_ISPOSITIVE(Rhs);
 273   return (*Lhs).value() > Rhs;
 274 }
 275
 276 /// Comparisons operators between Align.
 277 inline bool operator==(Align Lhs, Align Rhs) {
 278   return Lhs.ShiftValue == Rhs.ShiftValue;
 279 }
 280 inline bool operator!=(Align Lhs, Align Rhs) {
 281   return Lhs.ShiftValue != Rhs.ShiftValue;
 282 }
 283 inline bool operator<=(Align Lhs, Align Rhs) {
 284   return Lhs.ShiftValue <= Rhs.ShiftValue;
 285 }
 286 inline bool operator>=(Align Lhs, Align Rhs) {
 287   return Lhs.ShiftValue >= Rhs.ShiftValue;
 288 }
 289 inline bool operator<(Align Lhs, Align Rhs) {
 290   return Lhs.ShiftValue < Rhs.ShiftValue;
 291 }
 292 inline bool operator>(Align Lhs, Align Rhs) {
 293   return Lhs.ShiftValue > Rhs.ShiftValue;
 294 }
 295
 296 /// Comparisons operators between Align and MaybeAlign.
 297 inline bool operator==(Align Lhs, MaybeAlign Rhs) {
 298   ALIGN_CHECK_ISSET(Rhs);
 299   return Lhs.value() == (*Rhs).value();
 300 }
 301 inline bool operator!=(Align Lhs, MaybeAlign Rhs) {
 302   ALIGN_CHECK_ISSET(Rhs);
 303   return Lhs.value() != (*Rhs).value();
 304 }
 305 inline bool operator<=(Align Lhs, MaybeAlign Rhs) {
 306   ALIGN_CHECK_ISSET(Rhs);
 307   return Lhs.value() <= (*Rhs).value();
 308 }
 309 inline bool operator>=(Align Lhs, MaybeAlign Rhs) {
 310   ALIGN_CHECK_ISSET(Rhs);
 311   return Lhs.value() >= (*Rhs).value();
 312 }
 313 inline bool operator<(Align Lhs, MaybeAlign Rhs) {
 314   ALIGN_CHECK_ISSET(Rhs);
 315   return Lhs.value() < (*Rhs).value();
 316 }
 317 inline bool operator>(Align Lhs, MaybeAlign Rhs) {
 318   ALIGN_CHECK_ISSET(Rhs);
 319   return Lhs.value() > (*Rhs).value();
 320 }
 321
 322 /// Comparisons operators between MaybeAlign and Align.
 323 inline bool operator==(MaybeAlign Lhs, Align Rhs) {
 324   ALIGN_CHECK_ISSET(Lhs);
 325   return Lhs && (*Lhs).value() == Rhs.value();
 326 }
 327 inline bool operator!=(MaybeAlign Lhs, Align Rhs) {
 328   ALIGN_CHECK_ISSET(Lhs);
 329   return Lhs && (*Lhs).value() != Rhs.value();
 330 }
 331 inline bool operator<=(MaybeAlign Lhs, Align Rhs) {
 332   ALIGN_CHECK_ISSET(Lhs);
 333   return Lhs && (*Lhs).value() <= Rhs.value();
 334 }
 335 inline bool operator>=(MaybeAlign Lhs, Align Rhs) {
 336   ALIGN_CHECK_ISSET(Lhs);
 337   return Lhs && (*Lhs).value() >= Rhs.value();
 338 }
 339 inline bool operator<(MaybeAlign Lhs, Align Rhs) {
 340   ALIGN_CHECK_ISSET(Lhs);
 341   return Lhs && (*Lhs).value() < Rhs.value();
 342 }
 343 inline bool operator>(MaybeAlign Lhs, Align Rhs) {
 344   ALIGN_CHECK_ISSET(Lhs);
 345   return Lhs && (*Lhs).value() > Rhs.value();
 346 }
 347
 348 inline Align operator/(Align Lhs, uint64_t Divisor) {
 349   assert(llvm::isPowerOf2_64(Divisor) &&
 350          "Divisor must be positive and a power of 2");
 351   assert(Lhs != 1 && "Can't halve byte alignment");
 352   return Align(Lhs.value() / Divisor);
 353 }
 354
 355 inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) {
 356   assert(llvm::isPowerOf2_64(Divisor) &&
 357          "Divisor must be positive and a power of 2");
 358   return Lhs ? Lhs.getValue() / Divisor : MaybeAlign();
 359 }
 360
 361 inline Align max(MaybeAlign Lhs, Align Rhs) {
 362   return Lhs && *Lhs > Rhs ? *Lhs : Rhs;
 363 }
 364
 365 inline Align max(Align Lhs, MaybeAlign Rhs) {
 366   return Rhs && *Rhs > Lhs ? *Rhs : Lhs;
 367 }
 368
 369 #undef ALIGN_CHECK_ISPOSITIVE
 370 #undef ALIGN_CHECK_ISSET
 371
 372 } // namespace llvm
 373
 374 #endif // LLVM_SUPPORT_ALIGNMENT_H_