llvm-6502/include/llvm/ADT/Twine.h
Benjamin Kramer b357e06f67 Introduce Twine::toStringRef, a variant of toVector which avoids the copy if the
twine can be represented as a single StringRef. Use the new methode to simplify
some twine users.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@93317 91177308-0d34-0410-b5e6-96231b3b80d8
2010-01-13 12:45:23 +00:00

457 lines
15 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/System/DataTypes.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 \n
///
/// 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 \n
///
/// 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 pointer to an unsigned int value, to render as an unsigned decimal
/// integer.
DecUIKind,
/// A pointer to 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
};
private:
/// LHS - The prefix in the concatenation, which may be uninitialized for
/// Null or Empty kinds.
const void *LHS;
/// RHS - The suffix in the concatenation, which may be uninitialized for
/// Null or Empty kinds.
const void *RHS;
/// 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)
: LHS(&_LHS), RHS(&_RHS), LHSKind(TwineKind), RHSKind(TwineKind) {
assert(isValid() && "Invalid twine!");
}
/// Construct a twine from explicit values.
explicit Twine(const void *_LHS, NodeKind _LHSKind,
const void *_RHS, NodeKind _RHSKind)
: LHS(_LHS), RHS(_RHS), LHSKind(_LHSKind), RHSKind(_RHSKind) {
assert(isValid() && "Invalid twine!");
}
/// 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 &&
!static_cast<const Twine*>(LHS)->isBinary())
return false;
if (getRHSKind() == TwineKind &&
!static_cast<const Twine*>(RHS)->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 left-hand side.
NodeKind getRHSKind() const { return (NodeKind) RHSKind; }
/// printOneChild - Print one child from a twine.
void printOneChild(raw_ostream &OS, const void *Ptr, NodeKind Kind) const;
/// printOneChildRepr - Print the representation of one child from a twine.
void printOneChildRepr(raw_ostream &OS, const void *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 = Str;
LHSKind = CStringKind;
} else
LHSKind = EmptyKind;
assert(isValid() && "Invalid twine!");
}
/// Construct from an std::string.
/*implicit*/ Twine(const std::string &Str)
: LHS(&Str), LHSKind(StdStringKind), RHSKind(EmptyKind) {
assert(isValid() && "Invalid twine!");
}
/// Construct from a StringRef.
/*implicit*/ Twine(const StringRef &Str)
: LHS(&Str), LHSKind(StringRefKind), RHSKind(EmptyKind) {
assert(isValid() && "Invalid twine!");
}
/// Construct a twine to print \arg Val as an unsigned decimal integer.
explicit Twine(const unsigned int &Val)
: LHS(&Val), LHSKind(DecUIKind), RHSKind(EmptyKind) {
}
/// Construct a twine to print \arg Val as a signed decimal integer.
explicit Twine(const int &Val)
: LHS(&Val), LHSKind(DecIKind), RHSKind(EmptyKind) {
}
/// Construct a twine to print \arg Val as an unsigned decimal integer.
explicit Twine(const unsigned long &Val)
: LHS(&Val), LHSKind(DecULKind), RHSKind(EmptyKind) {
}
/// Construct a twine to print \arg Val as a signed decimal integer.
explicit Twine(const long &Val)
: LHS(&Val), LHSKind(DecLKind), RHSKind(EmptyKind) {
}
/// Construct a twine to print \arg Val as an unsigned decimal integer.
explicit Twine(const unsigned long long &Val)
: LHS(&Val), LHSKind(DecULLKind), RHSKind(EmptyKind) {
}
/// Construct a twine to print \arg Val as a signed decimal integer.
explicit Twine(const long long &Val)
: LHS(&Val), LHSKind(DecLLKind), RHSKind(EmptyKind) {
}
// 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)
: LHS(_LHS), RHS(&_RHS), LHSKind(CStringKind), RHSKind(StringRefKind) {
assert(isValid() && "Invalid twine!");
}
/// Construct as the concatenation of a StringRef and a C string.
/*implicit*/ Twine(const StringRef &_LHS, const char *_RHS)
: LHS(&_LHS), RHS(_RHS), LHSKind(StringRefKind), RHSKind(CStringKind) {
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 \arg Val as an unsigned hexadecimal integer.
static Twine utohexstr(const uint64_t &Val) {
return Twine(&Val, UHexKind, 0, 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: assert(0 && "Out of sync with isSingleStringRef");
case EmptyKind: return StringRef();
case CStringKind: return StringRef((const char*)LHS);
case StdStringKind: return StringRef(*(const std::string*)LHS);
case StringRefKind: return *(const StringRef*)LHS;
}
}
/// 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;
/// print - Write the concatenated string represented by this twine to the
/// stream \arg OS.
void print(raw_ostream &OS) const;
/// dump - Dump the concatenated string represented by this twine to stderr.
void dump() const;
/// print - Write the representation of this twine to the stream \arg OS.
void printRepr(raw_ostream &OS) const;
/// dumpRepr - 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.
const void *NewLHS = this, *NewRHS = &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