reference, declarationdefinition
definition → references, declarations, derived classes, virtual overrides
reference to multiple definitions → definitions
unreferenced
    1
    2
    3
    4
    5
    6
    7
    8
    9
   10
   11
   12
   13
   14
   15
   16
   17
   18
   19
   20
   21
   22
   23
   24
   25
   26
   27
   28
   29
   30
   31
   32
   33
   34
   35
   36
   37
   38
   39
   40
   41
   42
   43
   44
   45
   46
   47
   48
   49
   50
   51
   52
   53
   54
   55
   56
   57
   58
   59
   60
   61
   62
   63
   64
   65
   66
   67
   68
   69
   70
   71
   72
   73
   74
   75
   76
   77
   78
   79
   80
   81
   82
   83
   84
   85
   86
   87
   88
   89
   90
   91
   92
   93
   94
   95
   96
   97
   98
   99
  100
  101
  102
  103
  104
  105
  106
  107
  108
  109
  110
  111
  112
  113
  114
  115
  116
  117
  118
  119
  120
  121
  122
  123
  124
  125
  126
  127
  128
  129
  130
  131
  132
  133
  134
  135
  136
  137
  138
  139
  140
  141
  142
  143
  144
  145
  146
  147
  148
  149
  150
  151
  152
  153
  154
  155
  156
  157
  158
  159
  160
  161
  162
  163
  164
  165
  166
  167
  168
  169
  170
  171
  172
  173
  174
  175
  176
  177
  178
  179
  180
  181
  182
  183
  184
  185
  186
  187
  188
  189
  190
  191
  192
  193
  194
  195
  196
  197
  198
  199
  200
  201
  202
  203
  204
  205
  206
  207
  208
  209
  210
  211
  212
  213
  214
  215
  216
  217
  218
  219
  220
  221
  222
  223
  224
  225
  226
  227
  228
  229
  230
  231
  232
  233
  234
  235
  236
  237
  238
  239
  240
  241
  242
  243
  244
  245
  246
  247
  248
  249
  250
  251
  252
  253
  254
  255
  256
  257
  258
  259
  260
  261
  262
  263
  264
  265
  266
  267
  268
  269
  270
  271
  272
  273
  274
  275
  276
  277
  278
  279
  280
  281
  282
  283
  284
  285
  286
  287
  288
  289
  290
  291
  292
  293
  294
  295
  296
  297
  298
  299
  300
  301
  302
  303
  304
  305
  306
  307
  308
  309
  310
  311
  312
  313
  314
  315
  316
  317
  318
  319
  320
  321
  322
  323
  324
  325
  326
  327
  328
  329
  330
  331
  332
  333
  334
  335
  336
  337
  338
  339
  340
  341
  342
  343
  344
  345
  346
  347
  348
  349
  350
  351
  352
  353
  354
  355
  356
  357
  358
  359
  360
  361
  362
  363
  364
  365
  366
  367
  368
  369
  370
  371
  372
  373
  374
  375
  376
  377
  378
  379
  380
  381
  382
  383
  384
  385
  386
  387
  388
  389
  390
  391
  392
  393
  394
  395
  396
  397
  398
  399
  400
  401
  402
  403
  404
  405
  406
  407
  408
  409
  410
  411
  412
  413
  414
  415
  416
  417
  418
  419
  420
  421
  422
  423
  424
  425
  426
  427
  428
  429
  430
  431
  432
  433
  434
  435
  436
  437
  438
  439
  440
  441
  442
  443
  444
  445
  446
  447
  448
  449
  450
  451
  452
  453
  454
  455
  456
  457
  458
  459
  460
  461
  462
  463
  464
  465
  466
  467
  468
  469
  470
  471
  472
  473
  474
  475
  476
  477
  478
  479
  480
  481
  482
  483
  484
  485
  486
  487
  488
  489
  490
  491
  492
  493
  494
  495
  496
  497
  498
  499
  500
  501
  502
  503
  504
  505
  506
  507
  508
  509
  510
  511
  512
  513
  514
  515
  516
  517
  518
  519
  520
  521
  522
  523
  524
  525
  526
  527
  528
  529
  530
  531
  532
  533
  534
  535
  536
  537
  538
  539
  540
  541
  542
//===- Twine.h - Fast Temporary String Concatenation ------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_ADT_TWINE_H
#define LLVM_ADT_TWINE_H

#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <cstdint>
#include <string>

namespace llvm {

  class formatv_object_base;
  class raw_ostream;

  /// Twine - A lightweight data structure for efficiently representing the
  /// concatenation of temporary values as strings.
  ///
  /// A Twine is a kind of rope, it represents a concatenated string using a
  /// binary-tree, where the string is the preorder of the nodes. Since the
  /// Twine can be efficiently rendered into a buffer when its result is used,
  /// it avoids the cost of generating temporary values for intermediate string
  /// results -- particularly in cases when the Twine result is never
  /// required. By explicitly tracking the type of leaf nodes, we can also avoid
  /// the creation of temporary strings for conversions operations (such as
  /// appending an integer to a string).
  ///
  /// A Twine is not intended for use directly and should not be stored, its
  /// implementation relies on the ability to store pointers to temporary stack
  /// objects which may be deallocated at the end of a statement. Twines should
  /// only be used accepted as const references in arguments, when an API wishes
  /// to accept possibly-concatenated strings.
  ///
  /// Twines support a special 'null' value, which always concatenates to form
  /// itself, and renders as an empty string. This can be returned from APIs to
  /// effectively nullify any concatenations performed on the result.
  ///
  /// \b Implementation
  ///
  /// Given the nature of a Twine, it is not possible for the Twine's
  /// concatenation method to construct interior nodes; the result must be
  /// represented inside the returned value. For this reason a Twine object
  /// actually holds two values, the left- and right-hand sides of a
  /// concatenation. We also have nullary Twine objects, which are effectively
  /// sentinel values that represent empty strings.
  ///
  /// Thus, a Twine can effectively have zero, one, or two children. The \see
  /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
  /// testing the number of children.
  ///
  /// We maintain a number of invariants on Twine objects (FIXME: Why):
  ///  - Nullary twines are always represented with their Kind on the left-hand
  ///    side, and the Empty kind on the right-hand side.
  ///  - Unary twines are always represented with the value on the left-hand
  ///    side, and the Empty kind on the right-hand side.
  ///  - If a Twine has another Twine as a child, that child should always be
  ///    binary (otherwise it could have been folded into the parent).
  ///
  /// These invariants are check by \see isValid().
  ///
  /// \b Efficiency Considerations
  ///
  /// The Twine is designed to yield efficient and small code for common
  /// situations. For this reason, the concat() method is inlined so that
  /// concatenations of leaf nodes can be optimized into stores directly into a
  /// single stack allocated object.
  ///
  /// In practice, not all compilers can be trusted to optimize concat() fully,
  /// so we provide two additional methods (and accompanying operator+
  /// overloads) to guarantee that particularly important cases (cstring plus
  /// StringRef) codegen as desired.
  class Twine {
    /// NodeKind - Represent the type of an argument.
    enum NodeKind : unsigned char {
      /// An empty string; the result of concatenating anything with it is also
      /// empty.
      NullKind,

      /// The empty string.
      EmptyKind,

      /// A pointer to a Twine instance.
      TwineKind,

      /// A pointer to a C string instance.
      CStringKind,

      /// A pointer to an std::string instance.
      StdStringKind,

      /// A pointer to a StringRef instance.
      StringRefKind,

      /// A pointer to a SmallString instance.
      SmallStringKind,

      /// A pointer to a formatv_object_base instance.
      FormatvObjectKind,

      /// A char value, to render as a character.
      CharKind,

      /// An unsigned int value, to render as an unsigned decimal integer.
      DecUIKind,

      /// An int value, to render as a signed decimal integer.
      DecIKind,

      /// A pointer to an unsigned long value, to render as an unsigned decimal
      /// integer.
      DecULKind,

      /// A pointer to a long value, to render as a signed decimal integer.
      DecLKind,

      /// A pointer to an unsigned long long value, to render as an unsigned
      /// decimal integer.
      DecULLKind,

      /// A pointer to a long long value, to render as a signed decimal integer.
      DecLLKind,

      /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
      /// integer.
      UHexKind
    };

    union Child
    {
      const Twine *twine;
      const char *cString;
      const std::string *stdString;
      const StringRef *stringRef;
      const SmallVectorImpl<char> *smallString;
      const formatv_object_base *formatvObject;
      char character;
      unsigned int decUI;
      int decI;
      const unsigned long *decUL;
      const long *decL;
      const unsigned long long *decULL;
      const long long *decLL;
      const uint64_t *uHex;
    };

    /// LHS - The prefix in the concatenation, which may be uninitialized for
    /// Null or Empty kinds.
    Child LHS;

    /// RHS - The suffix in the concatenation, which may be uninitialized for
    /// Null or Empty kinds.
    Child RHS;

    /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
    NodeKind LHSKind = EmptyKind;

    /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
    NodeKind RHSKind = EmptyKind;

    /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
    explicit Twine(NodeKind Kind) : LHSKind(Kind) {
      assert(isNullary() && "Invalid kind!");
    }

    /// Construct a binary twine.
    explicit Twine(const Twine &LHS, const Twine &RHS)
        : LHSKind(TwineKind), RHSKind(TwineKind) {
      this->LHS.twine = &LHS;
      this->RHS.twine = &RHS;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct a twine from explicit values.
    explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
        : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
      assert(isValid() && "Invalid twine!");
    }

    /// Check for the null twine.
    bool isNull() const {
      return getLHSKind() == NullKind;
    }

    /// Check for the empty twine.
    bool isEmpty() const {
      return getLHSKind() == EmptyKind;
    }

    /// Check if this is a nullary twine (null or empty).
    bool isNullary() const {
      return isNull() || isEmpty();
    }

    /// Check if this is a unary twine.
    bool isUnary() const {
      return getRHSKind() == EmptyKind && !isNullary();
    }

    /// Check if this is a binary twine.
    bool isBinary() const {
      return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
    }

    /// Check if this is a valid twine (satisfying the invariants on
    /// order and number of arguments).
    bool isValid() const {
      // Nullary twines always have Empty on the RHS.
      if (isNullary() && getRHSKind() != EmptyKind)
        return false;

      // Null should never appear on the RHS.
      if (getRHSKind() == NullKind)
        return false;

      // The RHS cannot be non-empty if the LHS is empty.
      if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
        return false;

      // A twine child should always be binary.
      if (getLHSKind() == TwineKind &&
          !LHS.twine->isBinary())
        return false;
      if (getRHSKind() == TwineKind &&
          !RHS.twine->isBinary())
        return false;

      return true;
    }

    /// Get the NodeKind of the left-hand side.
    NodeKind getLHSKind() const { return LHSKind; }

    /// Get the NodeKind of the right-hand side.
    NodeKind getRHSKind() const { return RHSKind; }

    /// Print one child from a twine.
    void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;

    /// Print the representation of one child from a twine.
    void printOneChildRepr(raw_ostream &OS, Child Ptr,
                           NodeKind Kind) const;

  public:
    /// @name Constructors
    /// @{

    /// Construct from an empty string.
    /*implicit*/ Twine() {
      assert(isValid() && "Invalid twine!");
    }

    Twine(const Twine &) = default;

    /// Construct from a C string.
    ///
    /// We take care here to optimize "" into the empty twine -- this will be
    /// optimized out for string constants. This allows Twine arguments have
    /// default "" values, without introducing unnecessary string constants.
    /*implicit*/ Twine(const char *Str) {
      if (Str[0] != '\0') {
        LHS.cString = Str;
        LHSKind = CStringKind;
      } else
        LHSKind = EmptyKind;

      assert(isValid() && "Invalid twine!");
    }

    /// Construct from an std::string.
    /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {
      LHS.stdString = &Str;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct from a StringRef.
    /*implicit*/ Twine(const StringRef &Str) : LHSKind(StringRefKind) {
      LHS.stringRef = &Str;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct from a SmallString.
    /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
        : LHSKind(SmallStringKind) {
      LHS.smallString = &Str;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct from a formatv_object_base.
    /*implicit*/ Twine(const formatv_object_base &Fmt)
        : LHSKind(FormatvObjectKind) {
      LHS.formatvObject = &Fmt;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct from a char.
    explicit Twine(char Val) : LHSKind(CharKind) {
      LHS.character = Val;
    }

    /// Construct from a signed char.
    explicit Twine(signed char Val) : LHSKind(CharKind) {
      LHS.character = static_cast<char>(Val);
    }

    /// Construct from an unsigned char.
    explicit Twine(unsigned char Val) : LHSKind(CharKind) {
      LHS.character = static_cast<char>(Val);
    }

    /// Construct a twine to print \p Val as an unsigned decimal integer.
    explicit Twine(unsigned Val) : LHSKind(DecUIKind) {
      LHS.decUI = Val;
    }

    /// Construct a twine to print \p Val as a signed decimal integer.
    explicit Twine(int Val) : LHSKind(DecIKind) {
      LHS.decI = Val;
    }

    /// Construct a twine to print \p Val as an unsigned decimal integer.
    explicit Twine(const unsigned long &Val) : LHSKind(DecULKind) {
      LHS.decUL = &Val;
    }

    /// Construct a twine to print \p Val as a signed decimal integer.
    explicit Twine(const long &Val) : LHSKind(DecLKind) {
      LHS.decL = &Val;
    }

    /// Construct a twine to print \p Val as an unsigned decimal integer.
    explicit Twine(const unsigned long long &Val) : LHSKind(DecULLKind) {
      LHS.decULL = &Val;
    }

    /// Construct a twine to print \p Val as a signed decimal integer.
    explicit Twine(const long long &Val) : LHSKind(DecLLKind) {
      LHS.decLL = &Val;
    }

    // FIXME: Unfortunately, to make sure this is as efficient as possible we
    // need extra binary constructors from particular types. We can't rely on
    // the compiler to be smart enough to fold operator+()/concat() down to the
    // right thing. Yet.

    /// Construct as the concatenation of a C string and a StringRef.
    /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
        : LHSKind(CStringKind), RHSKind(StringRefKind) {
      this->LHS.cString = LHS;
      this->RHS.stringRef = &RHS;
      assert(isValid() && "Invalid twine!");
    }

    /// Construct as the concatenation of a StringRef and a C string.
    /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
        : LHSKind(StringRefKind), RHSKind(CStringKind) {
      this->LHS.stringRef = &LHS;
      this->RHS.cString = RHS;
      assert(isValid() && "Invalid twine!");
    }

    /// Since the intended use of twines is as temporary objects, assignments
    /// when concatenating might cause undefined behavior or stack corruptions
    Twine &operator=(const Twine &) = delete;

    /// Create a 'null' string, which is an empty string that always
    /// concatenates to form another empty string.
    static Twine createNull() {
      return Twine(NullKind);
    }

    /// @}
    /// @name Numeric Conversions
    /// @{

    // Construct a twine to print \p Val as an unsigned hexadecimal integer.
    static Twine utohexstr(const uint64_t &Val) {
      Child LHS, RHS;
      LHS.uHex = &Val;
      RHS.twine = nullptr;
      return Twine(LHS, UHexKind, RHS, EmptyKind);
    }

    /// @}
    /// @name Predicate Operations
    /// @{

    /// Check if this twine is trivially empty; a false return value does not
    /// necessarily mean the twine is empty.
    bool isTriviallyEmpty() const {
      return isNullary();
    }

    /// Return true if this twine can be dynamically accessed as a single
    /// StringRef value with getSingleStringRef().
    bool isSingleStringRef() const {
      if (getRHSKind() != EmptyKind) return false;

      switch (getLHSKind()) {
      case EmptyKind:
      case CStringKind:
      case StdStringKind:
      case StringRefKind:
      case SmallStringKind:
        return true;
      default:
        return false;
      }
    }

    /// @}
    /// @name String Operations
    /// @{

    Twine concat(const Twine &Suffix) const;

    /// @}
    /// @name Output & Conversion.
    /// @{

    /// Return the twine contents as a std::string.
    std::string str() const;

    /// Append the concatenated string into the given SmallString or SmallVector.
    void toVector(SmallVectorImpl<char> &Out) const;

    /// This returns the twine as a single StringRef.  This method is only valid
    /// if isSingleStringRef() is true.
    StringRef getSingleStringRef() const {
      assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
      switch (getLHSKind()) {
      default: llvm_unreachable("Out of sync with isSingleStringRef");
      case EmptyKind:      return StringRef();
      case CStringKind:    return StringRef(LHS.cString);
      case StdStringKind:  return StringRef(*LHS.stdString);
      case StringRefKind:  return *LHS.stringRef;
      case SmallStringKind:
        return StringRef(LHS.smallString->data(), LHS.smallString->size());
      }
    }

    /// This returns the twine as a single StringRef if it can be
    /// represented as such. Otherwise the twine is written into the given
    /// SmallVector and a StringRef to the SmallVector's data is returned.
    StringRef toStringRef(SmallVectorImpl<char> &Out) const {
      if (isSingleStringRef())
        return getSingleStringRef();
      toVector(Out);
      return StringRef(Out.data(), Out.size());
    }

    /// This returns the twine as a single null terminated StringRef if it
    /// can be represented as such. Otherwise the twine is written into the
    /// given SmallVector and a StringRef to the SmallVector's data is returned.
    ///
    /// The returned StringRef's size does not include the null terminator.
    StringRef toNullTerminatedStringRef(SmallVectorImpl<char> &Out) const;

    /// Write the concatenated string represented by this twine to the
    /// stream \p OS.
    void print(raw_ostream &OS) const;

    /// Dump the concatenated string represented by this twine to stderr.
    void dump() const;

    /// Write the representation of this twine to the stream \p OS.
    void printRepr(raw_ostream &OS) const;

    /// Dump the representation of this twine to stderr.
    void dumpRepr() const;

    /// @}
  };

  /// @name Twine Inline Implementations
  /// @{

  inline Twine Twine::concat(const Twine &Suffix) const {
    // Concatenation with null is null.
    if (isNull() || Suffix.isNull())
      return Twine(NullKind);

    // Concatenation with empty yields the other side.
    if (isEmpty())
      return Suffix;
    if (Suffix.isEmpty())
      return *this;

    // Otherwise we need to create a new node, taking care to fold in unary
    // twines.
    Child NewLHS, NewRHS;
    NewLHS.twine = this;
    NewRHS.twine = &Suffix;
    NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
    if (isUnary()) {
      NewLHS = LHS;
      NewLHSKind = getLHSKind();
    }
    if (Suffix.isUnary()) {
      NewRHS = Suffix.LHS;
      NewRHSKind = Suffix.getLHSKind();
    }

    return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
  }

  inline Twine operator+(const Twine &LHS, const Twine &RHS) {
    return LHS.concat(RHS);
  }

  /// Additional overload to guarantee simplified codegen; this is equivalent to
  /// concat().

  inline Twine operator+(const char *LHS, const StringRef &RHS) {
    return Twine(LHS, RHS);
  }

  /// Additional overload to guarantee simplified codegen; this is equivalent to
  /// concat().

  inline Twine operator+(const StringRef &LHS, const char *RHS) {
    return Twine(LHS, RHS);
  }

  inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
    RHS.print(OS);
    return OS;
  }

  /// @}

} // end namespace llvm

#endif // LLVM_ADT_TWINE_H