include/llvm/ADT/Twine.h

   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
  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.
 439     StringRef getSingleStringRef() const {
 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.
 455     StringRef toStringRef(SmallVectorImpl<char> &Out) const {
 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.
 467     StringRef toNullTerminatedStringRef(SmallVectorImpl<char> &Out) const;
 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