LLVM  3.7.0
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"
15 #include "llvm/Support/DataTypes.h"
17 #include <cassert>
18 #include <string>
19 
20 namespace llvm {
21  class raw_ostream;
22 
23  /// Twine - A lightweight data structure for efficiently representing the
24  /// concatenation of temporary values as strings.
25  ///
26  /// A Twine is a kind of rope, it represents a concatenated string using a
27  /// binary-tree, where the string is the preorder of the nodes. Since the
28  /// Twine can be efficiently rendered into a buffer when its result is used,
29  /// it avoids the cost of generating temporary values for intermediate string
30  /// results -- particularly in cases when the Twine result is never
31  /// required. By explicitly tracking the type of leaf nodes, we can also avoid
32  /// the creation of temporary strings for conversions operations (such as
33  /// appending an integer to a string).
34  ///
35  /// A Twine is not intended for use directly and should not be stored, its
36  /// implementation relies on the ability to store pointers to temporary stack
37  /// objects which may be deallocated at the end of a statement. Twines should
38  /// only be used accepted as const references in arguments, when an API wishes
39  /// to accept possibly-concatenated strings.
40  ///
41  /// Twines support a special 'null' value, which always concatenates to form
42  /// itself, and renders as an empty string. This can be returned from APIs to
43  /// effectively nullify any concatenations performed on the result.
44  ///
45  /// \b Implementation
46  ///
47  /// Given the nature of a Twine, it is not possible for the Twine's
48  /// concatenation method to construct interior nodes; the result must be
49  /// represented inside the returned value. For this reason a Twine object
50  /// actually holds two values, the left- and right-hand sides of a
51  /// concatenation. We also have nullary Twine objects, which are effectively
52  /// sentinel values that represent empty strings.
53  ///
54  /// Thus, a Twine can effectively have zero, one, or two children. The \see
55  /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
56  /// testing the number of children.
57  ///
58  /// We maintain a number of invariants on Twine objects (FIXME: Why):
59  /// - Nullary twines are always represented with their Kind on the left-hand
60  /// side, and the Empty kind on the right-hand side.
61  /// - Unary twines are always represented with the value on the left-hand
62  /// side, and the Empty kind on the right-hand side.
63  /// - If a Twine has another Twine as a child, that child should always be
64  /// binary (otherwise it could have been folded into the parent).
65  ///
66  /// These invariants are check by \see isValid().
67  ///
68  /// \b Efficiency Considerations
69  ///
70  /// The Twine is designed to yield efficient and small code for common
71  /// situations. For this reason, the concat() method is inlined so that
72  /// concatenations of leaf nodes can be optimized into stores directly into a
73  /// single stack allocated object.
74  ///
75  /// In practice, not all compilers can be trusted to optimize concat() fully,
76  /// so we provide two additional methods (and accompanying operator+
77  /// overloads) to guarantee that particularly important cases (cstring plus
78  /// StringRef) codegen as desired.
79  class Twine {
80  /// NodeKind - Represent the type of an argument.
81  enum NodeKind : unsigned char {
82  /// An empty string; the result of concatenating anything with it is also
83  /// empty.
84  NullKind,
85 
86  /// The empty string.
87  EmptyKind,
88 
89  /// A pointer to a Twine instance.
90  TwineKind,
91 
92  /// A pointer to a C string instance.
93  CStringKind,
94 
95  /// A pointer to an std::string instance.
96  StdStringKind,
97 
98  /// A pointer to a StringRef instance.
99  StringRefKind,
100 
101  /// A pointer to a SmallString instance.
102  SmallStringKind,
103 
104  /// A char value reinterpreted as a pointer, to render as a character.
105  CharKind,
106 
107  /// An unsigned int value reinterpreted as a pointer, to render as an
108  /// unsigned decimal integer.
109  DecUIKind,
110 
111  /// An int value reinterpreted as a pointer, to render as a signed
112  /// decimal integer.
113  DecIKind,
114 
115  /// A pointer to an unsigned long value, to render as an unsigned decimal
116  /// integer.
117  DecULKind,
118 
119  /// A pointer to a long value, to render as a signed decimal integer.
120  DecLKind,
121 
122  /// A pointer to an unsigned long long value, to render as an unsigned
123  /// decimal integer.
124  DecULLKind,
125 
126  /// A pointer to a long long value, to render as a signed decimal integer.
127  DecLLKind,
128 
129  /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
130  /// integer.
131  UHexKind
132  };
133 
134  union Child
135  {
136  const Twine *twine;
137  const char *cString;
138  const std::string *stdString;
139  const StringRef *stringRef;
140  const SmallVectorImpl<char> *smallString;
141  char character;
142  unsigned int decUI;
143  int decI;
144  const unsigned long *decUL;
145  const long *decL;
146  const unsigned long long *decULL;
147  const long long *decLL;
148  const uint64_t *uHex;
149  };
150 
151  private:
152  /// LHS - The prefix in the concatenation, which may be uninitialized for
153  /// Null or Empty kinds.
154  Child LHS;
155  /// RHS - The suffix in the concatenation, which may be uninitialized for
156  /// Null or Empty kinds.
157  Child RHS;
158  /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
159  NodeKind LHSKind;
160  /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
161  NodeKind RHSKind;
162 
163  private:
164  /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
165  explicit Twine(NodeKind Kind)
166  : LHSKind(Kind), RHSKind(EmptyKind) {
167  assert(isNullary() && "Invalid kind!");
168  }
169 
170  /// Construct a binary twine.
171  explicit Twine(const Twine &LHS, const Twine &RHS)
172  : LHSKind(TwineKind), RHSKind(TwineKind) {
173  this->LHS.twine = &LHS;
174  this->RHS.twine = &RHS;
175  assert(isValid() && "Invalid twine!");
176  }
177 
178  /// Construct a twine from explicit values.
179  explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
180  : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
181  assert(isValid() && "Invalid twine!");
182  }
183 
184  /// Since the intended use of twines is as temporary objects, assignments
185  /// when concatenating might cause undefined behavior or stack corruptions
186  Twine &operator=(const Twine &Other) = delete;
187 
188  /// Check for the null twine.
189  bool isNull() const {
190  return getLHSKind() == NullKind;
191  }
192 
193  /// Check for the empty twine.
194  bool isEmpty() const {
195  return getLHSKind() == EmptyKind;
196  }
197 
198  /// Check if this is a nullary twine (null or empty).
199  bool isNullary() const {
200  return isNull() || isEmpty();
201  }
202 
203  /// Check if this is a unary twine.
204  bool isUnary() const {
205  return getRHSKind() == EmptyKind && !isNullary();
206  }
207 
208  /// Check if this is a binary twine.
209  bool isBinary() const {
210  return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
211  }
212 
213  /// Check if this is a valid twine (satisfying the invariants on
214  /// order and number of arguments).
215  bool isValid() const {
216  // Nullary twines always have Empty on the RHS.
217  if (isNullary() && getRHSKind() != EmptyKind)
218  return false;
219 
220  // Null should never appear on the RHS.
221  if (getRHSKind() == NullKind)
222  return false;
223 
224  // The RHS cannot be non-empty if the LHS is empty.
225  if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
226  return false;
227 
228  // A twine child should always be binary.
229  if (getLHSKind() == TwineKind &&
230  !LHS.twine->isBinary())
231  return false;
232  if (getRHSKind() == TwineKind &&
233  !RHS.twine->isBinary())
234  return false;
235 
236  return true;
237  }
238 
239  /// Get the NodeKind of the left-hand side.
240  NodeKind getLHSKind() const { return LHSKind; }
241 
242  /// Get the NodeKind of the right-hand side.
243  NodeKind getRHSKind() const { return RHSKind; }
244 
245  /// Print one child from a twine.
246  void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
247 
248  /// Print the representation of one child from a twine.
249  void printOneChildRepr(raw_ostream &OS, Child Ptr,
250  NodeKind Kind) const;
251 
252  public:
253  /// @name Constructors
254  /// @{
255 
256  /// Construct from an empty string.
257  /*implicit*/ Twine() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
258  assert(isValid() && "Invalid twine!");
259  }
260 
261  Twine(const Twine &) = default;
262 
263  /// Construct from a C string.
264  ///
265  /// We take care here to optimize "" into the empty twine -- this will be
266  /// optimized out for string constants. This allows Twine arguments have
267  /// default "" values, without introducing unnecessary string constants.
268  /*implicit*/ Twine(const char *Str)
269  : RHSKind(EmptyKind) {
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 
279  /// Construct from an std::string.
280  /*implicit*/ Twine(const std::string &Str)
281  : LHSKind(StdStringKind), RHSKind(EmptyKind) {
282  LHS.stdString = &Str;
283  assert(isValid() && "Invalid twine!");
284  }
285 
286  /// Construct from a StringRef.
287  /*implicit*/ Twine(const StringRef &Str)
288  : LHSKind(StringRefKind), RHSKind(EmptyKind) {
289  LHS.stringRef = &Str;
290  assert(isValid() && "Invalid twine!");
291  }
292 
293  /// Construct from a SmallString.
294  /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
295  : LHSKind(SmallStringKind), RHSKind(EmptyKind) {
296  LHS.smallString = &Str;
297  assert(isValid() && "Invalid twine!");
298  }
299 
300  /// Construct from a char.
301  explicit Twine(char Val)
302  : LHSKind(CharKind), RHSKind(EmptyKind) {
303  LHS.character = Val;
304  }
305 
306  /// Construct from a signed char.
307  explicit Twine(signed char Val)
308  : LHSKind(CharKind), RHSKind(EmptyKind) {
309  LHS.character = static_cast<char>(Val);
310  }
311 
312  /// Construct from an unsigned char.
313  explicit Twine(unsigned char Val)
314  : LHSKind(CharKind), RHSKind(EmptyKind) {
315  LHS.character = static_cast<char>(Val);
316  }
317 
318  /// Construct a twine to print \p Val as an unsigned decimal integer.
319  explicit Twine(unsigned Val)
320  : LHSKind(DecUIKind), RHSKind(EmptyKind) {
321  LHS.decUI = Val;
322  }
323 
324  /// Construct a twine to print \p Val as a signed decimal integer.
325  explicit Twine(int Val)
326  : LHSKind(DecIKind), RHSKind(EmptyKind) {
327  LHS.decI = Val;
328  }
329 
330  /// Construct a twine to print \p Val as an unsigned decimal integer.
331  explicit Twine(const unsigned long &Val)
332  : LHSKind(DecULKind), RHSKind(EmptyKind) {
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)
338  : LHSKind(DecLKind), RHSKind(EmptyKind) {
339  LHS.decL = &Val;
340  }
341 
342  /// Construct a twine to print \p Val as an unsigned decimal integer.
343  explicit Twine(const unsigned long long &Val)
344  : LHSKind(DecULLKind), RHSKind(EmptyKind) {
345  LHS.decULL = &Val;
346  }
347 
348  /// Construct a twine to print \p Val as a signed decimal integer.
349  explicit Twine(const long long &Val)
350  : LHSKind(DecLLKind), RHSKind(EmptyKind) {
351  LHS.decLL = &Val;
352  }
353 
354  // FIXME: Unfortunately, to make sure this is as efficient as possible we
355  // need extra binary constructors from particular types. We can't rely on
356  // the compiler to be smart enough to fold operator+()/concat() down to the
357  // right thing. Yet.
358 
359  /// Construct as the concatenation of a C string and a StringRef.
360  /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
361  : LHSKind(CStringKind), RHSKind(StringRefKind) {
362  this->LHS.cString = LHS;
363  this->RHS.stringRef = &RHS;
364  assert(isValid() && "Invalid twine!");
365  }
366 
367  /// Construct as the concatenation of a StringRef and a C string.
368  /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
369  : LHSKind(StringRefKind), RHSKind(CStringKind) {
370  this->LHS.stringRef = &LHS;
371  this->RHS.cString = RHS;
372  assert(isValid() && "Invalid twine!");
373  }
374 
375  /// Create a 'null' string, which is an empty string that always
376  /// concatenates to form another empty string.
377  static Twine createNull() {
378  return Twine(NullKind);
379  }
380 
381  /// @}
382  /// @name Numeric Conversions
383  /// @{
384 
385  // Construct a twine to print \p Val as an unsigned hexadecimal integer.
386  static Twine utohexstr(const uint64_t &Val) {
387  Child LHS, RHS;
388  LHS.uHex = &Val;
389  RHS.twine = nullptr;
390  return Twine(LHS, UHexKind, RHS, EmptyKind);
391  }
392 
393  /// @}
394  /// @name Predicate Operations
395  /// @{
396 
397  /// Check if this twine is trivially empty; a false return value does not
398  /// necessarily mean the twine is empty.
399  bool isTriviallyEmpty() const {
400  return isNullary();
401  }
402 
403  /// Return true if this twine can be dynamically accessed as a single
404  /// StringRef value with getSingleStringRef().
405  bool isSingleStringRef() const {
406  if (getRHSKind() != EmptyKind) return false;
407 
408  switch (getLHSKind()) {
409  case EmptyKind:
410  case CStringKind:
411  case StdStringKind:
412  case StringRefKind:
413  case SmallStringKind:
414  return true;
415  default:
416  return false;
417  }
418  }
419 
420  /// @}
421  /// @name String Operations
422  /// @{
423 
424  Twine concat(const Twine &Suffix) const;
425 
426  /// @}
427  /// @name Output & Conversion.
428  /// @{
429 
430  /// Return the twine contents as a std::string.
431  std::string str() const;
432 
433  /// Append the concatenated string into the given SmallString or SmallVector.
434  void toVector(SmallVectorImpl<char> &Out) const;
435 
436  /// This returns the twine as a single StringRef. This method is only valid
437  /// if isSingleStringRef() is true.
439  assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
440  switch (getLHSKind()) {
441  default: llvm_unreachable("Out of sync with isSingleStringRef");
442  case EmptyKind: return StringRef();
443  case CStringKind: return StringRef(LHS.cString);
444  case StdStringKind: return StringRef(*LHS.stdString);
445  case StringRefKind: return *LHS.stringRef;
446  case SmallStringKind:
447  return StringRef(LHS.smallString->data(), LHS.smallString->size());
448  }
449  }
450 
451  /// This returns the twine as a single StringRef if it can be
452  /// represented as such. Otherwise the twine is written into the given
453  /// SmallVector and a StringRef to the SmallVector's data is returned.
455  if (isSingleStringRef())
456  return getSingleStringRef();
457  toVector(Out);
458  return StringRef(Out.data(), Out.size());
459  }
460 
461  /// This returns the twine as a single null terminated StringRef if it
462  /// can be represented as such. Otherwise the twine is written into the
463  /// given SmallVector and a StringRef to the SmallVector's data is returned.
464  ///
465  /// The returned StringRef's size does not include the null terminator.
467 
468  /// Write the concatenated string represented by this twine to the
469  /// stream \p OS.
470  void print(raw_ostream &OS) const;
471 
472  /// Dump the concatenated string represented by this twine to stderr.
473  void dump() const;
474 
475  /// Write the representation of this twine to the stream \p OS.
476  void printRepr(raw_ostream &OS) const;
477 
478  /// Dump the representation of this twine to stderr.
479  void dumpRepr() const;
480 
481  /// @}
482  };
483 
484  /// @name Twine Inline Implementations
485  /// @{
486 
487  inline Twine Twine::concat(const Twine &Suffix) const {
488  // Concatenation with null is null.
489  if (isNull() || Suffix.isNull())
490  return Twine(NullKind);
491 
492  // Concatenation with empty yields the other side.
493  if (isEmpty())
494  return Suffix;
495  if (Suffix.isEmpty())
496  return *this;
497 
498  // Otherwise we need to create a new node, taking care to fold in unary
499  // twines.
500  Child NewLHS, NewRHS;
501  NewLHS.twine = this;
502  NewRHS.twine = &Suffix;
503  NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
504  if (isUnary()) {
505  NewLHS = LHS;
506  NewLHSKind = getLHSKind();
507  }
508  if (Suffix.isUnary()) {
509  NewRHS = Suffix.LHS;
510  NewRHSKind = Suffix.getLHSKind();
511  }
512 
513  return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
514  }
515 
516  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
517  return LHS.concat(RHS);
518  }
519 
520  /// Additional overload to guarantee simplified codegen; this is equivalent to
521  /// concat().
522 
523  inline Twine operator+(const char *LHS, const StringRef &RHS) {
524  return Twine(LHS, RHS);
525  }
526 
527  /// Additional overload to guarantee simplified codegen; this is equivalent to
528  /// concat().
529 
530  inline Twine operator+(const StringRef &LHS, const char *RHS) {
531  return Twine(LHS, RHS);
532  }
533 
534  inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
535  RHS.print(OS);
536  return OS;
537  }
538 
539  /// @}
540 }
541 
542 #endif
void toVector(SmallVectorImpl< char > &Out) const
Append the concatenated string into the given SmallString or SmallVector.
Definition: Twine.cpp:26
Twine(signed char Val)
Construct from a signed char.
Definition: Twine.h:307
Twine(const char *Str)
Construct from a C string.
Definition: Twine.h:268
bool isSingleStringRef() const
Return true if this twine can be dynamically accessed as a single StringRef value with getSingleStrin...
Definition: Twine.h:405
Twine(const unsigned long long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:343
Twine(const StringRef &LHS, const char *RHS)
Construct as the concatenation of a StringRef and a C string.
Definition: Twine.h:368
Twine(const SmallVectorImpl< char > &Str)
Construct from a SmallString.
Definition: Twine.h:294
void dump() const
Dump the concatenated string represented by this twine to stderr.
Definition: Twine.cpp:164
void dumpRepr() const
Dump the representation of this twine to stderr.
Definition: Twine.cpp:168
std::string str() const
Return the twine contents as a std::string.
Definition: Twine.cpp:16
Twine - A lightweight data structure for efficiently representing the concatenation of temporary valu...
Definition: Twine.h:79
#define llvm_unreachable(msg)
Marks that the current location is not supposed to be reachable.
Definition: ErrorHandling.h:98
ELFYAML::ELF_STO Other
Definition: ELFYAML.cpp:591
StringRef getSingleStringRef() const
This returns the twine as a single StringRef.
Definition: Twine.h:438
Twine(char Val)
Construct from a char.
Definition: Twine.h:301
Twine()
Construct from an empty string.
Definition: Twine.h:257
Twine(const long long &Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:349
void printRepr(raw_ostream &OS) const
Write the representation of this twine to the stream OS.
Definition: Twine.cpp:156
static Twine createNull()
Create a 'null' string, which is an empty string that always concatenates to form another empty strin...
Definition: Twine.h:377
Twine(const StringRef &Str)
Construct from a StringRef.
Definition: Twine.h:287
Twine(unsigned char Val)
Construct from an unsigned char.
Definition: Twine.h:313
Twine concat(const Twine &Suffix) const
Definition: Twine.h:487
StringRef toStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single StringRef if it can be represented as such.
Definition: Twine.h:454
static Twine utohexstr(const uint64_t &Val)
Definition: Twine.h:386
Twine(const std::string &Str)
Construct from an std::string.
Definition: Twine.h:280
Twine(int Val)
Construct a twine to print Val as a signed decimal integer.
Definition: Twine.h:325
Twine(unsigned Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:319
pointer data()
Return a pointer to the vector's buffer, even if empty().
Definition: SmallVector.h:134
void operator+(int, ilist_iterator< T >)=delete
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:1738
const ARM::ArchExtKind Kind
Twine(const char *LHS, const StringRef &RHS)
Construct as the concatenation of a C string and a StringRef.
Definition: Twine.h:360
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:31
void print(raw_ostream &OS) const
Write the concatenated string represented by this twine to the stream OS.
Definition: Twine.cpp:151
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:399
This class implements an extremely fast bulk output stream that can only output to a stream...
Definition: raw_ostream.h:38
StringRef - Represent a constant reference to a string, i.e.
Definition: StringRef.h:40
Twine(const unsigned long &Val)
Construct a twine to print Val as an unsigned decimal integer.
Definition: Twine.h:331