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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 :
12 : #include "llvm/ADT/SmallVector.h"
13 : #include "llvm/ADT/StringRef.h"
14 : #include "llvm/Support/ErrorHandling.h"
15 : #include <cassert>
16 : #include <cstdint>
17 : #include <string>
18 : #include <string_view>
19 :
20 : namespace 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 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 and length representation that's also null-terminated.
106 : /// Guaranteed to be constructed from a compile-time string literal.
107 : StringLiteralKind,
108 :
109 : /// A pointer to a formatv_object_base instance.
110 : FormatvObjectKind,
111 :
112 : /// A char value, to render as a character.
113 : CharKind,
114 :
115 : /// An unsigned int value, to render as an unsigned decimal integer.
116 : DecUIKind,
117 :
118 : /// An int value, to render as a signed decimal integer.
119 : DecIKind,
120 :
121 : /// A pointer to an unsigned long value, to render as an unsigned decimal
122 : /// integer.
123 : DecULKind,
124 :
125 : /// A pointer to a long value, to render as a signed decimal integer.
126 : DecLKind,
127 :
128 : /// A pointer to an unsigned long long value, to render as an unsigned
129 : /// decimal integer.
130 : DecULLKind,
131 :
132 : /// A pointer to a long long value, to render as a signed decimal integer.
133 : DecLLKind,
134 :
135 : /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
136 : /// integer.
137 : UHexKind
138 : };
139 :
140 : union Child
141 : {
142 : const Twine *twine;
143 : const char *cString;
144 : const std::string *stdString;
145 : struct {
146 : const char *ptr;
147 : size_t length;
148 : } ptrAndLength;
149 : const formatv_object_base *formatvObject;
150 : char character;
151 : unsigned int decUI;
152 : int decI;
153 : const unsigned long *decUL;
154 : const long *decL;
155 : const unsigned long long *decULL;
156 : const long long *decLL;
157 : const uint64_t *uHex;
158 : };
159 :
160 : /// LHS - The prefix in the concatenation, which may be uninitialized for
161 : /// Null or Empty kinds.
162 : Child LHS;
163 :
164 : /// RHS - The suffix in the concatenation, which may be uninitialized for
165 : /// Null or Empty kinds.
166 : Child RHS;
167 :
168 : /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
169 : NodeKind LHSKind = EmptyKind;
170 :
171 : /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
172 : NodeKind RHSKind = EmptyKind;
173 :
174 : /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
175 : explicit Twine(NodeKind Kind) : LHSKind(Kind) {
176 : assert(isNullary() && "Invalid kind!");
177 : }
178 :
179 : /// Construct a binary twine.
180 : explicit Twine(const Twine &LHS, const Twine &RHS)
181 : : LHSKind(TwineKind), RHSKind(TwineKind) {
182 : this->LHS.twine = &LHS;
183 : this->RHS.twine = &RHS;
184 : assert(isValid() && "Invalid twine!");
185 : }
186 :
187 : /// Construct a twine from explicit values.
188 : explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
189 : : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
190 : assert(isValid() && "Invalid twine!");
191 : }
192 :
193 : /// Check for the null twine.
194 45 : bool isNull() const {
195 45 : return getLHSKind() == NullKind;
196 : }
197 :
198 : /// Check for the empty twine.
199 45 : bool isEmpty() const {
200 45 : return getLHSKind() == EmptyKind;
201 : }
202 :
203 : /// Check if this is a nullary twine (null or empty).
204 45 : bool isNullary() const {
205 45 : return isNull() || isEmpty();
206 : }
207 :
208 : /// Check if this is a unary twine.
209 : bool isUnary() const {
210 : return getRHSKind() == EmptyKind && !isNullary();
211 : }
212 :
213 : /// Check if this is a binary twine.
214 0 : bool isBinary() const {
215 0 : return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
216 : }
217 :
218 : /// Check if this is a valid twine (satisfying the invariants on
219 : /// order and number of arguments).
220 45 : bool isValid() const {
221 : // Nullary twines always have Empty on the RHS.
222 45 : if (isNullary() && getRHSKind() != EmptyKind)
223 0 : return false;
224 :
225 : // Null should never appear on the RHS.
226 45 : if (getRHSKind() == NullKind)
227 0 : return false;
228 :
229 : // The RHS cannot be non-empty if the LHS is empty.
230 45 : if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
231 0 : return false;
232 :
233 : // A twine child should always be binary.
234 45 : if (getLHSKind() == TwineKind &&
235 0 : !LHS.twine->isBinary())
236 0 : return false;
237 45 : if (getRHSKind() == TwineKind &&
238 0 : !RHS.twine->isBinary())
239 0 : return false;
240 :
241 45 : return true;
242 : }
243 :
244 : /// Get the NodeKind of the left-hand side.
245 135 : NodeKind getLHSKind() const { return LHSKind; }
246 :
247 : /// Get the NodeKind of the right-hand side.
248 135 : NodeKind getRHSKind() const { return RHSKind; }
249 :
250 : /// Print one child from a twine.
251 : void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
252 :
253 : /// Print the representation of one child from a twine.
254 : void printOneChildRepr(raw_ostream &OS, Child Ptr,
255 : NodeKind Kind) const;
256 :
257 : public:
258 : /// @name Constructors
259 : /// @{
260 :
261 : /// Construct from an empty string.
262 : /*implicit*/ Twine() {
263 : assert(isValid() && "Invalid twine!");
264 : }
265 :
266 : Twine(const Twine &) = default;
267 :
268 : /// Construct from a C string.
269 : ///
270 : /// We take care here to optimize "" into the empty twine -- this will be
271 : /// optimized out for string constants. This allows Twine arguments have
272 : /// default "" values, without introducing unnecessary string constants.
273 0 : /*implicit*/ Twine(const char *Str) {
274 0 : if (Str[0] != '\0') {
275 0 : LHS.cString = Str;
276 0 : LHSKind = CStringKind;
277 : } else
278 0 : LHSKind = EmptyKind;
279 :
280 0 : assert(isValid() && "Invalid twine!");
281 0 : }
282 : /// Delete the implicit conversion from nullptr as Twine(const char *)
283 : /// cannot take nullptr.
284 : /*implicit*/ Twine(std::nullptr_t) = delete;
285 :
286 : /// Construct from an std::string.
287 : /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {
288 : LHS.stdString = &Str;
289 : assert(isValid() && "Invalid twine!");
290 : }
291 :
292 : /// Construct from an std::string_view by converting it to a pointer and
293 : /// length. This handles string_views on a pure API basis, and avoids
294 : /// storing one (or a pointer to one) inside a Twine, which avoids problems
295 : /// when mixing code compiled under various C++ standards.
296 : /*implicit*/ Twine(const std::string_view &Str)
297 : : LHSKind(PtrAndLengthKind) {
298 : LHS.ptrAndLength.ptr = Str.data();
299 : LHS.ptrAndLength.length = Str.length();
300 : assert(isValid() && "Invalid twine!");
301 : }
302 :
303 : /// Construct from a StringRef.
304 45 : /*implicit*/ Twine(const StringRef &Str) : LHSKind(PtrAndLengthKind) {
305 45 : LHS.ptrAndLength.ptr = Str.data();
306 45 : LHS.ptrAndLength.length = Str.size();
307 45 : assert(isValid() && "Invalid twine!");
308 45 : }
309 :
310 : /// Construct from a StringLiteral.
311 : /*implicit*/ Twine(const StringLiteral &Str)
312 : : LHSKind(StringLiteralKind) {
313 : LHS.ptrAndLength.ptr = Str.data();
314 : LHS.ptrAndLength.length = Str.size();
315 : assert(isValid() && "Invalid twine!");
316 : }
317 :
318 : /// Construct from a SmallString.
319 : /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
320 : : LHSKind(PtrAndLengthKind) {
321 : LHS.ptrAndLength.ptr = Str.data();
322 : LHS.ptrAndLength.length = Str.size();
323 : assert(isValid() && "Invalid twine!");
324 : }
325 :
326 : /// Construct from a formatv_object_base.
327 : /*implicit*/ Twine(const formatv_object_base &Fmt)
328 : : LHSKind(FormatvObjectKind) {
329 : LHS.formatvObject = &Fmt;
330 : assert(isValid() && "Invalid twine!");
331 : }
332 :
333 : /// Construct from a char.
334 : explicit Twine(char Val) : LHSKind(CharKind) {
335 : LHS.character = Val;
336 : }
337 :
338 : /// Construct from a signed char.
339 : explicit Twine(signed char Val) : LHSKind(CharKind) {
340 : LHS.character = static_cast<char>(Val);
341 : }
342 :
343 : /// Construct from an unsigned char.
344 : explicit Twine(unsigned char Val) : LHSKind(CharKind) {
345 : LHS.character = static_cast<char>(Val);
346 : }
347 :
348 : /// Construct a twine to print \p Val as an unsigned decimal integer.
349 : explicit Twine(unsigned Val) : LHSKind(DecUIKind) {
350 : LHS.decUI = Val;
351 : }
352 :
353 : /// Construct a twine to print \p Val as a signed decimal integer.
354 : explicit Twine(int Val) : LHSKind(DecIKind) {
355 : LHS.decI = Val;
356 : }
357 :
358 : /// Construct a twine to print \p Val as an unsigned decimal integer.
359 : explicit Twine(const unsigned long &Val) : LHSKind(DecULKind) {
360 : LHS.decUL = &Val;
361 : }
362 :
363 : /// Construct a twine to print \p Val as a signed decimal integer.
364 : explicit Twine(const long &Val) : LHSKind(DecLKind) {
365 : LHS.decL = &Val;
366 : }
367 :
368 : /// Construct a twine to print \p Val as an unsigned decimal integer.
369 : explicit Twine(const unsigned long long &Val) : LHSKind(DecULLKind) {
370 : LHS.decULL = &Val;
371 : }
372 :
373 : /// Construct a twine to print \p Val as a signed decimal integer.
374 : explicit Twine(const long long &Val) : LHSKind(DecLLKind) {
375 : LHS.decLL = &Val;
376 : }
377 :
378 : // FIXME: Unfortunately, to make sure this is as efficient as possible we
379 : // need extra binary constructors from particular types. We can't rely on
380 : // the compiler to be smart enough to fold operator+()/concat() down to the
381 : // right thing. Yet.
382 :
383 : /// Construct as the concatenation of a C string and a StringRef.
384 : /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
385 : : LHSKind(CStringKind), RHSKind(PtrAndLengthKind) {
386 : this->LHS.cString = LHS;
387 : this->RHS.ptrAndLength.ptr = RHS.data();
388 : this->RHS.ptrAndLength.length = RHS.size();
389 : assert(isValid() && "Invalid twine!");
390 : }
391 :
392 : /// Construct as the concatenation of a StringRef and a C string.
393 : /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
394 : : LHSKind(PtrAndLengthKind), RHSKind(CStringKind) {
395 : this->LHS.ptrAndLength.ptr = LHS.data();
396 : this->LHS.ptrAndLength.length = LHS.size();
397 : this->RHS.cString = RHS;
398 : assert(isValid() && "Invalid twine!");
399 : }
400 :
401 : /// Since the intended use of twines is as temporary objects, assignments
402 : /// when concatenating might cause undefined behavior or stack corruptions
403 : Twine &operator=(const Twine &) = delete;
404 :
405 : /// Create a 'null' string, which is an empty string that always
406 : /// concatenates to form another empty string.
407 : static Twine createNull() {
408 : return Twine(NullKind);
409 : }
410 :
411 : /// @}
412 : /// @name Numeric Conversions
413 : /// @{
414 :
415 : // Construct a twine to print \p Val as an unsigned hexadecimal integer.
416 : static Twine utohexstr(const uint64_t &Val) {
417 : Child LHS, RHS;
418 : LHS.uHex = &Val;
419 : RHS.twine = nullptr;
420 : return Twine(LHS, UHexKind, RHS, EmptyKind);
421 : }
422 :
423 : /// @}
424 : /// @name Predicate Operations
425 : /// @{
426 :
427 : /// Check if this twine is trivially empty; a false return value does not
428 : /// necessarily mean the twine is empty.
429 : bool isTriviallyEmpty() const {
430 : return isNullary();
431 : }
432 :
433 : /// Check if this twine is guaranteed to refer to single string literal.
434 : bool isSingleStringLiteral() const {
435 : return isUnary() && getLHSKind() == StringLiteralKind;
436 : }
437 :
438 : /// Return true if this twine can be dynamically accessed as a single
439 : /// StringRef value with getSingleStringRef().
440 : bool isSingleStringRef() const {
441 : if (getRHSKind() != EmptyKind) return false;
442 :
443 : switch (getLHSKind()) {
444 : case EmptyKind:
445 : case CStringKind:
446 : case StdStringKind:
447 : case PtrAndLengthKind:
448 : case StringLiteralKind:
449 : return true;
450 : default:
451 : return false;
452 : }
453 : }
454 :
455 : /// @}
456 : /// @name String Operations
457 : /// @{
458 :
459 : Twine concat(const Twine &Suffix) const;
460 :
461 : /// @}
462 : /// @name Output & Conversion.
463 : /// @{
464 :
465 : /// Return the twine contents as a std::string.
466 : std::string str() const;
467 :
468 : /// Append the concatenated string into the given SmallString or SmallVector.
469 : void toVector(SmallVectorImpl<char> &Out) const;
470 :
471 : /// This returns the twine as a single StringRef. This method is only valid
472 : /// if isSingleStringRef() is true.
473 : StringRef getSingleStringRef() const {
474 : assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
475 : switch (getLHSKind()) {
476 : default: llvm_unreachable("Out of sync with isSingleStringRef");
477 : case EmptyKind:
478 : return StringRef();
479 : case CStringKind:
480 : return StringRef(LHS.cString);
481 : case StdStringKind:
482 : return StringRef(*LHS.stdString);
483 : case PtrAndLengthKind:
484 : case StringLiteralKind:
485 : return StringRef(LHS.ptrAndLength.ptr, LHS.ptrAndLength.length);
486 : }
487 : }
488 :
489 : /// This returns the twine as a single StringRef if it can be
490 : /// represented as such. Otherwise the twine is written into the given
491 : /// SmallVector and a StringRef to the SmallVector's data is returned.
492 : StringRef toStringRef(SmallVectorImpl<char> &Out) const {
493 : if (isSingleStringRef())
494 : return getSingleStringRef();
495 : toVector(Out);
496 : return StringRef(Out.data(), Out.size());
497 : }
498 :
499 : /// This returns the twine as a single null terminated StringRef if it
500 : /// can be represented as such. Otherwise the twine is written into the
501 : /// given SmallVector and a StringRef to the SmallVector's data is returned.
502 : ///
503 : /// The returned StringRef's size does not include the null terminator.
504 : StringRef toNullTerminatedStringRef(SmallVectorImpl<char> &Out) const;
505 :
506 : /// Write the concatenated string represented by this twine to the
507 : /// stream \p OS.
508 : void print(raw_ostream &OS) const;
509 :
510 : /// Dump the concatenated string represented by this twine to stderr.
511 : void dump() const;
512 :
513 : /// Write the representation of this twine to the stream \p OS.
514 : void printRepr(raw_ostream &OS) const;
515 :
516 : /// Dump the representation of this twine to stderr.
517 : void dumpRepr() const;
518 :
519 : /// @}
520 : };
521 :
522 : /// @name Twine Inline Implementations
523 : /// @{
524 :
525 : inline Twine Twine::concat(const Twine &Suffix) const {
526 : // Concatenation with null is null.
527 : if (isNull() || Suffix.isNull())
528 : return Twine(NullKind);
529 :
530 : // Concatenation with empty yields the other side.
531 : if (isEmpty())
532 : return Suffix;
533 : if (Suffix.isEmpty())
534 : return *this;
535 :
536 : // Otherwise we need to create a new node, taking care to fold in unary
537 : // twines.
538 : Child NewLHS, NewRHS;
539 : NewLHS.twine = this;
540 : NewRHS.twine = &Suffix;
541 : NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
542 : if (isUnary()) {
543 : NewLHS = LHS;
544 : NewLHSKind = getLHSKind();
545 : }
546 : if (Suffix.isUnary()) {
547 : NewRHS = Suffix.LHS;
548 : NewRHSKind = Suffix.getLHSKind();
549 : }
550 :
551 : return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
552 : }
553 :
554 : inline Twine operator+(const Twine &LHS, const Twine &RHS) {
555 : return LHS.concat(RHS);
556 : }
557 :
558 : /// Additional overload to guarantee simplified codegen; this is equivalent to
559 : /// concat().
560 :
561 : inline Twine operator+(const char *LHS, const StringRef &RHS) {
562 : return Twine(LHS, RHS);
563 : }
564 :
565 : /// Additional overload to guarantee simplified codegen; this is equivalent to
566 : /// concat().
567 :
568 : inline Twine operator+(const StringRef &LHS, const char *RHS) {
569 : return Twine(LHS, RHS);
570 : }
571 :
572 : inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
573 : RHS.print(OS);
574 : return OS;
575 : }
576 :
577 : /// @}
578 :
579 : } // end namespace llvm
580 :
581 : #endif // LLVM_ADT_TWINE_H
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