Twine.h revision ea03e10facd07f0b239dcc3a5e31346686acae3c
1//===-- Twine.h - Fast Temporary String Concatenation -----------*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9 10#ifndef LLVM_ADT_TWINE_H 11#define LLVM_ADT_TWINE_H 12 13#include "llvm/ADT/StringRef.h" 14#include "llvm/System/DataTypes.h" 15#include <cassert> 16#include <string> 17 18namespace llvm { 19 template <typename T> 20 class SmallVectorImpl; 21 class StringRef; 22 class raw_ostream; 23 24 /// Twine - A lightweight data structure for efficiently representing the 25 /// concatenation of temporary values as strings. 26 /// 27 /// A Twine is a kind of rope, it represents a concatenated string using a 28 /// binary-tree, where the string is the preorder of the nodes. Since the 29 /// Twine can be efficiently rendered into a buffer when its result is used, 30 /// it avoids the cost of generating temporary values for intermediate string 31 /// results -- particularly in cases when the Twine result is never 32 /// required. By explicitly tracking the type of leaf nodes, we can also avoid 33 /// the creation of temporary strings for conversions operations (such as 34 /// appending an integer to a string). 35 /// 36 /// A Twine is not intended for use directly and should not be stored, its 37 /// implementation relies on the ability to store pointers to temporary stack 38 /// objects which may be deallocated at the end of a statement. Twines should 39 /// only be used accepted as const references in arguments, when an API wishes 40 /// to accept possibly-concatenated strings. 41 /// 42 /// Twines support a special 'null' value, which always concatenates to form 43 /// itself, and renders as an empty string. This can be returned from APIs to 44 /// effectively nullify any concatenations performed on the result. 45 /// 46 /// \b Implementation \n 47 /// 48 /// Given the nature of a Twine, it is not possible for the Twine's 49 /// concatenation method to construct interior nodes; the result must be 50 /// represented inside the returned value. For this reason a Twine object 51 /// actually holds two values, the left- and right-hand sides of a 52 /// concatenation. We also have nullary Twine objects, which are effectively 53 /// sentinel values that represent empty strings. 54 /// 55 /// Thus, a Twine can effectively have zero, one, or two children. The \see 56 /// isNullary(), \see isUnary(), and \see isBinary() predicates exist for 57 /// testing the number of children. 58 /// 59 /// We maintain a number of invariants on Twine objects (FIXME: Why): 60 /// - Nullary twines are always represented with their Kind on the left-hand 61 /// side, and the Empty kind on the right-hand side. 62 /// - Unary twines are always represented with the value on the left-hand 63 /// side, and the Empty kind on the right-hand side. 64 /// - If a Twine has another Twine as a child, that child should always be 65 /// binary (otherwise it could have been folded into the parent). 66 /// 67 /// These invariants are check by \see isValid(). 68 /// 69 /// \b Efficiency Considerations \n 70 /// 71 /// The Twine is designed to yield efficient and small code for common 72 /// situations. For this reason, the concat() method is inlined so that 73 /// concatenations of leaf nodes can be optimized into stores directly into a 74 /// single stack allocated object. 75 /// 76 /// In practice, not all compilers can be trusted to optimize concat() fully, 77 /// so we provide two additional methods (and accompanying operator+ 78 /// overloads) to guarantee that particularly important cases (cstring plus 79 /// StringRef) codegen as desired. 80 class Twine { 81 /// NodeKind - Represent the type of an argument. 82 enum NodeKind { 83 /// An empty string; the result of concatenating anything with it is also 84 /// empty. 85 NullKind, 86 87 /// The empty string. 88 EmptyKind, 89 90 /// A pointer to a Twine instance. 91 TwineKind, 92 93 /// A pointer to a C string instance. 94 CStringKind, 95 96 /// A pointer to an std::string instance. 97 StdStringKind, 98 99 /// A pointer to a StringRef instance. 100 StringRefKind, 101 102 /// An unsigned int value reinterpreted as a pointer, to render as an 103 /// unsigned decimal integer. 104 DecUIKind, 105 106 /// An int value reinterpreted as a pointer, to render as a signed 107 /// decimal integer. 108 DecIKind, 109 110 /// A pointer to an unsigned long value, to render as an unsigned decimal 111 /// integer. 112 DecULKind, 113 114 /// A pointer to a long value, to render as a signed decimal integer. 115 DecLKind, 116 117 /// A pointer to an unsigned long long value, to render as an unsigned 118 /// decimal integer. 119 DecULLKind, 120 121 /// A pointer to a long long value, to render as a signed decimal integer. 122 DecLLKind, 123 124 /// A pointer to a uint64_t value, to render as an unsigned hexadecimal 125 /// integer. 126 UHexKind 127 }; 128 129 private: 130 /// LHS - The prefix in the concatenation, which may be uninitialized for 131 /// Null or Empty kinds. 132 const void *LHS; 133 /// RHS - The suffix in the concatenation, which may be uninitialized for 134 /// Null or Empty kinds. 135 const void *RHS; 136 /// LHSKind - The NodeKind of the left hand side, \see getLHSKind(). 137 unsigned char LHSKind; 138 /// RHSKind - The NodeKind of the left hand side, \see getLHSKind(). 139 unsigned char RHSKind; 140 141 private: 142 /// Construct a nullary twine; the kind must be NullKind or EmptyKind. 143 explicit Twine(NodeKind Kind) 144 : LHSKind(Kind), RHSKind(EmptyKind) { 145 assert(isNullary() && "Invalid kind!"); 146 } 147 148 /// Construct a binary twine. 149 explicit Twine(const Twine &_LHS, const Twine &_RHS) 150 : LHS(&_LHS), RHS(&_RHS), LHSKind(TwineKind), RHSKind(TwineKind) { 151 assert(isValid() && "Invalid twine!"); 152 } 153 154 /// Construct a twine from explicit values. 155 explicit Twine(const void *_LHS, NodeKind _LHSKind, 156 const void *_RHS, NodeKind _RHSKind) 157 : LHS(_LHS), RHS(_RHS), LHSKind(_LHSKind), RHSKind(_RHSKind) { 158 assert(isValid() && "Invalid twine!"); 159 } 160 161 /// isNull - Check for the null twine. 162 bool isNull() const { 163 return getLHSKind() == NullKind; 164 } 165 166 /// isEmpty - Check for the empty twine. 167 bool isEmpty() const { 168 return getLHSKind() == EmptyKind; 169 } 170 171 /// isNullary - Check if this is a nullary twine (null or empty). 172 bool isNullary() const { 173 return isNull() || isEmpty(); 174 } 175 176 /// isUnary - Check if this is a unary twine. 177 bool isUnary() const { 178 return getRHSKind() == EmptyKind && !isNullary(); 179 } 180 181 /// isBinary - Check if this is a binary twine. 182 bool isBinary() const { 183 return getLHSKind() != NullKind && getRHSKind() != EmptyKind; 184 } 185 186 /// isValid - Check if this is a valid twine (satisfying the invariants on 187 /// order and number of arguments). 188 bool isValid() const { 189 // Nullary twines always have Empty on the RHS. 190 if (isNullary() && getRHSKind() != EmptyKind) 191 return false; 192 193 // Null should never appear on the RHS. 194 if (getRHSKind() == NullKind) 195 return false; 196 197 // The RHS cannot be non-empty if the LHS is empty. 198 if (getRHSKind() != EmptyKind && getLHSKind() == EmptyKind) 199 return false; 200 201 // A twine child should always be binary. 202 if (getLHSKind() == TwineKind && 203 !static_cast<const Twine*>(LHS)->isBinary()) 204 return false; 205 if (getRHSKind() == TwineKind && 206 !static_cast<const Twine*>(RHS)->isBinary()) 207 return false; 208 209 return true; 210 } 211 212 /// getLHSKind - Get the NodeKind of the left-hand side. 213 NodeKind getLHSKind() const { return (NodeKind) LHSKind; } 214 215 /// getRHSKind - Get the NodeKind of the left-hand side. 216 NodeKind getRHSKind() const { return (NodeKind) RHSKind; } 217 218 /// printOneChild - Print one child from a twine. 219 void printOneChild(raw_ostream &OS, const void *Ptr, NodeKind Kind) const; 220 221 /// printOneChildRepr - Print the representation of one child from a twine. 222 void printOneChildRepr(raw_ostream &OS, const void *Ptr, 223 NodeKind Kind) const; 224 225 public: 226 /// @name Constructors 227 /// @{ 228 229 /// Construct from an empty string. 230 /*implicit*/ Twine() : LHSKind(EmptyKind), RHSKind(EmptyKind) { 231 assert(isValid() && "Invalid twine!"); 232 } 233 234 /// Construct from a C string. 235 /// 236 /// We take care here to optimize "" into the empty twine -- this will be 237 /// optimized out for string constants. This allows Twine arguments have 238 /// default "" values, without introducing unnecessary string constants. 239 /*implicit*/ Twine(const char *Str) 240 : RHSKind(EmptyKind) { 241 if (Str[0] != '\0') { 242 LHS = Str; 243 LHSKind = CStringKind; 244 } else 245 LHSKind = EmptyKind; 246 247 assert(isValid() && "Invalid twine!"); 248 } 249 250 /// Construct from an std::string. 251 /*implicit*/ Twine(const std::string &Str) 252 : LHS(&Str), LHSKind(StdStringKind), RHSKind(EmptyKind) { 253 assert(isValid() && "Invalid twine!"); 254 } 255 256 /// Construct from a StringRef. 257 /*implicit*/ Twine(const StringRef &Str) 258 : LHS(&Str), LHSKind(StringRefKind), RHSKind(EmptyKind) { 259 assert(isValid() && "Invalid twine!"); 260 } 261 262 /// Construct a twine to print \arg Val as an unsigned decimal integer. 263 explicit Twine(unsigned Val) 264 : LHS((void*)(intptr_t)Val), LHSKind(DecUIKind), RHSKind(EmptyKind) { 265 } 266 267 /// Construct a twine to print \arg Val as a signed decimal integer. 268 explicit Twine(int Val) 269 : LHS((void*)(intptr_t)Val), LHSKind(DecIKind), RHSKind(EmptyKind) { 270 } 271 272 /// Construct a twine to print \arg Val as an unsigned decimal integer. 273 explicit Twine(const unsigned long &Val) 274 : LHS(&Val), LHSKind(DecULKind), RHSKind(EmptyKind) { 275 } 276 277 /// Construct a twine to print \arg Val as a signed decimal integer. 278 explicit Twine(const long &Val) 279 : LHS(&Val), LHSKind(DecLKind), RHSKind(EmptyKind) { 280 } 281 282 /// Construct a twine to print \arg Val as an unsigned decimal integer. 283 explicit Twine(const unsigned long long &Val) 284 : LHS(&Val), LHSKind(DecULLKind), RHSKind(EmptyKind) { 285 } 286 287 /// Construct a twine to print \arg Val as a signed decimal integer. 288 explicit Twine(const long long &Val) 289 : LHS(&Val), LHSKind(DecLLKind), RHSKind(EmptyKind) { 290 } 291 292 // FIXME: Unfortunately, to make sure this is as efficient as possible we 293 // need extra binary constructors from particular types. We can't rely on 294 // the compiler to be smart enough to fold operator+()/concat() down to the 295 // right thing. Yet. 296 297 /// Construct as the concatenation of a C string and a StringRef. 298 /*implicit*/ Twine(const char *_LHS, const StringRef &_RHS) 299 : LHS(_LHS), RHS(&_RHS), LHSKind(CStringKind), RHSKind(StringRefKind) { 300 assert(isValid() && "Invalid twine!"); 301 } 302 303 /// Construct as the concatenation of a StringRef and a C string. 304 /*implicit*/ Twine(const StringRef &_LHS, const char *_RHS) 305 : LHS(&_LHS), RHS(_RHS), LHSKind(StringRefKind), RHSKind(CStringKind) { 306 assert(isValid() && "Invalid twine!"); 307 } 308 309 /// Create a 'null' string, which is an empty string that always 310 /// concatenates to form another empty string. 311 static Twine createNull() { 312 return Twine(NullKind); 313 } 314 315 /// @} 316 /// @name Numeric Conversions 317 /// @{ 318 319 // Construct a twine to print \arg Val as an unsigned hexadecimal integer. 320 static Twine utohexstr(const uint64_t &Val) { 321 return Twine(&Val, UHexKind, 0, EmptyKind); 322 } 323 324 /// @} 325 /// @name Predicate Operations 326 /// @{ 327 328 /// isTriviallyEmpty - Check if this twine is trivially empty; a false 329 /// return value does not necessarily mean the twine is empty. 330 bool isTriviallyEmpty() const { 331 return isNullary(); 332 } 333 334 /// isSingleStringRef - Return true if this twine can be dynamically 335 /// accessed as a single StringRef value with getSingleStringRef(). 336 bool isSingleStringRef() const { 337 if (getRHSKind() != EmptyKind) return false; 338 339 switch (getLHSKind()) { 340 case EmptyKind: 341 case CStringKind: 342 case StdStringKind: 343 case StringRefKind: 344 return true; 345 default: 346 return false; 347 } 348 } 349 350 /// @} 351 /// @name String Operations 352 /// @{ 353 354 Twine concat(const Twine &Suffix) const; 355 356 /// @} 357 /// @name Output & Conversion. 358 /// @{ 359 360 /// str - Return the twine contents as a std::string. 361 std::string str() const; 362 363 /// toVector - Write the concatenated string into the given SmallString or 364 /// SmallVector. 365 void toVector(SmallVectorImpl<char> &Out) const; 366 367 /// getSingleStringRef - This returns the twine as a single StringRef. This 368 /// method is only valid if isSingleStringRef() is true. 369 StringRef getSingleStringRef() const { 370 assert(isSingleStringRef() &&"This cannot be had as a single stringref!"); 371 switch (getLHSKind()) { 372 default: assert(0 && "Out of sync with isSingleStringRef"); 373 case EmptyKind: return StringRef(); 374 case CStringKind: return StringRef((const char*)LHS); 375 case StdStringKind: return StringRef(*(const std::string*)LHS); 376 case StringRefKind: return *(const StringRef*)LHS; 377 } 378 } 379 380 /// toStringRef - This returns the twine as a single StringRef if it can be 381 /// represented as such. Otherwise the twine is written into the given 382 /// SmallVector and a StringRef to the SmallVector's data is returned. 383 StringRef toStringRef(SmallVectorImpl<char> &Out) const; 384 385 /// print - Write the concatenated string represented by this twine to the 386 /// stream \arg OS. 387 void print(raw_ostream &OS) const; 388 389 /// dump - Dump the concatenated string represented by this twine to stderr. 390 void dump() const; 391 392 /// print - Write the representation of this twine to the stream \arg OS. 393 void printRepr(raw_ostream &OS) const; 394 395 /// dumpRepr - Dump the representation of this twine to stderr. 396 void dumpRepr() const; 397 398 /// @} 399 }; 400 401 /// @name Twine Inline Implementations 402 /// @{ 403 404 inline Twine Twine::concat(const Twine &Suffix) const { 405 // Concatenation with null is null. 406 if (isNull() || Suffix.isNull()) 407 return Twine(NullKind); 408 409 // Concatenation with empty yields the other side. 410 if (isEmpty()) 411 return Suffix; 412 if (Suffix.isEmpty()) 413 return *this; 414 415 // Otherwise we need to create a new node, taking care to fold in unary 416 // twines. 417 const void *NewLHS = this, *NewRHS = &Suffix; 418 NodeKind NewLHSKind = TwineKind, NewRHSKind = TwineKind; 419 if (isUnary()) { 420 NewLHS = LHS; 421 NewLHSKind = getLHSKind(); 422 } 423 if (Suffix.isUnary()) { 424 NewRHS = Suffix.LHS; 425 NewRHSKind = Suffix.getLHSKind(); 426 } 427 428 return Twine(NewLHS, NewLHSKind, NewRHS, NewRHSKind); 429 } 430 431 inline Twine operator+(const Twine &LHS, const Twine &RHS) { 432 return LHS.concat(RHS); 433 } 434 435 /// Additional overload to guarantee simplified codegen; this is equivalent to 436 /// concat(). 437 438 inline Twine operator+(const char *LHS, const StringRef &RHS) { 439 return Twine(LHS, RHS); 440 } 441 442 /// Additional overload to guarantee simplified codegen; this is equivalent to 443 /// concat(). 444 445 inline Twine operator+(const StringRef &LHS, const char *RHS) { 446 return Twine(LHS, RHS); 447 } 448 449 inline raw_ostream &operator<<(raw_ostream &OS, const Twine &RHS) { 450 RHS.print(OS); 451 return OS; 452 } 453 454 /// @} 455} 456 457#endif 458