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 // 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 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 value_or(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 Addr is a multiple of the alignment. 151 inline bool isAddrAligned(Align Lhs, const void *Addr) { 152 return isAligned(Lhs, reinterpret_cast<uintptr_t>(Addr)); 153 } 154 155 /// Returns a multiple of A needed to store `Size` bytes. 156 inline uint64_t alignTo(uint64_t Size, Align A) { 157 const uint64_t Value = A.value(); 158 // The following line is equivalent to `(Size + Value - 1) / Value * Value`. 159 160 // The division followed by a multiplication can be thought of as a right 161 // shift followed by a left shift which zeros out the extra bits produced in 162 // the bump; `~(Value - 1)` is a mask where all those bits being zeroed out 163 // are just zero. 164 165 // Most compilers can generate this code but the pattern may be missed when 166 // multiple functions gets inlined. 167 return (Size + Value - 1) & ~(Value - 1U); 168 } 169 170 /// If non-zero \p Skew is specified, the return value will be a minimal integer 171 /// that is greater than or equal to \p Size and equal to \p A * N + \p Skew for 172 /// some integer N. If \p Skew is larger than \p A, its value is adjusted to '\p 173 /// Skew mod \p A'. 174 /// 175 /// Examples: 176 /// \code 177 /// alignTo(5, Align(8), 7) = 7 178 /// alignTo(17, Align(8), 1) = 17 179 /// alignTo(~0LL, Align(8), 3) = 3 180 /// \endcode 181 inline uint64_t alignTo(uint64_t Size, Align A, uint64_t Skew) { 182 const uint64_t Value = A.value(); 183 Skew %= Value; 184 return alignTo(Size - Skew, A) + Skew; 185 } 186 187 /// Aligns `Addr` to `Alignment` bytes, rounding up. 188 inline uintptr_t alignAddr(const void *Addr, Align Alignment) { 189 uintptr_t ArithAddr = reinterpret_cast<uintptr_t>(Addr); 190 assert(static_cast<uintptr_t>(ArithAddr + Alignment.value() - 1) >= 191 ArithAddr && 192 "Overflow"); 193 return alignTo(ArithAddr, Alignment); 194 } 195 196 /// Returns the offset to the next integer (mod 2**64) that is greater than 197 /// or equal to \p Value and is a multiple of \p Align. 198 inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) { 199 return alignTo(Value, Alignment) - Value; 200 } 201 202 /// Returns the necessary adjustment for aligning `Addr` to `Alignment` 203 /// bytes, rounding up. 204 inline uint64_t offsetToAlignedAddr(const void *Addr, Align Alignment) { 205 return offsetToAlignment(reinterpret_cast<uintptr_t>(Addr), Alignment); 206 } 207 208 /// Returns the log2 of the alignment. 209 inline unsigned Log2(Align A) { return A.ShiftValue; } 210 211 /// Returns the alignment that satisfies both alignments. 212 /// Same semantic as MinAlign. 213 inline Align commonAlignment(Align A, uint64_t Offset) { 214 return Align(MinAlign(A.value(), Offset)); 215 } 216 217 /// Returns a representation of the alignment that encodes undefined as 0. 218 inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; } 219 220 /// Dual operation of the encode function above. 221 inline MaybeAlign decodeMaybeAlign(unsigned Value) { 222 if (Value == 0) 223 return MaybeAlign(); 224 Align Out; 225 Out.ShiftValue = Value - 1; 226 return Out; 227 } 228 229 /// Returns a representation of the alignment, the encoded value is positive by 230 /// definition. 231 inline unsigned encode(Align A) { return encode(MaybeAlign(A)); } 232 233 /// Comparisons between Align and scalars. Rhs must be positive. 234 inline bool operator==(Align Lhs, uint64_t Rhs) { 235 ALIGN_CHECK_ISPOSITIVE(Rhs); 236 return Lhs.value() == Rhs; 237 } 238 inline bool operator!=(Align Lhs, uint64_t Rhs) { 239 ALIGN_CHECK_ISPOSITIVE(Rhs); 240 return Lhs.value() != Rhs; 241 } 242 inline bool operator<=(Align Lhs, uint64_t Rhs) { 243 ALIGN_CHECK_ISPOSITIVE(Rhs); 244 return Lhs.value() <= Rhs; 245 } 246 inline bool operator>=(Align Lhs, uint64_t Rhs) { 247 ALIGN_CHECK_ISPOSITIVE(Rhs); 248 return Lhs.value() >= Rhs; 249 } 250 inline bool operator<(Align Lhs, uint64_t Rhs) { 251 ALIGN_CHECK_ISPOSITIVE(Rhs); 252 return Lhs.value() < Rhs; 253 } 254 inline bool operator>(Align Lhs, uint64_t Rhs) { 255 ALIGN_CHECK_ISPOSITIVE(Rhs); 256 return Lhs.value() > Rhs; 257 } 258 259 /// Comparisons operators between Align. 260 inline bool operator==(Align Lhs, Align Rhs) { 261 return Lhs.ShiftValue == Rhs.ShiftValue; 262 } 263 inline bool operator!=(Align Lhs, Align Rhs) { 264 return Lhs.ShiftValue != Rhs.ShiftValue; 265 } 266 inline bool operator<=(Align Lhs, Align Rhs) { 267 return Lhs.ShiftValue <= Rhs.ShiftValue; 268 } 269 inline bool operator>=(Align Lhs, Align Rhs) { 270 return Lhs.ShiftValue >= Rhs.ShiftValue; 271 } 272 inline bool operator<(Align Lhs, Align Rhs) { 273 return Lhs.ShiftValue < Rhs.ShiftValue; 274 } 275 inline bool operator>(Align Lhs, Align Rhs) { 276 return Lhs.ShiftValue > Rhs.ShiftValue; 277 } 278 279 // Don't allow relational comparisons with MaybeAlign. 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 bool operator>(Align Lhs, MaybeAlign Rhs) = delete; 284 285 bool operator<=(MaybeAlign Lhs, Align Rhs) = delete; 286 bool operator>=(MaybeAlign Lhs, Align Rhs) = delete; 287 bool operator<(MaybeAlign Lhs, Align Rhs) = delete; 288 bool operator>(MaybeAlign Lhs, Align Rhs) = delete; 289 290 bool operator<=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 291 bool operator>=(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 292 bool operator<(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 293 bool operator>(MaybeAlign Lhs, MaybeAlign Rhs) = delete; 294 295 #ifndef NDEBUG 296 // For usage in LLVM_DEBUG macros. 297 inline std::string DebugStr(const Align &A) { 298 return std::to_string(A.value()); 299 } 300 // For usage in LLVM_DEBUG macros. 301 inline std::string DebugStr(const MaybeAlign &MA) { 302 if (MA) 303 return std::to_string(MA->value()); 304 return "None"; 305 } 306 #endif // NDEBUG 307 308 #undef ALIGN_CHECK_ISPOSITIVE 309 310 } // namespace llvm 311 312 #endif // LLVM_SUPPORT_ALIGNMENT_H_ 313