ScalarEvolution.h revision 70a1fe704831f9b842be0b2a2af5f7082b0e540c
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; 216 217 /// F - The function we are analyzing. 218 /// 219 Function *F; 220 221 /// LI - The loop information for the function we are currently analyzing. 222 /// 223 LoopInfo *LI; 224 225 /// TD - The target data information for the target we are targetting. 226 /// 227 TargetData *TD; 228 229 /// UnknownValue - This SCEV is used to represent unknown trip counts and 230 /// things. 231 SCEVHandle UnknownValue; 232 233 /// Scalars - This is a cache of the scalars we have analyzed so far. 234 /// 235 std::map<SCEVCallbackVH, SCEVHandle> Scalars; 236 237 /// BackedgeTakenInfo - Information about the backedge-taken count 238 /// of a loop. This currently inclues an exact count and a maximum count. 239 /// 240 struct BackedgeTakenInfo { 241 /// Exact - An expression indicating the exact backedge-taken count of 242 /// the loop if it is known, or a SCEVCouldNotCompute otherwise. 243 SCEVHandle Exact; 244 245 /// Exact - An expression indicating the least maximum backedge-taken 246 /// count of the loop that is known, or a SCEVCouldNotCompute. 247 SCEVHandle Max; 248 249 /*implicit*/ BackedgeTakenInfo(SCEVHandle exact) : 250 Exact(exact), Max(exact) {} 251 252 /*implicit*/ BackedgeTakenInfo(const SCEV *exact) : 253 Exact(exact), Max(exact) {} 254 255 BackedgeTakenInfo(SCEVHandle exact, SCEVHandle max) : 256 Exact(exact), Max(max) {} 257 258 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any 259 /// computed information, or whether it's all SCEVCouldNotCompute 260 /// values. 261 bool hasAnyInfo() const { 262 return !isa<SCEVCouldNotCompute>(Exact) || 263 !isa<SCEVCouldNotCompute>(Max); 264 } 265 }; 266 267 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for 268 /// this function as they are computed. 269 std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts; 270 271 /// ConstantEvolutionLoopExitValue - This map contains entries for all of 272 /// the PHI instructions that we attempt to compute constant evolutions for. 273 /// This allows us to avoid potentially expensive recomputation of these 274 /// properties. An instruction maps to null if we are unable to compute its 275 /// exit value. 276 std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue; 277 278 /// ValuesAtScopes - This map contains entries for all the instructions 279 /// that we attempt to compute getSCEVAtScope information for without 280 /// using SCEV techniques, which can be expensive. 281 std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes; 282 283 /// createSCEV - We know that there is no SCEV for the specified value. 284 /// Analyze the expression. 285 SCEVHandle createSCEV(Value *V); 286 287 /// createNodeForPHI - Provide the special handling we need to analyze PHI 288 /// SCEVs. 289 SCEVHandle createNodeForPHI(PHINode *PN); 290 291 /// createNodeForGEP - Provide the special handling we need to analyze GEP 292 /// SCEVs. 293 SCEVHandle createNodeForGEP(User *GEP); 294 295 /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value 296 /// for the specified instruction and replaces any references to the 297 /// symbolic value SymName with the specified value. This is used during 298 /// PHI resolution. 299 void ReplaceSymbolicValueWithConcrete(Instruction *I, 300 const SCEVHandle &SymName, 301 const SCEVHandle &NewVal); 302 303 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given 304 /// loop, lazily computing new values if the loop hasn't been analyzed 305 /// yet. 306 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L); 307 308 /// ComputeBackedgeTakenCount - Compute the number of times the specified 309 /// loop will iterate. 310 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L); 311 312 /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition 313 /// of 'icmp op load X, cst', try to see if we can compute the trip count. 314 SCEVHandle 315 ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI, 316 Constant *RHS, 317 const Loop *L, 318 ICmpInst::Predicate p); 319 320 /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute 321 /// a constant number of times (the condition evolves only from constants), 322 /// try to evaluate a few iterations of the loop until we get the exit 323 /// condition gets a value of ExitWhen (true or false). If we cannot 324 /// evaluate the trip count of the loop, return UnknownValue. 325 SCEVHandle ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond, 326 bool ExitWhen); 327 328 /// HowFarToZero - Return the number of times a backedge comparing the 329 /// specified value to zero will execute. If not computable, return 330 /// UnknownValue. 331 SCEVHandle HowFarToZero(const SCEV *V, const Loop *L); 332 333 /// HowFarToNonZero - Return the number of times a backedge checking the 334 /// specified value for nonzero will execute. If not computable, return 335 /// UnknownValue. 336 SCEVHandle HowFarToNonZero(const SCEV *V, const Loop *L); 337 338 /// HowManyLessThans - Return the number of times a backedge containing the 339 /// specified less-than comparison will execute. If not computable, return 340 /// UnknownValue. isSigned specifies whether the less-than is signed. 341 BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS, 342 const Loop *L, bool isSigned); 343 344 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB 345 /// (which may not be an immediate predecessor) which has exactly one 346 /// successor from which BB is reachable, or null if no such block is 347 /// found. 348 BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB); 349 350 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is 351 /// in the header of its containing loop, we know the loop executes a 352 /// constant number of times, and the PHI node is just a recurrence 353 /// involving constants, fold it. 354 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs, 355 const Loop *L); 356 357 /// forgetLoopPHIs - Delete the memoized SCEVs associated with the 358 /// PHI nodes in the given loop. This is used when the trip count of 359 /// the loop may have changed. 360 void forgetLoopPHIs(const Loop *L); 361 362 public: 363 static char ID; // Pass identification, replacement for typeid 364 ScalarEvolution(); 365 366 /// isSCEVable - Test if values of the given type are analyzable within 367 /// the SCEV framework. This primarily includes integer types, and it 368 /// can optionally include pointer types if the ScalarEvolution class 369 /// has access to target-specific information. 370 bool isSCEVable(const Type *Ty) const; 371 372 /// getTypeSizeInBits - Return the size in bits of the specified type, 373 /// for which isSCEVable must return true. 374 uint64_t getTypeSizeInBits(const Type *Ty) const; 375 376 /// getEffectiveSCEVType - Return a type with the same bitwidth as 377 /// the given type and which represents how SCEV will treat the given 378 /// type, for which isSCEVable must return true. For pointer types, 379 /// this is the pointer-sized integer type. 380 const Type *getEffectiveSCEVType(const Type *Ty) const; 381 382 /// getSCEV - Return a SCEV expression handle for the full generality of the 383 /// specified expression. 384 SCEVHandle getSCEV(Value *V); 385 386 SCEVHandle getConstant(ConstantInt *V); 387 SCEVHandle getConstant(const APInt& Val); 388 SCEVHandle getTruncateExpr(const SCEVHandle &Op, const Type *Ty); 389 SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty); 390 SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty); 391 SCEVHandle getAddExpr(std::vector<SCEVHandle> &Ops); 392 SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 393 std::vector<SCEVHandle> Ops; 394 Ops.push_back(LHS); 395 Ops.push_back(RHS); 396 return getAddExpr(Ops); 397 } 398 SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1, 399 const SCEVHandle &Op2) { 400 std::vector<SCEVHandle> Ops; 401 Ops.push_back(Op0); 402 Ops.push_back(Op1); 403 Ops.push_back(Op2); 404 return getAddExpr(Ops); 405 } 406 SCEVHandle getMulExpr(std::vector<SCEVHandle> &Ops); 407 SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 408 std::vector<SCEVHandle> Ops; 409 Ops.push_back(LHS); 410 Ops.push_back(RHS); 411 return getMulExpr(Ops); 412 } 413 SCEVHandle getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 414 SCEVHandle getAddRecExpr(const SCEVHandle &Start, const SCEVHandle &Step, 415 const Loop *L); 416 SCEVHandle getAddRecExpr(std::vector<SCEVHandle> &Operands, 417 const Loop *L); 418 SCEVHandle getAddRecExpr(const std::vector<SCEVHandle> &Operands, 419 const Loop *L) { 420 std::vector<SCEVHandle> NewOp(Operands); 421 return getAddRecExpr(NewOp, L); 422 } 423 SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 424 SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands); 425 SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 426 SCEVHandle getUMaxExpr(std::vector<SCEVHandle> Operands); 427 SCEVHandle getUnknown(Value *V); 428 SCEVHandle getCouldNotCompute(); 429 430 /// getNegativeSCEV - Return the SCEV object corresponding to -V. 431 /// 432 SCEVHandle getNegativeSCEV(const SCEVHandle &V); 433 434 /// getNotSCEV - Return the SCEV object corresponding to ~V. 435 /// 436 SCEVHandle getNotSCEV(const SCEVHandle &V); 437 438 /// getMinusSCEV - Return LHS-RHS. 439 /// 440 SCEVHandle getMinusSCEV(const SCEVHandle &LHS, 441 const SCEVHandle &RHS); 442 443 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion 444 /// of the input value to the specified type. If the type must be 445 /// extended, it is zero extended. 446 SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty); 447 448 /// getTruncateOrSignExtend - 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 sign extended. 451 SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty); 452 453 /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of 454 /// the input value to the specified type. If the type must be extended, 455 /// it is zero extended. The conversion must not be narrowing. 456 SCEVHandle getNoopOrZeroExtend(const SCEVHandle &V, const Type *Ty); 457 458 /// getNoopOrSignExtend - 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 sign extended. The conversion must not be narrowing. 461 SCEVHandle getNoopOrSignExtend(const SCEVHandle &V, const Type *Ty); 462 463 /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the 464 /// input value to the specified type. The conversion must not be 465 /// widening. 466 SCEVHandle getTruncateOrNoop(const SCEVHandle &V, const Type *Ty); 467 468 /// getIntegerSCEV - Given an integer or FP type, create a constant for the 469 /// specified signed integer value and return a SCEV for the constant. 470 SCEVHandle getIntegerSCEV(int Val, const Type *Ty); 471 472 /// hasSCEV - Return true if the SCEV for this value has already been 473 /// computed. 474 bool hasSCEV(Value *V) const; 475 476 /// setSCEV - Insert the specified SCEV into the map of current SCEVs for 477 /// the specified value. 478 void setSCEV(Value *V, const SCEVHandle &H); 479 480 /// getSCEVAtScope - Return a SCEV expression handle for the specified value 481 /// at the specified scope in the program. The L value specifies a loop 482 /// nest to evaluate the expression at, where null is the top-level or a 483 /// specified loop is immediately inside of the loop. 484 /// 485 /// This method can be used to compute the exit value for a variable defined 486 /// in a loop by querying what the value will hold in the parent loop. 487 /// 488 /// If this value is not computable at this scope, a SCEVCouldNotCompute 489 /// object is returned. 490 SCEVHandle getSCEVAtScope(const SCEV *S, const Loop *L); 491 492 /// getSCEVAtScope - This is a convenience function which does 493 /// getSCEVAtScope(getSCEV(V), L). 494 SCEVHandle getSCEVAtScope(Value *V, const Loop *L); 495 496 /// isLoopGuardedByCond - Test whether entry to the loop is protected by 497 /// a conditional between LHS and RHS. This is used to help avoid max 498 /// expressions in loop trip counts. 499 bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred, 500 const SCEV *LHS, const SCEV *RHS); 501 502 /// getBackedgeTakenCount - If the specified loop has a predictable 503 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute 504 /// object. The backedge-taken count is the number of times the loop header 505 /// will be branched to from within the loop. This is one less than the 506 /// trip count of the loop, since it doesn't count the first iteration, 507 /// when the header is branched to from outside the loop. 508 /// 509 /// Note that it is not valid to call this method on a loop without a 510 /// loop-invariant backedge-taken count (see 511 /// hasLoopInvariantBackedgeTakenCount). 512 /// 513 SCEVHandle getBackedgeTakenCount(const Loop *L); 514 515 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except 516 /// return the least SCEV value that is known never to be less than the 517 /// actual backedge taken count. 518 SCEVHandle getMaxBackedgeTakenCount(const Loop *L); 519 520 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop 521 /// has an analyzable loop-invariant backedge-taken count. 522 bool hasLoopInvariantBackedgeTakenCount(const Loop *L); 523 524 /// forgetLoopBackedgeTakenCount - This method should be called by the 525 /// client when it has changed a loop in a way that may effect 526 /// ScalarEvolution's ability to compute a trip count, or if the loop 527 /// is deleted. 528 void forgetLoopBackedgeTakenCount(const Loop *L); 529 530 virtual bool runOnFunction(Function &F); 531 virtual void releaseMemory(); 532 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 533 void print(raw_ostream &OS, const Module* = 0) const; 534 virtual void print(std::ostream &OS, const Module* = 0) const; 535 void print(std::ostream *OS, const Module* M = 0) const { 536 if (OS) print(*OS, M); 537 } 538 }; 539} 540 541#endif 542