LLVM  6.0.0svn
Twine.h
Go to the documentation of this file.
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 
159  /// RHS - The suffix in the concatenation, which may be uninitialized for
160  /// Null or Empty kinds.
161  Child RHS;
162 
163  /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
164  NodeKind LHSKind = EmptyKind;
165 
166  /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
167  NodeKind RHSKind = EmptyKind;
168 
169  /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
170  explicit Twine(NodeKind Kind) : LHSKind(Kind) {
171  assert(isNullary() && "Invalid kind!");
172  }
173 
174  /// Construct a binary twine.
175  explicit Twine(const Twine &LHS, const Twine &RHS)
176  : LHSKind(TwineKind), RHSKind(TwineKind) {
177  this->LHS.twine = &LHS;
178  this->RHS.twine = &RHS;
179  assert(isValid() && "Invalid twine!");
180  }
181 
182  /// Construct a twine from explicit values.
183  explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
184  : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
185  assert(isValid() && "Invalid twine!");
186  }
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() {
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  if (Str[0] != '\0') {
270  LHS.cString = Str;
271  LHSKind = CStringKind;
272  } else
273  LHSKind = EmptyKind;
274 
275  assert(isValid() && "Invalid twine!");
276  }
277 
278  /// Construct from an std::string.
279  /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {
280  LHS.stdString = &Str;
281  assert(isValid() && "Invalid twine!");
282  }
283 
284  /// Construct from a StringRef.
285  /*implicit*/ Twine(const StringRef &Str) : LHSKind(StringRefKind) {
286  LHS.stringRef = &Str;
287  assert(isValid() && "Invalid twine!");
288  }
289 
290  /// Construct from a SmallString.
291  /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
292  : LHSKind(SmallStringKind) {
293  LHS.smallString = &Str;
294  assert(isValid() && "Invalid twine!");
295  }
296 
297  /// Construct from a formatv_object_base.
298  /*implicit*/ Twine(const formatv_object_base &Fmt)
299  : LHSKind(FormatvObjectKind) {
300  LHS.formatvObject = &Fmt;
301  assert(isValid() && "Invalid twine!");
302  }
303 
304  /// Construct from a char.
305  explicit Twine(char Val) : LHSKind(CharKind) {
306  LHS.character = Val;
307  }
308 
309  /// Construct from a signed char.
310  explicit Twine(signed char Val) : LHSKind(CharKind) {
311  LHS.character = static_cast<char>(Val);
312  }
313 
314  /// Construct from an unsigned char.
315  explicit Twine(unsigned char Val) : LHSKind(CharKind) {
316  LHS.character = static_cast<char>(Val);
317  }
318 
319  /// Construct a twine to print \p Val as an unsigned decimal integer.
320  explicit Twine(unsigned Val) : LHSKind(DecUIKind) {
321  LHS.decUI = Val;
322  }
323 
324  /// Construct a twine to print \p Val as a signed decimal integer.
325  explicit Twine(int Val) : LHSKind(DecIKind) {
326  LHS.decI = Val;
327  }
328 
329  /// Construct a twine to print \p Val as an unsigned decimal integer.
330  explicit Twine(const unsigned long &Val) : LHSKind(DecULKind) {
331  LHS.decUL = &Val;
332  }
333 
334  /// Construct a twine to print \p Val as a signed decimal integer.
335  explicit Twine(const long &Val) : LHSKind(DecLKind) {
336  LHS.decL = &Val;
337  }
338 
339  /// Construct a twine to print \p Val as an unsigned decimal integer.
340  explicit Twine(const unsigned long long &Val) : LHSKind(DecULLKind) {
341  LHS.decULL = &Val;
342  }
343 
344  /// Construct a twine to print \p Val as a signed decimal integer.
345  explicit Twine(const long long &Val) : LHSKind(DecLLKind) {
346  LHS.decLL = &Val;
347  }
348 
349  // FIXME: Unfortunately, to make sure this is as efficient as possible we
350  // need extra binary constructors from particular types. We can't rely on
351  // the compiler to be smart enough to fold operator+()/concat() down to the
352  // right thing. Yet.
353 
354  /// Construct as the concatenation of a C string and a StringRef.
355  /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
356  : LHSKind(CStringKind), RHSKind(StringRefKind) {
357  this->LHS.cString = LHS;
358  this->RHS.stringRef = &RHS;
359  assert(isValid() && "Invalid twine!");
360  }
361 
362  /// Construct as the concatenation of a StringRef and a C string.
363  /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
364  : LHSKind(StringRefKind), RHSKind(CStringKind) {
365  this->LHS.stringRef = &LHS;
366  this->RHS.cString = RHS;
367  assert(isValid() && "Invalid twine!");
368  }
369 
370  /// Since the intended use of twines is as temporary objects, assignments
371  /// when concatenating might cause undefined behavior or stack corruptions
372  Twine &operator=(const Twine &) = delete;
373 
374  /// Create a 'null' string, which is an empty string that always
375  /// concatenates to form another empty string.
376  static Twine createNull() {
377  return Twine(NullKind);
378  }
379 
380  /// @}
381  /// @name Numeric Conversions
382  /// @{
383 
384  // Construct a twine to print \p Val as an unsigned hexadecimal integer.
385  static Twine utohexstr(const uint64_t &Val) {
386  Child LHS, RHS;
387  LHS.uHex = &Val;
388  RHS.twine = nullptr;
389  return Twine(LHS, UHexKind, RHS, EmptyKind);
390  }
391 
392  /// @}
393  /// @name Predicate Operations
394  /// @{
395 
396  /// Check if this twine is trivially empty; a false return value does not
397  /// necessarily mean the twine is empty.
398  bool isTriviallyEmpty() const {
399  return isNullary();
400  }
401 
402  /// Return true if this twine can be dynamically accessed as a single
403  /// StringRef value with getSingleStringRef().
404  bool isSingleStringRef() const {
405  if (getRHSKind() != EmptyKind) return false;
406 
407  switch (getLHSKind()) {
408  case EmptyKind:
409  case CStringKind:
410  case StdStringKind:
411  case StringRefKind:
412  case SmallStringKind:
413  return true;
414  default:
415  return false;
416  }
417  }
418 
419  /// @}
420  /// @name String Operations
421  /// @{
422 
423  Twine concat(const Twine &Suffix) const;
424 
425  /// @}
426  /// @name Output & Conversion.
427  /// @{
428 
429  /// Return the twine contents as a std::string.
430  std::string str() const;
431 
432  /// Append the concatenated string into the given SmallString or SmallVector.
433  void toVector(SmallVectorImpl<char> &Out) const;
434 
435  /// This returns the twine as a single StringRef. This method is only valid
436  /// if isSingleStringRef() is true.
438  assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
439  switch (getLHSKind()) {
440  default: llvm_unreachable("Out of sync with isSingleStringRef");
441  case EmptyKind: return StringRef();
442  case CStringKind: return StringRef(LHS.cString);
443  case StdStringKind: return StringRef(*LHS.stdString);
444  case StringRefKind: return *LHS.stringRef;
445  case SmallStringKind:
446  return StringRef(LHS.smallString->data(), LHS.smallString->size());
447  }
448  }
449 
450  /// This returns the twine as a single StringRef if it can be
451  /// represented as such. Otherwise the twine is written into the given
452  /// SmallVector and a StringRef to the SmallVector's data is returned.
454  if (isSingleStringRef())
455  return getSingleStringRef();
456  toVector(Out);
457  return StringRef(Out.data(), Out.size());
458  }
459 
460  /// This returns the twine as a single null terminated StringRef if it
461  /// can be represented as such. Otherwise the twine is written into the
462  /// given SmallVector and a StringRef to the SmallVector's data is returned.
463  ///
464  /// The returned StringRef's size does not include the null terminator.
466 
467  /// Write the concatenated string represented by this twine to the
468  /// stream \p OS.
469  void print(raw_ostream &OS) const;
470 
471  /// Dump the concatenated string represented by this twine to stderr.
472  void dump() const;
473 
474  /// Write the representation of this twine to the stream \p OS.
475  void printRepr(raw_ostream &OS) const;
476 
477  /// Dump the representation of this twine to stderr.
478  void dumpRepr() const;
479 
480  /// @}
481  };
482 
483  /// @name Twine Inline Implementations
484  /// @{
485 
486  inline Twine Twine::concat(const Twine &Suffix) const {
487  // Concatenation with null is null.
488  if (isNull() || Suffix.isNull())
489  return Twine(NullKind);
490 
491  // Concatenation with empty yields the other side.
492  if (isEmpty())
493  return Suffix;
494  if (Suffix.isEmpty())
495  return *this;
496 
497  // Otherwise we need to create a new node, taking care to fold in unary
498  // twines.
499  Child NewLHS, NewRHS;
500  NewLHS.twine = this;
501  NewRHS.twine = &Suffix;
502  NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
503  if (isUnary()) {
504  NewLHS = LHS;
505  NewLHSKind = getLHSKind();
506  }
507  if (Suffix.isUnary()) {
508  NewRHS = Suffix.LHS;
509  NewRHSKind = Suffix.getLHSKind();
510  }
511 
512  return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
513  }
514 
515  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
516  return LHS.concat(RHS);
517  }
518 
519  /// Additional overload to guarantee simplified codegen; this is equivalent to
520  /// concat().
521 
522  inline Twine operator+(const char *LHS, const StringRef &RHS) {
523  return Twine(LHS, RHS);
524  }
525 
526  /// Additional overload to guarantee simplified codegen; this is equivalent to
527  /// concat().
528 
529  inline Twine operator+(const StringRef &LHS, const char *RHS) {
530  return Twine(LHS, RHS);
531  }
532 
533  inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
534  RHS.print(OS);
535  return OS;
536  }
537 
538  /// @}
539 
540 } // end namespace llvm
541 
542 #endif // LLVM_ADT_TWINE_H
Twine(signed char Val)
Construct from a signed char.
Definition: Twine.h:310
Twine(const char *Str)
Construct from a C string.
Definition: Twine.h:268
Twine(const formatv_object_base &Fmt)
Construct from a formatv_object_base.
Definition: Twine.h:298
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:340
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:363
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:398
StringRef toStringRef(SmallVectorImpl< char > &Out) const
This returns the twine as a single StringRef if it can be represented as such.
Definition: Twine.h:453
Twine(const SmallVectorImpl< char > &Str)
Construct from a SmallString.
Definition: Twine.h:291
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:437
bool isSingleStringRef() const
Return true if this twine can be dynamically accessed as a single StringRef value with getSingleStrin...
Definition: Twine.h:404
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:305
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:345
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:376
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:315
static Twine utohexstr(const uint64_t &Val)
Definition: Twine.h:385
Twine(const std::string &Str)
Construct from an std::string.
Definition: Twine.h:279
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:320
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:335
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:355
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:330
Twine concat(const Twine &Suffix) const
Definition: Twine.h:486
void print(raw_ostream &OS) const
Write the concatenated string represented by this twine to the stream OS.
Definition: Twine.cpp:163