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/MathExtras.h" 26 #include <cassert> 27 #ifndef NDEBUG 28 #include <string> 29 #endif // NDEBUG 30 31 namespace llvm { 32 33 #define ALIGN_CHECK_ISPOSITIVE(decl) \ 34 assert(decl > 0 && (#decl " should be defined")) 35 36 /// This struct is a compact representation of a valid (non-zero power of two) 37 /// alignment. 38 /// It is suitable for use as static global constants. 39 struct Align { 40 private: 41 uint8_t ShiftValue = 0; /// The log2 of the required alignment. 42 /// ShiftValue is less than 64 by construction. 43 44 friend struct MaybeAlign; 45 friend unsigned Log2(Align); 46 friend bool operator==(Align Lhs, Align Rhs); 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 unsigned encode(struct MaybeAlign A); 53 friend struct MaybeAlign decodeMaybeAlign(unsigned Value); 54 55 /// A trivial type to allow construction of constexpr Align. 56 /// This is currently needed to workaround a bug in GCC 5.3 which prevents 57 /// definition of constexpr assign operators. 58 /// https://stackoverflow.com/questions/46756288/explicitly-defaulted-function-cannot-be-declared-as-constexpr-because-the-implic 59 /// FIXME: Remove this, make all assign operators constexpr and introduce user 60 /// defined literals when we don't have to support GCC 5.3 anymore. 61 /// https://llvm.org/docs/GettingStarted.html#getting-a-modern-host-c-toolchain 62 struct LogValue { 63 uint8_t Log; 64 }; 65 66 public: 67 /// Default is byte-aligned. 68 constexpr Align() = default; 69 /// Do not perform checks in case of copy/move construct/assign, because the 70 /// checks have been performed when building `Other`. 71 constexpr Align(const Align &Other) = default; 72 constexpr Align(Align &&Other) = default; 73 Align &operator=(const Align &Other) = default; 74 Align &operator=(Align &&Other) = default; 75 76 explicit Align(uint64_t Value) { 77 assert(Value > 0 && "Value must not be 0"); 78 assert(llvm::isPowerOf2_64(Value) && "Alignment is not a power of 2"); 79 ShiftValue = Log2_64(Value); 80 assert(ShiftValue < 64 && "Broken invariant"); 81 } 82 83 /// This is a hole in the type system and should not be abused. 84 /// Needed to interact with C for instance. 85 uint64_t value() const { return uint64_t(1) << ShiftValue; } 86 87 /// Allow constructions of constexpr Align. 88 template <size_t kValue> constexpr static LogValue Constant() { 89 return LogValue{static_cast<uint8_t>(CTLog2<kValue>())}; 90 } 91 92 /// Allow constructions of constexpr Align from types. 93 /// Compile time equivalent to Align(alignof(T)). 94 template <typename T> constexpr static LogValue Of() { 95 return Constant<std::alignment_of<T>::value>(); 96 } 97 98 /// Constexpr constructor from LogValue type. 99 constexpr Align(LogValue CA) : ShiftValue(CA.Log) {} 100 }; 101 102 /// Treats the value 0 as a 1, so Align is always at least 1. 103 inline Align assumeAligned(uint64_t Value) { 104 return Value ? Align(Value) : Align(); 105 } 106 107 /// This struct is a compact representation of a valid (power of two) or 108 /// undefined (0) alignment. 109 struct MaybeAlign : public llvm::Optional<Align> { 110 private: 111 using UP = llvm::Optional<Align>; 112 113 public: 114 /// Default is undefined. 115 MaybeAlign() = default; 116 /// Do not perform checks in case of copy/move construct/assign, because the 117 /// checks have been performed when building `Other`. 118 MaybeAlign(const MaybeAlign &Other) = default; 119 MaybeAlign &operator=(const MaybeAlign &Other) = default; 120 MaybeAlign(MaybeAlign &&Other) = default; 121 MaybeAlign &operator=(MaybeAlign &&Other) = default; 122 123 /// Use llvm::Optional<Align> constructor. 124 using UP::UP; 125 126 explicit MaybeAlign(uint64_t Value) { 127 assert((Value == 0 || llvm::isPowerOf2_64(Value)) && 128 "Alignment is neither 0 nor a power of 2"); 129 if (Value) 130 emplace(Value); 131 } 132 133 /// For convenience, returns a valid alignment or 1 if undefined. 134 Align valueOrOne() const { return hasValue() ? getValue() : Align(); } 135 }; 136 137 /// Checks that SizeInBytes is a multiple of the alignment. 138 inline bool isAligned(Align Lhs, uint64_t SizeInBytes) { 139 return SizeInBytes % Lhs.value() == 0; 140 } 141 142 /// Checks that Addr is a multiple of the alignment. 143 inline bool isAddrAligned(Align Lhs, const void *Addr) { 144 return isAligned(Lhs, reinterpret_cast<uintptr_t>(Addr)); 145 } 146 147 /// Returns a multiple of A needed to store `Size` bytes. 148 inline uint64_t alignTo(uint64_t Size, Align A) { 149 const uint64_t Value = A.value(); 150 // The following line is equivalent to `(Size + Value - 1) / Value * Value`. 151 152 // The division followed by a multiplication can be thought of as a right 153 // shift followed by a left shift which zeros out the extra bits produced in 154 // the bump; `~(Value - 1)` is a mask where all those bits being zeroed out 155 // are just zero. 156 157 // Most compilers can generate this code but the pattern may be missed when 158 // multiple functions gets inlined. 159 return (Size + Value - 1) & ~(Value - 1U); 160 } 161 162 /// If non-zero \p Skew is specified, the return value will be a minimal integer 163 /// that is greater than or equal to \p Size and equal to \p A * N + \p Skew for 164 /// some integer N. If \p Skew is larger than \p A, its value is adjusted to '\p 165 /// Skew mod \p A'. 166 /// 167 /// Examples: 168 /// \code 169 /// alignTo(5, Align(8), 7) = 7 170 /// alignTo(17, Align(8), 1) = 17 171 /// alignTo(~0LL, Align(8), 3) = 3 172 /// \endcode 173 inline uint64_t alignTo(uint64_t Size, Align A, uint64_t Skew) { 174 const uint64_t Value = A.value(); 175 Skew %= Value; 176 return ((Size + Value - 1 - Skew) & ~(Value - 1U)) + Skew; 177 } 178 179 /// Returns a multiple of A needed to store `Size` bytes. 180 /// Returns `Size` if current alignment is undefined. 181 inline uint64_t alignTo(uint64_t Size, MaybeAlign A) { 182 return A ? alignTo(Size, A.getValue()) : Size; 183 } 184 185 /// Aligns `Addr` to `Alignment` bytes, rounding up. 186 inline uintptr_t alignAddr(const void *Addr, Align Alignment) { 187 uintptr_t ArithAddr = reinterpret_cast<uintptr_t>(Addr); 188 assert(static_cast<uintptr_t>(ArithAddr + Alignment.value() - 1) >= 189 ArithAddr && 190 "Overflow"); 191 return alignTo(ArithAddr, Alignment); 192 } 193 194 /// Returns the offset to the next integer (mod 2**64) that is greater than 195 /// or equal to \p Value and is a multiple of \p Align. 196 inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) { 197 return alignTo(Value, Alignment) - Value; 198 } 199 200 /// Returns the necessary adjustment for aligning `Addr` to `Alignment` 201 /// bytes, rounding up. 202 inline uint64_t offsetToAlignedAddr(const void *Addr, Align Alignment) { 203 return offsetToAlignment(reinterpret_cast<uintptr_t>(Addr), Alignment); 204 } 205 206 /// Returns the log2 of the alignment. 207 inline unsigned Log2(Align A) { return A.ShiftValue; } 208 209 /// Returns the alignment that satisfies both alignments. 210 /// Same semantic as MinAlign. 211 inline Align commonAlignment(Align A, Align B) { return std::min(A, B); } 212 213 /// Returns the alignment that satisfies both alignments. 214 /// Same semantic as MinAlign. 215 inline Align commonAlignment(Align A, uint64_t Offset) { 216 return Align(MinAlign(A.value(), Offset)); 217 } 218 219 /// Returns the alignment that satisfies both alignments. 220 /// Same semantic as MinAlign. 221 inline MaybeAlign commonAlignment(MaybeAlign A, MaybeAlign B) { 222 return A && B ? commonAlignment(*A, *B) : A ? A : B; 223 } 224 225 /// Returns the alignment that satisfies both alignments. 226 /// Same semantic as MinAlign. 227 inline MaybeAlign commonAlignment(MaybeAlign A, uint64_t Offset) { 228 return MaybeAlign(MinAlign((*A).value(), Offset)); 229 } 230 231 /// Returns a representation of the alignment that encodes undefined as 0. 232 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; } 233 234 /// Dual operation of the encode function above. 235 inline MaybeAlign decodeMaybeAlign(unsigned Value) { 236 if (Value == 0) 237 return MaybeAlign(); 238 Align Out; 239 Out.ShiftValue = Value - 1; 240 return Out; 241 } 242 243 /// Returns a representation of the alignment, the encoded value is positive by 244 /// definition. 245 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); } 246 247 /// Comparisons between Align and scalars. Rhs must be positive. 248 inline bool operator==(Align Lhs, uint64_t Rhs) { 249 ALIGN_CHECK_ISPOSITIVE(Rhs); 250 return Lhs.value() == Rhs; 251 } 252 inline bool operator!=(Align Lhs, uint64_t Rhs) { 253 ALIGN_CHECK_ISPOSITIVE(Rhs); 254 return Lhs.value() != Rhs; 255 } 256 inline bool operator<=(Align Lhs, uint64_t Rhs) { 257 ALIGN_CHECK_ISPOSITIVE(Rhs); 258 return Lhs.value() <= Rhs; 259 } 260 inline bool operator>=(Align Lhs, uint64_t Rhs) { 261 ALIGN_CHECK_ISPOSITIVE(Rhs); 262 return Lhs.value() >= Rhs; 263 } 264 inline bool operator<(Align Lhs, uint64_t Rhs) { 265 ALIGN_CHECK_ISPOSITIVE(Rhs); 266 return Lhs.value() < Rhs; 267 } 268 inline bool operator>(Align Lhs, uint64_t Rhs) { 269 ALIGN_CHECK_ISPOSITIVE(Rhs); 270 return Lhs.value() > Rhs; 271 } 272 273 /// Comparisons between MaybeAlign and scalars. 274 inline bool operator==(MaybeAlign Lhs, uint64_t Rhs) { 275 return Lhs ? (*Lhs).value() == Rhs : Rhs == 0; 276 } 277 inline bool operator!=(MaybeAlign Lhs, uint64_t Rhs) { 278 return Lhs ? (*Lhs).value() != Rhs : Rhs != 0; 279 } 280 281 /// Comparisons operators between Align. 282 inline bool operator==(Align Lhs, Align Rhs) { 283 return Lhs.ShiftValue == Rhs.ShiftValue; 284 } 285 inline bool operator!=(Align Lhs, Align Rhs) { 286 return Lhs.ShiftValue != Rhs.ShiftValue; 287 } 288 inline bool operator<=(Align Lhs, Align Rhs) { 289 return Lhs.ShiftValue <= Rhs.ShiftValue; 290 } 291 inline bool operator>=(Align Lhs, Align Rhs) { 292 return Lhs.ShiftValue >= Rhs.ShiftValue; 293 } 294 inline bool operator<(Align Lhs, Align Rhs) { 295 return Lhs.ShiftValue < Rhs.ShiftValue; 296 } 297 inline bool operator>(Align Lhs, Align Rhs) { 298 return Lhs.ShiftValue > Rhs.ShiftValue; 299 } 300 301 // Don't allow relational comparisons with MaybeAlign. 302 bool operator<=(Align Lhs, MaybeAlign Rhs) = delete; 303 bool operator>=(Align Lhs, MaybeAlign Rhs) = delete; 304 bool operator<(Align Lhs, MaybeAlign Rhs) = delete; 305 bool operator>(Align Lhs, MaybeAlign Rhs) = delete; 306 307 bool operator<=(MaybeAlign Lhs, Align Rhs) = delete; 308 bool operator>=(MaybeAlign Lhs, Align Rhs) = delete; 309 bool operator<(MaybeAlign Lhs, Align Rhs) = delete; 310 bool operator>(MaybeAlign Lhs, Align Rhs) = delete; 311 312 bool operator<=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 313 bool operator>=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 314 bool operator<(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 315 bool operator>(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 316 317 inline Align operator*(Align Lhs, uint64_t Rhs) { 318 assert(Rhs > 0 && "Rhs must be positive"); 319 return Align(Lhs.value() * Rhs); 320 } 321 322 inline MaybeAlign operator*(MaybeAlign Lhs, uint64_t Rhs) { 323 assert(Rhs > 0 && "Rhs must be positive"); 324 return Lhs ? Lhs.getValue() * Rhs : MaybeAlign(); 325 } 326 327 inline Align operator/(Align Lhs, uint64_t Divisor) { 328 assert(llvm::isPowerOf2_64(Divisor) && 329 "Divisor must be positive and a power of 2"); 330 assert(Lhs != 1 && "Can't halve byte alignment"); 331 return Align(Lhs.value() / Divisor); 332 } 333 334 inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) { 335 assert(llvm::isPowerOf2_64(Divisor) && 336 "Divisor must be positive and a power of 2"); 337 return Lhs ? Lhs.getValue() / Divisor : MaybeAlign(); 338 } 339 340 inline Align max(MaybeAlign Lhs, Align Rhs) { 341 return Lhs && *Lhs > Rhs ? *Lhs : Rhs; 342 } 343 344 inline Align max(Align Lhs, MaybeAlign Rhs) { 345 return Rhs && *Rhs > Lhs ? *Rhs : Lhs; 346 } 347 348 #ifndef NDEBUG 349 // For usage in LLVM_DEBUG macros. 350 inline std::string DebugStr(const Align &A) { 351 return std::to_string(A.value()); 352 } 353 // For usage in LLVM_DEBUG macros. 354 inline std::string DebugStr(const MaybeAlign &MA) { 355 if (MA) 356 return std::to_string(MA->value()); 357 return "None"; 358 } 359 #endif // NDEBUG 360 361 #undef ALIGN_CHECK_ISPOSITIVE 362 363 } // namespace llvm 364 365 #endif // LLVM_SUPPORT_ALIGNMENT_H_ 366