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/Support/MathExtras.h" 25 #include <cassert> 26 #include <optional> 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 // Returns the previous alignment. 88 Align previous() const { 89 assert(ShiftValue != 0 && "Undefined operation"); 90 Align Out; 91 Out.ShiftValue = ShiftValue - 1; 92 return Out; 93 } 94 95 /// Allow constructions of constexpr Align. 96 template <size_t kValue> constexpr static Align 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 Align 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 std::optional<Align> { 118 private: 119 using UP = std::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 constexpr MaybeAlign(std::nullopt_t None) : UP(None) {} 132 constexpr MaybeAlign(Align Value) : UP(Value) {} 133 explicit MaybeAlign(uint64_t Value) { 134 assert((Value == 0 || llvm::isPowerOf2_64(Value)) && 135 "Alignment is neither 0 nor a power of 2"); 136 if (Value) 137 emplace(Value); 138 } 139 140 /// For convenience, returns a valid alignment or 1 if undefined. 141 Align valueOrOne() const { return value_or(Align()); } 142 }; 143 144 /// Checks that SizeInBytes is a multiple of the alignment. 145 inline bool isAligned(Align Lhs, uint64_t SizeInBytes) { 146 return SizeInBytes % Lhs.value() == 0; 147 } 148 149 /// Checks that Addr is a multiple of the alignment. 150 inline bool isAddrAligned(Align Lhs, const void *Addr) { 151 return isAligned(Lhs, reinterpret_cast<uintptr_t>(Addr)); 152 } 153 154 /// Returns a multiple of A needed to store `Size` bytes. 155 inline uint64_t alignTo(uint64_t Size, Align A) { 156 const uint64_t Value = A.value(); 157 // The following line is equivalent to `(Size + Value - 1) / Value * Value`. 158 159 // The division followed by a multiplication can be thought of as a right 160 // shift followed by a left shift which zeros out the extra bits produced in 161 // the bump; `~(Value - 1)` is a mask where all those bits being zeroed out 162 // are just zero. 163 164 // Most compilers can generate this code but the pattern may be missed when 165 // multiple functions gets inlined. 166 return (Size + Value - 1) & ~(Value - 1U); 167 } 168 169 /// If non-zero \p Skew is specified, the return value will be a minimal integer 170 /// that is greater than or equal to \p Size and equal to \p A * N + \p Skew for 171 /// some integer N. If \p Skew is larger than \p A, its value is adjusted to '\p 172 /// Skew mod \p A'. 173 /// 174 /// Examples: 175 /// \code 176 /// alignTo(5, Align(8), 7) = 7 177 /// alignTo(17, Align(8), 1) = 17 178 /// alignTo(~0LL, Align(8), 3) = 3 179 /// \endcode 180 inline uint64_t alignTo(uint64_t Size, Align A, uint64_t Skew) { 181 const uint64_t Value = A.value(); 182 Skew %= Value; 183 return alignTo(Size - Skew, A) + Skew; 184 } 185 186 /// Aligns `Addr` to `Alignment` bytes, rounding up. 187 inline uintptr_t alignAddr(const void *Addr, Align Alignment) { 188 uintptr_t ArithAddr = reinterpret_cast<uintptr_t>(Addr); 189 assert(static_cast<uintptr_t>(ArithAddr + Alignment.value() - 1) >= 190 ArithAddr && 191 "Overflow"); 192 return alignTo(ArithAddr, Alignment); 193 } 194 195 /// Returns the offset to the next integer (mod 2**64) that is greater than 196 /// or equal to \p Value and is a multiple of \p Align. 197 inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) { 198 return alignTo(Value, Alignment) - Value; 199 } 200 201 /// Returns the necessary adjustment for aligning `Addr` to `Alignment` 202 /// bytes, rounding up. 203 inline uint64_t offsetToAlignedAddr(const void *Addr, Align Alignment) { 204 return offsetToAlignment(reinterpret_cast<uintptr_t>(Addr), Alignment); 205 } 206 207 /// Returns the log2 of the alignment. 208 inline unsigned Log2(Align A) { return A.ShiftValue; } 209 210 /// Returns the alignment that satisfies both alignments. 211 /// Same semantic as MinAlign. 212 inline Align commonAlignment(Align A, uint64_t Offset) { 213 return Align(MinAlign(A.value(), Offset)); 214 } 215 216 /// Returns a representation of the alignment that encodes undefined as 0. 217 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; } 218 219 /// Dual operation of the encode function above. 220 inline MaybeAlign decodeMaybeAlign(unsigned Value) { 221 if (Value == 0) 222 return MaybeAlign(); 223 Align Out; 224 Out.ShiftValue = Value - 1; 225 return Out; 226 } 227 228 /// Returns a representation of the alignment, the encoded value is positive by 229 /// definition. 230 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); } 231 232 /// Comparisons between Align and scalars. Rhs must be positive. 233 inline bool operator==(Align Lhs, uint64_t Rhs) { 234 ALIGN_CHECK_ISPOSITIVE(Rhs); 235 return Lhs.value() == Rhs; 236 } 237 inline bool operator!=(Align Lhs, uint64_t Rhs) { 238 ALIGN_CHECK_ISPOSITIVE(Rhs); 239 return Lhs.value() != Rhs; 240 } 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 } 257 258 /// Comparisons operators between Align. 259 inline bool operator==(Align Lhs, Align Rhs) { 260 return Lhs.ShiftValue == Rhs.ShiftValue; 261 } 262 inline bool operator!=(Align Lhs, Align Rhs) { 263 return Lhs.ShiftValue != Rhs.ShiftValue; 264 } 265 inline bool operator<=(Align Lhs, Align Rhs) { 266 return Lhs.ShiftValue <= Rhs.ShiftValue; 267 } 268 inline bool operator>=(Align Lhs, Align Rhs) { 269 return Lhs.ShiftValue >= Rhs.ShiftValue; 270 } 271 inline bool operator<(Align Lhs, Align Rhs) { 272 return Lhs.ShiftValue < Rhs.ShiftValue; 273 } 274 inline bool operator>(Align Lhs, Align Rhs) { 275 return Lhs.ShiftValue > Rhs.ShiftValue; 276 } 277 278 // Don't allow relational comparisons with MaybeAlign. 279 bool operator<=(Align Lhs, MaybeAlign Rhs) = delete; 280 bool operator>=(Align Lhs, MaybeAlign Rhs) = delete; 281 bool operator<(Align Lhs, MaybeAlign Rhs) = delete; 282 bool operator>(Align Lhs, MaybeAlign Rhs) = delete; 283 284 bool operator<=(MaybeAlign Lhs, Align Rhs) = delete; 285 bool operator>=(MaybeAlign Lhs, Align Rhs) = delete; 286 bool operator<(MaybeAlign Lhs, Align Rhs) = delete; 287 bool operator>(MaybeAlign Lhs, Align Rhs) = delete; 288 289 bool operator<=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 290 bool operator>=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 291 bool operator<(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 292 bool operator>(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 293 294 // Allow equality comparisons between Align and MaybeAlign. 295 inline bool operator==(MaybeAlign Lhs, Align Rhs) { return Lhs && *Lhs == Rhs; } 296 inline bool operator!=(MaybeAlign Lhs, Align Rhs) { return !(Lhs == Rhs); } 297 inline bool operator==(Align Lhs, MaybeAlign Rhs) { return Rhs == Lhs; } 298 inline bool operator!=(Align Lhs, MaybeAlign Rhs) { return !(Rhs == Lhs); } 299 // Allow equality comparisons with MaybeAlign. 300 inline bool operator==(MaybeAlign Lhs, MaybeAlign Rhs) { 301 return (Lhs && Rhs && (*Lhs == *Rhs)) || (!Lhs && !Rhs); 302 } 303 inline bool operator!=(MaybeAlign Lhs, MaybeAlign Rhs) { return !(Lhs == Rhs); } 304 // Allow equality comparisons with std::nullopt. 305 inline bool operator==(MaybeAlign Lhs, std::nullopt_t) { return !bool(Lhs); } 306 inline bool operator!=(MaybeAlign Lhs, std::nullopt_t) { return bool(Lhs); } 307 inline bool operator==(std::nullopt_t, MaybeAlign Rhs) { return !bool(Rhs); } 308 inline bool operator!=(std::nullopt_t, MaybeAlign Rhs) { return bool(Rhs); } 309 310 #ifndef NDEBUG 311 // For usage in LLVM_DEBUG macros. 312 inline std::string DebugStr(const Align &A) { 313 return std::to_string(A.value()); 314 } 315 // For usage in LLVM_DEBUG macros. 316 inline std::string DebugStr(const MaybeAlign &MA) { 317 if (MA) 318 return std::to_string(MA->value()); 319 return "None"; 320 } 321 #endif // NDEBUG 322 323 #undef ALIGN_CHECK_ISPOSITIVE 324 325 } // namespace llvm 326 327 #endif // LLVM_SUPPORT_ALIGNMENT_H_ 328