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Twine.h
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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"
15 #include <cassert>
16 #include <cstdint>
17 #include <string>
18 
19 namespace llvm {
20 
21  class formatv_object_base;
22  class raw_ostream;
23 
24  /// Twine - A lightweight data structure for efficiently representing the
25  /// concatenation of temporary values as strings.
26  ///
27  /// A Twine is a kind of rope, it represents a concatenated string using a
28  /// binary-tree, where the string is the preorder of the nodes. Since the
29  /// Twine can be efficiently rendered into a buffer when its result is used,
30  /// it avoids the cost of generating temporary values for intermediate string
31  /// results -- particularly in cases when the Twine result is never
32  /// required. By explicitly tracking the type of leaf nodes, we can also avoid
33  /// the creation of temporary strings for conversions operations (such as
34  /// appending an integer to a string).
35  ///
36  /// A Twine is not intended for use directly and should not be stored, its
37  /// implementation relies on the ability to store pointers to temporary stack
38  /// objects which may be deallocated at the end of a statement. Twines should
39  /// only be used accepted as const references in arguments, when an API wishes
40  /// to accept possibly-concatenated strings.
41  ///
42  /// Twines support a special 'null' value, which always concatenates to form
43  /// itself, and renders as an empty string. This can be returned from APIs to
44  /// effectively nullify any concatenations performed on the result.
45  ///
46  /// \b Implementation
47  ///
48  /// Given the nature of a Twine, it is not possible for the Twine's
49  /// concatenation method to construct interior nodes; the result must be
50  /// represented inside the returned value. For this reason a Twine object
51  /// actually holds two values, the left- and right-hand sides of a
52  /// concatenation. We also have nullary Twine objects, which are effectively
53  /// sentinel values that represent empty strings.
54  ///
55  /// Thus, a Twine can effectively have zero, one, or two children. The \see
56  /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
57  /// testing the number of children.
58  ///
59  /// We maintain a number of invariants on Twine objects (FIXME: Why):
60  /// - Nullary twines are always represented with their Kind on the left-hand
61  /// side, and the Empty kind on the right-hand side.
62  /// - Unary twines are always represented with the value on the left-hand
63  /// side, and the Empty kind on the right-hand side.
64  /// - If a Twine has another Twine as a child, that child should always be
65  /// binary (otherwise it could have been folded into the parent).
66  ///
67  /// These invariants are check by \see isValid().
68  ///
69  /// \b Efficiency Considerations
70  ///
71  /// The Twine is designed to yield efficient and small code for common
72  /// situations. For this reason, the concat() method is inlined so that
73  /// concatenations of leaf nodes can be optimized into stores directly into a
74  /// single stack allocated object.
75  ///
76  /// In practice, not all compilers can be trusted to optimize concat() fully,
77  /// so we provide two additional methods (and accompanying operator+
78  /// overloads) to guarantee that particularly important cases (cstring plus
79  /// StringRef) codegen as desired.
80  class Twine {
81  /// NodeKind - Represent the type of an argument.
82  enum NodeKind : unsigned char {
83  /// An empty string; the result of concatenating anything with it is also
84  /// empty.
85  NullKind,
86 
87  /// The empty string.
88  EmptyKind,
89 
90  /// A pointer to a Twine instance.
91  TwineKind,
92 
93  /// A pointer to a C string instance.
94  CStringKind,
95 
96  /// A pointer to an std::string instance.
97  StdStringKind,
98 
99  /// A pointer to a StringRef instance.
100  StringRefKind,
101 
102  /// A pointer to a SmallString instance.
103  SmallStringKind,
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  const StringRef *stringRef;
142  const SmallVectorImpl<char> *smallString;
143  const formatv_object_base *formatvObject;
144  char character;
145  unsigned int decUI;
146  int decI;
147  const unsigned long *decUL;
148  const long *decL;
149  const unsigned long long *decULL;
150  const long long *decLL;
151  const uint64_t *uHex;
152  };
153 
154  /// LHS - The prefix in the concatenation, which may be uninitialized for
155  /// Null or Empty kinds.
156  Child LHS;
157 
158  /// RHS - The suffix in the concatenation, which may be uninitialized for
159  /// Null or Empty kinds.
160  Child RHS;
161 
162  /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
163  NodeKind LHSKind = EmptyKind;
164 
165  /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
166  NodeKind RHSKind = EmptyKind;
167 
168  /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
169  explicit Twine(NodeKind Kind) : LHSKind(Kind) {
170  assert(isNullary() && "Invalid kind!");
171  }
172 
173  /// Construct a binary twine.
174  explicit Twine(const Twine &LHS, const Twine &RHS)
175  : LHSKind(TwineKind), RHSKind(TwineKind) {
176  this->LHS.twine = &LHS;
177  this->RHS.twine = &RHS;
178  assert(isValid() && "Invalid twine!");
179  }
180 
181  /// Construct a twine from explicit values.
182  explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
183  : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
184  assert(isValid() && "Invalid twine!");
185  }
186 
187  /// Check for the null twine.
188  bool isNull() const {
189  return getLHSKind() == NullKind;
190  }
191 
192  /// Check for the empty twine.
193  bool isEmpty() const {
194  return getLHSKind() == EmptyKind;
195  }
196 
197  /// Check if this is a nullary twine (null or empty).
198  bool isNullary() const {
199  return isNull() || isEmpty();
200  }
201 
202  /// Check if this is a unary twine.
203  bool isUnary() const {
204  return getRHSKind() == EmptyKind && !isNullary();
205  }
206 
207  /// Check if this is a binary twine.
208  bool isBinary() const {
209  return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
210  }
211 
212  /// Check if this is a valid twine (satisfying the invariants on
213  /// order and number of arguments).
214  bool isValid() const {
215  // Nullary twines always have Empty on the RHS.
216  if (isNullary() && getRHSKind() != EmptyKind)
217  return false;
218 
219  // Null should never appear on the RHS.
220  if (getRHSKind() == NullKind)
221  return false;
222 
223  // The RHS cannot be non-empty if the LHS is empty.
224  if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
225  return false;
226 
227  // A twine child should always be binary.
228  if (getLHSKind() == TwineKind &&
229  !LHS.twine->isBinary())
230  return false;
231  if (getRHSKind() == TwineKind &&
232  !RHS.twine->isBinary())
233  return false;
234 
235  return true;
236  }
237 
238  /// Get the NodeKind of the left-hand side.
239  NodeKind getLHSKind() const { return LHSKind; }
240 
241  /// Get the NodeKind of the right-hand side.
242  NodeKind getRHSKind() const { return RHSKind; }
243 
244  /// Print one child from a twine.
245  void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
246 
247  /// Print the representation of one child from a twine.
248  void printOneChildRepr(raw_ostream &OS, Child Ptr,
249  NodeKind Kind) const;
250 
251  public:
252  /// @name Constructors
253  /// @{
254 
255  /// Construct from an empty string.
256  /*implicit*/ Twine() {
257  assert(isValid() && "Invalid twine!");
258  }
259 
260  Twine(const Twine &) = default;
261 
262  /// Construct from a C string.
263  ///
264  /// We take care here to optimize "" into the empty twine -- this will be
265  /// optimized out for string constants. This allows Twine arguments have
266  /// default "" values, without introducing unnecessary string constants.
267  /*implicit*/ Twine(const char *Str) {
268  if (Str[0] != '\0') {
269  LHS.cString = Str;
270  LHSKind = CStringKind;
271  } else
272  LHSKind = EmptyKind;
273 
274  assert(isValid() && "Invalid twine!");
275  }
276  /// Delete the implicit conversion from nullptr as Twine(const char *)
277  /// cannot take nullptr.
278  /*implicit*/ Twine(std::nullptr_t) = delete;
279 
280  /// Construct from an std::string.
281  /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {
282  LHS.stdString = &Str;
283  assert(isValid() && "Invalid twine!");
284  }
285 
286  /// Construct from a StringRef.
287  /*implicit*/ Twine(const StringRef &Str) : LHSKind(StringRefKind) {
288  LHS.stringRef = &Str;
289  assert(isValid() && "Invalid twine!");
290  }
291 
292  /// Construct from a SmallString.
293  /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
294  : LHSKind(SmallStringKind) {
295  LHS.smallString = &Str;
296  assert(isValid() && "Invalid twine!");
297  }
298 
299  /// Construct from a formatv_object_base.
300  /*implicit*/ Twine(const formatv_object_base &Fmt)
301  : LHSKind(FormatvObjectKind) {
302  LHS.formatvObject = &Fmt;
303  assert(isValid() && "Invalid twine!");
304  }
305 
306  /// Construct from a char.
307  explicit Twine(char Val) : LHSKind(CharKind) {
308  LHS.character = Val;
309  }
310 
311  /// Construct from a signed char.
312  explicit Twine(signed char Val) : LHSKind(CharKind) {
313  LHS.character = static_cast<char>(Val);
314  }
315 
316  /// Construct from an unsigned char.
317  explicit Twine(unsigned char Val) : LHSKind(CharKind) {
318  LHS.character = static_cast<char>(Val);
319  }
320 
321  /// Construct a twine to print \p Val as an unsigned decimal integer.
322  explicit Twine(unsigned Val) : LHSKind(DecUIKind) {
323  LHS.decUI = Val;
324  }
325 
326  /// Construct a twine to print \p Val as a signed decimal integer.
327  explicit Twine(int Val) : LHSKind(DecIKind) {
328  LHS.decI = Val;
329  }
330 
331  /// Construct a twine to print \p Val as an unsigned decimal integer.
332  explicit Twine(const unsigned long &Val) : LHSKind(DecULKind) {
333  LHS.decUL = &Val;
334  }
335 
336  /// Construct a twine to print \p Val as a signed decimal integer.
337  explicit Twine(const long &Val) : LHSKind(DecLKind) {
338  LHS.decL = &Val;
339  }
340 
341  /// Construct a twine to print \p Val as an unsigned decimal integer.
342  explicit Twine(const unsigned long long &Val) : LHSKind(DecULLKind) {
343  LHS.decULL = &Val;
344  }
345 
346  /// Construct a twine to print \p Val as a signed decimal integer.
347  explicit Twine(const long long &Val) : LHSKind(DecLLKind) {
348  LHS.decLL = &Val;
349  }
350 
351  // FIXME: Unfortunately, to make sure this is as efficient as possible we
352  // need extra binary constructors from particular types. We can't rely on
353  // the compiler to be smart enough to fold operator+()/concat() down to the
354  // right thing. Yet.
355 
356  /// Construct as the concatenation of a C string and a StringRef.
357  /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
358  : LHSKind(CStringKind), RHSKind(StringRefKind) {
359  this->LHS.cString = LHS;
360  this->RHS.stringRef = &RHS;
361  assert(isValid() && "Invalid twine!");
362  }
363 
364  /// Construct as the concatenation of a StringRef and a C string.
365  /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
366  : LHSKind(StringRefKind), RHSKind(CStringKind) {
367  this->LHS.stringRef = &LHS;
368  this->RHS.cString = RHS;
369  assert(isValid() && "Invalid twine!");
370  }
371 
372  /// Since the intended use of twines is as temporary objects, assignments
373  /// when concatenating might cause undefined behavior or stack corruptions
374  Twine &operator=(const Twine &) = delete;
375 
376  /// Create a 'null' string, which is an empty string that always
377  /// concatenates to form another empty string.
378  static Twine createNull() {
379  return Twine(NullKind);
380  }
381 
382  /// @}
383  /// @name Numeric Conversions
384  /// @{
385 
386  // Construct a twine to print \p Val as an unsigned hexadecimal integer.
387  static Twine utohexstr(const uint64_t &Val) {
388  Child LHS, RHS;
389  LHS.uHex = &Val;
390  RHS.twine = nullptr;
391  return Twine(LHS, UHexKind, RHS, EmptyKind);
392  }
393 
394  /// @}
395  /// @name Predicate Operations
396  /// @{
397 
398  /// Check if this twine is trivially empty; a false return value does not
399  /// necessarily mean the twine is empty.
400  bool isTriviallyEmpty() const {
401  return isNullary();
402  }
403 
404  /// Return true if this twine can be dynamically accessed as a single
405  /// StringRef value with getSingleStringRef().
406  bool isSingleStringRef() const {
407  if (getRHSKind() != EmptyKind) return false;
408 
409  switch (getLHSKind()) {
410  case EmptyKind:
411  case CStringKind:
412  case StdStringKind:
413  case StringRefKind:
414  case SmallStringKind:
415  return true;
416  default:
417  return false;
418  }
419  }
420 
421  /// @}
422  /// @name String Operations
423  /// @{
424 
425  Twine concat(const Twine &Suffix) const;
426 
427  /// @}
428  /// @name Output & Conversion.
429  /// @{
430 
431  /// Return the twine contents as a std::string.
432  std::string str() const;
433 
434  /// Append the concatenated string into the given SmallString or SmallVector.
435  void toVector(SmallVectorImpl<char> &Out) const;
436 
437  /// This returns the twine as a single StringRef. This method is only valid
438  /// if isSingleStringRef() is true.
440  assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
441  switch (getLHSKind()) {
442  default: llvm_unreachable("Out of sync with isSingleStringRef");
443  case EmptyKind: return StringRef();
444  case CStringKind: return StringRef(LHS.cString);
445  case StdStringKind: return StringRef(*LHS.stdString);
446  case StringRefKind: return *LHS.stringRef;
447  case SmallStringKind:
448  return StringRef(LHS.smallString->data(), LHS.smallString->size());
449  }
450  }
451 
452  /// This returns the twine as a single StringRef if it can be
453  /// represented as such. Otherwise the twine is written into the given
454  /// SmallVector and a StringRef to the SmallVector's data is returned.
456  if (isSingleStringRef())
457  return getSingleStringRef();
458  toVector(Out);
459  return StringRef(Out.data(), Out.size());
460  }
461 
462  /// This returns the twine as a single null terminated StringRef if it
463  /// can be represented as such. Otherwise the twine is written into the
464  /// given SmallVector and a StringRef to the SmallVector's data is returned.
465  ///
466  /// The returned StringRef's size does not include the null terminator.
468 
469  /// Write the concatenated string represented by this twine to the
470  /// stream \p OS.
471  void print(raw_ostream &OS) const;
472 
473  /// Dump the concatenated string represented by this twine to stderr.
474  void dump() const;
475 
476  /// Write the representation of this twine to the stream \p OS.
477  void printRepr(raw_ostream &OS) const;
478 
479  /// Dump the representation of this twine to stderr.
480  void dumpRepr() const;
481 
482  /// @}
483  };
484 
485  /// @name Twine Inline Implementations
486  /// @{
487 
488  inline Twine Twine::concat(const Twine &Suffix) const {
489  // Concatenation with null is null.
490  if (isNull() || Suffix.isNull())
491  return Twine(NullKind);
492 
493  // Concatenation with empty yields the other side.
494  if (isEmpty())
495  return Suffix;
496  if (Suffix.isEmpty())
497  return *this;
498 
499  // Otherwise we need to create a new node, taking care to fold in unary
500  // twines.
501  Child NewLHS, NewRHS;
502  NewLHS.twine = this;
503  NewRHS.twine = &Suffix;
504  NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
505  if (isUnary()) {
506  NewLHS = LHS;
507  NewLHSKind = getLHSKind();
508  }
509  if (Suffix.isUnary()) {
510  NewRHS = Suffix.LHS;
511  NewRHSKind = Suffix.getLHSKind();
512  }
513 
514  return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
515  }
516 
517  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
518  return LHS.concat(RHS);
519  }
520 
521  /// Additional overload to guarantee simplified codegen; this is equivalent to
522  /// concat().
523 
524  inline Twine operator+(const char *LHS, const StringRef &RHS) {
525  return Twine(LHS, RHS);
526  }
527 
528  /// Additional overload to guarantee simplified codegen; this is equivalent to
529  /// concat().
530 
531  inline Twine operator+(const StringRef &LHS, const char *RHS) {
532  return Twine(LHS, RHS);
533  }
534 
535  inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
536  RHS.print(OS);
537  return OS;
538  }
539 
540  /// @}
541 
542 } // end namespace llvm
543 
544 #endif // LLVM_ADT_TWINE_H
Twine(signed char Val)
Construct from a signed char.
Definition: Twine.h:312
Twine(const char *Str)
Construct from a C string.
Definition: Twine.h:267
Twine(const formatv_object_base &Fmt)
Construct from a formatv_object_base.
Definition: Twine.h:300
APInt operator+(APInt a, const APInt &b)
Definition: APInt.h:2048
Twine(const unsigned long long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:342
This class represents lattice values for constants.
Definition: AllocatorList.h:23
Twine(const StringRef &LHS, const char *RHS)
Construct as the concatenation of a StringRef and a C string.
Definition: Twine.h:365
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:400
StringRef toStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single StringRef if it can be represented as such.
Definition: Twine.h:455
Twine(const SmallVectorImpl< char > &Str)
Construct from a SmallString.
Definition: Twine.h:293
Twine & operator=(const Twine &)=delete
Since the intended use of twines is as temporary objects, assignments when concatenating might cause ...
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
Definition: Twine.h:80
void dumpRepr() const
Dump the representation of this twine to stderr.
Definition: Twine.cpp:181
StringRef getSingleStringRef() const
This returns the twine as a single StringRef.
Definition: Twine.h:439
bool isSingleStringRef() const
Return true if this twine can be dynamically accessed as a single StringRef value with getSingleStrin...
Definition: Twine.h:406
void dump() const
Dump the concatenated string represented by this twine to stderr.
Definition: Twine.cpp:177
Twine(char Val)
Construct from a char.
Definition: Twine.h:307
Twine()
Construct from an empty string.
Definition: Twine.h:256
Twine(const long long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:347
static Twine createNull()
Create a &#39;null&#39; string, which is an empty string that always concatenates to form another empty strin...
Definition: Twine.h:378
Twine(const StringRef &Str)
Construct from a StringRef.
Definition: Twine.h:287
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
void toVector(SmallVectorImpl< char > &Out) const
Append the concatenated string into the given SmallString or SmallVector.
Definition: Twine.cpp:32
Determine the kind of a node from its type.
size_t size() const
Definition: SmallVector.h:52
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
Twine(unsigned char Val)
Construct from an unsigned char.
Definition: Twine.h:317
static Twine utohexstr(const uint64_t &Val)
Definition: Twine.h:387
Twine(const std::string &Str)
Construct from an std::string.
Definition: Twine.h:281
Twine(int Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:327
Twine(unsigned Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:322
pointer data()
Return a pointer to the vector&#39;s buffer, even if empty().
Definition: SmallVector.h:144
Twine(const long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:337
raw_ostream & operator<<(raw_ostream &OS, const APInt &I)
Definition: APInt.h:2038
std::string str() const
Return the twine contents as a std::string.
Definition: Twine.cpp:17
const unsigned Kind
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
Twine(const char *LHS, const StringRef &RHS)
Construct as the concatenation of a C string and a StringRef.
Definition: Twine.h:357
void printRepr(raw_ostream &OS) const
Write the representation of this twine to the stream OS.
Definition: Twine.cpp:168
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:45
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:48
Twine(const unsigned long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:332
Twine concat(const Twine &Suffix) const
Definition: Twine.h:488
void print(raw_ostream &OS) const
Write the concatenated string represented by this twine to the stream OS.
Definition: Twine.cpp:163