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//===- Twine.h - Fast Temporary String Concatenation ------------*- C++ -*-===//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

#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>

#include <string_view>

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 and Length representation. Used for std::string_view,

      /// StringRef, and SmallString.  Can't use a StringRef here

      /// because they are not trivally constructible.

      PtrAndLengthKind,

      /// 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;

      struct {

        const char *ptr;

        size_t length;

      } ptrAndLength;

      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!");

    }

    /// Delete the implicit conversion from nullptr as Twine(const char *)

    /// cannot take nullptr.

    /*implicit*/ Twine(std::nullptr_t) = delete;

    /// Construct from an std::string.

    /*implicit*/ Twine(const std::string &Str) : LHSKind(StdStringKind) {

      LHS.stdString = &Str;

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

    }

    /// Construct from an std::string_view by converting it to a pointer and

    /// length.  This handles string_views on a pure API basis, and avoids

    /// storing one (or a pointer to one) inside a Twine, which avoids problems

    /// when mixing code compiled under various C++ standards.

    /*implicit*/ Twine(const std::string_view &Str)

        : LHSKind(PtrAndLengthKind) {

      LHS.ptrAndLength.ptr = Str.data();

      LHS.ptrAndLength.length = Str.length();

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

    }

    /// Construct from a StringRef.

    /*implicit*/ Twine(const StringRef &Str) : LHSKind(PtrAndLengthKind) {

      LHS.ptrAndLength.ptr = Str.data();

      LHS.ptrAndLength.length = Str.size();

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

    }

    /// Construct from a SmallString.

    /*implicit*/ Twine(const SmallVectorImpl<char> &Str)

        : LHSKind(PtrAndLengthKind) {

      LHS.ptrAndLength.ptr = Str.data();

      LHS.ptrAndLength.length = Str.size();

      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(PtrAndLengthKind) {

      this->LHS.cString = LHS;

      this->RHS.ptrAndLength.ptr = RHS.data();

      this->RHS.ptrAndLength.length = RHS.size();

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

    }

    /// Construct as the concatenation of a StringRef and a C string.

    /*implicit*/ Twine(const StringRef &LHS, const char *RHS)

        : LHSKind(PtrAndLengthKind), RHSKind(CStringKind) {

      this->LHS.ptrAndLength.ptr = LHS.data();

      this->LHS.ptrAndLength.length = LHS.size();

      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 PtrAndLengthKind:

        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 PtrAndLengthKind:

        return StringRef(LHS.ptrAndLength.ptr, LHS.ptrAndLength.length);

      }

    }

    /// 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