LLVM 17.0.0git
Twine.h
Go to the documentation of this file.
1//===- Twine.h - Fast Temporary String Concatenation ------------*- 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#ifndef LLVM_ADT_TWINE_H
10#define LLVM_ADT_TWINE_H
11
13#include "llvm/ADT/StringRef.h"
15#include <cassert>
16#include <cstdint>
17#include <string>
18#include <string_view>
19
20namespace llvm {
21
22 class formatv_object_base;
23 class raw_ostream;
24
25 /// Twine - A lightweight data structure for efficiently representing the
26 /// concatenation of temporary values as strings.
27 ///
28 /// A Twine is a kind of rope, it represents a concatenated string using a
29 /// binary-tree, where the string is the preorder of the nodes. Since the
30 /// Twine can be efficiently rendered into a buffer when its result is used,
31 /// it avoids the cost of generating temporary values for intermediate string
32 /// results -- particularly in cases when the Twine result is never
33 /// required. By explicitly tracking the type of leaf nodes, we can also avoid
34 /// the creation of temporary strings for conversions operations (such as
35 /// appending an integer to a string).
36 ///
37 /// A Twine is not intended for use directly and should not be stored, its
38 /// implementation relies on the ability to store pointers to temporary stack
39 /// objects which may be deallocated at the end of a statement. Twines should
40 /// only be used accepted as const references in arguments, when an API wishes
41 /// to accept possibly-concatenated strings.
42 ///
43 /// Twines support a special 'null' value, which always concatenates to form
44 /// itself, and renders as an empty string. This can be returned from APIs to
45 /// effectively nullify any concatenations performed on the result.
46 ///
47 /// \b Implementation
48 ///
49 /// Given the nature of a Twine, it is not possible for the Twine's
50 /// concatenation method to construct interior nodes; the result must be
51 /// represented inside the returned value. For this reason a Twine object
52 /// actually holds two values, the left- and right-hand sides of a
53 /// concatenation. We also have nullary Twine objects, which are effectively
54 /// sentinel values that represent empty strings.
55 ///
56 /// Thus, a Twine can effectively have zero, one, or two children. The \see
57 /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
58 /// testing the number of children.
59 ///
60 /// We maintain a number of invariants on Twine objects (FIXME: Why):
61 /// - Nullary twines are always represented with their Kind on the left-hand
62 /// side, and the Empty kind on the right-hand side.
63 /// - Unary twines are always represented with the value on the left-hand
64 /// side, and the Empty kind on the right-hand side.
65 /// - If a Twine has another Twine as a child, that child should always be
66 /// binary (otherwise it could have been folded into the parent).
67 ///
68 /// These invariants are check by \see isValid().
69 ///
70 /// \b Efficiency Considerations
71 ///
72 /// The Twine is designed to yield efficient and small code for common
73 /// situations. For this reason, the concat() method is inlined so that
74 /// concatenations of leaf nodes can be optimized into stores directly into a
75 /// single stack allocated object.
76 ///
77 /// In practice, not all compilers can be trusted to optimize concat() fully,
78 /// so we provide two additional methods (and accompanying operator+
79 /// overloads) to guarantee that particularly important cases (cstring plus
80 /// StringRef) codegen as desired.
81 class Twine {
82 /// NodeKind - Represent the type of an argument.
83 enum NodeKind : unsigned char {
84 /// An empty string; the result of concatenating anything with it is also
85 /// empty.
86 NullKind,
87
88 /// The empty string.
89 EmptyKind,
90
91 /// A pointer to a Twine instance.
92 TwineKind,
93
94 /// A pointer to a C string instance.
95 CStringKind,
96
97 /// A pointer to an std::string instance.
98 StdStringKind,
99
100 /// A Pointer and Length representation. Used for std::string_view,
101 /// StringRef, and SmallString. Can't use a StringRef here
102 /// because they are not trivally constructible.
103 PtrAndLengthKind,
104
105 /// A pointer to a formatv_object_base instance.
106 FormatvObjectKind,
107
108 /// A char value, to render as a character.
109 CharKind,
110
111 /// An unsigned int value, to render as an unsigned decimal integer.
112 DecUIKind,
113
114 /// An int value, to render as a signed decimal integer.
115 DecIKind,
116
117 /// A pointer to an unsigned long value, to render as an unsigned decimal
118 /// integer.
119 DecULKind,
120
121 /// A pointer to a long value, to render as a signed decimal integer.
122 DecLKind,
123
124 /// A pointer to an unsigned long long value, to render as an unsigned
125 /// decimal integer.
126 DecULLKind,
127
128 /// A pointer to a long long value, to render as a signed decimal integer.
129 DecLLKind,
130
131 /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
132 /// integer.
133 UHexKind
134 };
135
136 union Child
137 {
138 const Twine *twine;
139 const char *cString;
140 const std::string *stdString;
141 struct {
142 const char *ptr;
143 size_t length;
144 } ptrAndLength;
145 const formatv_object_base *formatvObject;
146 char character;
147 unsigned int decUI;
148 int decI;
149 const unsigned long *decUL;
150 const long *decL;
151 const unsigned long long *decULL;
152 const long long *decLL;
153 const uint64_t *uHex;
154 };
155
156 /// LHS - The prefix in the concatenation, which may be uninitialized for
157 /// Null or Empty kinds.
158 Child LHS;
159
160 /// RHS - The suffix in the concatenation, which may be uninitialized for
161 /// Null or Empty kinds.
162 Child RHS;
163
164 /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
165 NodeKind LHSKind = EmptyKind;
166
167 /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
168 NodeKind RHSKind = EmptyKind;
169
170 /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
171 explicit Twine(NodeKind Kind) : LHSKind(Kind) {
172 assert(isNullary() && "Invalid kind!");
173 }
174
175 /// Construct a binary twine.
176 explicit Twine(const Twine &LHS, const Twine &RHS)
177 : LHSKind(TwineKind), RHSKind(TwineKind) {
178 this->LHS.twine = &LHS;
179 this->RHS.twine = &RHS;
180 assert(isValid() && "Invalid twine!");
181 }
182
183 /// Construct a twine from explicit values.
184 explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
185 : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
186 assert(isValid() && "Invalid twine!");
187 }
188
189 /// Check for the null twine.
190 bool isNull() const {
191 return getLHSKind() == NullKind;
192 }
193
194 /// Check for the empty twine.
195 bool isEmpty() const {
196 return getLHSKind() == EmptyKind;
197 }
198
199 /// Check if this is a nullary twine (null or empty).
200 bool isNullary() const {
201 return isNull() || isEmpty();
202 }
203
204 /// Check if this is a unary twine.
205 bool isUnary() const {
206 return getRHSKind() == EmptyKind && !isNullary();
207 }
208
209 /// Check if this is a binary twine.
210 bool isBinary() const {
211 return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
212 }
213
214 /// Check if this is a valid twine (satisfying the invariants on
215 /// order and number of arguments).
216 bool isValid() const {
217 // Nullary twines always have Empty on the RHS.
218 if (isNullary() && getRHSKind() != EmptyKind)
219 return false;
220
221 // Null should never appear on the RHS.
222 if (getRHSKind() == NullKind)
223 return false;
224
225 // The RHS cannot be non-empty if the LHS is empty.
226 if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
227 return false;
228
229 // A twine child should always be binary.
230 if (getLHSKind() == TwineKind &&
231 !LHS.twine->isBinary())
232 return false;
233 if (getRHSKind() == TwineKind &&
234 !RHS.twine->isBinary())
235 return false;
236
237 return true;
238 }
239
240 /// Get the NodeKind of the left-hand side.
241 NodeKind getLHSKind() const { return LHSKind; }
242
243 /// Get the NodeKind of the right-hand side.
244 NodeKind getRHSKind() const { return RHSKind; }
245
246 /// Print one child from a twine.
247 void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
248
249 /// Print the representation of one child from a twine.
250 void printOneChildRepr(raw_ostream &OS, Child Ptr,
251 NodeKind Kind) const;
252
253 public:
254 /// @name Constructors
255 /// @{
256
257 /// Construct from an empty string.
258 /*implicit*/ Twine() {
259 assert(isValid() && "Invalid twine!");
260 }
261
262 Twine(const Twine &) = default;
263
264 /// Construct from a C string.
265 ///
266 /// We take care here to optimize "" into the empty twine -- this will be
267 /// optimized out for string constants. This allows Twine arguments have
268 /// default "" values, without introducing unnecessary string constants.
269 /*implicit*/ Twine(const char *Str) {
270 if (Str[0] != '\0') {
271 LHS.cString = Str;
272 LHSKind = CStringKind;
273 } else
274 LHSKind = EmptyKind;
275
276 assert(isValid() && "Invalid twine!");
277 }
278 /// Delete the implicit conversion from nullptr as Twine(const char *)
279 /// cannot take nullptr.
280 /*implicit*/ Twine(std::nullptr_t) = delete;
281
282 /// Construct from an std::string.
283 /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {
284 LHS.stdString = &Str;
285 assert(isValid() && "Invalid twine!");
286 }
287
288 /// Construct from an std::string_view by converting it to a pointer and
289 /// length. This handles string_views on a pure API basis, and avoids
290 /// storing one (or a pointer to one) inside a Twine, which avoids problems
291 /// when mixing code compiled under various C++ standards.
292 /*implicit*/ Twine(const std::string_view &Str)
293 : LHSKind(PtrAndLengthKind) {
294 LHS.ptrAndLength.ptr = Str.data();
295 LHS.ptrAndLength.length = Str.length();
296 assert(isValid() && "Invalid twine!");
297 }
298
299 /// Construct from a StringRef.
300 /*implicit*/ Twine(const StringRef &Str) : LHSKind(PtrAndLengthKind) {
301 LHS.ptrAndLength.ptr = Str.data();
302 LHS.ptrAndLength.length = Str.size();
303 assert(isValid() && "Invalid twine!");
304 }
305
306 /// Construct from a SmallString.
307 /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
308 : LHSKind(PtrAndLengthKind) {
309 LHS.ptrAndLength.ptr = Str.data();
310 LHS.ptrAndLength.length = Str.size();
311 assert(isValid() && "Invalid twine!");
312 }
313
314 /// Construct from a formatv_object_base.
315 /*implicit*/ Twine(const formatv_object_base &Fmt)
316 : LHSKind(FormatvObjectKind) {
317 LHS.formatvObject = &Fmt;
318 assert(isValid() && "Invalid twine!");
319 }
320
321 /// Construct from a char.
322 explicit Twine(char Val) : LHSKind(CharKind) {
323 LHS.character = Val;
324 }
325
326 /// Construct from a signed char.
327 explicit Twine(signed char Val) : LHSKind(CharKind) {
328 LHS.character = static_cast<char>(Val);
329 }
330
331 /// Construct from an unsigned char.
332 explicit Twine(unsigned char Val) : LHSKind(CharKind) {
333 LHS.character = static_cast<char>(Val);
334 }
335
336 /// Construct a twine to print \p Val as an unsigned decimal integer.
337 explicit Twine(unsigned Val) : LHSKind(DecUIKind) {
338 LHS.decUI = Val;
339 }
340
341 /// Construct a twine to print \p Val as a signed decimal integer.
342 explicit Twine(int Val) : LHSKind(DecIKind) {
343 LHS.decI = Val;
344 }
345
346 /// Construct a twine to print \p Val as an unsigned decimal integer.
347 explicit Twine(const unsigned long &Val) : LHSKind(DecULKind) {
348 LHS.decUL = &Val;
349 }
350
351 /// Construct a twine to print \p Val as a signed decimal integer.
352 explicit Twine(const long &Val) : LHSKind(DecLKind) {
353 LHS.decL = &Val;
354 }
355
356 /// Construct a twine to print \p Val as an unsigned decimal integer.
357 explicit Twine(const unsigned long long &Val) : LHSKind(DecULLKind) {
358 LHS.decULL = &Val;
359 }
360
361 /// Construct a twine to print \p Val as a signed decimal integer.
362 explicit Twine(const long long &Val) : LHSKind(DecLLKind) {
363 LHS.decLL = &Val;
364 }
365
366 // FIXME: Unfortunately, to make sure this is as efficient as possible we
367 // need extra binary constructors from particular types. We can't rely on
368 // the compiler to be smart enough to fold operator+()/concat() down to the
369 // right thing. Yet.
370
371 /// Construct as the concatenation of a C string and a StringRef.
372 /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
373 : LHSKind(CStringKind), RHSKind(PtrAndLengthKind) {
374 this->LHS.cString = LHS;
375 this->RHS.ptrAndLength.ptr = RHS.data();
376 this->RHS.ptrAndLength.length = RHS.size();
377 assert(isValid() && "Invalid twine!");
378 }
379
380 /// Construct as the concatenation of a StringRef and a C string.
381 /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
382 : LHSKind(PtrAndLengthKind), RHSKind(CStringKind) {
383 this->LHS.ptrAndLength.ptr = LHS.data();
384 this->LHS.ptrAndLength.length = LHS.size();
385 this->RHS.cString = RHS;
386 assert(isValid() && "Invalid twine!");
387 }
388
389 /// Since the intended use of twines is as temporary objects, assignments
390 /// when concatenating might cause undefined behavior or stack corruptions
391 Twine &operator=(const Twine &) = delete;
392
393 /// Create a 'null' string, which is an empty string that always
394 /// concatenates to form another empty string.
395 static Twine createNull() {
396 return Twine(NullKind);
397 }
398
399 /// @}
400 /// @name Numeric Conversions
401 /// @{
402
403 // Construct a twine to print \p Val as an unsigned hexadecimal integer.
404 static Twine utohexstr(const uint64_t &Val) {
405 Child LHS, RHS;
406 LHS.uHex = &Val;
407 RHS.twine = nullptr;
408 return Twine(LHS, UHexKind, RHS, EmptyKind);
409 }
410
411 /// @}
412 /// @name Predicate Operations
413 /// @{
414
415 /// Check if this twine is trivially empty; a false return value does not
416 /// necessarily mean the twine is empty.
417 bool isTriviallyEmpty() const {
418 return isNullary();
419 }
420
421 /// Return true if this twine can be dynamically accessed as a single
422 /// StringRef value with getSingleStringRef().
423 bool isSingleStringRef() const {
424 if (getRHSKind() != EmptyKind) return false;
425
426 switch (getLHSKind()) {
427 case EmptyKind:
428 case CStringKind:
429 case StdStringKind:
430 case PtrAndLengthKind:
431 return true;
432 default:
433 return false;
434 }
435 }
436
437 /// @}
438 /// @name String Operations
439 /// @{
440
441 Twine concat(const Twine &Suffix) const;
442
443 /// @}
444 /// @name Output & Conversion.
445 /// @{
446
447 /// Return the twine contents as a std::string.
448 std::string str() const;
449
450 /// Append the concatenated string into the given SmallString or SmallVector.
451 void toVector(SmallVectorImpl<char> &Out) const;
452
453 /// This returns the twine as a single StringRef. This method is only valid
454 /// if isSingleStringRef() is true.
456 assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
457 switch (getLHSKind()) {
458 default: llvm_unreachable("Out of sync with isSingleStringRef");
459 case EmptyKind:
460 return StringRef();
461 case CStringKind:
462 return StringRef(LHS.cString);
463 case StdStringKind:
464 return StringRef(*LHS.stdString);
465 case PtrAndLengthKind:
466 return StringRef(LHS.ptrAndLength.ptr, LHS.ptrAndLength.length);
467 }
468 }
469
470 /// This returns the twine as a single StringRef if it can be
471 /// represented as such. Otherwise the twine is written into the given
472 /// SmallVector and a StringRef to the SmallVector's data is returned.
474 if (isSingleStringRef())
475 return getSingleStringRef();
476 toVector(Out);
477 return StringRef(Out.data(), Out.size());
478 }
479
480 /// This returns the twine as a single null terminated StringRef if it
481 /// can be represented as such. Otherwise the twine is written into the
482 /// given SmallVector and a StringRef to the SmallVector's data is returned.
483 ///
484 /// The returned StringRef's size does not include the null terminator.
486
487 /// Write the concatenated string represented by this twine to the
488 /// stream \p OS.
489 void print(raw_ostream &OS) const;
490
491 /// Dump the concatenated string represented by this twine to stderr.
492 void dump() const;
493
494 /// Write the representation of this twine to the stream \p OS.
495 void printRepr(raw_ostream &OS) const;
496
497 /// Dump the representation of this twine to stderr.
498 void dumpRepr() const;
499
500 /// @}
501 };
502
503 /// @name Twine Inline Implementations
504 /// @{
505
506 inline Twine Twine::concat(const Twine &Suffix) const {
507 // Concatenation with null is null.
508 if (isNull() || Suffix.isNull())
509 return Twine(NullKind);
510
511 // Concatenation with empty yields the other side.
512 if (isEmpty())
513 return Suffix;
514 if (Suffix.isEmpty())
515 return *this;
516
517 // Otherwise we need to create a new node, taking care to fold in unary
518 // twines.
519 Child NewLHS, NewRHS;
520 NewLHS.twine = this;
521 NewRHS.twine = &Suffix;
522 NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
523 if (isUnary()) {
524 NewLHS = LHS;
525 NewLHSKind = getLHSKind();
526 }
527 if (Suffix.isUnary()) {
528 NewRHS = Suffix.LHS;
529 NewRHSKind = Suffix.getLHSKind();
530 }
531
532 return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
533 }
534
535 inline Twine operator+(const Twine &LHS, const Twine &RHS) {
536 return LHS.concat(RHS);
537 }
538
539 /// Additional overload to guarantee simplified codegen; this is equivalent to
540 /// concat().
541
542 inline Twine operator+(const char *LHS, const StringRef &RHS) {
543 return Twine(LHS, RHS);
544 }
545
546 /// Additional overload to guarantee simplified codegen; this is equivalent to
547 /// concat().
548
549 inline Twine operator+(const StringRef &LHS, const char *RHS) {
550 return Twine(LHS, RHS);
551 }
552
554 RHS.print(OS);
555 return OS;
556 }
557
558 /// @}
559
560} // end namespace llvm
561
562#endif // LLVM_ADT_TWINE_H
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
This file defines the SmallVector class.
Value * RHS
Value * LHS
size_t size() const
Definition: SmallVector.h:91
This class consists of common code factored out of the SmallVector class to reduce code duplication b...
Definition: SmallVector.h:577
pointer data()
Return a pointer to the vector's buffer, even if empty().
Definition: SmallVector.h:289
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:50
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
Definition: Twine.h:81
Twine()
Construct from an empty string.
Definition: Twine.h:258
Twine(const formatv_object_base &Fmt)
Construct from a formatv_object_base.
Definition: Twine.h:315
Twine & operator=(const Twine &)=delete
Since the intended use of twines is as temporary objects, assignments when concatenating might cause ...
Twine(const long long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:362
bool isSingleStringRef() const
Return true if this twine can be dynamically accessed as a single StringRef value with getSingleStrin...
Definition: Twine.h:423
Twine(const unsigned long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:347
Twine(const SmallVectorImpl< char > &Str)
Construct from a SmallString.
Definition: Twine.h:307
std::string str() const
Return the twine contents as a std::string.
Definition: Twine.cpp:17
Twine concat(const Twine &Suffix) const
Definition: Twine.h:506
Twine(unsigned Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:337
void print(raw_ostream &OS) const
Write the concatenated string represented by this twine to the stream OS.
Definition: Twine.cpp:157
StringRef toNullTerminatedStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single null terminated StringRef if it can be represented as such.
Definition: Twine.cpp:37
Twine(const std::string &Str)
Construct from an std::string.
Definition: Twine.h:283
Twine(unsigned char Val)
Construct from an unsigned char.
Definition: Twine.h:332
void dump() const
Dump the concatenated string represented by this twine to stderr.
Definition: Twine.cpp:171
Twine(const char *LHS, const StringRef &RHS)
Construct as the concatenation of a C string and a StringRef.
Definition: Twine.h:372
Twine(std::nullptr_t)=delete
Delete the implicit conversion from nullptr as Twine(const char *) cannot take nullptr.
bool isTriviallyEmpty() const
Check if this twine is trivially empty; a false return value does not necessarily mean the twine is e...
Definition: Twine.h:417
static Twine createNull()
Create a 'null' string, which is an empty string that always concatenates to form another empty strin...
Definition: Twine.h:395
Twine(const long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:352
void printRepr(raw_ostream &OS) const
Write the representation of this twine to the stream OS.
Definition: Twine.cpp:162
Twine(signed char Val)
Construct from a signed char.
Definition: Twine.h:327
Twine(const Twine &)=default
Twine(const std::string_view &Str)
Construct from an std::string_view by converting it to a pointer and length.
Definition: Twine.h:292
Twine(const StringRef &LHS, const char *RHS)
Construct as the concatenation of a StringRef and a C string.
Definition: Twine.h:381
StringRef toStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single StringRef if it can be represented as such.
Definition: Twine.h:473
static Twine utohexstr(const uint64_t &Val)
Definition: Twine.h:404
Twine(int Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:342
Twine(const StringRef &Str)
Construct from a StringRef.
Definition: Twine.h:300
StringRef getSingleStringRef() const
This returns the twine as a single StringRef.
Definition: Twine.h:455
void toVector(SmallVectorImpl< char > &Out) const
Append the concatenated string into the given SmallString or SmallVector.
Definition: Twine.cpp:32
Twine(char Val)
Construct from a char.
Definition: Twine.h:322
void dumpRepr() const
Dump the representation of this twine to stderr.
Definition: Twine.cpp:175
Twine(const unsigned long long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:357
Twine(const char *Str)
Construct from a C string.
Definition: Twine.h:269
void print(raw_ostream &O, bool IsForDebug=false) const
Implement operator<< on Value.
Definition: AsmWriter.cpp:4695
This class implements an extremely fast bulk output stream that can only output to a stream.
Definition: raw_ostream.h:52
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
This is an optimization pass for GlobalISel generic memory operations.
Definition: AddressRanges.h:18
raw_ostream & operator<<(raw_ostream &OS, const APFixedPoint &FX)
Definition: APFixedPoint.h:292
APInt operator+(APInt a, const APInt &b)
Definition: APInt.h:2120
Determine the kind of a node from its type.