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 public:
  57   /// Default is byte-aligned.
  58   Align() = default;
  59   /// Do not perform checks in case of copy/move construct/assign, because the
  60   /// checks have been performed when building `Other`.
  61   Align(const Align &Other) = default;
  62   Align &operator=(const Align &Other) = default;
  63   Align(Align &&Other) = default;
  64   Align &operator=(Align &&Other) = default;
  65
  66   explicit Align(uint64_t Value) {
  67     assert(Value > 0 && "Value must not be 0");
  68     assert(llvm::isPowerOf2_64(Value) && "Alignment is not a power of 2");
  69     ShiftValue = Log2_64(Value);
  70     assert(ShiftValue < 64 && "Broken invariant");
  71   }
  72
  73   /// This is a hole in the type system and should not be abused.
  74   /// Needed to interact with C for instance.
  75   uint64_t value() const { return uint64_t(1) << ShiftValue; }
  76 };
  77
  78 /// Treats the value 0 as a 1, so Align is always at least 1.
  79 inline Align assumeAligned(uint64_t Value) {
  80   return Value ? Align(Value) : Align();
  81 }
  82
  83 /// This struct is a compact representation of a valid (power of two) or
  84 /// undefined (0) alignment.
  85 struct MaybeAlign : public llvm::Optional<Align> {
  86 private:
  87   using UP = llvm::Optional<Align>;
  88
  89 public:
  90   /// Default is undefined.
  91   MaybeAlign() = default;
  92   /// Do not perform checks in case of copy/move construct/assign, because the
  93   /// checks have been performed when building `Other`.
  94   MaybeAlign(const MaybeAlign &Other) = default;
  95   MaybeAlign &operator=(const MaybeAlign &Other) = default;
  96   MaybeAlign(MaybeAlign &&Other) = default;
  97   MaybeAlign &operator=(MaybeAlign &&Other) = default;
  98
  99   /// Use llvm::Optional<Align> constructor.
 100   using UP::UP;
 101
 102   explicit MaybeAlign(uint64_t Value) {
 103     assert((Value == 0 || llvm::isPowerOf2_64(Value)) &&
 104            "Alignment is neither 0 nor a power of 2");
 105     if (Value)
 106       emplace(Value);
 107   }
 108
 109   /// For convenience, returns a valid alignment or 1 if undefined.
 110   Align valueOrOne() const { return hasValue() ? getValue() : Align(); }
 111 };
 112
 113 /// Checks that SizeInBytes is a multiple of the alignment.
 114 inline bool isAligned(Align Lhs, uint64_t SizeInBytes) {
 115   return SizeInBytes % Lhs.value() == 0;
 116 }
 117
 118 /// Checks that SizeInBytes is a multiple of the alignment.
 119 /// Returns false if the alignment is undefined.
 120 inline bool isAligned(MaybeAlign Lhs, uint64_t SizeInBytes) {
 121   ALIGN_CHECK_ISSET(Lhs);
 122   return SizeInBytes % (*Lhs).value() == 0;
 123 }
 124
 125 /// Returns a multiple of A needed to store `Size` bytes.
 126 inline uint64_t alignTo(uint64_t Size, Align A) {
 127   return (Size + A.value() - 1) / A.value() * A.value();
 128 }
 129
 130 /// Returns a multiple of A needed to store `Size` bytes.
 131 /// Returns `Size` if current alignment is undefined.
 132 inline uint64_t alignTo(uint64_t Size, MaybeAlign A) {
 133   return A ? alignTo(Size, A.getValue()) : Size;
 134 }
 135
 136 /// Returns the log2 of the alignment.
 137 inline unsigned Log2(Align A) { return A.ShiftValue; }
 138
 139 /// Returns the log2 of the alignment.
 140 /// \pre A must be defined.
 141 inline unsigned Log2(MaybeAlign A) {
 142   ALIGN_CHECK_ISSET(A);
 143   return Log2(A.getValue());
 144 }
 145
 146 /// Returns the alignment that satisfies both alignments.
 147 /// Same semantic as MinAlign.
 148 inline Align commonAlignment(Align A, Align B) { return std::min(A, B); }
 149
 150 /// Returns the alignment that satisfies both alignments.
 151 /// Same semantic as MinAlign.
 152 inline Align commonAlignment(Align A, uint64_t Offset) {
 153   return Align(MinAlign(A.value(), Offset));
 154 }
 155
 156 /// Returns the alignment that satisfies both alignments.
 157 /// Same semantic as MinAlign.
 158 inline MaybeAlign commonAlignment(MaybeAlign A, MaybeAlign B) {
 159   return A && B ? commonAlignment(*A, *B) : A ? A : B;
 160 }
 161
 162 /// Returns the alignment that satisfies both alignments.
 163 /// Same semantic as MinAlign.
 164 inline MaybeAlign commonAlignment(MaybeAlign A, uint64_t Offset) {
 165   return MaybeAlign(MinAlign((*A).value(), Offset));
 166 }
 167
 168 /// Returns a representation of the alignment that encodes undefined as 0.
 169 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; }
 170
 171 /// Dual operation of the encode function above.
 172 inline MaybeAlign decodeMaybeAlign(unsigned Value) {
 173   if (Value == 0)
 174     return MaybeAlign();
 175   Align Out;
 176   Out.ShiftValue = Value - 1;
 177   return Out;
 178 }
 179
 180 /// Returns a representation of the alignment, the encoded value is positive by
 181 /// definition.
 182 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); }
 183
 184 /// Comparisons between Align and scalars. Rhs must be positive.
 185 inline bool operator==(Align Lhs, uint64_t Rhs) {
 186   ALIGN_CHECK_ISPOSITIVE(Rhs);
 187   return Lhs.value() == Rhs;
 188 }
 189 inline bool operator!=(Align Lhs, uint64_t Rhs) {
 190   ALIGN_CHECK_ISPOSITIVE(Rhs);
 191   return Lhs.value() != Rhs;
 192 }
 193 inline bool operator<=(Align Lhs, uint64_t Rhs) {
 194   ALIGN_CHECK_ISPOSITIVE(Rhs);
 195   return Lhs.value() <= Rhs;
 196 }
 197 inline bool operator>=(Align Lhs, uint64_t Rhs) {
 198   ALIGN_CHECK_ISPOSITIVE(Rhs);
 199   return Lhs.value() >= Rhs;
 200 }
 201 inline bool operator<(Align Lhs, uint64_t Rhs) {
 202   ALIGN_CHECK_ISPOSITIVE(Rhs);
 203   return Lhs.value() < Rhs;
 204 }
 205 inline bool operator>(Align Lhs, uint64_t Rhs) {
 206   ALIGN_CHECK_ISPOSITIVE(Rhs);
 207   return Lhs.value() > Rhs;
 208 }
 209
 210 /// Comparisons between MaybeAlign and scalars.
 211 inline bool operator==(MaybeAlign Lhs, uint64_t Rhs) {
 212   return Lhs ? (*Lhs).value() == Rhs : Rhs == 0;
 213 }
 214 inline bool operator!=(MaybeAlign Lhs, uint64_t Rhs) {
 215   return Lhs ? (*Lhs).value() != Rhs : Rhs != 0;
 216 }
 217 inline bool operator<=(MaybeAlign Lhs, uint64_t Rhs) {
 218   ALIGN_CHECK_ISSET(Lhs);
 219   ALIGN_CHECK_ISPOSITIVE(Rhs);
 220   return (*Lhs).value() <= Rhs;
 221 }
 222 inline bool operator>=(MaybeAlign Lhs, uint64_t Rhs) {
 223   ALIGN_CHECK_ISSET(Lhs);
 224   ALIGN_CHECK_ISPOSITIVE(Rhs);
 225   return (*Lhs).value() >= Rhs;
 226 }
 227 inline bool operator<(MaybeAlign Lhs, uint64_t Rhs) {
 228   ALIGN_CHECK_ISSET(Lhs);
 229   ALIGN_CHECK_ISPOSITIVE(Rhs);
 230   return (*Lhs).value() < Rhs;
 231 }
 232 inline bool operator>(MaybeAlign Lhs, uint64_t Rhs) {
 233   ALIGN_CHECK_ISSET(Lhs);
 234   ALIGN_CHECK_ISPOSITIVE(Rhs);
 235   return (*Lhs).value() > Rhs;
 236 }
 237
 238 /// Comparisons operators between Align.
 239 inline bool operator==(Align Lhs, Align Rhs) {
 240   return Lhs.ShiftValue == Rhs.ShiftValue;
 241 }
 242 inline bool operator!=(Align Lhs, Align Rhs) {
 243   return Lhs.ShiftValue != Rhs.ShiftValue;
 244 }
 245 inline bool operator<=(Align Lhs, Align Rhs) {
 246   return Lhs.ShiftValue <= Rhs.ShiftValue;
 247 }
 248 inline bool operator>=(Align Lhs, Align Rhs) {
 249   return Lhs.ShiftValue >= Rhs.ShiftValue;
 250 }
 251 inline bool operator<(Align Lhs, Align Rhs) {
 252   return Lhs.ShiftValue < Rhs.ShiftValue;
 253 }
 254 inline bool operator>(Align Lhs, Align Rhs) {
 255   return Lhs.ShiftValue > Rhs.ShiftValue;
 256 }
 257
 258 /// Comparisons operators between Align and MaybeAlign.
 259 inline bool operator==(Align Lhs, MaybeAlign Rhs) {
 260   ALIGN_CHECK_ISSET(Rhs);
 261   return Lhs.value() == (*Rhs).value();
 262 }
 263 inline bool operator!=(Align Lhs, MaybeAlign Rhs) {
 264   ALIGN_CHECK_ISSET(Rhs);
 265   return Lhs.value() != (*Rhs).value();
 266 }
 267 inline bool operator<=(Align Lhs, MaybeAlign Rhs) {
 268   ALIGN_CHECK_ISSET(Rhs);
 269   return Lhs.value() <= (*Rhs).value();
 270 }
 271 inline bool operator>=(Align Lhs, MaybeAlign Rhs) {
 272   ALIGN_CHECK_ISSET(Rhs);
 273   return Lhs.value() >= (*Rhs).value();
 274 }
 275 inline bool operator<(Align Lhs, MaybeAlign Rhs) {
 276   ALIGN_CHECK_ISSET(Rhs);
 277   return Lhs.value() < (*Rhs).value();
 278 }
 279 inline bool operator>(Align Lhs, MaybeAlign Rhs) {
 280   ALIGN_CHECK_ISSET(Rhs);
 281   return Lhs.value() > (*Rhs).value();
 282 }
 283
 284 /// Comparisons operators between MaybeAlign and Align.
 285 inline bool operator==(MaybeAlign Lhs, Align Rhs) {
 286   ALIGN_CHECK_ISSET(Lhs);
 287   return Lhs && (*Lhs).value() == Rhs.value();
 288 }
 289 inline bool operator!=(MaybeAlign Lhs, Align Rhs) {
 290   ALIGN_CHECK_ISSET(Lhs);
 291   return Lhs && (*Lhs).value() != Rhs.value();
 292 }
 293 inline bool operator<=(MaybeAlign Lhs, Align Rhs) {
 294   ALIGN_CHECK_ISSET(Lhs);
 295   return Lhs && (*Lhs).value() <= Rhs.value();
 296 }
 297 inline bool operator>=(MaybeAlign Lhs, Align Rhs) {
 298   ALIGN_CHECK_ISSET(Lhs);
 299   return Lhs && (*Lhs).value() >= Rhs.value();
 300 }
 301 inline bool operator<(MaybeAlign Lhs, Align Rhs) {
 302   ALIGN_CHECK_ISSET(Lhs);
 303   return Lhs && (*Lhs).value() < Rhs.value();
 304 }
 305 inline bool operator>(MaybeAlign Lhs, Align Rhs) {
 306   ALIGN_CHECK_ISSET(Lhs);
 307   return Lhs && (*Lhs).value() > Rhs.value();
 308 }
 309
 310 inline Align operator/(Align Lhs, uint64_t Divisor) {
 311   assert(llvm::isPowerOf2_64(Divisor) &&
 312          "Divisor must be positive and a power of 2");
 313   assert(Lhs != 1 && "Can't halve byte alignment");
 314   return Align(Lhs.value() / Divisor);
 315 }
 316
 317 inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) {
 318   assert(llvm::isPowerOf2_64(Divisor) &&
 319          "Divisor must be positive and a power of 2");
 320   return Lhs ? Lhs.getValue() / Divisor : MaybeAlign();
 321 }
 322
 323 #undef ALIGN_CHECK_ISPOSITIVE
 324 #undef ALIGN_CHECK_ISSET
 325
 326 } // namespace llvm
 327
 328 #endif // LLVM_SUPPORT_ALIGNMENT_H_