third_party/llvm-subzero/include/llvm/ADT/Twine.h - SwiftShader - Git at Google

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

     /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
     explicit Twine(NodeKind Kind)
       : LHSKind(Kind), RHSKind(EmptyKind) {
       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() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
       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)
       : RHSKind(EmptyKind) {
       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), RHSKind(EmptyKind) {
       LHS.stdString = &Str;
       assert(isValid() && "Invalid twine!");
     }

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

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

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

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

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

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

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

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

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

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

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

     /// Construct a twine to print \p Val as a signed decimal integer.
     explicit Twine(const long long &Val)
       : LHSKind(DecLLKind), RHSKind(EmptyKind) {
       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
	//===-- 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;
	/// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
	NodeKind RHSKind;

	/// Construct a nullary twine; the kind must be NullKind or EmptyKind.
	explicit Twine(NodeKind Kind)
	: LHSKind(Kind), RHSKind(EmptyKind) {
	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() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
	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)
	: RHSKind(EmptyKind) {
	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), RHSKind(EmptyKind) {
	LHS.stdString = &Str;
	assert(isValid() && "Invalid twine!");
	}

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

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

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

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

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

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

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

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

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

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

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

	/// Construct a twine to print \p Val as a signed decimal integer.
	explicit Twine(const long long &Val)
	: LHSKind(DecLLKind), RHSKind(EmptyKind) {
	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