ScalarEvolution.h revision 5be18e84766fb495b0bde3c8244c1df459a18683
1//===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- 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// The ScalarEvolution class is an LLVM pass which can be used to analyze and 11// catagorize scalar expressions in loops. It specializes in recognizing 12// general induction variables, representing them with the abstract and opaque 13// SCEV class. Given this analysis, trip counts of loops and other important 14// properties can be obtained. 15// 16// This analysis is primarily useful for induction variable substitution and 17// strength reduction. 18// 19//===----------------------------------------------------------------------===// 20 21#ifndef LLVM_ANALYSIS_SCALAREVOLUTION_H 22#define LLVM_ANALYSIS_SCALAREVOLUTION_H 23 24#include "llvm/Pass.h" 25#include "llvm/Analysis/LoopInfo.h" 26#include "llvm/Support/DataTypes.h" 27#include "llvm/Support/ValueHandle.h" 28#include <iosfwd> 29 30namespace llvm { 31 class APInt; 32 class ConstantInt; 33 class Type; 34 class SCEVHandle; 35 class ScalarEvolution; 36 class TargetData; 37 38 /// SCEV - This class represent an analyzed expression in the program. These 39 /// are reference counted opaque objects that the client is not allowed to 40 /// do much with directly. 41 /// 42 class SCEV { 43 const unsigned SCEVType; // The SCEV baseclass this node corresponds to 44 mutable unsigned RefCount; 45 46 friend class SCEVHandle; 47 void addRef() const { ++RefCount; } 48 void dropRef() const { 49 if (--RefCount == 0) 50 delete this; 51 } 52 53 SCEV(const SCEV &); // DO NOT IMPLEMENT 54 void operator=(const SCEV &); // DO NOT IMPLEMENT 55 protected: 56 virtual ~SCEV(); 57 public: 58 explicit SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {} 59 60 unsigned getSCEVType() const { return SCEVType; } 61 62 /// isLoopInvariant - Return true if the value of this SCEV is unchanging in 63 /// the specified loop. 64 virtual bool isLoopInvariant(const Loop *L) const = 0; 65 66 /// hasComputableLoopEvolution - Return true if this SCEV changes value in a 67 /// known way in the specified loop. This property being true implies that 68 /// the value is variant in the loop AND that we can emit an expression to 69 /// compute the value of the expression at any particular loop iteration. 70 virtual bool hasComputableLoopEvolution(const Loop *L) const = 0; 71 72 /// getType - Return the LLVM type of this SCEV expression. 73 /// 74 virtual const Type *getType() const = 0; 75 76 /// isZero - Return true if the expression is a constant zero. 77 /// 78 bool isZero() const; 79 80 /// isOne - Return true if the expression is a constant one. 81 /// 82 bool isOne() const; 83 84 /// replaceSymbolicValuesWithConcrete - If this SCEV internally references 85 /// the symbolic value "Sym", construct and return a new SCEV that produces 86 /// the same value, but which uses the concrete value Conc instead of the 87 /// symbolic value. If this SCEV does not use the symbolic value, it 88 /// returns itself. 89 virtual SCEVHandle 90 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym, 91 const SCEVHandle &Conc, 92 ScalarEvolution &SE) const = 0; 93 94 /// dominates - Return true if elements that makes up this SCEV dominates 95 /// the specified basic block. 96 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const = 0; 97 98 /// print - Print out the internal representation of this scalar to the 99 /// specified stream. This should really only be used for debugging 100 /// purposes. 101 virtual void print(raw_ostream &OS) const = 0; 102 void print(std::ostream &OS) const; 103 void print(std::ostream *OS) const { if (OS) print(*OS); } 104 105 /// dump - This method is used for debugging. 106 /// 107 void dump() const; 108 }; 109 110 inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) { 111 S.print(OS); 112 return OS; 113 } 114 115 inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) { 116 S.print(OS); 117 return OS; 118 } 119 120 /// SCEVCouldNotCompute - An object of this class is returned by queries that 121 /// could not be answered. For example, if you ask for the number of 122 /// iterations of a linked-list traversal loop, you will get one of these. 123 /// None of the standard SCEV operations are valid on this class, it is just a 124 /// marker. 125 struct SCEVCouldNotCompute : public SCEV { 126 SCEVCouldNotCompute(); 127 ~SCEVCouldNotCompute(); 128 129 // None of these methods are valid for this object. 130 virtual bool isLoopInvariant(const Loop *L) const; 131 virtual const Type *getType() const; 132 virtual bool hasComputableLoopEvolution(const Loop *L) const; 133 virtual void print(raw_ostream &OS) const; 134 virtual SCEVHandle 135 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym, 136 const SCEVHandle &Conc, 137 ScalarEvolution &SE) const; 138 139 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const { 140 return true; 141 } 142 143 /// Methods for support type inquiry through isa, cast, and dyn_cast: 144 static inline bool classof(const SCEVCouldNotCompute *S) { return true; } 145 static bool classof(const SCEV *S); 146 }; 147 148 /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be 149 /// notified whenever a Value is deleted. 150 class SCEVCallbackVH : public CallbackVH { 151 ScalarEvolution *SE; 152 virtual void deleted(); 153 virtual void allUsesReplacedWith(Value *New); 154 public: 155 SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0); 156 }; 157 158 /// SCEVHandle - This class is used to maintain the SCEV object's refcounts, 159 /// freeing the objects when the last reference is dropped. 160 class SCEVHandle { 161 const SCEV *S; 162 SCEVHandle(); // DO NOT IMPLEMENT 163 public: 164 SCEVHandle(const SCEV *s) : S(s) { 165 assert(S && "Cannot create a handle to a null SCEV!"); 166 S->addRef(); 167 } 168 SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) { 169 S->addRef(); 170 } 171 ~SCEVHandle() { S->dropRef(); } 172 173 operator const SCEV*() const { return S; } 174 175 const SCEV &operator*() const { return *S; } 176 const SCEV *operator->() const { return S; } 177 178 bool operator==(const SCEV *RHS) const { return S == RHS; } 179 bool operator!=(const SCEV *RHS) const { return S != RHS; } 180 181 const SCEVHandle &operator=(SCEV *RHS) { 182 if (S != RHS) { 183 S->dropRef(); 184 S = RHS; 185 S->addRef(); 186 } 187 return *this; 188 } 189 190 const SCEVHandle &operator=(const SCEVHandle &RHS) { 191 if (S != RHS.S) { 192 S->dropRef(); 193 S = RHS.S; 194 S->addRef(); 195 } 196 return *this; 197 } 198 }; 199 200 template<typename From> struct simplify_type; 201 template<> struct simplify_type<const SCEVHandle> { 202 typedef const SCEV* SimpleType; 203 static SimpleType getSimplifiedValue(const SCEVHandle &Node) { 204 return Node; 205 } 206 }; 207 template<> struct simplify_type<SCEVHandle> 208 : public simplify_type<const SCEVHandle> {}; 209 210 /// ScalarEvolution - This class is the main scalar evolution driver. Because 211 /// client code (intentionally) can't do much with the SCEV objects directly, 212 /// they must ask this class for services. 213 /// 214 class ScalarEvolution : public FunctionPass { 215 friend class SCEVCallbackVH; 216 friend class SCEVExpander; 217 218 /// F - The function we are analyzing. 219 /// 220 Function *F; 221 222 /// LI - The loop information for the function we are currently analyzing. 223 /// 224 LoopInfo *LI; 225 226 /// TD - The target data information for the target we are targetting. 227 /// 228 TargetData *TD; 229 230 /// UnknownValue - This SCEV is used to represent unknown trip counts and 231 /// things. 232 SCEVHandle UnknownValue; 233 234 /// Scalars - This is a cache of the scalars we have analyzed so far. 235 /// 236 std::map<SCEVCallbackVH, SCEVHandle> Scalars; 237 238 /// BackedgeTakenInfo - Information about the backedge-taken count 239 /// of a loop. This currently inclues an exact count and a maximum count. 240 /// 241 struct BackedgeTakenInfo { 242 /// Exact - An expression indicating the exact backedge-taken count of 243 /// the loop if it is known, or a SCEVCouldNotCompute otherwise. 244 SCEVHandle Exact; 245 246 /// Exact - An expression indicating the least maximum backedge-taken 247 /// count of the loop that is known, or a SCEVCouldNotCompute. 248 SCEVHandle Max; 249 250 /*implicit*/ BackedgeTakenInfo(SCEVHandle exact) : 251 Exact(exact), Max(exact) {} 252 253 /*implicit*/ BackedgeTakenInfo(const SCEV *exact) : 254 Exact(exact), Max(exact) {} 255 256 BackedgeTakenInfo(SCEVHandle exact, SCEVHandle max) : 257 Exact(exact), Max(max) {} 258 259 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any 260 /// computed information, or whether it's all SCEVCouldNotCompute 261 /// values. 262 bool hasAnyInfo() const { 263 return !isa<SCEVCouldNotCompute>(Exact) || 264 !isa<SCEVCouldNotCompute>(Max); 265 } 266 }; 267 268 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for 269 /// this function as they are computed. 270 std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts; 271 272 /// ConstantEvolutionLoopExitValue - This map contains entries for all of 273 /// the PHI instructions that we attempt to compute constant evolutions for. 274 /// This allows us to avoid potentially expensive recomputation of these 275 /// properties. An instruction maps to null if we are unable to compute its 276 /// exit value. 277 std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue; 278 279 /// ValuesAtScopes - This map contains entries for all the instructions 280 /// that we attempt to compute getSCEVAtScope information for without 281 /// using SCEV techniques, which can be expensive. 282 std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes; 283 284 /// createSCEV - We know that there is no SCEV for the specified value. 285 /// Analyze the expression. 286 SCEVHandle createSCEV(Value *V); 287 288 /// createNodeForPHI - Provide the special handling we need to analyze PHI 289 /// SCEVs. 290 SCEVHandle createNodeForPHI(PHINode *PN); 291 292 /// createNodeForGEP - Provide the special handling we need to analyze GEP 293 /// SCEVs. 294 SCEVHandle createNodeForGEP(User *GEP); 295 296 /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value 297 /// for the specified instruction and replaces any references to the 298 /// symbolic value SymName with the specified value. This is used during 299 /// PHI resolution. 300 void ReplaceSymbolicValueWithConcrete(Instruction *I, 301 const SCEVHandle &SymName, 302 const SCEVHandle &NewVal); 303 304 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given 305 /// loop, lazily computing new values if the loop hasn't been analyzed 306 /// yet. 307 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L); 308 309 /// ComputeBackedgeTakenCount - Compute the number of times the specified 310 /// loop will iterate. 311 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L); 312 313 /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition 314 /// of 'icmp op load X, cst', try to see if we can compute the trip count. 315 SCEVHandle 316 ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI, 317 Constant *RHS, 318 const Loop *L, 319 ICmpInst::Predicate p); 320 321 /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute 322 /// a constant number of times (the condition evolves only from constants), 323 /// try to evaluate a few iterations of the loop until we get the exit 324 /// condition gets a value of ExitWhen (true or false). If we cannot 325 /// evaluate the trip count of the loop, return UnknownValue. 326 SCEVHandle ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond, 327 bool ExitWhen); 328 329 /// HowFarToZero - Return the number of times a backedge comparing the 330 /// specified value to zero will execute. If not computable, return 331 /// UnknownValue. 332 SCEVHandle HowFarToZero(const SCEV *V, const Loop *L); 333 334 /// HowFarToNonZero - Return the number of times a backedge checking the 335 /// specified value for nonzero will execute. If not computable, return 336 /// UnknownValue. 337 SCEVHandle HowFarToNonZero(const SCEV *V, const Loop *L); 338 339 /// HowManyLessThans - Return the number of times a backedge containing the 340 /// specified less-than comparison will execute. If not computable, return 341 /// UnknownValue. isSigned specifies whether the less-than is signed. 342 BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS, 343 const Loop *L, bool isSigned); 344 345 /// getLoopPredecessor - If the given loop's header has exactly one unique 346 /// predecessor outside the loop, return it. Otherwise return null. 347 BasicBlock *getLoopPredecessor(const Loop *L); 348 349 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB 350 /// (which may not be an immediate predecessor) which has exactly one 351 /// successor from which BB is reachable, or null if no such block is 352 /// found. 353 BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB); 354 355 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is 356 /// in the header of its containing loop, we know the loop executes a 357 /// constant number of times, and the PHI node is just a recurrence 358 /// involving constants, fold it. 359 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs, 360 const Loop *L); 361 362 /// forgetLoopPHIs - Delete the memoized SCEVs associated with the 363 /// PHI nodes in the given loop. This is used when the trip count of 364 /// the loop may have changed. 365 void forgetLoopPHIs(const Loop *L); 366 367 public: 368 static char ID; // Pass identification, replacement for typeid 369 ScalarEvolution(); 370 371 /// isSCEVable - Test if values of the given type are analyzable within 372 /// the SCEV framework. This primarily includes integer types, and it 373 /// can optionally include pointer types if the ScalarEvolution class 374 /// has access to target-specific information. 375 bool isSCEVable(const Type *Ty) const; 376 377 /// getTypeSizeInBits - Return the size in bits of the specified type, 378 /// for which isSCEVable must return true. 379 uint64_t getTypeSizeInBits(const Type *Ty) const; 380 381 /// getEffectiveSCEVType - Return a type with the same bitwidth as 382 /// the given type and which represents how SCEV will treat the given 383 /// type, for which isSCEVable must return true. For pointer types, 384 /// this is the pointer-sized integer type. 385 const Type *getEffectiveSCEVType(const Type *Ty) const; 386 387 /// getSCEV - Return a SCEV expression handle for the full generality of the 388 /// specified expression. 389 SCEVHandle getSCEV(Value *V); 390 391 SCEVHandle getConstant(ConstantInt *V); 392 SCEVHandle getConstant(const APInt& Val); 393 SCEVHandle getTruncateExpr(const SCEVHandle &Op, const Type *Ty); 394 SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty); 395 SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty); 396 SCEVHandle getAddExpr(std::vector<SCEVHandle> &Ops); 397 SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 398 std::vector<SCEVHandle> Ops; 399 Ops.push_back(LHS); 400 Ops.push_back(RHS); 401 return getAddExpr(Ops); 402 } 403 SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1, 404 const SCEVHandle &Op2) { 405 std::vector<SCEVHandle> Ops; 406 Ops.push_back(Op0); 407 Ops.push_back(Op1); 408 Ops.push_back(Op2); 409 return getAddExpr(Ops); 410 } 411 SCEVHandle getMulExpr(std::vector<SCEVHandle> &Ops); 412 SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 413 std::vector<SCEVHandle> Ops; 414 Ops.push_back(LHS); 415 Ops.push_back(RHS); 416 return getMulExpr(Ops); 417 } 418 SCEVHandle getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 419 SCEVHandle getAddRecExpr(const SCEVHandle &Start, const SCEVHandle &Step, 420 const Loop *L); 421 SCEVHandle getAddRecExpr(std::vector<SCEVHandle> &Operands, 422 const Loop *L); 423 SCEVHandle getAddRecExpr(const std::vector<SCEVHandle> &Operands, 424 const Loop *L) { 425 std::vector<SCEVHandle> NewOp(Operands); 426 return getAddRecExpr(NewOp, L); 427 } 428 SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 429 SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands); 430 SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 431 SCEVHandle getUMaxExpr(std::vector<SCEVHandle> Operands); 432 SCEVHandle getUnknown(Value *V); 433 SCEVHandle getCouldNotCompute(); 434 435 /// getNegativeSCEV - Return the SCEV object corresponding to -V. 436 /// 437 SCEVHandle getNegativeSCEV(const SCEVHandle &V); 438 439 /// getNotSCEV - Return the SCEV object corresponding to ~V. 440 /// 441 SCEVHandle getNotSCEV(const SCEVHandle &V); 442 443 /// getMinusSCEV - Return LHS-RHS. 444 /// 445 SCEVHandle getMinusSCEV(const SCEVHandle &LHS, 446 const SCEVHandle &RHS); 447 448 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion 449 /// of the input value to the specified type. If the type must be 450 /// extended, it is zero extended. 451 SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty); 452 453 /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion 454 /// of the input value to the specified type. If the type must be 455 /// extended, it is sign extended. 456 SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty); 457 458 /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of 459 /// the input value to the specified type. If the type must be extended, 460 /// it is zero extended. The conversion must not be narrowing. 461 SCEVHandle getNoopOrZeroExtend(const SCEVHandle &V, const Type *Ty); 462 463 /// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of 464 /// the input value to the specified type. If the type must be extended, 465 /// it is sign extended. The conversion must not be narrowing. 466 SCEVHandle getNoopOrSignExtend(const SCEVHandle &V, const Type *Ty); 467 468 /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the 469 /// input value to the specified type. The conversion must not be 470 /// widening. 471 SCEVHandle getTruncateOrNoop(const SCEVHandle &V, const Type *Ty); 472 473 /// getIntegerSCEV - Given an integer or FP type, create a constant for the 474 /// specified signed integer value and return a SCEV for the constant. 475 SCEVHandle getIntegerSCEV(int Val, const Type *Ty); 476 477 /// hasSCEV - Return true if the SCEV for this value has already been 478 /// computed. 479 bool hasSCEV(Value *V) const; 480 481 /// setSCEV - Insert the specified SCEV into the map of current SCEVs for 482 /// the specified value. 483 void setSCEV(Value *V, const SCEVHandle &H); 484 485 /// getSCEVAtScope - Return a SCEV expression handle for the specified value 486 /// at the specified scope in the program. The L value specifies a loop 487 /// nest to evaluate the expression at, where null is the top-level or a 488 /// specified loop is immediately inside of the loop. 489 /// 490 /// This method can be used to compute the exit value for a variable defined 491 /// in a loop by querying what the value will hold in the parent loop. 492 /// 493 /// If this value is not computable at this scope, a SCEVCouldNotCompute 494 /// object is returned. 495 SCEVHandle getSCEVAtScope(const SCEV *S, const Loop *L); 496 497 /// getSCEVAtScope - This is a convenience function which does 498 /// getSCEVAtScope(getSCEV(V), L). 499 SCEVHandle getSCEVAtScope(Value *V, const Loop *L); 500 501 /// isLoopGuardedByCond - Test whether entry to the loop is protected by 502 /// a conditional between LHS and RHS. This is used to help avoid max 503 /// expressions in loop trip counts. 504 bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred, 505 const SCEV *LHS, const SCEV *RHS); 506 507 /// getBackedgeTakenCount - If the specified loop has a predictable 508 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute 509 /// object. The backedge-taken count is the number of times the loop header 510 /// will be branched to from within the loop. This is one less than the 511 /// trip count of the loop, since it doesn't count the first iteration, 512 /// when the header is branched to from outside the loop. 513 /// 514 /// Note that it is not valid to call this method on a loop without a 515 /// loop-invariant backedge-taken count (see 516 /// hasLoopInvariantBackedgeTakenCount). 517 /// 518 SCEVHandle getBackedgeTakenCount(const Loop *L); 519 520 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except 521 /// return the least SCEV value that is known never to be less than the 522 /// actual backedge taken count. 523 SCEVHandle getMaxBackedgeTakenCount(const Loop *L); 524 525 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop 526 /// has an analyzable loop-invariant backedge-taken count. 527 bool hasLoopInvariantBackedgeTakenCount(const Loop *L); 528 529 /// forgetLoopBackedgeTakenCount - This method should be called by the 530 /// client when it has changed a loop in a way that may effect 531 /// ScalarEvolution's ability to compute a trip count, or if the loop 532 /// is deleted. 533 void forgetLoopBackedgeTakenCount(const Loop *L); 534 535 virtual bool runOnFunction(Function &F); 536 virtual void releaseMemory(); 537 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 538 void print(raw_ostream &OS, const Module* = 0) const; 539 virtual void print(std::ostream &OS, const Module* = 0) const; 540 void print(std::ostream *OS, const Module* M = 0) const { 541 if (OS) print(*OS, M); 542 } 543 }; 544} 545 546#endif 547