1//===- Sequence.h - Utility for producing sequences of values ---*- 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/// \file
9/// Provides some synthesis utilities to produce sequences of values. The names
10/// are intentionally kept very short as they tend to occur in common and
11/// widely used contexts.
12///
13/// The `seq(A, B)` function produces a sequence of values from `A` to up to
14/// (but not including) `B`, i.e., [`A`, `B`), that can be safely iterated over.
15/// `seq` supports both integral (e.g., `int`, `char`, `uint32_t`) and enum
16/// types. `seq_inclusive(A, B)` produces a sequence of values from `A` to `B`,
17/// including `B`.
18///
19/// Examples with integral types:
20/// ```
21/// for (int x : seq(0, 3))
22/// outs() << x << " ";
23/// ```
24///
25/// Prints: `0 1 2 `.
26///
27/// ```
28/// for (int x : seq_inclusive(0, 3))
29/// outs() << x << " ";
30/// ```
31///
32/// Prints: `0 1 2 3 `.
33///
34/// Similar to `seq` and `seq_inclusive`, the `enum_seq` and
35/// `enum_seq_inclusive` functions produce sequences of enum values that can be
36/// iterated over.
37/// To enable iteration with enum types, you need to either mark enums as safe
38/// to iterate on by specializing `enum_iteration_traits`, or opt into
39/// potentially unsafe iteration at every callsite by passing
40/// `force_iteration_on_noniterable_enum`.
41///
42/// Examples with enum types:
43/// ```
44/// namespace X {
45/// enum class MyEnum : unsigned {A = 0, B, C};
46/// } // namespace X
47///
48/// template <> struct enum_iteration_traits<X::MyEnum> {
49/// static contexpr bool is_iterable = true;
50/// };
51///
52/// class MyClass {
53/// public:
54/// enum Safe { D = 3, E, F };
55/// enum MaybeUnsafe { G = 1, H = 2, I = 4 };
56/// };
57///
58/// template <> struct enum_iteration_traits<MyClass::Safe> {
59/// static contexpr bool is_iterable = true;
60/// };
61/// ```
62///
63/// ```
64/// for (auto v : enum_seq(MyClass::Safe::D, MyClass::Safe::F))
65/// outs() << int(v) << " ";
66/// ```
67///
68/// Prints: `3 4 `.
69///
70/// ```
71/// for (auto v : enum_seq(MyClass::MaybeUnsafe::H, MyClass::MaybeUnsafe::I,
72/// force_iteration_on_noniterable_enum))
73/// outs() << int(v) << " ";
74/// ```
75///
76/// Prints: `2 3 `.
77///
78//===----------------------------------------------------------------------===//
79
80#ifndef LLVM_ADT_SEQUENCE_H
81#define LLVM_ADT_SEQUENCE_H
82
83#include <cassert> // assert
84#include <iterator> // std::random_access_iterator_tag
85#include <limits> // std::numeric_limits
86#include <type_traits> // std::is_integral, std::is_enum, std::underlying_type,
87 // std::enable_if
88
89#include "llvm/Support/MathExtras.h" // AddOverflow / SubOverflow
90
91namespace llvm {
92
93// Enum traits that marks enums as safe or unsafe to iterate over.
94// By default, enum types are *not* considered safe for iteration.
95// To allow iteration for your enum type, provide a specialization with
96// `is_iterable` set to `true` in the `llvm` namespace.
97// Alternatively, you can pass the `force_iteration_on_noniterable_enum` tag
98// to `enum_seq` or `enum_seq_inclusive`.
99template <typename EnumT> struct enum_iteration_traits {
100 static constexpr bool is_iterable = false;
101};
102
103struct force_iteration_on_noniterable_enum_t {
104 explicit force_iteration_on_noniterable_enum_t() = default;
105};
106
107inline constexpr force_iteration_on_noniterable_enum_t
108 force_iteration_on_noniterable_enum;
109
110namespace detail {
111
112// Returns whether a value of type U can be represented with type T.
113template <typename T, typename U> bool canTypeFitValue(const U Value) {
114 const intmax_t BotT = intmax_t(std::numeric_limits<T>::min());
115 const intmax_t BotU = intmax_t(std::numeric_limits<U>::min());
116 const uintmax_t TopT = uintmax_t(std::numeric_limits<T>::max());
117 const uintmax_t TopU = uintmax_t(std::numeric_limits<U>::max());
118 return !((BotT > BotU && Value < static_cast<U>(BotT)) ||
119 (TopT < TopU && Value > static_cast<U>(TopT)));
120}
121
122// An integer type that asserts when:
123// - constructed from a value that doesn't fit into intmax_t,
124// - casted to a type that cannot hold the current value,
125// - its internal representation overflows.
126struct CheckedInt {
127 // Integral constructor, asserts if Value cannot be represented as intmax_t.
128 template <typename Integral, typename std::enable_if_t<
129 std::is_integral<Integral>::value, bool> = 0>
130 static CheckedInt from(Integral FromValue) {
131 if (!canTypeFitValue<intmax_t>(FromValue))
132 assertOutOfBounds();
133 CheckedInt Result;
134 Result.Value = static_cast<intmax_t>(FromValue);
135 return Result;
136 }
137
138 // Enum constructor, asserts if Value cannot be represented as intmax_t.
139 template <typename Enum,
140 typename std::enable_if_t<std::is_enum<Enum>::value, bool> = 0>
141 static CheckedInt from(Enum FromValue) {
142 using type = typename std::underlying_type<Enum>::type;
143 return from<type>(static_cast<type>(FromValue));
144 }
145
146 // Equality
147 bool operator==(const CheckedInt &O) const { return Value == O.Value; }
148 bool operator!=(const CheckedInt &O) const { return Value != O.Value; }
149
150 CheckedInt operator+(intmax_t Offset) const {
151 CheckedInt Result;
152 if (AddOverflow(Value, Offset, Result.Value))
153 assertOutOfBounds();
154 return Result;
155 }
156
157 intmax_t operator-(CheckedInt Other) const {
158 intmax_t Result;
159 if (SubOverflow(Value, Other.Value, Result))
160 assertOutOfBounds();
161 return Result;
162 }
163
164 // Convert to integral, asserts if Value cannot be represented as Integral.
165 template <typename Integral, typename std::enable_if_t<
166 std::is_integral<Integral>::value, bool> = 0>
167 Integral to() const {
168 if (!canTypeFitValue<Integral>(Value))
169 assertOutOfBounds();
170 return static_cast<Integral>(Value);
171 }
172
173 // Convert to enum, asserts if Value cannot be represented as Enum's
174 // underlying type.
175 template <typename Enum,
176 typename std::enable_if_t<std::is_enum<Enum>::value, bool> = 0>
177 Enum to() const {
178 using type = typename std::underlying_type<Enum>::type;
179 return Enum(to<type>());
180 }
181
182private:
183 static void assertOutOfBounds() { assert(false && "Out of bounds"); }
184
185 intmax_t Value;
186};
187
188template <typename T, bool IsReverse> struct SafeIntIterator {
189 using iterator_category = std::random_access_iterator_tag;
190 using value_type = T;
191 using difference_type = intmax_t;
192 using pointer = T *;
193 using reference = T &;
194
195 // Construct from T.
196 explicit SafeIntIterator(T Value) : SI(CheckedInt::from<T>(Value)) {}
197 // Construct from other direction.
198 SafeIntIterator(const SafeIntIterator<T, !IsReverse> &O) : SI(O.SI) {}
199
200 // Dereference
201 value_type operator*() const { return SI.to<T>(); }
202 // Indexing
203 value_type operator[](intmax_t Offset) const { return *(*this + Offset); }
204
205 // Can be compared for equivalence using the equality/inequality operators.
206 bool operator==(const SafeIntIterator &O) const { return SI == O.SI; }
207 bool operator!=(const SafeIntIterator &O) const { return SI != O.SI; }
208 // Comparison
209 bool operator<(const SafeIntIterator &O) const { return (*this - O) < 0; }
210 bool operator>(const SafeIntIterator &O) const { return (*this - O) > 0; }
211 bool operator<=(const SafeIntIterator &O) const { return (*this - O) <= 0; }
212 bool operator>=(const SafeIntIterator &O) const { return (*this - O) >= 0; }
213
214 // Pre Increment/Decrement
215 void operator++() { offset(1); }
216 void operator--() { offset(-1); }
217
218 // Post Increment/Decrement
219 SafeIntIterator operator++(int) {
220 const auto Copy = *this;
221 ++*this;
222 return Copy;
223 }
224 SafeIntIterator operator--(int) {
225 const auto Copy = *this;
226 --*this;
227 return Copy;
228 }
229
230 // Compound assignment operators
231 void operator+=(intmax_t Offset) { offset(Offset); }
232 void operator-=(intmax_t Offset) { offset(-Offset); }
233
234 // Arithmetic
235 SafeIntIterator operator+(intmax_t Offset) const { return add(Offset); }
236 SafeIntIterator operator-(intmax_t Offset) const { return add(-Offset); }
237
238 // Difference
239 intmax_t operator-(const SafeIntIterator &O) const {
240 return IsReverse ? O.SI - SI : SI - O.SI;
241 }
242
243private:
244 SafeIntIterator(const CheckedInt &SI) : SI(SI) {}
245
246 static intmax_t getOffset(intmax_t Offset) {
247 return IsReverse ? -Offset : Offset;
248 }
249
250 CheckedInt add(intmax_t Offset) const { return SI + getOffset(Offset); }
251
252 void offset(intmax_t Offset) { SI = SI + getOffset(Offset); }
253
254 CheckedInt SI;
255
256 // To allow construction from the other direction.
257 template <typename, bool> friend struct SafeIntIterator;
258};
259
260} // namespace detail
261
262template <typename T> struct iota_range {
263 using value_type = T;
264 using reference = T &;
265 using const_reference = const T &;
266 using iterator = detail::SafeIntIterator<value_type, false>;
267 using const_iterator = iterator;
268 using reverse_iterator = detail::SafeIntIterator<value_type, true>;
269 using const_reverse_iterator = reverse_iterator;
270 using difference_type = intmax_t;
271 using size_type = std::size_t;
272
273 explicit iota_range(T Begin, T End, bool Inclusive)
274 : BeginValue(Begin), PastEndValue(End) {
275 assert(Begin <= End && "Begin must be less or equal to End.");
276 if (Inclusive)
277 ++PastEndValue;
278 }
279
280 size_t size() const { return PastEndValue - BeginValue; }
281 bool empty() const { return BeginValue == PastEndValue; }
282
283 auto begin() const { return const_iterator(BeginValue); }
284 auto end() const { return const_iterator(PastEndValue); }
285
286 auto rbegin() const { return const_reverse_iterator(PastEndValue - 1); }
287 auto rend() const { return const_reverse_iterator(BeginValue - 1); }
288
289private:
290 static_assert(std::is_integral<T>::value || std::is_enum<T>::value,
291 "T must be an integral or enum type");
292 static_assert(std::is_same<T, std::remove_cv_t<T>>::value,
293 "T must not be const nor volatile");
294
295 iterator BeginValue;
296 iterator PastEndValue;
297};
298
299/// Iterate over an integral type from Begin up to - but not including - End.
300/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX] for
301/// forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX] for reverse
302/// iteration).
303template <typename T, typename = std::enable_if_t<std::is_integral<T>::value &&
304 !std::is_enum<T>::value>>
305auto seq(T Begin, T End) {
306 return iota_range<T>(Begin, End, false);
307}
308
309/// Iterate over an integral type from Begin to End inclusive.
310/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX - 1]
311/// for forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX - 1] for reverse
312/// iteration).
313template <typename T, typename = std::enable_if_t<std::is_integral<T>::value &&
314 !std::is_enum<T>::value>>
315auto seq_inclusive(T Begin, T End) {
316 return iota_range<T>(Begin, End, true);
317}
318
319/// Iterate over an enum type from Begin up to - but not including - End.
320/// Note: `enum_seq` will generate each consecutive value, even if no
321/// enumerator with that value exists.
322/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX] for
323/// forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX] for reverse
324/// iteration).
325template <typename EnumT,
326 typename = std::enable_if_t<std::is_enum<EnumT>::value>>
327auto enum_seq(EnumT Begin, EnumT End) {
328 static_assert(enum_iteration_traits<EnumT>::is_iterable,
329 "Enum type is not marked as iterable.");
330 return iota_range<EnumT>(Begin, End, false);
331}
332
333/// Iterate over an enum type from Begin up to - but not including - End, even
334/// when `EnumT` is not marked as safely iterable by `enum_iteration_traits`.
335/// Note: `enum_seq` will generate each consecutive value, even if no
336/// enumerator with that value exists.
337/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX] for
338/// forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX] for reverse
339/// iteration).
340template <typename EnumT,
341 typename = std::enable_if_t<std::is_enum<EnumT>::value>>
342auto enum_seq(EnumT Begin, EnumT End, force_iteration_on_noniterable_enum_t) {
343 return iota_range<EnumT>(Begin, End, false);
344}
345
346/// Iterate over an enum type from Begin to End inclusive.
347/// Note: `enum_seq_inclusive` will generate each consecutive value, even if no
348/// enumerator with that value exists.
349/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX - 1]
350/// for forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX - 1] for reverse
351/// iteration).
352template <typename EnumT,
353 typename = std::enable_if_t<std::is_enum<EnumT>::value>>
354auto enum_seq_inclusive(EnumT Begin, EnumT End) {
355 static_assert(enum_iteration_traits<EnumT>::is_iterable,
356 "Enum type is not marked as iterable.");
357 return iota_range<EnumT>(Begin, End, true);
358}
359
360/// Iterate over an enum type from Begin to End inclusive, even when `EnumT`
361/// is not marked as safely iterable by `enum_iteration_traits`.
362/// Note: `enum_seq_inclusive` will generate each consecutive value, even if no
363/// enumerator with that value exists.
364/// Note: Begin and End values have to be within [INTMAX_MIN, INTMAX_MAX - 1]
365/// for forward iteration (resp. [INTMAX_MIN + 1, INTMAX_MAX - 1] for reverse
366/// iteration).
367template <typename EnumT,
368 typename = std::enable_if_t<std::is_enum<EnumT>::value>>
369auto enum_seq_inclusive(EnumT Begin, EnumT End,
370 force_iteration_on_noniterable_enum_t) {
371 return iota_range<EnumT>(Begin, End, true);
372}
373
374} // end namespace llvm
375
376#endif // LLVM_ADT_SEQUENCE_H
377

source code of llvm/include/llvm/ADT/Sequence.h