//===- 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