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 | |