llvm-6502/include/llvm/ADT/Twine.h
Reid Kleckner fa68048322 [ADT] Delete the Twine assignment operator
This makes it slightly harder to misuse Twines.  It is still possible to
refer to destroyed temporaries with the regular constructors, though.

Patch by Marco Alesiani!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209832 91177308-0d34-0410-b5e6-96231b3b80d8
2014-05-29 17:12:05 +00:00

529 lines
17 KiB
C++

//===-- 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/StringRef.h"
#include "llvm/Support/DataTypes.h"
#include "llvm/Support/ErrorHandling.h"
#include <cassert>
#include <string>
namespace llvm {
template <typename T>
class SmallVectorImpl;
class StringRef;
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 {
/// 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 char value reinterpreted as a pointer, to render as a character.
CharKind,
/// An unsigned int value reinterpreted as a pointer, to render as an
/// unsigned decimal integer.
DecUIKind,
/// An int value reinterpreted as a pointer, 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;
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;
};
private:
/// 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;
// enums stored as unsigned chars to save on space while some compilers
// don't support specifying the backing type for an enum
/// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
unsigned char LHSKind;
/// RHSKind - The NodeKind of the left hand side, \see getLHSKind().
unsigned char RHSKind;
private:
/// 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) {
LHS.twine = &_LHS;
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!");
}
/// Since the intended use of twines is as temporary objects, assignments
/// when concatenating might cause undefined behavior or stack corruptions
Twine &operator=(const Twine &Other) LLVM_DELETED_FUNCTION;
/// isNull - Check for the null twine.
bool isNull() const {
return getLHSKind() == NullKind;
}
/// isEmpty - Check for the empty twine.
bool isEmpty() const {
return getLHSKind() == EmptyKind;
}
/// isNullary - Check if this is a nullary twine (null or empty).
bool isNullary() const {
return isNull() || isEmpty();
}
/// isUnary - Check if this is a unary twine.
bool isUnary() const {
return getRHSKind() == EmptyKind && !isNullary();
}
/// isBinary - Check if this is a binary twine.
bool isBinary() const {
return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
}
/// isValid - 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;
}
/// getLHSKind - Get the NodeKind of the left-hand side.
NodeKind getLHSKind() const { return (NodeKind) LHSKind; }
/// getRHSKind - Get the NodeKind of the right-hand side.
NodeKind getRHSKind() const { return (NodeKind) RHSKind; }
/// printOneChild - Print one child from a twine.
void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
/// printOneChildRepr - 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!");
}
/// 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 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) {
LHS.cString = _LHS;
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) {
LHS.stringRef = &_LHS;
RHS.cString = _RHS;
assert(isValid() && "Invalid twine!");
}
/// 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
/// @{
/// isTriviallyEmpty - Check if this twine is trivially empty; a false
/// return value does not necessarily mean the twine is empty.
bool isTriviallyEmpty() const {
return isNullary();
}
/// isSingleStringRef - 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:
return true;
default:
return false;
}
}
/// @}
/// @name String Operations
/// @{
Twine concat(const Twine &Suffix) const;
/// @}
/// @name Output & Conversion.
/// @{
/// str - Return the twine contents as a std::string.
std::string str() const;
/// toVector - Write the concatenated string into the given SmallString or
/// SmallVector.
void toVector(SmallVectorImpl<char> &Out) const;
/// getSingleStringRef - 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;
}
}
/// toStringRef - 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;
/// toNullTerminatedStringRef - 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;
}
/// @}
}
#endif