Alignment.h revision 360784
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 30namespace 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. 40struct Align { 41private: 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 67public: 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{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. 111inline 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. 117struct MaybeAlign : public llvm::Optional<Align> { 118private: 119 using UP = llvm::Optional<Align>; 120 121public: 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. 146inline 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. 152inline bool isAligned(MaybeAlign Lhs, uint64_t SizeInBytes) { 153 ALIGN_CHECK_ISSET(Lhs); 154 return SizeInBytes % (*Lhs).value() == 0; 155} 156 157/// Checks that Addr is a multiple of the alignment. 158inline bool isAddrAligned(Align Lhs, const void *Addr) { 159 return isAligned(Lhs, reinterpret_cast<uintptr_t>(Addr)); 160} 161 162/// Returns a multiple of A needed to store `Size` bytes. 163inline uint64_t alignTo(uint64_t Size, Align A) { 164 const uint64_t value = A.value(); 165 // The following line is equivalent to `(Size + value - 1) / value * value`. 166 167 // The division followed by a multiplication can be thought of as a right 168 // shift followed by a left shift which zeros out the extra bits produced in 169 // the bump; `~(value - 1)` is a mask where all those bits being zeroed out 170 // are just zero. 171 172 // Most compilers can generate this code but the pattern may be missed when 173 // multiple functions gets inlined. 174 return (Size + value - 1) & ~(value - 1); 175} 176 177/// Returns a multiple of A needed to store `Size` bytes. 178/// Returns `Size` if current alignment is undefined. 179inline uint64_t alignTo(uint64_t Size, MaybeAlign A) { 180 return A ? alignTo(Size, A.getValue()) : Size; 181} 182 183/// Aligns `Addr` to `Alignment` bytes, rounding up. 184inline uintptr_t alignAddr(const void *Addr, Align Alignment) { 185 uintptr_t ArithAddr = reinterpret_cast<uintptr_t>(Addr); 186 assert(static_cast<uintptr_t>(ArithAddr + Alignment.value() - 1) >= 187 ArithAddr && "Overflow"); 188 return alignTo(ArithAddr, Alignment); 189} 190 191/// Returns the offset to the next integer (mod 2**64) that is greater than 192/// or equal to \p Value and is a multiple of \p Align. 193inline uint64_t offsetToAlignment(uint64_t Value, Align Alignment) { 194 return alignTo(Value, Alignment) - Value; 195} 196 197/// Returns the necessary adjustment for aligning `Addr` to `Alignment` 198/// bytes, rounding up. 199inline uint64_t offsetToAlignedAddr(const void *Addr, Align Alignment) { 200 return offsetToAlignment(reinterpret_cast<uintptr_t>(Addr), Alignment); 201} 202 203/// Returns the log2 of the alignment. 204inline unsigned Log2(Align A) { return A.ShiftValue; } 205 206/// Returns the log2 of the alignment. 207/// \pre A must be defined. 208inline unsigned Log2(MaybeAlign A) { 209 ALIGN_CHECK_ISSET(A); 210 return Log2(A.getValue()); 211} 212 213/// Returns the alignment that satisfies both alignments. 214/// Same semantic as MinAlign. 215inline Align commonAlignment(Align A, Align B) { return std::min(A, B); } 216 217/// Returns the alignment that satisfies both alignments. 218/// Same semantic as MinAlign. 219inline Align commonAlignment(Align A, uint64_t Offset) { 220 return Align(MinAlign(A.value(), Offset)); 221} 222 223/// Returns the alignment that satisfies both alignments. 224/// Same semantic as MinAlign. 225inline MaybeAlign commonAlignment(MaybeAlign A, MaybeAlign B) { 226 return A && B ? commonAlignment(*A, *B) : A ? A : B; 227} 228 229/// Returns the alignment that satisfies both alignments. 230/// Same semantic as MinAlign. 231inline MaybeAlign commonAlignment(MaybeAlign A, uint64_t Offset) { 232 return MaybeAlign(MinAlign((*A).value(), Offset)); 233} 234 235/// Returns a representation of the alignment that encodes undefined as 0. 236inline unsigned encode(MaybeAlign A) { return A ? A->ShiftValue + 1 : 0; } 237 238/// Dual operation of the encode function above. 239inline MaybeAlign decodeMaybeAlign(unsigned Value) { 240 if (Value == 0) 241 return MaybeAlign(); 242 Align Out; 243 Out.ShiftValue = Value - 1; 244 return Out; 245} 246 247/// Returns a representation of the alignment, the encoded value is positive by 248/// definition. 249inline unsigned encode(Align A) { return encode(MaybeAlign(A)); } 250 251/// Comparisons between Align and scalars. Rhs must be positive. 252inline bool operator==(Align Lhs, uint64_t Rhs) { 253 ALIGN_CHECK_ISPOSITIVE(Rhs); 254 return Lhs.value() == Rhs; 255} 256inline bool operator!=(Align Lhs, uint64_t Rhs) { 257 ALIGN_CHECK_ISPOSITIVE(Rhs); 258 return Lhs.value() != Rhs; 259} 260inline bool operator<=(Align Lhs, uint64_t Rhs) { 261 ALIGN_CHECK_ISPOSITIVE(Rhs); 262 return Lhs.value() <= Rhs; 263} 264inline bool operator>=(Align Lhs, uint64_t Rhs) { 265 ALIGN_CHECK_ISPOSITIVE(Rhs); 266 return Lhs.value() >= Rhs; 267} 268inline bool operator<(Align Lhs, uint64_t Rhs) { 269 ALIGN_CHECK_ISPOSITIVE(Rhs); 270 return Lhs.value() < Rhs; 271} 272inline bool operator>(Align Lhs, uint64_t Rhs) { 273 ALIGN_CHECK_ISPOSITIVE(Rhs); 274 return Lhs.value() > Rhs; 275} 276 277/// Comparisons between MaybeAlign and scalars. 278inline bool operator==(MaybeAlign Lhs, uint64_t Rhs) { 279 return Lhs ? (*Lhs).value() == Rhs : Rhs == 0; 280} 281inline bool operator!=(MaybeAlign Lhs, uint64_t Rhs) { 282 return Lhs ? (*Lhs).value() != Rhs : Rhs != 0; 283} 284inline bool operator<=(MaybeAlign Lhs, uint64_t Rhs) { 285 ALIGN_CHECK_ISSET(Lhs); 286 ALIGN_CHECK_ISPOSITIVE(Rhs); 287 return (*Lhs).value() <= Rhs; 288} 289inline bool operator>=(MaybeAlign Lhs, uint64_t Rhs) { 290 ALIGN_CHECK_ISSET(Lhs); 291 ALIGN_CHECK_ISPOSITIVE(Rhs); 292 return (*Lhs).value() >= Rhs; 293} 294inline bool operator<(MaybeAlign Lhs, uint64_t Rhs) { 295 ALIGN_CHECK_ISSET(Lhs); 296 ALIGN_CHECK_ISPOSITIVE(Rhs); 297 return (*Lhs).value() < Rhs; 298} 299inline bool operator>(MaybeAlign Lhs, uint64_t Rhs) { 300 ALIGN_CHECK_ISSET(Lhs); 301 ALIGN_CHECK_ISPOSITIVE(Rhs); 302 return (*Lhs).value() > Rhs; 303} 304 305/// Comparisons operators between Align. 306inline bool operator==(Align Lhs, Align Rhs) { 307 return Lhs.ShiftValue == Rhs.ShiftValue; 308} 309inline bool operator!=(Align Lhs, Align Rhs) { 310 return Lhs.ShiftValue != Rhs.ShiftValue; 311} 312inline bool operator<=(Align Lhs, Align Rhs) { 313 return Lhs.ShiftValue <= Rhs.ShiftValue; 314} 315inline bool operator>=(Align Lhs, Align Rhs) { 316 return Lhs.ShiftValue >= Rhs.ShiftValue; 317} 318inline bool operator<(Align Lhs, Align Rhs) { 319 return Lhs.ShiftValue < Rhs.ShiftValue; 320} 321inline bool operator>(Align Lhs, Align Rhs) { 322 return Lhs.ShiftValue > Rhs.ShiftValue; 323} 324 325/// Comparisons operators between Align and MaybeAlign. 326inline bool operator==(Align Lhs, MaybeAlign Rhs) { 327 ALIGN_CHECK_ISSET(Rhs); 328 return Lhs.value() == (*Rhs).value(); 329} 330inline bool operator!=(Align Lhs, MaybeAlign Rhs) { 331 ALIGN_CHECK_ISSET(Rhs); 332 return Lhs.value() != (*Rhs).value(); 333} 334inline bool operator<=(Align Lhs, MaybeAlign Rhs) { 335 ALIGN_CHECK_ISSET(Rhs); 336 return Lhs.value() <= (*Rhs).value(); 337} 338inline bool operator>=(Align Lhs, MaybeAlign Rhs) { 339 ALIGN_CHECK_ISSET(Rhs); 340 return Lhs.value() >= (*Rhs).value(); 341} 342inline bool operator<(Align Lhs, MaybeAlign Rhs) { 343 ALIGN_CHECK_ISSET(Rhs); 344 return Lhs.value() < (*Rhs).value(); 345} 346inline bool operator>(Align Lhs, MaybeAlign Rhs) { 347 ALIGN_CHECK_ISSET(Rhs); 348 return Lhs.value() > (*Rhs).value(); 349} 350 351/// Comparisons operators between MaybeAlign and Align. 352inline bool operator==(MaybeAlign Lhs, Align Rhs) { 353 ALIGN_CHECK_ISSET(Lhs); 354 return Lhs && (*Lhs).value() == Rhs.value(); 355} 356inline bool operator!=(MaybeAlign Lhs, Align Rhs) { 357 ALIGN_CHECK_ISSET(Lhs); 358 return Lhs && (*Lhs).value() != Rhs.value(); 359} 360inline bool operator<=(MaybeAlign Lhs, Align Rhs) { 361 ALIGN_CHECK_ISSET(Lhs); 362 return Lhs && (*Lhs).value() <= Rhs.value(); 363} 364inline bool operator>=(MaybeAlign Lhs, Align Rhs) { 365 ALIGN_CHECK_ISSET(Lhs); 366 return Lhs && (*Lhs).value() >= Rhs.value(); 367} 368inline bool operator<(MaybeAlign Lhs, Align Rhs) { 369 ALIGN_CHECK_ISSET(Lhs); 370 return Lhs && (*Lhs).value() < Rhs.value(); 371} 372inline bool operator>(MaybeAlign Lhs, Align Rhs) { 373 ALIGN_CHECK_ISSET(Lhs); 374 return Lhs && (*Lhs).value() > Rhs.value(); 375} 376 377inline Align operator/(Align Lhs, uint64_t Divisor) { 378 assert(llvm::isPowerOf2_64(Divisor) && 379 "Divisor must be positive and a power of 2"); 380 assert(Lhs != 1 && "Can't halve byte alignment"); 381 return Align(Lhs.value() / Divisor); 382} 383 384inline MaybeAlign operator/(MaybeAlign Lhs, uint64_t Divisor) { 385 assert(llvm::isPowerOf2_64(Divisor) && 386 "Divisor must be positive and a power of 2"); 387 return Lhs ? Lhs.getValue() / Divisor : MaybeAlign(); 388} 389 390inline Align max(MaybeAlign Lhs, Align Rhs) { 391 return Lhs && *Lhs > Rhs ? *Lhs : Rhs; 392} 393 394inline Align max(Align Lhs, MaybeAlign Rhs) { 395 return Rhs && *Rhs > Lhs ? *Rhs : Lhs; 396} 397 398#undef ALIGN_CHECK_ISPOSITIVE 399#undef ALIGN_CHECK_ISSET 400 401} // namespace llvm 402 403#endif // LLVM_SUPPORT_ALIGNMENT_H_ 404