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/Analysis/LoopInfo.h"
26 #include "llvm/Support/DataTypes.h"
27 #include "llvm/Support/ValueHandle.h"
35 class ScalarEvolution;
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.
43 const unsigned SCEVType; // The SCEV baseclass this node corresponds to
44 mutable unsigned RefCount;
46 friend class SCEVHandle;
47 void addRef() const { ++RefCount; }
48 void dropRef() const {
53 SCEV(const SCEV &); // DO NOT IMPLEMENT
54 void operator=(const SCEV &); // DO NOT IMPLEMENT
58 explicit SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {}
60 unsigned getSCEVType() const { return SCEVType; }
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;
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;
72 /// getType - Return the LLVM type of this SCEV expression.
74 virtual const Type *getType() const = 0;
76 /// isZero - Return true if the expression is a constant zero.
80 /// isOne - Return true if the expression is a constant one.
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
90 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
91 const SCEVHandle &Conc,
92 ScalarEvolution &SE) const = 0;
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;
98 /// print - Print out the internal representation of this scalar to the
99 /// specified stream. This should really only be used for debugging
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); }
105 /// dump - This method is used for debugging.
110 inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) {
115 inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
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
125 struct SCEVCouldNotCompute : public SCEV {
126 SCEVCouldNotCompute();
127 ~SCEVCouldNotCompute();
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;
135 replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
136 const SCEVHandle &Conc,
137 ScalarEvolution &SE) const;
139 virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const {
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);
148 /// SCEVHandle - This class is used to maintain the SCEV object's refcounts,
149 /// freeing the objects when the last reference is dropped.
152 SCEVHandle(); // DO NOT IMPLEMENT
154 SCEVHandle(const SCEV *s) : S(s) {
155 assert(S && "Cannot create a handle to a null SCEV!");
158 SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) {
161 ~SCEVHandle() { S->dropRef(); }
163 operator const SCEV*() const { return S; }
165 const SCEV &operator*() const { return *S; }
166 const SCEV *operator->() const { return S; }
168 bool operator==(const SCEV *RHS) const { return S == RHS; }
169 bool operator!=(const SCEV *RHS) const { return S != RHS; }
171 const SCEVHandle &operator=(SCEV *RHS) {
180 const SCEVHandle &operator=(const SCEVHandle &RHS) {
190 template<typename From> struct simplify_type;
191 template<> struct simplify_type<const SCEVHandle> {
192 typedef const SCEV* SimpleType;
193 static SimpleType getSimplifiedValue(const SCEVHandle &Node) {
197 template<> struct simplify_type<SCEVHandle>
198 : public simplify_type<const SCEVHandle> {};
200 /// ScalarEvolution - This class is the main scalar evolution driver. Because
201 /// client code (intentionally) can't do much with the SCEV objects directly,
202 /// they must ask this class for services.
204 class ScalarEvolution : public FunctionPass {
205 /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be
206 /// notified whenever a Value is deleted.
207 class SCEVCallbackVH : public CallbackVH {
209 virtual void deleted();
210 virtual void allUsesReplacedWith(Value *New);
212 SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0);
215 friend class SCEVCallbackVH;
216 friend class SCEVExpander;
218 /// F - The function we are analyzing.
222 /// LI - The loop information for the function we are currently analyzing.
226 /// TD - The target data information for the target we are targetting.
230 /// UnknownValue - This SCEV is used to represent unknown trip counts and
232 SCEVHandle UnknownValue;
234 /// Scalars - This is a cache of the scalars we have analyzed so far.
236 std::map<SCEVCallbackVH, SCEVHandle> Scalars;
238 /// BackedgeTakenInfo - Information about the backedge-taken count
239 /// of a loop. This currently inclues an exact count and a maximum count.
241 struct BackedgeTakenInfo {
242 /// Exact - An expression indicating the exact backedge-taken count of
243 /// the loop if it is known, or a SCEVCouldNotCompute otherwise.
246 /// Exact - An expression indicating the least maximum backedge-taken
247 /// count of the loop that is known, or a SCEVCouldNotCompute.
250 /*implicit*/ BackedgeTakenInfo(SCEVHandle exact) :
251 Exact(exact), Max(exact) {}
253 /*implicit*/ BackedgeTakenInfo(const SCEV *exact) :
254 Exact(exact), Max(exact) {}
256 BackedgeTakenInfo(SCEVHandle exact, SCEVHandle max) :
257 Exact(exact), Max(max) {}
259 /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any
260 /// computed information, or whether it's all SCEVCouldNotCompute
262 bool hasAnyInfo() const {
263 return !isa<SCEVCouldNotCompute>(Exact) ||
264 !isa<SCEVCouldNotCompute>(Max);
268 /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
269 /// this function as they are computed.
270 std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts;
272 /// ConstantEvolutionLoopExitValue - This map contains entries for all of
273 /// the PHI instructions that we attempt to compute constant evolutions for.
274 /// This allows us to avoid potentially expensive recomputation of these
275 /// properties. An instruction maps to null if we are unable to compute its
277 std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue;
279 /// ValuesAtScopes - This map contains entries for all the instructions
280 /// that we attempt to compute getSCEVAtScope information for without
281 /// using SCEV techniques, which can be expensive.
282 std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes;
284 /// createSCEV - We know that there is no SCEV for the specified value.
285 /// Analyze the expression.
286 SCEVHandle createSCEV(Value *V);
288 /// createNodeForPHI - Provide the special handling we need to analyze PHI
290 SCEVHandle createNodeForPHI(PHINode *PN);
292 /// createNodeForGEP - Provide the special handling we need to analyze GEP
294 SCEVHandle createNodeForGEP(User *GEP);
296 /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value
297 /// for the specified instruction and replaces any references to the
298 /// symbolic value SymName with the specified value. This is used during
300 void ReplaceSymbolicValueWithConcrete(Instruction *I,
301 const SCEVHandle &SymName,
302 const SCEVHandle &NewVal);
304 /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
305 /// loop, lazily computing new values if the loop hasn't been analyzed
307 const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L);
309 /// ComputeBackedgeTakenCount - Compute the number of times the specified
310 /// loop will iterate.
311 BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L);
313 /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
314 /// of 'icmp op load X, cst', try to see if we can compute the trip count.
316 ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
319 ICmpInst::Predicate p);
321 /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute
322 /// a constant number of times (the condition evolves only from constants),
323 /// try to evaluate a few iterations of the loop until we get the exit
324 /// condition gets a value of ExitWhen (true or false). If we cannot
325 /// evaluate the trip count of the loop, return UnknownValue.
326 SCEVHandle ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond,
329 /// HowFarToZero - Return the number of times a backedge comparing the
330 /// specified value to zero will execute. If not computable, return
332 SCEVHandle HowFarToZero(const SCEV *V, const Loop *L);
334 /// HowFarToNonZero - Return the number of times a backedge checking the
335 /// specified value for nonzero will execute. If not computable, return
337 SCEVHandle HowFarToNonZero(const SCEV *V, const Loop *L);
339 /// HowManyLessThans - Return the number of times a backedge containing the
340 /// specified less-than comparison will execute. If not computable, return
341 /// UnknownValue. isSigned specifies whether the less-than is signed.
342 BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
343 const Loop *L, bool isSigned);
345 /// getLoopPredecessor - If the given loop's header has exactly one unique
346 /// predecessor outside the loop, return it. Otherwise return null.
347 BasicBlock *getLoopPredecessor(const Loop *L);
349 /// getPredecessorWithUniqueSuccessorForBB - Return a predecessor of BB
350 /// (which may not be an immediate predecessor) which has exactly one
351 /// successor from which BB is reachable, or null if no such block is
353 BasicBlock* getPredecessorWithUniqueSuccessorForBB(BasicBlock *BB);
355 /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
356 /// in the header of its containing loop, we know the loop executes a
357 /// constant number of times, and the PHI node is just a recurrence
358 /// involving constants, fold it.
359 Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
362 /// forgetLoopPHIs - Delete the memoized SCEVs associated with the
363 /// PHI nodes in the given loop. This is used when the trip count of
364 /// the loop may have changed.
365 void forgetLoopPHIs(const Loop *L);
368 static char ID; // Pass identification, replacement for typeid
371 /// isSCEVable - Test if values of the given type are analyzable within
372 /// the SCEV framework. This primarily includes integer types, and it
373 /// can optionally include pointer types if the ScalarEvolution class
374 /// has access to target-specific information.
375 bool isSCEVable(const Type *Ty) const;
377 /// getTypeSizeInBits - Return the size in bits of the specified type,
378 /// for which isSCEVable must return true.
379 uint64_t getTypeSizeInBits(const Type *Ty) const;
381 /// getEffectiveSCEVType - Return a type with the same bitwidth as
382 /// the given type and which represents how SCEV will treat the given
383 /// type, for which isSCEVable must return true. For pointer types,
384 /// this is the pointer-sized integer type.
385 const Type *getEffectiveSCEVType(const Type *Ty) const;
387 /// getSCEV - Return a SCEV expression handle for the full generality of the
388 /// specified expression.
389 SCEVHandle getSCEV(Value *V);
391 SCEVHandle getConstant(ConstantInt *V);
392 SCEVHandle getConstant(const APInt& Val);
393 SCEVHandle getTruncateExpr(const SCEVHandle &Op, const Type *Ty);
394 SCEVHandle getZeroExtendExpr(const SCEVHandle &Op, const Type *Ty);
395 SCEVHandle getSignExtendExpr(const SCEVHandle &Op, const Type *Ty);
396 SCEVHandle getAddExpr(std::vector<SCEVHandle> &Ops);
397 SCEVHandle getAddExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
398 std::vector<SCEVHandle> Ops;
401 return getAddExpr(Ops);
403 SCEVHandle getAddExpr(const SCEVHandle &Op0, const SCEVHandle &Op1,
404 const SCEVHandle &Op2) {
405 std::vector<SCEVHandle> Ops;
409 return getAddExpr(Ops);
411 SCEVHandle getMulExpr(std::vector<SCEVHandle> &Ops);
412 SCEVHandle getMulExpr(const SCEVHandle &LHS, const SCEVHandle &RHS) {
413 std::vector<SCEVHandle> Ops;
416 return getMulExpr(Ops);
418 SCEVHandle getUDivExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
419 SCEVHandle getAddRecExpr(const SCEVHandle &Start, const SCEVHandle &Step,
421 SCEVHandle getAddRecExpr(std::vector<SCEVHandle> &Operands,
423 SCEVHandle getAddRecExpr(const std::vector<SCEVHandle> &Operands,
425 std::vector<SCEVHandle> NewOp(Operands);
426 return getAddRecExpr(NewOp, L);
428 SCEVHandle getSMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
429 SCEVHandle getSMaxExpr(std::vector<SCEVHandle> Operands);
430 SCEVHandle getUMaxExpr(const SCEVHandle &LHS, const SCEVHandle &RHS);
431 SCEVHandle getUMaxExpr(std::vector<SCEVHandle> Operands);
432 SCEVHandle getUnknown(Value *V);
433 SCEVHandle getCouldNotCompute();
435 /// getNegativeSCEV - Return the SCEV object corresponding to -V.
437 SCEVHandle getNegativeSCEV(const SCEVHandle &V);
439 /// getNotSCEV - Return the SCEV object corresponding to ~V.
441 SCEVHandle getNotSCEV(const SCEVHandle &V);
443 /// getMinusSCEV - Return LHS-RHS.
445 SCEVHandle getMinusSCEV(const SCEVHandle &LHS,
446 const SCEVHandle &RHS);
448 /// getTruncateOrZeroExtend - Return a SCEV corresponding to a conversion
449 /// of the input value to the specified type. If the type must be
450 /// extended, it is zero extended.
451 SCEVHandle getTruncateOrZeroExtend(const SCEVHandle &V, const Type *Ty);
453 /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
454 /// of the input value to the specified type. If the type must be
455 /// extended, it is sign extended.
456 SCEVHandle getTruncateOrSignExtend(const SCEVHandle &V, const Type *Ty);
458 /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of
459 /// the input value to the specified type. If the type must be extended,
460 /// it is zero extended. The conversion must not be narrowing.
461 SCEVHandle getNoopOrZeroExtend(const SCEVHandle &V, const Type *Ty);
463 /// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of
464 /// the input value to the specified type. If the type must be extended,
465 /// it is sign extended. The conversion must not be narrowing.
466 SCEVHandle getNoopOrSignExtend(const SCEVHandle &V, const Type *Ty);
468 /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the
469 /// input value to the specified type. The conversion must not be
471 SCEVHandle getTruncateOrNoop(const SCEVHandle &V, const Type *Ty);
473 /// getIntegerSCEV - Given an integer or FP type, create a constant for the
474 /// specified signed integer value and return a SCEV for the constant.
475 SCEVHandle getIntegerSCEV(int Val, const Type *Ty);
477 /// hasSCEV - Return true if the SCEV for this value has already been
479 bool hasSCEV(Value *V) const;
481 /// setSCEV - Insert the specified SCEV into the map of current SCEVs for
482 /// the specified value.
483 void setSCEV(Value *V, const SCEVHandle &H);
485 /// getSCEVAtScope - Return a SCEV expression handle for the specified value
486 /// at the specified scope in the program. The L value specifies a loop
487 /// nest to evaluate the expression at, where null is the top-level or a
488 /// specified loop is immediately inside of the loop.
490 /// This method can be used to compute the exit value for a variable defined
491 /// in a loop by querying what the value will hold in the parent loop.
493 /// If this value is not computable at this scope, a SCEVCouldNotCompute
494 /// object is returned.
495 SCEVHandle getSCEVAtScope(const SCEV *S, const Loop *L);
497 /// getSCEVAtScope - This is a convenience function which does
498 /// getSCEVAtScope(getSCEV(V), L).
499 SCEVHandle getSCEVAtScope(Value *V, const Loop *L);
501 /// isLoopGuardedByCond - Test whether entry to the loop is protected by
502 /// a conditional between LHS and RHS. This is used to help avoid max
503 /// expressions in loop trip counts.
504 bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
505 const SCEV *LHS, const SCEV *RHS);
507 /// getBackedgeTakenCount - If the specified loop has a predictable
508 /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
509 /// object. The backedge-taken count is the number of times the loop header
510 /// will be branched to from within the loop. This is one less than the
511 /// trip count of the loop, since it doesn't count the first iteration,
512 /// when the header is branched to from outside the loop.
514 /// Note that it is not valid to call this method on a loop without a
515 /// loop-invariant backedge-taken count (see
516 /// hasLoopInvariantBackedgeTakenCount).
518 SCEVHandle getBackedgeTakenCount(const Loop *L);
520 /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except
521 /// return the least SCEV value that is known never to be less than the
522 /// actual backedge taken count.
523 SCEVHandle getMaxBackedgeTakenCount(const Loop *L);
525 /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop
526 /// has an analyzable loop-invariant backedge-taken count.
527 bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
529 /// forgetLoopBackedgeTakenCount - This method should be called by the
530 /// client when it has changed a loop in a way that may effect
531 /// ScalarEvolution's ability to compute a trip count, or if the loop
533 void forgetLoopBackedgeTakenCount(const Loop *L);
535 virtual bool runOnFunction(Function &F);
536 virtual void releaseMemory();
537 virtual void getAnalysisUsage(AnalysisUsage &AU) const;
538 void print(raw_ostream &OS, const Module* = 0) const;
539 virtual void print(std::ostream &OS, const Module* = 0) const;
540 void print(std::ostream *OS, const Module* M = 0) const {
541 if (OS) print(*OS, M);