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Twine.h
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1 //===-- Twine.h - Fast Temporary String Concatenation -----------*- C++ -*-===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #ifndef LLVM_ADT_TWINE_H
11 #define LLVM_ADT_TWINE_H
12 
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/ADT/StringRef.h"
16 #include <cassert>
17 #include <cstdint>
18 #include <string>
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 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 to a StringRef instance.
101  StringRefKind,
102 
103  /// A pointer to a SmallString instance.
104  SmallStringKind,
105 
106  /// A pointer to a formatv_object_base instance.
107  FormatvObjectKind,
108 
109  /// A char value, to render as a character.
110  CharKind,
111 
112  /// An unsigned int value, to render as an unsigned decimal integer.
113  DecUIKind,
114 
115  /// An int value, to render as a signed decimal integer.
116  DecIKind,
117 
118  /// A pointer to an unsigned long value, to render as an unsigned decimal
119  /// integer.
120  DecULKind,
121 
122  /// A pointer to a long value, to render as a signed decimal integer.
123  DecLKind,
124 
125  /// A pointer to an unsigned long long value, to render as an unsigned
126  /// decimal integer.
127  DecULLKind,
128 
129  /// A pointer to a long long value, to render as a signed decimal integer.
130  DecLLKind,
131 
132  /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
133  /// integer.
134  UHexKind
135  };
136 
137  union Child
138  {
139  const Twine *twine;
140  const char *cString;
141  const std::string *stdString;
142  const StringRef *stringRef;
143  const SmallVectorImpl<char> *smallString;
144  const formatv_object_base *formatvObject;
145  char character;
146  unsigned int decUI;
147  int decI;
148  const unsigned long *decUL;
149  const long *decL;
150  const unsigned long long *decULL;
151  const long long *decLL;
152  const uint64_t *uHex;
153  };
154 
155  /// LHS - The prefix in the concatenation, which may be uninitialized for
156  /// Null or Empty kinds.
157  Child LHS;
158  /// RHS - The suffix in the concatenation, which may be uninitialized for
159  /// Null or Empty kinds.
160  Child RHS;
161  /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
162  NodeKind LHSKind;
163  /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
164  NodeKind RHSKind;
165 
166  /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
167  explicit Twine(NodeKind Kind)
168  : LHSKind(Kind), RHSKind(EmptyKind) {
169  assert(isNullary() && "Invalid kind!");
170  }
171 
172  /// Construct a binary twine.
173  explicit Twine(const Twine &LHS, const Twine &RHS)
174  : LHSKind(TwineKind), RHSKind(TwineKind) {
175  this->LHS.twine = &LHS;
176  this->RHS.twine = &RHS;
177  assert(isValid() && "Invalid twine!");
178  }
179 
180  /// Construct a twine from explicit values.
181  explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
182  : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
183  assert(isValid() && "Invalid twine!");
184  }
185 
186  /// Check for the null twine.
187  bool isNull() const {
188  return getLHSKind() == NullKind;
189  }
190 
191  /// Check for the empty twine.
192  bool isEmpty() const {
193  return getLHSKind() == EmptyKind;
194  }
195 
196  /// Check if this is a nullary twine (null or empty).
197  bool isNullary() const {
198  return isNull() || isEmpty();
199  }
200 
201  /// Check if this is a unary twine.
202  bool isUnary() const {
203  return getRHSKind() == EmptyKind && !isNullary();
204  }
205 
206  /// Check if this is a binary twine.
207  bool isBinary() const {
208  return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
209  }
210 
211  /// Check if this is a valid twine (satisfying the invariants on
212  /// order and number of arguments).
213  bool isValid() const {
214  // Nullary twines always have Empty on the RHS.
215  if (isNullary() && getRHSKind() != EmptyKind)
216  return false;
217 
218  // Null should never appear on the RHS.
219  if (getRHSKind() == NullKind)
220  return false;
221 
222  // The RHS cannot be non-empty if the LHS is empty.
223  if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
224  return false;
225 
226  // A twine child should always be binary.
227  if (getLHSKind() == TwineKind &&
228  !LHS.twine->isBinary())
229  return false;
230  if (getRHSKind() == TwineKind &&
231  !RHS.twine->isBinary())
232  return false;
233 
234  return true;
235  }
236 
237  /// Get the NodeKind of the left-hand side.
238  NodeKind getLHSKind() const { return LHSKind; }
239 
240  /// Get the NodeKind of the right-hand side.
241  NodeKind getRHSKind() const { return RHSKind; }
242 
243  /// Print one child from a twine.
244  void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
245 
246  /// Print the representation of one child from a twine.
247  void printOneChildRepr(raw_ostream &OS, Child Ptr,
248  NodeKind Kind) const;
249 
250  public:
251  /// @name Constructors
252  /// @{
253 
254  /// Construct from an empty string.
255  /*implicit*/ Twine() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
256  assert(isValid() && "Invalid twine!");
257  }
258 
259  Twine(const Twine &) = default;
260 
261  /// Construct from a C string.
262  ///
263  /// We take care here to optimize "" into the empty twine -- this will be
264  /// optimized out for string constants. This allows Twine arguments have
265  /// default "" values, without introducing unnecessary string constants.
266  /*implicit*/ Twine(const char *Str)
267  : RHSKind(EmptyKind) {
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 
277  /// Construct from an std::string.
278  /*implicit*/ Twine(const std::string &Str)
279  : LHSKind(StdStringKind), RHSKind(EmptyKind) {
280  LHS.stdString = &Str;
281  assert(isValid() && "Invalid twine!");
282  }
283 
284  /// Construct from a StringRef.
285  /*implicit*/ Twine(const StringRef &Str)
286  : LHSKind(StringRefKind), RHSKind(EmptyKind) {
287  LHS.stringRef = &Str;
288  assert(isValid() && "Invalid twine!");
289  }
290 
291  /// Construct from a SmallString.
292  /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
293  : LHSKind(SmallStringKind), RHSKind(EmptyKind) {
294  LHS.smallString = &Str;
295  assert(isValid() && "Invalid twine!");
296  }
297 
298  /// Construct from a formatv_object_base.
299  /*implicit*/ Twine(const formatv_object_base &Fmt)
300  : LHSKind(FormatvObjectKind), RHSKind(EmptyKind) {
301  LHS.formatvObject = &Fmt;
302  assert(isValid() && "Invalid twine!");
303  }
304 
305  /// Construct from a char.
306  explicit Twine(char Val)
307  : LHSKind(CharKind), RHSKind(EmptyKind) {
308  LHS.character = Val;
309  }
310 
311  /// Construct from a signed char.
312  explicit Twine(signed char Val)
313  : LHSKind(CharKind), RHSKind(EmptyKind) {
314  LHS.character = static_cast<char>(Val);
315  }
316 
317  /// Construct from an unsigned char.
318  explicit Twine(unsigned char Val)
319  : LHSKind(CharKind), RHSKind(EmptyKind) {
320  LHS.character = static_cast<char>(Val);
321  }
322 
323  /// Construct a twine to print \p Val as an unsigned decimal integer.
324  explicit Twine(unsigned Val)
325  : LHSKind(DecUIKind), RHSKind(EmptyKind) {
326  LHS.decUI = Val;
327  }
328 
329  /// Construct a twine to print \p Val as a signed decimal integer.
330  explicit Twine(int Val)
331  : LHSKind(DecIKind), RHSKind(EmptyKind) {
332  LHS.decI = Val;
333  }
334 
335  /// Construct a twine to print \p Val as an unsigned decimal integer.
336  explicit Twine(const unsigned long &Val)
337  : LHSKind(DecULKind), RHSKind(EmptyKind) {
338  LHS.decUL = &Val;
339  }
340 
341  /// Construct a twine to print \p Val as a signed decimal integer.
342  explicit Twine(const long &Val)
343  : LHSKind(DecLKind), RHSKind(EmptyKind) {
344  LHS.decL = &Val;
345  }
346 
347  /// Construct a twine to print \p Val as an unsigned decimal integer.
348  explicit Twine(const unsigned long long &Val)
349  : LHSKind(DecULLKind), RHSKind(EmptyKind) {
350  LHS.decULL = &Val;
351  }
352 
353  /// Construct a twine to print \p Val as a signed decimal integer.
354  explicit Twine(const long long &Val)
355  : LHSKind(DecLLKind), RHSKind(EmptyKind) {
356  LHS.decLL = &Val;
357  }
358 
359  // FIXME: Unfortunately, to make sure this is as efficient as possible we
360  // need extra binary constructors from particular types. We can't rely on
361  // the compiler to be smart enough to fold operator+()/concat() down to the
362  // right thing. Yet.
363 
364  /// Construct as the concatenation of a C string and a StringRef.
365  /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
366  : LHSKind(CStringKind), RHSKind(StringRefKind) {
367  this->LHS.cString = LHS;
368  this->RHS.stringRef = &RHS;
369  assert(isValid() && "Invalid twine!");
370  }
371 
372  /// Construct as the concatenation of a StringRef and a C string.
373  /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
374  : LHSKind(StringRefKind), RHSKind(CStringKind) {
375  this->LHS.stringRef = &LHS;
376  this->RHS.cString = RHS;
377  assert(isValid() && "Invalid twine!");
378  }
379 
380  /// Since the intended use of twines is as temporary objects, assignments
381  /// when concatenating might cause undefined behavior or stack corruptions
382  Twine &operator=(const Twine &) = delete;
383 
384  /// Create a 'null' string, which is an empty string that always
385  /// concatenates to form another empty string.
386  static Twine createNull() {
387  return Twine(NullKind);
388  }
389 
390  /// @}
391  /// @name Numeric Conversions
392  /// @{
393 
394  // Construct a twine to print \p Val as an unsigned hexadecimal integer.
395  static Twine utohexstr(const uint64_t &Val) {
396  Child LHS, RHS;
397  LHS.uHex = &Val;
398  RHS.twine = nullptr;
399  return Twine(LHS, UHexKind, RHS, EmptyKind);
400  }
401 
402  /// @}
403  /// @name Predicate Operations
404  /// @{
405 
406  /// Check if this twine is trivially empty; a false return value does not
407  /// necessarily mean the twine is empty.
408  bool isTriviallyEmpty() const {
409  return isNullary();
410  }
411 
412  /// Return true if this twine can be dynamically accessed as a single
413  /// StringRef value with getSingleStringRef().
414  bool isSingleStringRef() const {
415  if (getRHSKind() != EmptyKind) return false;
416 
417  switch (getLHSKind()) {
418  case EmptyKind:
419  case CStringKind:
420  case StdStringKind:
421  case StringRefKind:
422  case SmallStringKind:
423  return true;
424  default:
425  return false;
426  }
427  }
428 
429  /// @}
430  /// @name String Operations
431  /// @{
432 
433  Twine concat(const Twine &Suffix) const;
434 
435  /// @}
436  /// @name Output & Conversion.
437  /// @{
438 
439  /// Return the twine contents as a std::string.
440  std::string str() const;
441 
442  /// Append the concatenated string into the given SmallString or SmallVector.
443  void toVector(SmallVectorImpl<char> &Out) const;
444 
445  /// This returns the twine as a single StringRef. This method is only valid
446  /// if isSingleStringRef() is true.
448  assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
449  switch (getLHSKind()) {
450  default: llvm_unreachable("Out of sync with isSingleStringRef");
451  case EmptyKind: return StringRef();
452  case CStringKind: return StringRef(LHS.cString);
453  case StdStringKind: return StringRef(*LHS.stdString);
454  case StringRefKind: return *LHS.stringRef;
455  case SmallStringKind:
456  return StringRef(LHS.smallString->data(), LHS.smallString->size());
457  }
458  }
459 
460  /// This returns the twine as a single StringRef if it can be
461  /// represented as such. Otherwise the twine is written into the given
462  /// SmallVector and a StringRef to the SmallVector's data is returned.
464  if (isSingleStringRef())
465  return getSingleStringRef();
466  toVector(Out);
467  return StringRef(Out.data(), Out.size());
468  }
469 
470  /// This returns the twine as a single null terminated StringRef if it
471  /// can be represented as such. Otherwise the twine is written into the
472  /// given SmallVector and a StringRef to the SmallVector's data is returned.
473  ///
474  /// The returned StringRef's size does not include the null terminator.
476 
477  /// Write the concatenated string represented by this twine to the
478  /// stream \p OS.
479  void print(raw_ostream &OS) const;
480 
481  /// Dump the concatenated string represented by this twine to stderr.
482  void dump() const;
483 
484  /// Write the representation of this twine to the stream \p OS.
485  void printRepr(raw_ostream &OS) const;
486 
487  /// Dump the representation of this twine to stderr.
488  void dumpRepr() const;
489 
490  /// @}
491  };
492 
493  /// @name Twine Inline Implementations
494  /// @{
495 
496  inline Twine Twine::concat(const Twine &Suffix) const {
497  // Concatenation with null is null.
498  if (isNull() || Suffix.isNull())
499  return Twine(NullKind);
500 
501  // Concatenation with empty yields the other side.
502  if (isEmpty())
503  return Suffix;
504  if (Suffix.isEmpty())
505  return *this;
506 
507  // Otherwise we need to create a new node, taking care to fold in unary
508  // twines.
509  Child NewLHS, NewRHS;
510  NewLHS.twine = this;
511  NewRHS.twine = &Suffix;
512  NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
513  if (isUnary()) {
514  NewLHS = LHS;
515  NewLHSKind = getLHSKind();
516  }
517  if (Suffix.isUnary()) {
518  NewRHS = Suffix.LHS;
519  NewRHSKind = Suffix.getLHSKind();
520  }
521 
522  return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
523  }
524 
525  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
526  return LHS.concat(RHS);
527  }
528 
529  /// Additional overload to guarantee simplified codegen; this is equivalent to
530  /// concat().
531 
532  inline Twine operator+(const char *LHS, const StringRef &RHS) {
533  return Twine(LHS, RHS);
534  }
535 
536  /// Additional overload to guarantee simplified codegen; this is equivalent to
537  /// concat().
538 
539  inline Twine operator+(const StringRef &LHS, const char *RHS) {
540  return Twine(LHS, RHS);
541  }
542 
543  inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
544  RHS.print(OS);
545  return OS;
546  }
547 
548  /// @}
549 
550 } // end namespace llvm
551 
552 #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:266
Twine(const formatv_object_base &Fmt)
Construct from a formatv_object_base.
Definition: Twine.h:299
APInt operator+(APInt a, const APInt &b)
Definition: APInt.h:2028
Twine(const unsigned long long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:348
Compute iterated dominance frontiers using a linear time algorithm.
Definition: AllocatorList.h:24
LLVM_ATTRIBUTE_ALWAYS_INLINE size_type size() const
Definition: SmallVector.h:136
Twine(const StringRef &LHS, const char *RHS)
Construct as the concatenation of a StringRef and a C string.
Definition: Twine.h:373
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:408
StringRef toStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single StringRef if it can be represented as such.
Definition: Twine.h:463
Twine(const SmallVectorImpl< char > &Str)
Construct from a SmallString.
Definition: Twine.h:292
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:81
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:447
bool isSingleStringRef() const
Return true if this twine can be dynamically accessed as a single StringRef value with getSingleStrin...
Definition: Twine.h:414
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:306
Twine()
Construct from an empty string.
Definition: Twine.h:255
Twine(const long long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:354
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:386
Twine(const StringRef &Str)
Construct from a StringRef.
Definition: Twine.h:285
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
#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:318
static Twine utohexstr(const uint64_t &Val)
Definition: Twine.h:395
Twine(const std::string &Str)
Construct from an std::string.
Definition: Twine.h:278
Twine(int Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:330
Twine(unsigned Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:324
pointer data()
Return a pointer to the vector&#39;s buffer, even if empty().
Definition: SmallVector.h:143
Twine(const long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:342
raw_ostream & operator<<(raw_ostream &OS, const APInt &I)
Definition: APInt.h:2018
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:365
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:44
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:49
Twine(const unsigned long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:336
int * Ptr
Twine concat(const Twine &Suffix) const
Definition: Twine.h:496
void print(raw_ostream &OS) const
Write the concatenated string represented by this twine to the stream OS.
Definition: Twine.cpp:163