1 //===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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.
16 // This analysis is primarily useful for induction variable substitution and
17 // strength reduction.
19 //===----------------------------------------------------------------------===//
21 #ifndef LLVM_ANALYSIS_SCALAREVOLUTION_H
22 #define LLVM_ANALYSIS_SCALAREVOLUTION_H
24 #include "llvm/Pass.h"
25 #include "llvm/Instructions.h"
26 #include "llvm/Support/DataTypes.h"
27 #include "llvm/Support/ValueHandle.h"
28 #include "llvm/Support/Allocator.h"
29 #include "llvm/Support/ConstantRange.h"
30 #include "llvm/ADT/FoldingSet.h"
31 #include "llvm/ADT/DenseMap.h"
41 class ScalarEvolution;
47 /// SCEV - This class represents an analyzed expression in the program. These
48 /// are opaque objects that the client is not allowed to do much with
51 class SCEV : public FastFoldingSetNode {
52 const unsigned SCEVType; // The SCEV baseclass this node corresponds to
54 SCEV(const SCEV &); // DO NOT IMPLEMENT
55 void operator=(const SCEV &); // DO NOT IMPLEMENT
59 explicit SCEV(const FoldingSetNodeID &ID, unsigned SCEVTy) :
60 FastFoldingSetNode(ID), SCEVType(SCEVTy) {}
62 unsigned getSCEVType() const { return SCEVType; }
64 /// isLoopInvariant - Return true if the value of this SCEV is unchanging in
65 /// the specified loop.
66 virtual bool isLoopInvariant(const Loop *L) const = 0;
68 /// hasComputableLoopEvolution - Return true if this SCEV changes value in a
69 /// known way in the specified loop. This property being true implies that
70 /// the value is variant in the loop AND that we can emit an expression to
71 /// compute the value of the expression at any particular loop iteration.
72 virtual bool hasComputableLoopEvolution(const Loop *L) const = 0;
74 /// getType - Return the LLVM type of this SCEV expression.
76 virtual const Type *getType() const = 0;
78 /// isZero - Return true if the expression is a constant zero.
82 /// isOne - Return true if the expression is a constant one.
86 /// isAllOnesValue - Return true if the expression is a constant
89 bool isAllOnesValue() const;
91 /// replaceSymbolicValuesWithConcrete - If this SCEV internally references
92 /// the symbolic value "Sym", construct and return a new SCEV that produces
93 /// the same value, but which uses the concrete value Conc instead of the
94 /// symbolic value. If this SCEV does not use the symbolic value, it
97 replaceSymbolicValuesWithConcrete(const SCEV *Sym,
99 ScalarEvolution &SE) const = 0;
101 /// dominates - Return true if elements that makes up this SCEV dominates
102 /// the specified basic block.
103 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const = 0;
105 /// print - Print out the internal representation of this scalar to the
106 /// specified stream. This should really only be used for debugging
108 virtual void print(raw_ostream &OS) const = 0;
109 void print(std::ostream &OS) const;
110 void print(std::ostream *OS) const { if (OS) print(*OS); }
112 /// dump - This method is used for debugging.
117 inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) {
122 inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
127 /// SCEVCouldNotCompute - An object of this class is returned by queries that
128 /// could not be answered. For example, if you ask for the number of
129 /// iterations of a linked-list traversal loop, you will get one of these.
130 /// None of the standard SCEV operations are valid on this class, it is just a
132 struct SCEVCouldNotCompute : public SCEV {
133 SCEVCouldNotCompute();
135 // None of these methods are valid for this object.
136 virtual bool isLoopInvariant(const Loop *L) const;
137 virtual const Type *getType() const;
138 virtual bool hasComputableLoopEvolution(const Loop *L) const;
139 virtual void print(raw_ostream &OS) const;
141 replaceSymbolicValuesWithConcrete(const SCEV *Sym,
143 ScalarEvolution &SE) const;
145 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const {
149 /// Methods for support type inquiry through isa, cast, and dyn_cast:
150 static inline bool classof(const SCEVCouldNotCompute *S) { return true; }
151 static bool classof(const SCEV *S);
154 /// ScalarEvolution - This class is the main scalar evolution driver. Because
155 /// client code (intentionally) can't do much with the SCEV objects directly,
156 /// they must ask this class for services.
158 class ScalarEvolution : public FunctionPass {
159 /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be
160 /// notified whenever a Value is deleted.
161 class SCEVCallbackVH : public CallbackVH {
163 virtual void deleted();
164 virtual void allUsesReplacedWith(Value *New);
166 SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0);
169 friend class SCEVCallbackVH;
170 friend struct SCEVExpander;
172 /// F - The function we are analyzing.
176 /// LI - The loop information for the function we are currently analyzing.
180 /// TD - The target data information for the target we are targetting.
184 /// CouldNotCompute - This SCEV is used to represent unknown trip
185 /// counts and things.
186 SCEVCouldNotCompute CouldNotCompute;
188 /// Scalars - This is a cache of the scalars we have analyzed so far.
190 std::map<SCEVCallbackVH, const SCEV *> Scalars;
192 /// BackedgeTakenInfo - Information about the backedge-taken count
193 /// of a loop. This currently inclues an exact count and a maximum count.
195 struct BackedgeTakenInfo {
196 /// Exact - An expression indicating the exact backedge-taken count of
197 /// the loop if it is known, or a SCEVCouldNotCompute otherwise.
200 /// Max - An expression indicating the least maximum backedge-taken
201 /// count of the loop that is known, or a SCEVCouldNotCompute.
204 /*implicit*/ BackedgeTakenInfo(const SCEV *exact) :
205 Exact(exact), Max(exact) {}
207 BackedgeTakenInfo(const SCEV *exact, const SCEV *max) :
208 Exact(exact), Max(max) {}
210 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any
211 /// computed information, or whether it's all SCEVCouldNotCompute
213 bool hasAnyInfo() const {
214 return !isa<SCEVCouldNotCompute>(Exact) ||
215 !isa<SCEVCouldNotCompute>(Max);
219 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
220 /// this function as they are computed.
221 std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts;
223 /// ConstantEvolutionLoopExitValue - This map contains entries for all of
224 /// the PHI instructions that we attempt to compute constant evolutions for.
225 /// This allows us to avoid potentially expensive recomputation of these
226 /// properties. An instruction maps to null if we are unable to compute its
228 std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue;
230 /// ValuesAtScopes - This map contains entries for all the instructions
231 /// that we attempt to compute getSCEVAtScope information for without
232 /// using SCEV techniques, which can be expensive.
233 std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes;
235 /// createSCEV - We know that there is no SCEV for the specified value.
236 /// Analyze the expression.
237 const SCEV *createSCEV(Value *V);
239 /// createNodeForPHI - Provide the special handling we need to analyze PHI
241 const SCEV *createNodeForPHI(PHINode *PN);
243 /// createNodeForGEP - Provide the special handling we need to analyze GEP
245 const SCEV *createNodeForGEP(User *GEP);
247 /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value
248 /// for the specified instruction and replaces any references to the
249 /// symbolic value SymName with the specified value. This is used during
251 void ReplaceSymbolicValueWithConcrete(Instruction *I,
255 /// getBECount - Subtract the end and start values and divide by the step,
256 /// rounding up, to get the number of times the backedge is executed. Return
257 /// CouldNotCompute if an intermediate computation overflows.
258 const SCEV *getBECount(const SCEV *Start,
262 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
263 /// loop, lazily computing new values if the loop hasn't been analyzed
265 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L);
267 /// ComputeBackedgeTakenCount - Compute the number of times the specified
268 /// loop will iterate.
269 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L);
271 /// ComputeBackedgeTakenCountFromExit - Compute the number of times the
272 /// backedge of the specified loop will execute if it exits via the
274 BackedgeTakenInfo ComputeBackedgeTakenCountFromExit(const Loop *L,
275 BasicBlock *ExitingBlock);
277 /// ComputeBackedgeTakenCountFromExitCond - Compute the number of times the
278 /// backedge of the specified loop will execute if its exit condition
279 /// were a conditional branch of ExitCond, TBB, and FBB.
281 ComputeBackedgeTakenCountFromExitCond(const Loop *L,
286 /// ComputeBackedgeTakenCountFromExitCondICmp - Compute the number of
287 /// times the backedge of the specified loop will execute if its exit
288 /// condition were a conditional branch of the ICmpInst ExitCond, TBB,
291 ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
296 /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
297 /// of 'icmp op load X, cst', try to see if we can compute the trip count.
299 ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
302 ICmpInst::Predicate p);
304 /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute
305 /// a constant number of times (the condition evolves only from constants),
306 /// try to evaluate a few iterations of the loop until we get the exit
307 /// condition gets a value of ExitWhen (true or false). If we cannot
308 /// evaluate the trip count of the loop, return CouldNotCompute.
309 const SCEV *ComputeBackedgeTakenCountExhaustively(const Loop *L,
313 /// HowFarToZero - Return the number of times a backedge comparing the
314 /// specified value to zero will execute. If not computable, return
316 const SCEV *HowFarToZero(const SCEV *V, const Loop *L);
318 /// HowFarToNonZero - Return the number of times a backedge checking the
319 /// specified value for nonzero will execute. If not computable, return
321 const SCEV *HowFarToNonZero(const SCEV *V, const Loop *L);
323 /// HowManyLessThans - Return the number of times a backedge containing the
324 /// specified less-than comparison will execute. If not computable, return
325 /// CouldNotCompute. isSigned specifies whether the less-than is signed.
326 BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
327 const Loop *L, bool isSigned);
329 /// getLoopPredecessor - If the given loop's header has exactly one unique
330 /// predecessor outside the loop, return it. Otherwise return null.
331 BasicBlock *getLoopPredecessor(const Loop *L);
333 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB
334 /// (which may not be an immediate predecessor) which has exactly one
335 /// successor from which BB is reachable, or null if no such block is
337 BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB);
339 /// isNecessaryCond - Test whether the condition described by Pred, LHS,
340 /// and RHS is a necessary condition for the given Cond value to evaluate
342 bool isNecessaryCond(Value *Cond, ICmpInst::Predicate Pred,
343 const SCEV *LHS, const SCEV *RHS,
346 /// isNecessaryCondOperands - Test whether the condition described by Pred,
347 /// LHS, and RHS is a necessary condition for the condition described by
348 /// Pred, FoundLHS, and FoundRHS to evaluate to true.
349 bool isNecessaryCondOperands(ICmpInst::Predicate Pred,
350 const SCEV *LHS, const SCEV *RHS,
351 const SCEV *FoundLHS, const SCEV *FoundRHS);
353 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
354 /// in the header of its containing loop, we know the loop executes a
355 /// constant number of times, and the PHI node is just a recurrence
356 /// involving constants, fold it.
357 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
361 static char ID; // Pass identification, replacement for typeid
364 LLVMContext *getContext() const { return Context; }
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;
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;
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;
382 /// getSCEV - Return a SCEV expression handle for the full generality of the
383 /// specified expression.
384 const SCEV *getSCEV(Value *V);
386 const SCEV *getConstant(ConstantInt *V);
387 const SCEV *getConstant(const APInt& Val);
388 const SCEV *getConstant(const Type *Ty, uint64_t V, bool isSigned = false);
389 const SCEV *getTruncateExpr(const SCEV *Op, const Type *Ty);
390 const SCEV *getZeroExtendExpr(const SCEV *Op, const Type *Ty);
391 const SCEV *getSignExtendExpr(const SCEV *Op, const Type *Ty);
392 const SCEV *getAnyExtendExpr(const SCEV *Op, const Type *Ty);
393 const SCEV *getAddExpr(SmallVectorImpl<const SCEV *> &Ops);
394 const SCEV *getAddExpr(const SCEV *LHS, const SCEV *RHS) {
395 SmallVector<const SCEV *, 2> Ops;
398 return getAddExpr(Ops);
400 const SCEV *getAddExpr(const SCEV *Op0, const SCEV *Op1,
402 SmallVector<const SCEV *, 3> Ops;
406 return getAddExpr(Ops);
408 const SCEV *getMulExpr(SmallVectorImpl<const SCEV *> &Ops);
409 const SCEV *getMulExpr(const SCEV *LHS, const SCEV *RHS) {
410 SmallVector<const SCEV *, 2> Ops;
413 return getMulExpr(Ops);
415 const SCEV *getUDivExpr(const SCEV *LHS, const SCEV *RHS);
416 const SCEV *getAddRecExpr(const SCEV *Start, const SCEV *Step,
418 const SCEV *getAddRecExpr(SmallVectorImpl<const SCEV *> &Operands,
420 const SCEV *getAddRecExpr(const SmallVectorImpl<const SCEV *> &Operands,
422 SmallVector<const SCEV *, 4> NewOp(Operands.begin(), Operands.end());
423 return getAddRecExpr(NewOp, L);
425 const SCEV *getSMaxExpr(const SCEV *LHS, const SCEV *RHS);
426 const SCEV *getSMaxExpr(SmallVectorImpl<const SCEV *> &Operands);
427 const SCEV *getUMaxExpr(const SCEV *LHS, const SCEV *RHS);
428 const SCEV *getUMaxExpr(SmallVectorImpl<const SCEV *> &Operands);
429 const SCEV *getSMinExpr(const SCEV *LHS, const SCEV *RHS);
430 const SCEV *getUMinExpr(const SCEV *LHS, const SCEV *RHS);
431 const SCEV *getUnknown(Value *V);
432 const SCEV *getCouldNotCompute();
434 /// getNegativeSCEV - Return the SCEV object corresponding to -V.
436 const SCEV *getNegativeSCEV(const SCEV *V);
438 /// getNotSCEV - Return the SCEV object corresponding to ~V.
440 const SCEV *getNotSCEV(const SCEV *V);
442 /// getMinusSCEV - Return LHS-RHS.
444 const SCEV *getMinusSCEV(const SCEV *LHS,
447 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion
448 /// of the input value to the specified type. If the type must be
449 /// extended, it is zero extended.
450 const SCEV *getTruncateOrZeroExtend(const SCEV *V, const Type *Ty);
452 /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
453 /// of the input value to the specified type. If the type must be
454 /// extended, it is sign extended.
455 const SCEV *getTruncateOrSignExtend(const SCEV *V, const Type *Ty);
457 /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of
458 /// the input value to the specified type. If the type must be extended,
459 /// it is zero extended. The conversion must not be narrowing.
460 const SCEV *getNoopOrZeroExtend(const SCEV *V, const Type *Ty);
462 /// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of
463 /// the input value to the specified type. If the type must be extended,
464 /// it is sign extended. The conversion must not be narrowing.
465 const SCEV *getNoopOrSignExtend(const SCEV *V, const Type *Ty);
467 /// getNoopOrAnyExtend - Return a SCEV corresponding to a conversion of
468 /// the input value to the specified type. If the type must be extended,
469 /// it is extended with unspecified bits. The conversion must not be
471 const SCEV *getNoopOrAnyExtend(const SCEV *V, const Type *Ty);
473 /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the
474 /// input value to the specified type. The conversion must not be
476 const SCEV *getTruncateOrNoop(const SCEV *V, const Type *Ty);
478 /// getIntegerSCEV - Given a SCEVable type, create a constant for the
479 /// specified signed integer value and return a SCEV for the constant.
480 const SCEV *getIntegerSCEV(int Val, const Type *Ty);
482 /// getUMaxFromMismatchedTypes - Promote the operands to the wider of
483 /// the types using zero-extension, and then perform a umax operation
485 const SCEV *getUMaxFromMismatchedTypes(const SCEV *LHS,
488 /// getUMinFromMismatchedTypes - Promote the operands to the wider of
489 /// the types using zero-extension, and then perform a umin operation
491 const SCEV *getUMinFromMismatchedTypes(const SCEV *LHS,
494 /// getSCEVAtScope - Return a SCEV expression handle for the specified value
495 /// at the specified scope in the program. The L value specifies a loop
496 /// nest to evaluate the expression at, where null is the top-level or a
497 /// specified loop is immediately inside of the loop.
499 /// This method can be used to compute the exit value for a variable defined
500 /// in a loop by querying what the value will hold in the parent loop.
502 /// In the case that a relevant loop exit value cannot be computed, the
503 /// original value V is returned.
504 const SCEV *getSCEVAtScope(const SCEV *S, const Loop *L);
506 /// getSCEVAtScope - This is a convenience function which does
507 /// getSCEVAtScope(getSCEV(V), L).
508 const SCEV *getSCEVAtScope(Value *V, const Loop *L);
510 /// isLoopGuardedByCond - Test whether entry to the loop is protected by
511 /// a conditional between LHS and RHS. This is used to help avoid max
512 /// expressions in loop trip counts, and to eliminate casts.
513 bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
514 const SCEV *LHS, const SCEV *RHS);
516 /// isLoopBackedgeGuardedByCond - Test whether the backedge of the loop is
517 /// protected by a conditional between LHS and RHS. This is used to
518 /// to eliminate casts.
519 bool isLoopBackedgeGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
520 const SCEV *LHS, const SCEV *RHS);
522 /// getBackedgeTakenCount - If the specified loop has a predictable
523 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
524 /// object. The backedge-taken count is the number of times the loop header
525 /// will be branched to from within the loop. This is one less than the
526 /// trip count of the loop, since it doesn't count the first iteration,
527 /// when the header is branched to from outside the loop.
529 /// Note that it is not valid to call this method on a loop without a
530 /// loop-invariant backedge-taken count (see
531 /// hasLoopInvariantBackedgeTakenCount).
533 const SCEV *getBackedgeTakenCount(const Loop *L);
535 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except
536 /// return the least SCEV value that is known never to be less than the
537 /// actual backedge taken count.
538 const SCEV *getMaxBackedgeTakenCount(const Loop *L);
540 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop
541 /// has an analyzable loop-invariant backedge-taken count.
542 bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
544 /// forgetLoopBackedgeTakenCount - This method should be called by the
545 /// client when it has changed a loop in a way that may effect
546 /// ScalarEvolution's ability to compute a trip count, or if the loop
548 void forgetLoopBackedgeTakenCount(const Loop *L);
550 /// GetMinTrailingZeros - Determine the minimum number of zero bits that S
551 /// is guaranteed to end in (at every loop iteration). It is, at the same
552 /// time, the minimum number of times S is divisible by 2. For example,
553 /// given {4,+,8} it returns 2. If S is guaranteed to be 0, it returns the
555 uint32_t GetMinTrailingZeros(const SCEV *S);
557 /// getUnsignedRange - Determine the unsigned range for a particular SCEV.
559 ConstantRange getUnsignedRange(const SCEV *S);
561 /// getSignedRange - Determine the signed range for a particular SCEV.
563 ConstantRange getSignedRange(const SCEV *S);
565 /// isKnownNegative - Test if the given expression is known to be negative.
567 bool isKnownNegative(const SCEV *S);
569 /// isKnownPositive - Test if the given expression is known to be positive.
571 bool isKnownPositive(const SCEV *S);
573 /// isKnownNonNegative - Test if the given expression is known to be
576 bool isKnownNonNegative(const SCEV *S);
578 /// isKnownNonPositive - Test if the given expression is known to be
581 bool isKnownNonPositive(const SCEV *S);
583 /// isKnownNonZero - Test if the given expression is known to be
586 bool isKnownNonZero(const SCEV *S);
588 /// isKnownNonZero - Test if the given expression is known to satisfy
589 /// the condition described by Pred, LHS, and RHS.
591 bool isKnownPredicate(ICmpInst::Predicate Pred,
592 const SCEV *LHS, const SCEV *RHS);
594 virtual bool runOnFunction(Function &F);
595 virtual void releaseMemory();
596 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
597 void print(raw_ostream &OS, const Module* = 0) const;
598 virtual void print(std::ostream &OS, const Module* = 0) const;
599 void print(std::ostream *OS, const Module* M = 0) const {
600 if (OS) print(*OS, M);
604 FoldingSet<SCEV> UniqueSCEVs;
605 BumpPtrAllocator SCEVAllocator;