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 // categorize 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/ADT/DenseSet.h" 25 #include "llvm/ADT/FoldingSet.h" 26 #include "llvm/IR/ConstantRange.h" 27 #include "llvm/IR/Function.h" 28 #include "llvm/IR/Instructions.h" 29 #include "llvm/IR/Operator.h" 30 #include "llvm/IR/ValueHandle.h" 31 #include "llvm/Pass.h" 32 #include "llvm/Support/Allocator.h" 33 #include "llvm/Support/DataTypes.h" 34 #include <map> 35 36 namespace llvm { 37 class APInt; 38 class AssumptionCache; 39 class Constant; 40 class ConstantInt; 41 class DominatorTree; 42 class Type; 43 class ScalarEvolution; 44 class DataLayout; 45 class TargetLibraryInfo; 46 class LLVMContext; 47 class Loop; 48 class LoopInfo; 49 class Operator; 50 class SCEVUnknown; 51 class SCEV; 52 template<> struct FoldingSetTrait<SCEV>; 53 54 /// SCEV - This class represents an analyzed expression in the program. These 55 /// are opaque objects that the client is not allowed to do much with 56 /// directly. 57 /// 58 class SCEV : public FoldingSetNode { 59 friend struct FoldingSetTrait<SCEV>; 60 61 /// FastID - A reference to an Interned FoldingSetNodeID for this node. 62 /// The ScalarEvolution's BumpPtrAllocator holds the data. 63 FoldingSetNodeIDRef FastID; 64 65 // The SCEV baseclass this node corresponds to 66 const unsigned short SCEVType; 67 68 protected: 69 /// SubclassData - This field is initialized to zero and may be used in 70 /// subclasses to store miscellaneous information. 71 unsigned short SubclassData; 72 73 private: 74 SCEV(const SCEV &) = delete; 75 void operator=(const SCEV &) = delete; 76 77 public: 78 /// NoWrapFlags are bitfield indices into SubclassData. 79 /// 80 /// Add and Mul expressions may have no-unsigned-wrap <NUW> or 81 /// no-signed-wrap <NSW> properties, which are derived from the IR 82 /// operator. NSW is a misnomer that we use to mean no signed overflow or 83 /// underflow. 84 /// 85 /// AddRec expressions may have a no-self-wraparound <NW> property if, in 86 /// the integer domain, abs(step) * max-iteration(loop) <= 87 /// unsigned-max(bitwidth). This means that the recurrence will never reach 88 /// its start value if the step is non-zero. Computing the same value on 89 /// each iteration is not considered wrapping, and recurrences with step = 0 90 /// are trivially <NW>. <NW> is independent of the sign of step and the 91 /// value the add recurrence starts with. 92 /// 93 /// Note that NUW and NSW are also valid properties of a recurrence, and 94 /// either implies NW. For convenience, NW will be set for a recurrence 95 /// whenever either NUW or NSW are set. 96 enum NoWrapFlags { FlagAnyWrap = 0, // No guarantee. 97 FlagNW = (1 << 0), // No self-wrap. 98 FlagNUW = (1 << 1), // No unsigned wrap. 99 FlagNSW = (1 << 2), // No signed wrap. 100 NoWrapMask = (1 << 3) -1 }; 101 102 explicit SCEV(const FoldingSetNodeIDRef ID, unsigned SCEVTy) : 103 FastID(ID), SCEVType(SCEVTy), SubclassData(0) {} 104 105 unsigned getSCEVType() const { return SCEVType; } 106 107 /// getType - Return the LLVM type of this SCEV expression. 108 /// 109 Type *getType() const; 110 111 /// isZero - Return true if the expression is a constant zero. 112 /// 113 bool isZero() const; 114 115 /// isOne - Return true if the expression is a constant one. 116 /// 117 bool isOne() const; 118 119 /// isAllOnesValue - Return true if the expression is a constant 120 /// all-ones value. 121 /// 122 bool isAllOnesValue() const; 123 124 /// isNonConstantNegative - Return true if the specified scev is negated, 125 /// but not a constant. 126 bool isNonConstantNegative() const; 127 128 /// print - Print out the internal representation of this scalar to the 129 /// specified stream. This should really only be used for debugging 130 /// purposes. 131 void print(raw_ostream &OS) const; 132 133 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP) 134 /// dump - This method is used for debugging. 135 /// 136 void dump() const; 137 #endif 138 }; 139 140 // Specialize FoldingSetTrait for SCEV to avoid needing to compute 141 // temporary FoldingSetNodeID values. 142 template<> struct FoldingSetTrait<SCEV> : DefaultFoldingSetTrait<SCEV> { 143 static void Profile(const SCEV &X, FoldingSetNodeID& ID) { 144 ID = X.FastID; 145 } 146 static bool Equals(const SCEV &X, const FoldingSetNodeID &ID, 147 unsigned IDHash, FoldingSetNodeID &TempID) { 148 return ID == X.FastID; 149 } 150 static unsigned ComputeHash(const SCEV &X, FoldingSetNodeID &TempID) { 151 return X.FastID.ComputeHash(); 152 } 153 }; 154 155 inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) { 156 S.print(OS); 157 return OS; 158 } 159 160 /// SCEVCouldNotCompute - An object of this class is returned by queries that 161 /// could not be answered. For example, if you ask for the number of 162 /// iterations of a linked-list traversal loop, you will get one of these. 163 /// None of the standard SCEV operations are valid on this class, it is just a 164 /// marker. 165 struct SCEVCouldNotCompute : public SCEV { 166 SCEVCouldNotCompute(); 167 168 /// Methods for support type inquiry through isa, cast, and dyn_cast: 169 static bool classof(const SCEV *S); 170 }; 171 172 /// ScalarEvolution - This class is the main scalar evolution driver. Because 173 /// client code (intentionally) can't do much with the SCEV objects directly, 174 /// they must ask this class for services. 175 /// 176 class ScalarEvolution : public FunctionPass { 177 public: 178 /// LoopDisposition - An enum describing the relationship between a 179 /// SCEV and a loop. 180 enum LoopDisposition { 181 LoopVariant, ///< The SCEV is loop-variant (unknown). 182 LoopInvariant, ///< The SCEV is loop-invariant. 183 LoopComputable ///< The SCEV varies predictably with the loop. 184 }; 185 186 /// BlockDisposition - An enum describing the relationship between a 187 /// SCEV and a basic block. 188 enum BlockDisposition { 189 DoesNotDominateBlock, ///< The SCEV does not dominate the block. 190 DominatesBlock, ///< The SCEV dominates the block. 191 ProperlyDominatesBlock ///< The SCEV properly dominates the block. 192 }; 193 194 /// Convenient NoWrapFlags manipulation that hides enum casts and is 195 /// visible in the ScalarEvolution name space. 196 static SCEV::NoWrapFlags LLVM_ATTRIBUTE_UNUSED_RESULT 197 maskFlags(SCEV::NoWrapFlags Flags, int Mask) { 198 return (SCEV::NoWrapFlags)(Flags & Mask); 199 } 200 static SCEV::NoWrapFlags LLVM_ATTRIBUTE_UNUSED_RESULT 201 setFlags(SCEV::NoWrapFlags Flags, SCEV::NoWrapFlags OnFlags) { 202 return (SCEV::NoWrapFlags)(Flags | OnFlags); 203 } 204 static SCEV::NoWrapFlags LLVM_ATTRIBUTE_UNUSED_RESULT 205 clearFlags(SCEV::NoWrapFlags Flags, SCEV::NoWrapFlags OffFlags) { 206 return (SCEV::NoWrapFlags)(Flags & ~OffFlags); 207 } 208 209 private: 210 /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be 211 /// notified whenever a Value is deleted. 212 class SCEVCallbackVH : public CallbackVH { 213 ScalarEvolution *SE; 214 void deleted() override; 215 void allUsesReplacedWith(Value *New) override; 216 public: 217 SCEVCallbackVH(Value *V, ScalarEvolution *SE = nullptr); 218 }; 219 220 friend class SCEVCallbackVH; 221 friend class SCEVExpander; 222 friend class SCEVUnknown; 223 224 /// F - The function we are analyzing. 225 /// 226 Function *F; 227 228 /// The tracker for @llvm.assume intrinsics in this function. 229 AssumptionCache *AC; 230 231 /// LI - The loop information for the function we are currently analyzing. 232 /// 233 LoopInfo *LI; 234 235 /// TLI - The target library information for the target we are targeting. 236 /// 237 TargetLibraryInfo *TLI; 238 239 /// DT - The dominator tree. 240 /// 241 DominatorTree *DT; 242 243 /// CouldNotCompute - This SCEV is used to represent unknown trip 244 /// counts and things. 245 SCEVCouldNotCompute CouldNotCompute; 246 247 /// ValueExprMapType - The typedef for ValueExprMap. 248 /// 249 typedef DenseMap<SCEVCallbackVH, const SCEV *, DenseMapInfo<Value *> > 250 ValueExprMapType; 251 252 /// ValueExprMap - This is a cache of the values we have analyzed so far. 253 /// 254 ValueExprMapType ValueExprMap; 255 256 /// Mark predicate values currently being processed by isImpliedCond. 257 DenseSet<Value*> PendingLoopPredicates; 258 259 /// Set to true by isLoopBackedgeGuardedByCond when we're walking the set of 260 /// conditions dominating the backedge of a loop. 261 bool WalkingBEDominatingConds; 262 263 /// ExitLimit - Information about the number of loop iterations for which a 264 /// loop exit's branch condition evaluates to the not-taken path. This is a 265 /// temporary pair of exact and max expressions that are eventually 266 /// summarized in ExitNotTakenInfo and BackedgeTakenInfo. 267 struct ExitLimit { 268 const SCEV *Exact; 269 const SCEV *Max; 270 271 /*implicit*/ ExitLimit(const SCEV *E) : Exact(E), Max(E) {} 272 273 ExitLimit(const SCEV *E, const SCEV *M) : Exact(E), Max(M) {} 274 275 /// hasAnyInfo - Test whether this ExitLimit contains any computed 276 /// information, or whether it's all SCEVCouldNotCompute values. 277 bool hasAnyInfo() const { 278 return !isa<SCEVCouldNotCompute>(Exact) || 279 !isa<SCEVCouldNotCompute>(Max); 280 } 281 }; 282 283 /// ExitNotTakenInfo - Information about the number of times a particular 284 /// loop exit may be reached before exiting the loop. 285 struct ExitNotTakenInfo { 286 AssertingVH<BasicBlock> ExitingBlock; 287 const SCEV *ExactNotTaken; 288 PointerIntPair<ExitNotTakenInfo*, 1> NextExit; 289 290 ExitNotTakenInfo() : ExitingBlock(nullptr), ExactNotTaken(nullptr) {} 291 292 /// isCompleteList - Return true if all loop exits are computable. 293 bool isCompleteList() const { 294 return NextExit.getInt() == 0; 295 } 296 297 void setIncomplete() { NextExit.setInt(1); } 298 299 /// getNextExit - Return a pointer to the next exit's not-taken info. 300 ExitNotTakenInfo *getNextExit() const { 301 return NextExit.getPointer(); 302 } 303 304 void setNextExit(ExitNotTakenInfo *ENT) { NextExit.setPointer(ENT); } 305 }; 306 307 /// BackedgeTakenInfo - Information about the backedge-taken count 308 /// of a loop. This currently includes an exact count and a maximum count. 309 /// 310 class BackedgeTakenInfo { 311 /// ExitNotTaken - A list of computable exits and their not-taken counts. 312 /// Loops almost never have more than one computable exit. 313 ExitNotTakenInfo ExitNotTaken; 314 315 /// Max - An expression indicating the least maximum backedge-taken 316 /// count of the loop that is known, or a SCEVCouldNotCompute. 317 const SCEV *Max; 318 319 public: 320 BackedgeTakenInfo() : Max(nullptr) {} 321 322 /// Initialize BackedgeTakenInfo from a list of exact exit counts. 323 BackedgeTakenInfo( 324 SmallVectorImpl< std::pair<BasicBlock *, const SCEV *> > &ExitCounts, 325 bool Complete, const SCEV *MaxCount); 326 327 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any 328 /// computed information, or whether it's all SCEVCouldNotCompute 329 /// values. 330 bool hasAnyInfo() const { 331 return ExitNotTaken.ExitingBlock || !isa<SCEVCouldNotCompute>(Max); 332 } 333 334 /// getExact - Return an expression indicating the exact backedge-taken 335 /// count of the loop if it is known, or SCEVCouldNotCompute 336 /// otherwise. This is the number of times the loop header can be 337 /// guaranteed to execute, minus one. 338 const SCEV *getExact(ScalarEvolution *SE) const; 339 340 /// getExact - Return the number of times this loop exit may fall through 341 /// to the back edge, or SCEVCouldNotCompute. The loop is guaranteed not 342 /// to exit via this block before this number of iterations, but may exit 343 /// via another block. 344 const SCEV *getExact(BasicBlock *ExitingBlock, ScalarEvolution *SE) const; 345 346 /// getMax - Get the max backedge taken count for the loop. 347 const SCEV *getMax(ScalarEvolution *SE) const; 348 349 /// Return true if any backedge taken count expressions refer to the given 350 /// subexpression. 351 bool hasOperand(const SCEV *S, ScalarEvolution *SE) const; 352 353 /// clear - Invalidate this result and free associated memory. 354 void clear(); 355 }; 356 357 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for 358 /// this function as they are computed. 359 DenseMap<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts; 360 361 /// ConstantEvolutionLoopExitValue - This map contains entries for all of 362 /// the PHI instructions that we attempt to compute constant evolutions for. 363 /// This allows us to avoid potentially expensive recomputation of these 364 /// properties. An instruction maps to null if we are unable to compute its 365 /// exit value. 366 DenseMap<PHINode*, Constant*> ConstantEvolutionLoopExitValue; 367 368 /// ValuesAtScopes - This map contains entries for all the expressions 369 /// that we attempt to compute getSCEVAtScope information for, which can 370 /// be expensive in extreme cases. 371 DenseMap<const SCEV *, 372 SmallVector<std::pair<const Loop *, const SCEV *>, 2> > ValuesAtScopes; 373 374 /// LoopDispositions - Memoized computeLoopDisposition results. 375 DenseMap<const SCEV *, 376 SmallVector<PointerIntPair<const Loop *, 2, LoopDisposition>, 2>> 377 LoopDispositions; 378 379 /// computeLoopDisposition - Compute a LoopDisposition value. 380 LoopDisposition computeLoopDisposition(const SCEV *S, const Loop *L); 381 382 /// BlockDispositions - Memoized computeBlockDisposition results. 383 DenseMap< 384 const SCEV *, 385 SmallVector<PointerIntPair<const BasicBlock *, 2, BlockDisposition>, 2>> 386 BlockDispositions; 387 388 /// computeBlockDisposition - Compute a BlockDisposition value. 389 BlockDisposition computeBlockDisposition(const SCEV *S, const BasicBlock *BB); 390 391 /// UnsignedRanges - Memoized results from getRange 392 DenseMap<const SCEV *, ConstantRange> UnsignedRanges; 393 394 /// SignedRanges - Memoized results from getRange 395 DenseMap<const SCEV *, ConstantRange> SignedRanges; 396 397 /// RangeSignHint - Used to parameterize getRange 398 enum RangeSignHint { HINT_RANGE_UNSIGNED, HINT_RANGE_SIGNED }; 399 400 /// setRange - Set the memoized range for the given SCEV. 401 const ConstantRange &setRange(const SCEV *S, RangeSignHint Hint, 402 const ConstantRange &CR) { 403 DenseMap<const SCEV *, ConstantRange> &Cache = 404 Hint == HINT_RANGE_UNSIGNED ? UnsignedRanges : SignedRanges; 405 406 std::pair<DenseMap<const SCEV *, ConstantRange>::iterator, bool> Pair = 407 Cache.insert(std::make_pair(S, CR)); 408 if (!Pair.second) 409 Pair.first->second = CR; 410 return Pair.first->second; 411 } 412 413 /// getRange - Determine the range for a particular SCEV. 414 ConstantRange getRange(const SCEV *S, RangeSignHint Hint); 415 416 /// createSCEV - We know that there is no SCEV for the specified value. 417 /// Analyze the expression. 418 const SCEV *createSCEV(Value *V); 419 420 /// createNodeForPHI - Provide the special handling we need to analyze PHI 421 /// SCEVs. 422 const SCEV *createNodeForPHI(PHINode *PN); 423 424 /// createNodeForGEP - Provide the special handling we need to analyze GEP 425 /// SCEVs. 426 const SCEV *createNodeForGEP(GEPOperator *GEP); 427 428 /// computeSCEVAtScope - Implementation code for getSCEVAtScope; called 429 /// at most once for each SCEV+Loop pair. 430 /// 431 const SCEV *computeSCEVAtScope(const SCEV *S, const Loop *L); 432 433 /// ForgetSymbolicValue - This looks up computed SCEV values for all 434 /// instructions that depend on the given instruction and removes them from 435 /// the ValueExprMap map if they reference SymName. This is used during PHI 436 /// resolution. 437 void ForgetSymbolicName(Instruction *I, const SCEV *SymName); 438 439 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given 440 /// loop, lazily computing new values if the loop hasn't been analyzed 441 /// yet. 442 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L); 443 444 /// ComputeBackedgeTakenCount - Compute the number of times the specified 445 /// loop will iterate. 446 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L); 447 448 /// ComputeExitLimit - Compute the number of times the backedge of the 449 /// specified loop will execute if it exits via the specified block. 450 ExitLimit ComputeExitLimit(const Loop *L, BasicBlock *ExitingBlock); 451 452 /// ComputeExitLimitFromCond - Compute the number of times the backedge of 453 /// the specified loop will execute if its exit condition were a conditional 454 /// branch of ExitCond, TBB, and FBB. 455 ExitLimit ComputeExitLimitFromCond(const Loop *L, 456 Value *ExitCond, 457 BasicBlock *TBB, 458 BasicBlock *FBB, 459 bool IsSubExpr); 460 461 /// ComputeExitLimitFromICmp - Compute the number of times the backedge of 462 /// the specified loop will execute if its exit condition were a conditional 463 /// branch of the ICmpInst ExitCond, TBB, and FBB. 464 ExitLimit ComputeExitLimitFromICmp(const Loop *L, 465 ICmpInst *ExitCond, 466 BasicBlock *TBB, 467 BasicBlock *FBB, 468 bool IsSubExpr); 469 470 /// ComputeExitLimitFromSingleExitSwitch - Compute the number of times the 471 /// backedge of the specified loop will execute if its exit condition were a 472 /// switch with a single exiting case to ExitingBB. 473 ExitLimit 474 ComputeExitLimitFromSingleExitSwitch(const Loop *L, SwitchInst *Switch, 475 BasicBlock *ExitingBB, bool IsSubExpr); 476 477 /// ComputeLoadConstantCompareExitLimit - Given an exit condition 478 /// of 'icmp op load X, cst', try to see if we can compute the 479 /// backedge-taken count. 480 ExitLimit ComputeLoadConstantCompareExitLimit(LoadInst *LI, 481 Constant *RHS, 482 const Loop *L, 483 ICmpInst::Predicate p); 484 485 /// ComputeExitCountExhaustively - If the loop is known to execute a 486 /// constant number of times (the condition evolves only from constants), 487 /// try to evaluate a few iterations of the loop until we get the exit 488 /// condition gets a value of ExitWhen (true or false). If we cannot 489 /// evaluate the exit count of the loop, return CouldNotCompute. 490 const SCEV *ComputeExitCountExhaustively(const Loop *L, 491 Value *Cond, 492 bool ExitWhen); 493 494 /// HowFarToZero - Return the number of times an exit condition comparing 495 /// the specified value to zero will execute. If not computable, return 496 /// CouldNotCompute. 497 ExitLimit HowFarToZero(const SCEV *V, const Loop *L, bool IsSubExpr); 498 499 /// HowFarToNonZero - Return the number of times an exit condition checking 500 /// the specified value for nonzero will execute. If not computable, return 501 /// CouldNotCompute. 502 ExitLimit HowFarToNonZero(const SCEV *V, const Loop *L); 503 504 /// HowManyLessThans - Return the number of times an exit condition 505 /// containing the specified less-than comparison will execute. If not 506 /// computable, return CouldNotCompute. isSigned specifies whether the 507 /// less-than is signed. 508 ExitLimit HowManyLessThans(const SCEV *LHS, const SCEV *RHS, 509 const Loop *L, bool isSigned, bool IsSubExpr); 510 ExitLimit HowManyGreaterThans(const SCEV *LHS, const SCEV *RHS, 511 const Loop *L, bool isSigned, bool IsSubExpr); 512 513 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB 514 /// (which may not be an immediate predecessor) which has exactly one 515 /// successor from which BB is reachable, or null if no such block is 516 /// found. 517 std::pair<BasicBlock *, BasicBlock *> 518 getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB); 519 520 /// isImpliedCond - Test whether the condition described by Pred, LHS, and 521 /// RHS is true whenever the given FoundCondValue value evaluates to true. 522 bool isImpliedCond(ICmpInst::Predicate Pred, 523 const SCEV *LHS, const SCEV *RHS, 524 Value *FoundCondValue, 525 bool Inverse); 526 527 /// isImpliedCondOperands - Test whether the condition described by Pred, 528 /// LHS, and RHS is true whenever the condition described by Pred, FoundLHS, 529 /// and FoundRHS is true. 530 bool isImpliedCondOperands(ICmpInst::Predicate Pred, 531 const SCEV *LHS, const SCEV *RHS, 532 const SCEV *FoundLHS, const SCEV *FoundRHS); 533 534 /// isImpliedCondOperandsHelper - Test whether the condition described by 535 /// Pred, LHS, and RHS is true whenever the condition described by Pred, 536 /// FoundLHS, and FoundRHS is true. 537 bool isImpliedCondOperandsHelper(ICmpInst::Predicate Pred, 538 const SCEV *LHS, const SCEV *RHS, 539 const SCEV *FoundLHS, 540 const SCEV *FoundRHS); 541 542 /// isImpliedCondOperandsViaRanges - Test whether the condition described by 543 /// Pred, LHS, and RHS is true whenever the condition described by Pred, 544 /// FoundLHS, and FoundRHS is true. Utility function used by 545 /// isImpliedCondOperands. 546 bool isImpliedCondOperandsViaRanges(ICmpInst::Predicate Pred, 547 const SCEV *LHS, const SCEV *RHS, 548 const SCEV *FoundLHS, 549 const SCEV *FoundRHS); 550 551 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is 552 /// in the header of its containing loop, we know the loop executes a 553 /// constant number of times, and the PHI node is just a recurrence 554 /// involving constants, fold it. 555 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs, 556 const Loop *L); 557 558 /// isKnownPredicateWithRanges - Test if the given expression is known to 559 /// satisfy the condition described by Pred and the known constant ranges 560 /// of LHS and RHS. 561 /// 562 bool isKnownPredicateWithRanges(ICmpInst::Predicate Pred, 563 const SCEV *LHS, const SCEV *RHS); 564 565 /// forgetMemoizedResults - Drop memoized information computed for S. 566 void forgetMemoizedResults(const SCEV *S); 567 568 /// Return false iff given SCEV contains a SCEVUnknown with NULL value- 569 /// pointer. 570 bool checkValidity(const SCEV *S) const; 571 572 // Return true if `ExtendOpTy`({`Start`,+,`Step`}) can be proved to be equal 573 // to {`ExtendOpTy`(`Start`),+,`ExtendOpTy`(`Step`)}. This is equivalent to 574 // proving no signed (resp. unsigned) wrap in {`Start`,+,`Step`} if 575 // `ExtendOpTy` is `SCEVSignExtendExpr` (resp. `SCEVZeroExtendExpr`). 576 // 577 template<typename ExtendOpTy> 578 bool proveNoWrapByVaryingStart(const SCEV *Start, const SCEV *Step, 579 const Loop *L); 580 581 public: 582 static char ID; // Pass identification, replacement for typeid 583 ScalarEvolution(); 584 585 LLVMContext &getContext() const { return F->getContext(); } 586 587 /// isSCEVable - Test if values of the given type are analyzable within 588 /// the SCEV framework. This primarily includes integer types, and it 589 /// can optionally include pointer types if the ScalarEvolution class 590 /// has access to target-specific information. 591 bool isSCEVable(Type *Ty) const; 592 593 /// getTypeSizeInBits - Return the size in bits of the specified type, 594 /// for which isSCEVable must return true. 595 uint64_t getTypeSizeInBits(Type *Ty) const; 596 597 /// getEffectiveSCEVType - Return a type with the same bitwidth as 598 /// the given type and which represents how SCEV will treat the given 599 /// type, for which isSCEVable must return true. For pointer types, 600 /// this is the pointer-sized integer type. 601 Type *getEffectiveSCEVType(Type *Ty) const; 602 603 /// getSCEV - Return a SCEV expression for the full generality of the 604 /// specified expression. 605 const SCEV *getSCEV(Value *V); 606 607 const SCEV *getConstant(ConstantInt *V); 608 const SCEV *getConstant(const APInt& Val); 609 const SCEV *getConstant(Type *Ty, uint64_t V, bool isSigned = false); 610 const SCEV *getTruncateExpr(const SCEV *Op, Type *Ty); 611 const SCEV *getZeroExtendExpr(const SCEV *Op, Type *Ty); 612 const SCEV *getSignExtendExpr(const SCEV *Op, Type *Ty); 613 const SCEV *getAnyExtendExpr(const SCEV *Op, Type *Ty); 614 const SCEV *getAddExpr(SmallVectorImpl<const SCEV *> &Ops, 615 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap); 616 const SCEV *getAddExpr(const SCEV *LHS, const SCEV *RHS, 617 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap) { 618 SmallVector<const SCEV *, 2> Ops; 619 Ops.push_back(LHS); 620 Ops.push_back(RHS); 621 return getAddExpr(Ops, Flags); 622 } 623 const SCEV *getAddExpr(const SCEV *Op0, const SCEV *Op1, const SCEV *Op2, 624 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap) { 625 SmallVector<const SCEV *, 3> Ops; 626 Ops.push_back(Op0); 627 Ops.push_back(Op1); 628 Ops.push_back(Op2); 629 return getAddExpr(Ops, Flags); 630 } 631 const SCEV *getMulExpr(SmallVectorImpl<const SCEV *> &Ops, 632 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap); 633 const SCEV *getMulExpr(const SCEV *LHS, const SCEV *RHS, 634 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap) 635 { 636 SmallVector<const SCEV *, 2> Ops; 637 Ops.push_back(LHS); 638 Ops.push_back(RHS); 639 return getMulExpr(Ops, Flags); 640 } 641 const SCEV *getMulExpr(const SCEV *Op0, const SCEV *Op1, const SCEV *Op2, 642 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap) { 643 SmallVector<const SCEV *, 3> Ops; 644 Ops.push_back(Op0); 645 Ops.push_back(Op1); 646 Ops.push_back(Op2); 647 return getMulExpr(Ops, Flags); 648 } 649 const SCEV *getUDivExpr(const SCEV *LHS, const SCEV *RHS); 650 const SCEV *getUDivExactExpr(const SCEV *LHS, const SCEV *RHS); 651 const SCEV *getAddRecExpr(const SCEV *Start, const SCEV *Step, 652 const Loop *L, SCEV::NoWrapFlags Flags); 653 const SCEV *getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands, 654 const Loop *L, SCEV::NoWrapFlags Flags); 655 const SCEV *getAddRecExpr(const SmallVectorImpl<const SCEV *> &Operands, 656 const Loop *L, SCEV::NoWrapFlags Flags) { 657 SmallVector<const SCEV *, 4> NewOp(Operands.begin(), Operands.end()); 658 return getAddRecExpr(NewOp, L, Flags); 659 } 660 const SCEV *getSMaxExpr(const SCEV *LHS, const SCEV *RHS); 661 const SCEV *getSMaxExpr(SmallVectorImpl<const SCEV *> &Operands); 662 const SCEV *getUMaxExpr(const SCEV *LHS, const SCEV *RHS); 663 const SCEV *getUMaxExpr(SmallVectorImpl<const SCEV *> &Operands); 664 const SCEV *getSMinExpr(const SCEV *LHS, const SCEV *RHS); 665 const SCEV *getUMinExpr(const SCEV *LHS, const SCEV *RHS); 666 const SCEV *getUnknown(Value *V); 667 const SCEV *getCouldNotCompute(); 668 669 /// getSizeOfExpr - Return an expression for sizeof AllocTy that is type 670 /// IntTy 671 /// 672 const SCEV *getSizeOfExpr(Type *IntTy, Type *AllocTy); 673 674 /// getOffsetOfExpr - Return an expression for offsetof on the given field 675 /// with type IntTy 676 /// 677 const SCEV *getOffsetOfExpr(Type *IntTy, StructType *STy, unsigned FieldNo); 678 679 /// getNegativeSCEV - Return the SCEV object corresponding to -V. 680 /// 681 const SCEV *getNegativeSCEV(const SCEV *V); 682 683 /// getNotSCEV - Return the SCEV object corresponding to ~V. 684 /// 685 const SCEV *getNotSCEV(const SCEV *V); 686 687 /// getMinusSCEV - Return LHS-RHS. Minus is represented in SCEV as A+B*-1. 688 const SCEV *getMinusSCEV(const SCEV *LHS, const SCEV *RHS, 689 SCEV::NoWrapFlags Flags = SCEV::FlagAnyWrap); 690 691 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion 692 /// of the input value to the specified type. If the type must be 693 /// extended, it is zero extended. 694 const SCEV *getTruncateOrZeroExtend(const SCEV *V, Type *Ty); 695 696 /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion 697 /// of the input value to the specified type. If the type must be 698 /// extended, it is sign extended. 699 const SCEV *getTruncateOrSignExtend(const SCEV *V, Type *Ty); 700 701 /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of 702 /// the input value to the specified type. If the type must be extended, 703 /// it is zero extended. The conversion must not be narrowing. 704 const SCEV *getNoopOrZeroExtend(const SCEV *V, Type *Ty); 705 706 /// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of 707 /// the input value to the specified type. If the type must be extended, 708 /// it is sign extended. The conversion must not be narrowing. 709 const SCEV *getNoopOrSignExtend(const SCEV *V, Type *Ty); 710 711 /// getNoopOrAnyExtend - Return a SCEV corresponding to a conversion of 712 /// the input value to the specified type. If the type must be extended, 713 /// it is extended with unspecified bits. The conversion must not be 714 /// narrowing. 715 const SCEV *getNoopOrAnyExtend(const SCEV *V, Type *Ty); 716 717 /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the 718 /// input value to the specified type. The conversion must not be 719 /// widening. 720 const SCEV *getTruncateOrNoop(const SCEV *V, Type *Ty); 721 722 /// getUMaxFromMismatchedTypes - Promote the operands to the wider of 723 /// the types using zero-extension, and then perform a umax operation 724 /// with them. 725 const SCEV *getUMaxFromMismatchedTypes(const SCEV *LHS, 726 const SCEV *RHS); 727 728 /// getUMinFromMismatchedTypes - Promote the operands to the wider of 729 /// the types using zero-extension, and then perform a umin operation 730 /// with them. 731 const SCEV *getUMinFromMismatchedTypes(const SCEV *LHS, 732 const SCEV *RHS); 733 734 /// getPointerBase - Transitively follow the chain of pointer-type operands 735 /// until reaching a SCEV that does not have a single pointer operand. This 736 /// returns a SCEVUnknown pointer for well-formed pointer-type expressions, 737 /// but corner cases do exist. 738 const SCEV *getPointerBase(const SCEV *V); 739 740 /// getSCEVAtScope - Return a SCEV expression for the specified value 741 /// at the specified scope in the program. The L value specifies a loop 742 /// nest to evaluate the expression at, where null is the top-level or a 743 /// specified loop is immediately inside of the loop. 744 /// 745 /// This method can be used to compute the exit value for a variable defined 746 /// in a loop by querying what the value will hold in the parent loop. 747 /// 748 /// In the case that a relevant loop exit value cannot be computed, the 749 /// original value V is returned. 750 const SCEV *getSCEVAtScope(const SCEV *S, const Loop *L); 751 752 /// getSCEVAtScope - This is a convenience function which does 753 /// getSCEVAtScope(getSCEV(V), L). 754 const SCEV *getSCEVAtScope(Value *V, const Loop *L); 755 756 /// isLoopEntryGuardedByCond - Test whether entry to the loop is protected 757 /// by a conditional between LHS and RHS. This is used to help avoid max 758 /// expressions in loop trip counts, and to eliminate casts. 759 bool isLoopEntryGuardedByCond(const Loop *L, ICmpInst::Predicate Pred, 760 const SCEV *LHS, const SCEV *RHS); 761 762 /// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is 763 /// protected by a conditional between LHS and RHS. This is used to 764 /// to eliminate casts. 765 bool isLoopBackedgeGuardedByCond(const Loop *L, ICmpInst::Predicate Pred, 766 const SCEV *LHS, const SCEV *RHS); 767 768 /// \brief Returns the maximum trip count of the loop if it is a single-exit 769 /// loop and we can compute a small maximum for that loop. 770 /// 771 /// Implemented in terms of the \c getSmallConstantTripCount overload with 772 /// the single exiting block passed to it. See that routine for details. 773 unsigned getSmallConstantTripCount(Loop *L); 774 775 /// getSmallConstantTripCount - Returns the maximum trip count of this loop 776 /// as a normal unsigned value. Returns 0 if the trip count is unknown or 777 /// not constant. This "trip count" assumes that control exits via 778 /// ExitingBlock. More precisely, it is the number of times that control may 779 /// reach ExitingBlock before taking the branch. For loops with multiple 780 /// exits, it may not be the number times that the loop header executes if 781 /// the loop exits prematurely via another branch. 782 unsigned getSmallConstantTripCount(Loop *L, BasicBlock *ExitingBlock); 783 784 /// \brief Returns the largest constant divisor of the trip count of the 785 /// loop if it is a single-exit loop and we can compute a small maximum for 786 /// that loop. 787 /// 788 /// Implemented in terms of the \c getSmallConstantTripMultiple overload with 789 /// the single exiting block passed to it. See that routine for details. 790 unsigned getSmallConstantTripMultiple(Loop *L); 791 792 /// getSmallConstantTripMultiple - Returns the largest constant divisor of 793 /// the trip count of this loop as a normal unsigned value, if 794 /// possible. This means that the actual trip count is always a multiple of 795 /// the returned value (don't forget the trip count could very well be zero 796 /// as well!). As explained in the comments for getSmallConstantTripCount, 797 /// this assumes that control exits the loop via ExitingBlock. 798 unsigned getSmallConstantTripMultiple(Loop *L, BasicBlock *ExitingBlock); 799 800 // getExitCount - Get the expression for the number of loop iterations for 801 // which this loop is guaranteed not to exit via ExitingBlock. Otherwise 802 // return SCEVCouldNotCompute. 803 const SCEV *getExitCount(Loop *L, BasicBlock *ExitingBlock); 804 805 /// getBackedgeTakenCount - If the specified loop has a predictable 806 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute 807 /// object. The backedge-taken count is the number of times the loop header 808 /// will be branched to from within the loop. This is one less than the 809 /// trip count of the loop, since it doesn't count the first iteration, 810 /// when the header is branched to from outside the loop. 811 /// 812 /// Note that it is not valid to call this method on a loop without a 813 /// loop-invariant backedge-taken count (see 814 /// hasLoopInvariantBackedgeTakenCount). 815 /// 816 const SCEV *getBackedgeTakenCount(const Loop *L); 817 818 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except 819 /// return the least SCEV value that is known never to be less than the 820 /// actual backedge taken count. 821 const SCEV *getMaxBackedgeTakenCount(const Loop *L); 822 823 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop 824 /// has an analyzable loop-invariant backedge-taken count. 825 bool hasLoopInvariantBackedgeTakenCount(const Loop *L); 826 827 /// forgetLoop - This method should be called by the client when it has 828 /// changed a loop in a way that may effect ScalarEvolution's ability to 829 /// compute a trip count, or if the loop is deleted. This call is 830 /// potentially expensive for large loop bodies. 831 void forgetLoop(const Loop *L); 832 833 /// forgetValue - This method should be called by the client when it has 834 /// changed a value in a way that may effect its value, or which may 835 /// disconnect it from a def-use chain linking it to a loop. 836 void forgetValue(Value *V); 837 838 /// \brief Called when the client has changed the disposition of values in 839 /// this loop. 840 /// 841 /// We don't have a way to invalidate per-loop dispositions. Clear and 842 /// recompute is simpler. 843 void forgetLoopDispositions(const Loop *L) { LoopDispositions.clear(); } 844 845 /// GetMinTrailingZeros - Determine the minimum number of zero bits that S 846 /// is guaranteed to end in (at every loop iteration). It is, at the same 847 /// time, the minimum number of times S is divisible by 2. For example, 848 /// given {4,+,8} it returns 2. If S is guaranteed to be 0, it returns the 849 /// bitwidth of S. 850 uint32_t GetMinTrailingZeros(const SCEV *S); 851 852 /// getUnsignedRange - Determine the unsigned range for a particular SCEV. 853 /// 854 ConstantRange getUnsignedRange(const SCEV *S) { 855 return getRange(S, HINT_RANGE_UNSIGNED); 856 } 857 858 /// getSignedRange - Determine the signed range for a particular SCEV. 859 /// 860 ConstantRange getSignedRange(const SCEV *S) { 861 return getRange(S, HINT_RANGE_SIGNED); 862 } 863 864 /// isKnownNegative - Test if the given expression is known to be negative. 865 /// 866 bool isKnownNegative(const SCEV *S); 867 868 /// isKnownPositive - Test if the given expression is known to be positive. 869 /// 870 bool isKnownPositive(const SCEV *S); 871 872 /// isKnownNonNegative - Test if the given expression is known to be 873 /// non-negative. 874 /// 875 bool isKnownNonNegative(const SCEV *S); 876 877 /// isKnownNonPositive - Test if the given expression is known to be 878 /// non-positive. 879 /// 880 bool isKnownNonPositive(const SCEV *S); 881 882 /// isKnownNonZero - Test if the given expression is known to be 883 /// non-zero. 884 /// 885 bool isKnownNonZero(const SCEV *S); 886 887 /// isKnownPredicate - Test if the given expression is known to satisfy 888 /// the condition described by Pred, LHS, and RHS. 889 /// 890 bool isKnownPredicate(ICmpInst::Predicate Pred, 891 const SCEV *LHS, const SCEV *RHS); 892 893 /// SimplifyICmpOperands - Simplify LHS and RHS in a comparison with 894 /// predicate Pred. Return true iff any changes were made. If the 895 /// operands are provably equal or unequal, LHS and RHS are set to 896 /// the same value and Pred is set to either ICMP_EQ or ICMP_NE. 897 /// 898 bool SimplifyICmpOperands(ICmpInst::Predicate &Pred, 899 const SCEV *&LHS, 900 const SCEV *&RHS, 901 unsigned Depth = 0); 902 903 /// getLoopDisposition - Return the "disposition" of the given SCEV with 904 /// respect to the given loop. 905 LoopDisposition getLoopDisposition(const SCEV *S, const Loop *L); 906 907 /// isLoopInvariant - Return true if the value of the given SCEV is 908 /// unchanging in the specified loop. 909 bool isLoopInvariant(const SCEV *S, const Loop *L); 910 911 /// hasComputableLoopEvolution - Return true if the given SCEV changes value 912 /// in a known way in the specified loop. This property being true implies 913 /// that the value is variant in the loop AND that we can emit an expression 914 /// to compute the value of the expression at any particular loop iteration. 915 bool hasComputableLoopEvolution(const SCEV *S, const Loop *L); 916 917 /// getLoopDisposition - Return the "disposition" of the given SCEV with 918 /// respect to the given block. 919 BlockDisposition getBlockDisposition(const SCEV *S, const BasicBlock *BB); 920 921 /// dominates - Return true if elements that makes up the given SCEV 922 /// dominate the specified basic block. 923 bool dominates(const SCEV *S, const BasicBlock *BB); 924 925 /// properlyDominates - Return true if elements that makes up the given SCEV 926 /// properly dominate the specified basic block. 927 bool properlyDominates(const SCEV *S, const BasicBlock *BB); 928 929 /// hasOperand - Test whether the given SCEV has Op as a direct or 930 /// indirect operand. 931 bool hasOperand(const SCEV *S, const SCEV *Op) const; 932 933 /// Return the size of an element read or written by Inst. 934 const SCEV *getElementSize(Instruction *Inst); 935 936 /// Compute the array dimensions Sizes from the set of Terms extracted from 937 /// the memory access function of this SCEVAddRecExpr. 938 void findArrayDimensions(SmallVectorImpl<const SCEV *> &Terms, 939 SmallVectorImpl<const SCEV *> &Sizes, 940 const SCEV *ElementSize) const; 941 942 bool runOnFunction(Function &F) override; 943 void releaseMemory() override; 944 void getAnalysisUsage(AnalysisUsage &AU) const override; 945 void print(raw_ostream &OS, const Module* = nullptr) const override; 946 void verifyAnalysis() const override; 947 948 private: 949 /// Compute the backedge taken count knowing the interval difference, the 950 /// stride and presence of the equality in the comparison. 951 const SCEV *computeBECount(const SCEV *Delta, const SCEV *Stride, 952 bool Equality); 953 954 /// Verify if an linear IV with positive stride can overflow when in a 955 /// less-than comparison, knowing the invariant term of the comparison, 956 /// the stride and the knowledge of NSW/NUW flags on the recurrence. 957 bool doesIVOverflowOnLT(const SCEV *RHS, const SCEV *Stride, 958 bool IsSigned, bool NoWrap); 959 960 /// Verify if an linear IV with negative stride can overflow when in a 961 /// greater-than comparison, knowing the invariant term of the comparison, 962 /// the stride and the knowledge of NSW/NUW flags on the recurrence. 963 bool doesIVOverflowOnGT(const SCEV *RHS, const SCEV *Stride, 964 bool IsSigned, bool NoWrap); 965 966 private: 967 FoldingSet<SCEV> UniqueSCEVs; 968 BumpPtrAllocator SCEVAllocator; 969 970 /// FirstUnknown - The head of a linked list of all SCEVUnknown 971 /// values that have been allocated. This is used by releaseMemory 972 /// to locate them all and call their destructors. 973 SCEVUnknown *FirstUnknown; 974 }; 975 } 976 977 #endif 978
