ScalarEvolution.h revision 35738ac150afafe2359268d4b2169498c6c98c5f
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 /// replaceSymbolicValuesWithConcrete - If this SCEV internally references 81 /// the symbolic value "Sym", construct and return a new SCEV that produces 82 /// the same value, but which uses the concrete value Conc instead of the 83 /// symbolic value. If this SCEV does not use the symbolic value, it 84 /// returns itself. 85 virtual SCEVHandle 86 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym, 87 const SCEVHandle &Conc, 88 ScalarEvolution &SE) const = 0; 89 90 /// dominates - Return true if elements that makes up this SCEV dominates 91 /// the specified basic block. 92 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const = 0; 93 94 /// print - Print out the internal representation of this scalar to the 95 /// specified stream. This should really only be used for debugging 96 /// purposes. 97 virtual void print(raw_ostream &OS) const = 0; 98 void print(std::ostream &OS) const; 99 void print(std::ostream *OS) const { if (OS) print(*OS); } 100 101 /// dump - This method is used for debugging. 102 /// 103 void dump() const; 104 }; 105 106 inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) { 107 S.print(OS); 108 return OS; 109 } 110 111 inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) { 112 S.print(OS); 113 return OS; 114 } 115 116 /// SCEVCouldNotCompute - An object of this class is returned by queries that 117 /// could not be answered. For example, if you ask for the number of 118 /// iterations of a linked-list traversal loop, you will get one of these. 119 /// None of the standard SCEV operations are valid on this class, it is just a 120 /// marker. 121 struct SCEVCouldNotCompute : public SCEV { 122 SCEVCouldNotCompute(); 123 ~SCEVCouldNotCompute(); 124 125 // None of these methods are valid for this object. 126 virtual bool isLoopInvariant(const Loop *L) const; 127 virtual const Type *getType() const; 128 virtual bool hasComputableLoopEvolution(const Loop *L) const; 129 virtual void print(raw_ostream &OS) const; 130 virtual SCEVHandle 131 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym, 132 const SCEVHandle &Conc, 133 ScalarEvolution &SE) const; 134 135 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const { 136 return true; 137 } 138 139 /// Methods for support type inquiry through isa, cast, and dyn_cast: 140 static inline bool classof(const SCEVCouldNotCompute *S) { return true; } 141 static bool classof(const SCEV *S); 142 }; 143 144 /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be 145 /// notified whenever a Value is deleted. 146 class SCEVCallbackVH : public CallbackVH { 147 ScalarEvolution *SE; 148 virtual void deleted(); 149 virtual void allUsesReplacedWith(Value *New); 150 public: 151 SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0); 152 }; 153 154 /// SCEVHandle - This class is used to maintain the SCEV object's refcounts, 155 /// freeing the objects when the last reference is dropped. 156 class SCEVHandle { 157 const SCEV *S; 158 SCEVHandle(); // DO NOT IMPLEMENT 159 public: 160 SCEVHandle(const SCEV *s) : S(s) { 161 assert(S && "Cannot create a handle to a null SCEV!"); 162 S->addRef(); 163 } 164 SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) { 165 S->addRef(); 166 } 167 ~SCEVHandle() { S->dropRef(); } 168 169 operator const SCEV*() const { return S; } 170 171 const SCEV &operator*() const { return *S; } 172 const SCEV *operator->() const { return S; } 173 174 bool operator==(const SCEV *RHS) const { return S == RHS; } 175 bool operator!=(const SCEV *RHS) const { return S != RHS; } 176 177 const SCEVHandle &operator=(SCEV *RHS) { 178 if (S != RHS) { 179 S->dropRef(); 180 S = RHS; 181 S->addRef(); 182 } 183 return *this; 184 } 185 186 const SCEVHandle &operator=(const SCEVHandle &RHS) { 187 if (S != RHS.S) { 188 S->dropRef(); 189 S = RHS.S; 190 S->addRef(); 191 } 192 return *this; 193 } 194 }; 195 196 template<typename From> struct simplify_type; 197 template<> struct simplify_type<const SCEVHandle> { 198 typedef const SCEV* SimpleType; 199 static SimpleType getSimplifiedValue(const SCEVHandle &Node) { 200 return Node; 201 } 202 }; 203 template<> struct simplify_type<SCEVHandle> 204 : public simplify_type<const SCEVHandle> {}; 205 206 /// ScalarEvolution - This class is the main scalar evolution driver. Because 207 /// client code (intentionally) can't do much with the SCEV objects directly, 208 /// they must ask this class for services. 209 /// 210 class ScalarEvolution : public FunctionPass { 211 friend class SCEVCallbackVH; 212 213 /// F - The function we are analyzing. 214 /// 215 Function *F; 216 217 /// LI - The loop information for the function we are currently analyzing. 218 /// 219 LoopInfo *LI; 220 221 /// TD - The target data information for the target we are targetting. 222 /// 223 TargetData *TD; 224 225 /// UnknownValue - This SCEV is used to represent unknown trip counts and 226 /// things. 227 SCEVHandle UnknownValue; 228 229 /// Scalars - This is a cache of the scalars we have analyzed so far. 230 /// 231 std::map<SCEVCallbackVH, SCEVHandle> Scalars; 232 233 /// BackedgeTakenInfo - Information about the backedge-taken count 234 /// of a loop. This currently inclues an exact count and a maximum count. 235 /// 236 struct BackedgeTakenInfo { 237 /// Exact - An expression indicating the exact backedge-taken count of 238 /// the loop if it is known, or a SCEVCouldNotCompute otherwise. 239 SCEVHandle Exact; 240 241 /// Exact - An expression indicating the least maximum backedge-taken 242 /// count of the loop that is known, or a SCEVCouldNotCompute. 243 SCEVHandle Max; 244 245 /*implicit*/ BackedgeTakenInfo(SCEVHandle exact) : 246 Exact(exact), Max(exact) {} 247 248 /*implicit*/ BackedgeTakenInfo(const SCEV *exact) : 249 Exact(exact), Max(exact) {} 250 251 BackedgeTakenInfo(SCEVHandle exact, SCEVHandle max) : 252 Exact(exact), Max(max) {} 253 254 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any 255 /// computed information, or whether it's all SCEVCouldNotCompute 256 /// values. 257 bool hasAnyInfo() const { 258 return !isa<SCEVCouldNotCompute>(Exact) || 259 !isa<SCEVCouldNotCompute>(Max); 260 } 261 }; 262 263 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for 264 /// this function as they are computed. 265 std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts; 266 267 /// ConstantEvolutionLoopExitValue - This map contains entries for all of 268 /// the PHI instructions that we attempt to compute constant evolutions for. 269 /// This allows us to avoid potentially expensive recomputation of these 270 /// properties. An instruction maps to null if we are unable to compute its 271 /// exit value. 272 std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue; 273 274 /// createSCEV - We know that there is no SCEV for the specified value. 275 /// Analyze the expression. 276 SCEVHandle createSCEV(Value *V); 277 278 /// createNodeForPHI - Provide the special handling we need to analyze PHI 279 /// SCEVs. 280 SCEVHandle createNodeForPHI(PHINode *PN); 281 282 /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value 283 /// for the specified instruction and replaces any references to the 284 /// symbolic value SymName with the specified value. This is used during 285 /// PHI resolution. 286 void ReplaceSymbolicValueWithConcrete(Instruction *I, 287 const SCEVHandle &SymName, 288 const SCEVHandle &NewVal); 289 290 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given 291 /// loop, lazily computing new values if the loop hasn't been analyzed 292 /// yet. 293 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L); 294 295 /// ComputeBackedgeTakenCount - Compute the number of times the specified 296 /// loop will iterate. 297 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L); 298 299 /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition 300 /// of 'icmp op load X, cst', try to see if we can compute the trip count. 301 SCEVHandle 302 ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI, 303 Constant *RHS, 304 const Loop *L, 305 ICmpInst::Predicate p); 306 307 /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute 308 /// a constant number of times (the condition evolves only from constants), 309 /// try to evaluate a few iterations of the loop until we get the exit 310 /// condition gets a value of ExitWhen (true or false). If we cannot 311 /// evaluate the trip count of the loop, return UnknownValue. 312 SCEVHandle ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond, 313 bool ExitWhen); 314 315 /// HowFarToZero - Return the number of times a backedge comparing the 316 /// specified value to zero will execute. If not computable, return 317 /// UnknownValue. 318 SCEVHandle HowFarToZero(const SCEV *V, const Loop *L); 319 320 /// HowFarToNonZero - Return the number of times a backedge checking the 321 /// specified value for nonzero will execute. If not computable, return 322 /// UnknownValue. 323 SCEVHandle HowFarToNonZero(const SCEV *V, const Loop *L); 324 325 /// HowManyLessThans - Return the number of times a backedge containing the 326 /// specified less-than comparison will execute. If not computable, return 327 /// UnknownValue. isSigned specifies whether the less-than is signed. 328 BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS, 329 const Loop *L, bool isSigned); 330 331 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB 332 /// (which may not be an immediate predecessor) which has exactly one 333 /// successor from which BB is reachable, or null if no such block is 334 /// found. 335 BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB); 336 337 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is 338 /// in the header of its containing loop, we know the loop executes a 339 /// constant number of times, and the PHI node is just a recurrence 340 /// involving constants, fold it. 341 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs, 342 const Loop *L); 343 344 /// getSCEVAtScope - Compute the value of the specified expression within 345 /// the indicated loop (which may be null to indicate in no loop). If the 346 /// expression cannot be evaluated, return UnknownValue itself. 347 SCEVHandle getSCEVAtScope(const SCEV *S, const Loop *L); 348 349 /// forgetLoopPHIs - Delete the memoized SCEVs associated with the 350 /// PHI nodes in the given loop. This is used when the trip count of 351 /// the loop may have changed. 352 void forgetLoopPHIs(const Loop *L); 353 354 public: 355 static char ID; // Pass identification, replacement for typeid 356 ScalarEvolution(); 357 358 /// isSCEVable - Test if values of the given type are analyzable within 359 /// the SCEV framework. This primarily includes integer types, and it 360 /// can optionally include pointer types if the ScalarEvolution class 361 /// has access to target-specific information. 362 bool isSCEVable(const Type *Ty) const; 363 364 /// getTypeSizeInBits - Return the size in bits of the specified type, 365 /// for which isSCEVable must return true. 366 uint64_t getTypeSizeInBits(const Type *Ty) const; 367 368 /// getEffectiveSCEVType - Return a type with the same bitwidth as 369 /// the given type and which represents how SCEV will treat the given 370 /// type, for which isSCEVable must return true. For pointer types, 371 /// this is the pointer-sized integer type. 372 const Type *getEffectiveSCEVType(const Type *Ty) const; 373 374 /// getSCEV - Return a SCEV expression handle for the full generality of the 375 /// specified expression. 376 SCEVHandle getSCEV(Value *V); 377 378 SCEVHandle getConstant(ConstantInt *V); 379 SCEVHandle getConstant(const APInt& Val); 380 SCEVHandle getTruncateExpr(const SCEVHandle &Op, const Type *Ty); 381 SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty); 382 SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty); 383 SCEVHandle getAddExpr(std::vector<SCEVHandle> &Ops); 384 SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 385 std::vector<SCEVHandle> Ops; 386 Ops.push_back(LHS); 387 Ops.push_back(RHS); 388 return getAddExpr(Ops); 389 } 390 SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1, 391 const SCEVHandle &Op2) { 392 std::vector<SCEVHandle> Ops; 393 Ops.push_back(Op0); 394 Ops.push_back(Op1); 395 Ops.push_back(Op2); 396 return getAddExpr(Ops); 397 } 398 SCEVHandle getMulExpr(std::vector<SCEVHandle> &Ops); 399 SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) { 400 std::vector<SCEVHandle> Ops; 401 Ops.push_back(LHS); 402 Ops.push_back(RHS); 403 return getMulExpr(Ops); 404 } 405 SCEVHandle getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 406 SCEVHandle getAddRecExpr(const SCEVHandle &Start, const SCEVHandle &Step, 407 const Loop *L); 408 SCEVHandle getAddRecExpr(std::vector<SCEVHandle> &Operands, 409 const Loop *L); 410 SCEVHandle getAddRecExpr(const std::vector<SCEVHandle> &Operands, 411 const Loop *L) { 412 std::vector<SCEVHandle> NewOp(Operands); 413 return getAddRecExpr(NewOp, L); 414 } 415 SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 416 SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands); 417 SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS); 418 SCEVHandle getUMaxExpr(std::vector<SCEVHandle> Operands); 419 SCEVHandle getUnknown(Value *V); 420 SCEVHandle getCouldNotCompute(); 421 422 /// getNegativeSCEV - Return the SCEV object corresponding to -V. 423 /// 424 SCEVHandle getNegativeSCEV(const SCEVHandle &V); 425 426 /// getNotSCEV - Return the SCEV object corresponding to ~V. 427 /// 428 SCEVHandle getNotSCEV(const SCEVHandle &V); 429 430 /// getMinusSCEV - Return LHS-RHS. 431 /// 432 SCEVHandle getMinusSCEV(const SCEVHandle &LHS, 433 const SCEVHandle &RHS); 434 435 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion 436 /// of the input value to the specified type. If the type must be 437 /// extended, it is zero extended. 438 SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty); 439 440 /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion 441 /// of the input value to the specified type. If the type must be 442 /// extended, it is sign extended. 443 SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty); 444 445 /// getIntegerSCEV - Given an integer or FP type, create a constant for the 446 /// specified signed integer value and return a SCEV for the constant. 447 SCEVHandle getIntegerSCEV(int Val, const Type *Ty); 448 449 /// hasSCEV - Return true if the SCEV for this value has already been 450 /// computed. 451 bool hasSCEV(Value *V) const; 452 453 /// setSCEV - Insert the specified SCEV into the map of current SCEVs for 454 /// the specified value. 455 void setSCEV(Value *V, const SCEVHandle &H); 456 457 /// getSCEVAtScope - Return a SCEV expression handle for the specified value 458 /// at the specified scope in the program. The L value specifies a loop 459 /// nest to evaluate the expression at, where null is the top-level or a 460 /// specified loop is immediately inside of the loop. 461 /// 462 /// This method can be used to compute the exit value for a variable defined 463 /// in a loop by querying what the value will hold in the parent loop. 464 /// 465 /// If this value is not computable at this scope, a SCEVCouldNotCompute 466 /// object is returned. 467 SCEVHandle getSCEVAtScope(Value *V, const Loop *L); 468 469 /// isLoopGuardedByCond - Test whether entry to the loop is protected by 470 /// a conditional between LHS and RHS. This is used to help avoid max 471 /// expressions in loop trip counts. 472 bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred, 473 const SCEV *LHS, const SCEV *RHS); 474 475 /// getBackedgeTakenCount - If the specified loop has a predictable 476 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute 477 /// object. The backedge-taken count is the number of times the loop header 478 /// will be branched to from within the loop. This is one less than the 479 /// trip count of the loop, since it doesn't count the first iteration, 480 /// when the header is branched to from outside the loop. 481 /// 482 /// Note that it is not valid to call this method on a loop without a 483 /// loop-invariant backedge-taken count (see 484 /// hasLoopInvariantBackedgeTakenCount). 485 /// 486 SCEVHandle getBackedgeTakenCount(const Loop *L); 487 488 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except 489 /// return the least SCEV value that is known never to be less than the 490 /// actual backedge taken count. 491 SCEVHandle getMaxBackedgeTakenCount(const Loop *L); 492 493 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop 494 /// has an analyzable loop-invariant backedge-taken count. 495 bool hasLoopInvariantBackedgeTakenCount(const Loop *L); 496 497 /// forgetLoopBackedgeTakenCount - This method should be called by the 498 /// client when it has changed a loop in a way that may effect 499 /// ScalarEvolution's ability to compute a trip count, or if the loop 500 /// is deleted. 501 void forgetLoopBackedgeTakenCount(const Loop *L); 502 503 virtual bool runOnFunction(Function &F); 504 virtual void releaseMemory(); 505 virtual void getAnalysisUsage(AnalysisUsage &AU) const; 506 void print(raw_ostream &OS, const Module* = 0) const; 507 virtual void print(std::ostream &OS, const Module* = 0) const; 508 void print(std::ostream *OS, const Module* M = 0) const { 509 if (OS) print(*OS, M); 510 } 511 }; 512} 513 514#endif 515