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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 : 0 : bool isNull() const {
195 : 0 : return getLHSKind() == NullKind;
196 : : }
197 : :
198 : : /// Check for the empty twine.
199 : 0 : bool isEmpty() const {
200 : 0 : return getLHSKind() == EmptyKind;
201 : : }
202 : :
203 : : /// Check if this is a nullary twine (null or empty).
204 : 0 : bool isNullary() const {
205 [ # # # # ]: 0 : 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 : 0 : bool isValid() const {
221 : : // Nullary twines always have Empty on the RHS.
222 [ # # # # : 0 : if (isNullary() && getRHSKind() != EmptyKind)
# # ]
223 : 0 : return false;
224 : :
225 : : // Null should never appear on the RHS.
226 [ # # ]: 0 : if (getRHSKind() == NullKind)
227 : 0 : return false;
228 : :
229 : : // The RHS cannot be non-empty if the LHS is empty.
230 [ # # # # : 0 : if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
# # ]
231 : 0 : return false;
232 : :
233 : : // A twine child should always be binary.
234 [ # # # # ]: 0 : if (getLHSKind() == TwineKind &&
235 [ # # ]: 0 : !LHS.twine->isBinary())
236 : 0 : return false;
237 [ # # # # ]: 0 : if (getRHSKind() == TwineKind &&
238 [ # # ]: 0 : !RHS.twine->isBinary())
239 : 0 : return false;
240 : :
241 : 0 : return true;
242 : : }
243 : :
244 : : /// Get the NodeKind of the left-hand side.
245 : 0 : NodeKind getLHSKind() const { return LHSKind; }
246 : :
247 : : /// Get the NodeKind of the right-hand side.
248 : 0 : 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 : 0 : /*implicit*/ Twine(const StringRef &Str) : LHSKind(PtrAndLengthKind) {
305 : 0 : LHS.ptrAndLength.ptr = Str.data();
306 : 0 : LHS.ptrAndLength.length = Str.size();
307 [ # # ]: 0 : assert(isValid() && "Invalid twine!");
308 : 0 : }
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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