1 //===-- Twine.h - Fast Temporary String Concatenation -----------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 #ifndef LLVM_ADT_TWINE_H
11 #define LLVM_ADT_TWINE_H
13 #include "llvm/ADT/SmallVector.h"
14 #include "llvm/ADT/StringRef.h"
15 #include "llvm/Support/ErrorHandling.h"
22 class formatv_object_base;
25 /// Twine - A lightweight data structure for efficiently representing the
26 /// concatenation of temporary values as strings.
28 /// A Twine is a kind of rope, it represents a concatenated string using a
29 /// binary-tree, where the string is the preorder of the nodes. Since the
30 /// Twine can be efficiently rendered into a buffer when its result is used,
31 /// it avoids the cost of generating temporary values for intermediate string
32 /// results -- particularly in cases when the Twine result is never
33 /// required. By explicitly tracking the type of leaf nodes, we can also avoid
34 /// the creation of temporary strings for conversions operations (such as
35 /// appending an integer to a string).
37 /// A Twine is not intended for use directly and should not be stored, its
38 /// implementation relies on the ability to store pointers to temporary stack
39 /// objects which may be deallocated at the end of a statement. Twines should
40 /// only be used accepted as const references in arguments, when an API wishes
41 /// to accept possibly-concatenated strings.
43 /// Twines support a special 'null' value, which always concatenates to form
44 /// itself, and renders as an empty string. This can be returned from APIs to
45 /// effectively nullify any concatenations performed on the result.
49 /// Given the nature of a Twine, it is not possible for the Twine's
50 /// concatenation method to construct interior nodes; the result must be
51 /// represented inside the returned value. For this reason a Twine object
52 /// actually holds two values, the left- and right-hand sides of a
53 /// concatenation. We also have nullary Twine objects, which are effectively
54 /// sentinel values that represent empty strings.
56 /// Thus, a Twine can effectively have zero, one, or two children. The \see
57 /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for
58 /// testing the number of children.
60 /// We maintain a number of invariants on Twine objects (FIXME: Why):
61 /// - Nullary twines are always represented with their Kind on the left-hand
62 /// side, and the Empty kind on the right-hand side.
63 /// - Unary twines are always represented with the value on the left-hand
64 /// side, and the Empty kind on the right-hand side.
65 /// - If a Twine has another Twine as a child, that child should always be
66 /// binary (otherwise it could have been folded into the parent).
68 /// These invariants are check by \see isValid().
70 /// \b Efficiency Considerations
72 /// The Twine is designed to yield efficient and small code for common
73 /// situations. For this reason, the concat() method is inlined so that
74 /// concatenations of leaf nodes can be optimized into stores directly into a
75 /// single stack allocated object.
77 /// In practice, not all compilers can be trusted to optimize concat() fully,
78 /// so we provide two additional methods (and accompanying operator+
79 /// overloads) to guarantee that particularly important cases (cstring plus
80 /// StringRef) codegen as desired.
82 /// NodeKind - Represent the type of an argument.
83 enum NodeKind : unsigned char {
84 /// An empty string; the result of concatenating anything with it is also
91 /// A pointer to a Twine instance.
94 /// A pointer to a C string instance.
97 /// A pointer to an std::string instance.
100 /// A pointer to a StringRef instance.
103 /// A pointer to a SmallString instance.
106 /// A pointer to a formatv_object_base instance.
109 /// A char value, to render as a character.
112 /// An unsigned int value, to render as an unsigned decimal integer.
115 /// An int value, to render as a signed decimal integer.
118 /// A pointer to an unsigned long value, to render as an unsigned decimal
122 /// A pointer to a long value, to render as a signed decimal integer.
125 /// A pointer to an unsigned long long value, to render as an unsigned
129 /// A pointer to a long long value, to render as a signed decimal integer.
132 /// A pointer to a uint64_t value, to render as an unsigned hexadecimal
141 const std::string *stdString;
142 const StringRef *stringRef;
143 const SmallVectorImpl<char> *smallString;
144 const formatv_object_base *formatvObject;
148 const unsigned long *decUL;
150 const unsigned long long *decULL;
151 const long long *decLL;
152 const uint64_t *uHex;
155 /// LHS - The prefix in the concatenation, which may be uninitialized for
156 /// Null or Empty kinds.
158 /// RHS - The suffix in the concatenation, which may be uninitialized for
159 /// Null or Empty kinds.
161 /// LHSKind - The NodeKind of the left hand side, \see getLHSKind().
163 /// RHSKind - The NodeKind of the right hand side, \see getRHSKind().
166 /// Construct a nullary twine; the kind must be NullKind or EmptyKind.
167 explicit Twine(NodeKind Kind)
168 : LHSKind(Kind), RHSKind(EmptyKind) {
169 assert(isNullary() && "Invalid kind!");
172 /// Construct a binary twine.
173 explicit Twine(const Twine &LHS, const Twine &RHS)
174 : LHSKind(TwineKind), RHSKind(TwineKind) {
175 this->LHS.twine = &LHS;
176 this->RHS.twine = &RHS;
177 assert(isValid() && "Invalid twine!");
180 /// Construct a twine from explicit values.
181 explicit Twine(Child LHS, NodeKind LHSKind, Child RHS, NodeKind RHSKind)
182 : LHS(LHS), RHS(RHS), LHSKind(LHSKind), RHSKind(RHSKind) {
183 assert(isValid() && "Invalid twine!");
186 /// Check for the null twine.
187 bool isNull() const {
188 return getLHSKind() == NullKind;
191 /// Check for the empty twine.
192 bool isEmpty() const {
193 return getLHSKind() == EmptyKind;
196 /// Check if this is a nullary twine (null or empty).
197 bool isNullary() const {
198 return isNull() || isEmpty();
201 /// Check if this is a unary twine.
202 bool isUnary() const {
203 return getRHSKind() == EmptyKind && !isNullary();
206 /// Check if this is a binary twine.
207 bool isBinary() const {
208 return getLHSKind() != NullKind && getRHSKind() != EmptyKind;
211 /// Check if this is a valid twine (satisfying the invariants on
212 /// order and number of arguments).
213 bool isValid() const {
214 // Nullary twines always have Empty on the RHS.
215 if (isNullary() && getRHSKind() != EmptyKind)
218 // Null should never appear on the RHS.
219 if (getRHSKind() == NullKind)
222 // The RHS cannot be non-empty if the LHS is empty.
223 if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind)
226 // A twine child should always be binary.
227 if (getLHSKind() == TwineKind &&
228 !LHS.twine->isBinary())
230 if (getRHSKind() == TwineKind &&
231 !RHS.twine->isBinary())
237 /// Get the NodeKind of the left-hand side.
238 NodeKind getLHSKind() const { return LHSKind; }
240 /// Get the NodeKind of the right-hand side.
241 NodeKind getRHSKind() const { return RHSKind; }
243 /// Print one child from a twine.
244 void printOneChild(raw_ostream &OS, Child Ptr, NodeKind Kind) const;
246 /// Print the representation of one child from a twine.
247 void printOneChildRepr(raw_ostream &OS, Child Ptr,
248 NodeKind Kind) const;
251 /// @name Constructors
254 /// Construct from an empty string.
255 /*implicit*/ Twine() : LHSKind(EmptyKind), RHSKind(EmptyKind) {
256 assert(isValid() && "Invalid twine!");
259 Twine(const Twine &) = default;
261 /// Construct from a C string.
263 /// We take care here to optimize "" into the empty twine -- this will be
264 /// optimized out for string constants. This allows Twine arguments have
265 /// default "" values, without introducing unnecessary string constants.
266 /*implicit*/ Twine(const char *Str)
267 : RHSKind(EmptyKind) {
268 if (Str[0] != '\0') {
270 LHSKind = CStringKind;
274 assert(isValid() && "Invalid twine!");
277 /// Construct from an std::string.
278 /*implicit*/ Twine(const std::string &Str)
279 : LHSKind(StdStringKind), RHSKind(EmptyKind) {
280 LHS.stdString = &Str;
281 assert(isValid() && "Invalid twine!");
284 /// Construct from a StringRef.
285 /*implicit*/ Twine(const StringRef &Str)
286 : LHSKind(StringRefKind), RHSKind(EmptyKind) {
287 LHS.stringRef = &Str;
288 assert(isValid() && "Invalid twine!");
291 /// Construct from a SmallString.
292 /*implicit*/ Twine(const SmallVectorImpl<char> &Str)
293 : LHSKind(SmallStringKind), RHSKind(EmptyKind) {
294 LHS.smallString = &Str;
295 assert(isValid() && "Invalid twine!");
298 /// Construct from a formatv_object_base.
299 /*implicit*/ Twine(const formatv_object_base &Fmt)
300 : LHSKind(FormatvObjectKind), RHSKind(EmptyKind) {
301 LHS.formatvObject = &Fmt;
302 assert(isValid() && "Invalid twine!");
305 /// Construct from a char.
306 explicit Twine(char Val)
307 : LHSKind(CharKind), RHSKind(EmptyKind) {
311 /// Construct from a signed char.
312 explicit Twine(signed char Val)
313 : LHSKind(CharKind), RHSKind(EmptyKind) {
314 LHS.character = static_cast<char>(Val);
317 /// Construct from an unsigned char.
318 explicit Twine(unsigned char Val)
319 : LHSKind(CharKind), RHSKind(EmptyKind) {
320 LHS.character = static_cast<char>(Val);
323 /// Construct a twine to print \p Val as an unsigned decimal integer.
324 explicit Twine(unsigned Val)
325 : LHSKind(DecUIKind), RHSKind(EmptyKind) {
329 /// Construct a twine to print \p Val as a signed decimal integer.
330 explicit Twine(int Val)
331 : LHSKind(DecIKind), RHSKind(EmptyKind) {
335 /// Construct a twine to print \p Val as an unsigned decimal integer.
336 explicit Twine(const unsigned long &Val)
337 : LHSKind(DecULKind), RHSKind(EmptyKind) {
341 /// Construct a twine to print \p Val as a signed decimal integer.
342 explicit Twine(const long &Val)
343 : LHSKind(DecLKind), RHSKind(EmptyKind) {
347 /// Construct a twine to print \p Val as an unsigned decimal integer.
348 explicit Twine(const unsigned long long &Val)
349 : LHSKind(DecULLKind), RHSKind(EmptyKind) {
353 /// Construct a twine to print \p Val as a signed decimal integer.
354 explicit Twine(const long long &Val)
355 : LHSKind(DecLLKind), RHSKind(EmptyKind) {
359 // FIXME: Unfortunately, to make sure this is as efficient as possible we
360 // need extra binary constructors from particular types. We can't rely on
361 // the compiler to be smart enough to fold operator+()/concat() down to the
364 /// Construct as the concatenation of a C string and a StringRef.
365 /*implicit*/ Twine(const char *LHS, const StringRef &RHS)
366 : LHSKind(CStringKind), RHSKind(StringRefKind) {
367 this->LHS.cString = LHS;
368 this->RHS.stringRef = &RHS;
369 assert(isValid() && "Invalid twine!");
372 /// Construct as the concatenation of a StringRef and a C string.
373 /*implicit*/ Twine(const StringRef &LHS, const char *RHS)
374 : LHSKind(StringRefKind), RHSKind(CStringKind) {
375 this->LHS.stringRef = &LHS;
376 this->RHS.cString = RHS;
377 assert(isValid() && "Invalid twine!");
380 /// Since the intended use of twines is as temporary objects, assignments
381 /// when concatenating might cause undefined behavior or stack corruptions
382 Twine &operator=(const Twine &) = delete;
384 /// Create a 'null' string, which is an empty string that always
385 /// concatenates to form another empty string.
386 static Twine createNull() {
387 return Twine(NullKind);
391 /// @name Numeric Conversions
394 // Construct a twine to print \p Val as an unsigned hexadecimal integer.
395 static Twine utohexstr(const uint64_t &Val) {
399 return Twine(LHS, UHexKind, RHS, EmptyKind);
403 /// @name Predicate Operations
406 /// Check if this twine is trivially empty; a false return value does not
407 /// necessarily mean the twine is empty.
408 bool isTriviallyEmpty() const {
412 /// Return true if this twine can be dynamically accessed as a single
413 /// StringRef value with getSingleStringRef().
414 bool isSingleStringRef() const {
415 if (getRHSKind() != EmptyKind) return false;
417 switch (getLHSKind()) {
422 case SmallStringKind:
430 /// @name String Operations
433 Twine concat(const Twine &Suffix) const;
436 /// @name Output & Conversion.
439 /// Return the twine contents as a std::string.
440 std::string str() const;
442 /// Append the concatenated string into the given SmallString or SmallVector.
443 void toVector(SmallVectorImpl<char> &Out) const;
445 /// This returns the twine as a single StringRef. This method is only valid
446 /// if isSingleStringRef() is true.
447 StringRef getSingleStringRef() const {
448 assert(isSingleStringRef() &&"This cannot be had as a single stringref!");
449 switch (getLHSKind()) {
450 default: llvm_unreachable("Out of sync with isSingleStringRef");
451 case EmptyKind: return StringRef();
452 case CStringKind: return StringRef(LHS.cString);
453 case StdStringKind: return StringRef(*LHS.stdString);
454 case StringRefKind: return *LHS.stringRef;
455 case SmallStringKind:
456 return StringRef(LHS.smallString->data(), LHS.smallString->size());
460 /// This returns the twine as a single StringRef if it can be
461 /// represented as such. Otherwise the twine is written into the given
462 /// SmallVector and a StringRef to the SmallVector's data is returned.
463 StringRef toStringRef(SmallVectorImpl<char> &Out) const {
464 if (isSingleStringRef())
465 return getSingleStringRef();
467 return StringRef(Out.data(), Out.size());
470 /// This returns the twine as a single null terminated StringRef if it
471 /// can be represented as such. Otherwise the twine is written into the
472 /// given SmallVector and a StringRef to the SmallVector's data is returned.
474 /// The returned StringRef's size does not include the null terminator.
475 StringRef toNullTerminatedStringRef(SmallVectorImpl<char> &Out) const;
477 /// Write the concatenated string represented by this twine to the
479 void print(raw_ostream &OS) const;
481 /// Dump the concatenated string represented by this twine to stderr.
484 /// Write the representation of this twine to the stream \p OS.
485 void printRepr(raw_ostream &OS) const;
487 /// Dump the representation of this twine to stderr.
488 void dumpRepr() const;
493 /// @name Twine Inline Implementations
496 inline Twine Twine::concat(const Twine &Suffix) const {
497 // Concatenation with null is null.
498 if (isNull() || Suffix.isNull())
499 return Twine(NullKind);
501 // Concatenation with empty yields the other side.
504 if (Suffix.isEmpty())
507 // Otherwise we need to create a new node, taking care to fold in unary
509 Child NewLHS, NewRHS;
511 NewRHS.twine = &Suffix;
512 NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind;
515 NewLHSKind = getLHSKind();
517 if (Suffix.isUnary()) {
519 NewRHSKind = Suffix.getLHSKind();
522 return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind);
525 inline Twine operator+(const Twine &LHS, const Twine &RHS) {
526 return LHS.concat(RHS);
529 /// Additional overload to guarantee simplified codegen; this is equivalent to
532 inline Twine operator+(const char *LHS, const StringRef &RHS) {
533 return Twine(LHS, RHS);
536 /// Additional overload to guarantee simplified codegen; this is equivalent to
539 inline Twine operator+(const StringRef &LHS, const char *RHS) {
540 return Twine(LHS, RHS);
543 inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) {
550 } // end namespace llvm
552 #endif // LLVM_ADT_TWINE_H