ScalarEvolution.h revision 40a5a1b39ee1cd40ff9d04740386b667fb27b340
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 "llvm/ADT/DenseMap.h"
29#include <iosfwd>
30
31namespace llvm {
32  class APInt;
33  class ConstantInt;
34  class Type;
35  class ScalarEvolution;
36  class TargetData;
37  class SCEVConstant;
38  class SCEVTruncateExpr;
39  class SCEVZeroExtendExpr;
40  class SCEVCommutativeExpr;
41  class SCEVUDivExpr;
42  class SCEVSignExtendExpr;
43  class SCEVAddRecExpr;
44  class SCEVUnknown;
45
46  /// SCEV - This class represents an analyzed expression in the program.  These
47  /// are reference-counted opaque objects that the client is not allowed to
48  /// do much with directly.
49  ///
50  class SCEV {
51    const unsigned SCEVType;      // The SCEV baseclass this node corresponds to
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) :
59      SCEVType(SCEVTy) {}
60
61    unsigned getSCEVType() const { return SCEVType; }
62
63    /// isLoopInvariant - Return true if the value of this SCEV is unchanging in
64    /// the specified loop.
65    virtual bool isLoopInvariant(const Loop *L) const = 0;
66
67    /// hasComputableLoopEvolution - Return true if this SCEV changes value in a
68    /// known way in the specified loop.  This property being true implies that
69    /// the value is variant in the loop AND that we can emit an expression to
70    /// compute the value of the expression at any particular loop iteration.
71    virtual bool hasComputableLoopEvolution(const Loop *L) const = 0;
72
73    /// getType - Return the LLVM type of this SCEV expression.
74    ///
75    virtual const Type *getType() const = 0;
76
77    /// isZero - Return true if the expression is a constant zero.
78    ///
79    bool isZero() const;
80
81    /// isOne - Return true if the expression is a constant one.
82    ///
83    bool isOne() const;
84
85    /// isAllOnesValue - Return true if the expression is a constant
86    /// all-ones value.
87    ///
88    bool isAllOnesValue() const;
89
90    /// replaceSymbolicValuesWithConcrete - If this SCEV internally references
91    /// the symbolic value "Sym", construct and return a new SCEV that produces
92    /// the same value, but which uses the concrete value Conc instead of the
93    /// symbolic value.  If this SCEV does not use the symbolic value, it
94    /// returns itself.
95    virtual const SCEV*
96    replaceSymbolicValuesWithConcrete(const SCEV* Sym,
97                                      const SCEV* Conc,
98                                      ScalarEvolution &SE) const = 0;
99
100    /// dominates - Return true if elements that makes up this SCEV dominates
101    /// the specified basic block.
102    virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const = 0;
103
104    /// print - Print out the internal representation of this scalar to the
105    /// specified stream.  This should really only be used for debugging
106    /// purposes.
107    virtual void print(raw_ostream &OS) const = 0;
108    void print(std::ostream &OS) const;
109    void print(std::ostream *OS) const { if (OS) print(*OS); }
110
111    /// dump - This method is used for debugging.
112    ///
113    void dump() const;
114  };
115
116  inline raw_ostream &operator<<(raw_ostream &OS, const SCEV &S) {
117    S.print(OS);
118    return OS;
119  }
120
121  inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
122    S.print(OS);
123    return OS;
124  }
125
126  /// SCEVCouldNotCompute - An object of this class is returned by queries that
127  /// could not be answered.  For example, if you ask for the number of
128  /// iterations of a linked-list traversal loop, you will get one of these.
129  /// None of the standard SCEV operations are valid on this class, it is just a
130  /// marker.
131  struct SCEVCouldNotCompute : public SCEV {
132    SCEVCouldNotCompute();
133
134    // None of these methods are valid for this object.
135    virtual bool isLoopInvariant(const Loop *L) const;
136    virtual const Type *getType() const;
137    virtual bool hasComputableLoopEvolution(const Loop *L) const;
138    virtual void print(raw_ostream &OS) const;
139    virtual const SCEV*
140    replaceSymbolicValuesWithConcrete(const SCEV* Sym,
141                                      const SCEV* Conc,
142                                      ScalarEvolution &SE) const;
143
144    virtual bool dominates(BasicBlock *BB, DominatorTree *DT) const {
145      return true;
146    }
147
148    /// Methods for support type inquiry through isa, cast, and dyn_cast:
149    static inline bool classof(const SCEVCouldNotCompute *S) { return true; }
150    static bool classof(const SCEV *S);
151  };
152
153  /// ScalarEvolution - This class is the main scalar evolution driver.  Because
154  /// client code (intentionally) can't do much with the SCEV objects directly,
155  /// they must ask this class for services.
156  ///
157  class ScalarEvolution : public FunctionPass {
158    /// SCEVCallbackVH - A CallbackVH to arrange for ScalarEvolution to be
159    /// notified whenever a Value is deleted.
160    class SCEVCallbackVH : public CallbackVH {
161      ScalarEvolution *SE;
162      virtual void deleted();
163      virtual void allUsesReplacedWith(Value *New);
164    public:
165      SCEVCallbackVH(Value *V, ScalarEvolution *SE = 0);
166    };
167
168    friend class SCEVCallbackVH;
169    friend class SCEVExpander;
170
171    /// F - The function we are analyzing.
172    ///
173    Function *F;
174
175    /// LI - The loop information for the function we are currently analyzing.
176    ///
177    LoopInfo *LI;
178
179    /// TD - The target data information for the target we are targetting.
180    ///
181    TargetData *TD;
182
183    /// CouldNotCompute - This SCEV is used to represent unknown trip
184    /// counts and things.
185    const SCEV* CouldNotCompute;
186
187    /// Scalars - This is a cache of the scalars we have analyzed so far.
188    ///
189    std::map<SCEVCallbackVH, const SCEV*> Scalars;
190
191    /// BackedgeTakenInfo - Information about the backedge-taken count
192    /// of a loop. This currently inclues an exact count and a maximum count.
193    ///
194    struct BackedgeTakenInfo {
195      /// Exact - An expression indicating the exact backedge-taken count of
196      /// the loop if it is known, or a SCEVCouldNotCompute otherwise.
197      const SCEV* Exact;
198
199      /// Exact - An expression indicating the least maximum backedge-taken
200      /// count of the loop that is known, or a SCEVCouldNotCompute.
201      const SCEV* Max;
202
203      /*implicit*/ BackedgeTakenInfo(const SCEV* exact) :
204        Exact(exact), Max(exact) {}
205
206      BackedgeTakenInfo(const SCEV* exact, const SCEV* max) :
207        Exact(exact), Max(max) {}
208
209      /// hasAnyInfo - Test whether this BackedgeTakenInfo contains any
210      /// computed information, or whether it's all SCEVCouldNotCompute
211      /// values.
212      bool hasAnyInfo() const {
213        return !isa<SCEVCouldNotCompute>(Exact) ||
214               !isa<SCEVCouldNotCompute>(Max);
215      }
216    };
217
218    /// BackedgeTakenCounts - Cache the backedge-taken count of the loops for
219    /// this function as they are computed.
220    std::map<const Loop*, BackedgeTakenInfo> BackedgeTakenCounts;
221
222    /// ConstantEvolutionLoopExitValue - This map contains entries for all of
223    /// the PHI instructions that we attempt to compute constant evolutions for.
224    /// This allows us to avoid potentially expensive recomputation of these
225    /// properties.  An instruction maps to null if we are unable to compute its
226    /// exit value.
227    std::map<PHINode*, Constant*> ConstantEvolutionLoopExitValue;
228
229    /// ValuesAtScopes - This map contains entries for all the instructions
230    /// that we attempt to compute getSCEVAtScope information for without
231    /// using SCEV techniques, which can be expensive.
232    std::map<Instruction *, std::map<const Loop *, Constant *> > ValuesAtScopes;
233
234    /// createSCEV - We know that there is no SCEV for the specified value.
235    /// Analyze the expression.
236    const SCEV* createSCEV(Value *V);
237
238    /// createNodeForPHI - Provide the special handling we need to analyze PHI
239    /// SCEVs.
240    const SCEV* createNodeForPHI(PHINode *PN);
241
242    /// createNodeForGEP - Provide the special handling we need to analyze GEP
243    /// SCEVs.
244    const SCEV* createNodeForGEP(User *GEP);
245
246    /// ReplaceSymbolicValueWithConcrete - This looks up the computed SCEV value
247    /// for the specified instruction and replaces any references to the
248    /// symbolic value SymName with the specified value.  This is used during
249    /// PHI resolution.
250    void ReplaceSymbolicValueWithConcrete(Instruction *I,
251                                          const SCEV* SymName,
252                                          const SCEV* NewVal);
253
254    /// getBECount - Subtract the end and start values and divide by the step,
255    /// rounding up, to get the number of times the backedge is executed. Return
256    /// CouldNotCompute if an intermediate computation overflows.
257    const SCEV* getBECount(const SCEV* Start,
258                          const SCEV* End,
259                          const SCEV* Step);
260
261    /// getBackedgeTakenInfo - Return the BackedgeTakenInfo for the given
262    /// loop, lazily computing new values if the loop hasn't been analyzed
263    /// yet.
264    const BackedgeTakenInfo &getBackedgeTakenInfo(const Loop *L);
265
266    /// ComputeBackedgeTakenCount - Compute the number of times the specified
267    /// loop will iterate.
268    BackedgeTakenInfo ComputeBackedgeTakenCount(const Loop *L);
269
270    /// ComputeBackedgeTakenCountFromExit - Compute the number of times the
271    /// backedge of the specified loop will execute if it exits via the
272    /// specified block.
273    BackedgeTakenInfo ComputeBackedgeTakenCountFromExit(const Loop *L,
274                                                      BasicBlock *ExitingBlock);
275
276    /// ComputeBackedgeTakenCountFromExitCond - Compute the number of times the
277    /// backedge of the specified loop will execute if its exit condition
278    /// were a conditional branch of ExitCond, TBB, and FBB.
279    BackedgeTakenInfo
280      ComputeBackedgeTakenCountFromExitCond(const Loop *L,
281                                            Value *ExitCond,
282                                            BasicBlock *TBB,
283                                            BasicBlock *FBB);
284
285    /// ComputeBackedgeTakenCountFromExitCondICmp - Compute the number of
286    /// times the backedge of the specified loop will execute if its exit
287    /// condition were a conditional branch of the ICmpInst ExitCond, TBB,
288    /// and FBB.
289    BackedgeTakenInfo
290      ComputeBackedgeTakenCountFromExitCondICmp(const Loop *L,
291                                                ICmpInst *ExitCond,
292                                                BasicBlock *TBB,
293                                                BasicBlock *FBB);
294
295    /// ComputeLoadConstantCompareBackedgeTakenCount - Given an exit condition
296    /// of 'icmp op load X, cst', try to see if we can compute the trip count.
297    const SCEV*
298      ComputeLoadConstantCompareBackedgeTakenCount(LoadInst *LI,
299                                                   Constant *RHS,
300                                                   const Loop *L,
301                                                   ICmpInst::Predicate p);
302
303    /// ComputeBackedgeTakenCountExhaustively - If the trip is known to execute
304    /// a constant number of times (the condition evolves only from constants),
305    /// try to evaluate a few iterations of the loop until we get the exit
306    /// condition gets a value of ExitWhen (true or false).  If we cannot
307    /// evaluate the trip count of the loop, return CouldNotCompute.
308    const SCEV* ComputeBackedgeTakenCountExhaustively(const Loop *L, Value *Cond,
309                                                     bool ExitWhen);
310
311    /// HowFarToZero - Return the number of times a backedge comparing the
312    /// specified value to zero will execute.  If not computable, return
313    /// CouldNotCompute.
314    const SCEV* HowFarToZero(const SCEV *V, const Loop *L);
315
316    /// HowFarToNonZero - Return the number of times a backedge checking the
317    /// specified value for nonzero will execute.  If not computable, return
318    /// CouldNotCompute.
319    const SCEV* HowFarToNonZero(const SCEV *V, const Loop *L);
320
321    /// HowManyLessThans - Return the number of times a backedge containing the
322    /// specified less-than comparison will execute.  If not computable, return
323    /// CouldNotCompute. isSigned specifies whether the less-than is signed.
324    BackedgeTakenInfo HowManyLessThans(const SCEV *LHS, const SCEV *RHS,
325                                       const Loop *L, bool isSigned);
326
327    /// getLoopPredecessor - If the given loop's header has exactly one unique
328    /// predecessor outside the loop, return it. Otherwise return null.
329    BasicBlock *getLoopPredecessor(const Loop *L);
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    /// isNecessaryCond - Test whether the given CondValue value is a condition
338    /// which is at least as strict as the one described by Pred, LHS, and RHS.
339    bool isNecessaryCond(Value *Cond, ICmpInst::Predicate Pred,
340                         const SCEV *LHS, const SCEV *RHS,
341                         bool Inverse);
342
343    /// getConstantEvolutionLoopExitValue - If we know that the specified Phi is
344    /// in the header of its containing loop, we know the loop executes a
345    /// constant number of times, and the PHI node is just a recurrence
346    /// involving constants, fold it.
347    Constant *getConstantEvolutionLoopExitValue(PHINode *PN, const APInt& BEs,
348                                                const Loop *L);
349
350    /// forgetLoopPHIs - Delete the memoized SCEVs associated with the
351    /// PHI nodes in the given loop. This is used when the trip count of
352    /// the loop may have changed.
353    void forgetLoopPHIs(const Loop *L);
354
355  public:
356    static char ID; // Pass identification, replacement for typeid
357    ScalarEvolution();
358
359    /// isSCEVable - Test if values of the given type are analyzable within
360    /// the SCEV framework. This primarily includes integer types, and it
361    /// can optionally include pointer types if the ScalarEvolution class
362    /// has access to target-specific information.
363    bool isSCEVable(const Type *Ty) const;
364
365    /// getTypeSizeInBits - Return the size in bits of the specified type,
366    /// for which isSCEVable must return true.
367    uint64_t getTypeSizeInBits(const Type *Ty) const;
368
369    /// getEffectiveSCEVType - Return a type with the same bitwidth as
370    /// the given type and which represents how SCEV will treat the given
371    /// type, for which isSCEVable must return true. For pointer types,
372    /// this is the pointer-sized integer type.
373    const Type *getEffectiveSCEVType(const Type *Ty) const;
374
375    /// getSCEV - Return a SCEV expression handle for the full generality of the
376    /// specified expression.
377    const SCEV* getSCEV(Value *V);
378
379    const SCEV* getConstant(ConstantInt *V);
380    const SCEV* getConstant(const APInt& Val);
381    const SCEV* getConstant(const Type *Ty, uint64_t V, bool isSigned = false);
382    const SCEV* getTruncateExpr(const SCEV* Op, const Type *Ty);
383    const SCEV* getZeroExtendExpr(const SCEV* Op, const Type *Ty);
384    const SCEV* getSignExtendExpr(const SCEV* Op, const Type *Ty);
385    const SCEV* getAnyExtendExpr(const SCEV* Op, const Type *Ty);
386    const SCEV* getAddExpr(SmallVectorImpl<const SCEV*> &Ops);
387    const SCEV* getAddExpr(const SCEV* LHS, const SCEV* RHS) {
388      SmallVector<const SCEV*, 2> Ops;
389      Ops.push_back(LHS);
390      Ops.push_back(RHS);
391      return getAddExpr(Ops);
392    }
393    const SCEV* getAddExpr(const SCEV* Op0, const SCEV* Op1,
394                          const SCEV* Op2) {
395      SmallVector<const SCEV*, 3> Ops;
396      Ops.push_back(Op0);
397      Ops.push_back(Op1);
398      Ops.push_back(Op2);
399      return getAddExpr(Ops);
400    }
401    const SCEV* getMulExpr(SmallVectorImpl<const SCEV*> &Ops);
402    const SCEV* getMulExpr(const SCEV* LHS, const SCEV* RHS) {
403      SmallVector<const SCEV*, 2> Ops;
404      Ops.push_back(LHS);
405      Ops.push_back(RHS);
406      return getMulExpr(Ops);
407    }
408    const SCEV* getUDivExpr(const SCEV* LHS, const SCEV* RHS);
409    const SCEV* getAddRecExpr(const SCEV* Start, const SCEV* Step,
410                             const Loop *L);
411    const SCEV* getAddRecExpr(SmallVectorImpl<const SCEV*> &Operands,
412                             const Loop *L);
413    const SCEV* getAddRecExpr(const SmallVectorImpl<const SCEV*> &Operands,
414                             const Loop *L) {
415      SmallVector<const SCEV*, 4> NewOp(Operands.begin(), Operands.end());
416      return getAddRecExpr(NewOp, L);
417    }
418    const SCEV* getSMaxExpr(const SCEV* LHS, const SCEV* RHS);
419    const SCEV* getSMaxExpr(SmallVectorImpl<const SCEV*> &Operands);
420    const SCEV* getUMaxExpr(const SCEV* LHS, const SCEV* RHS);
421    const SCEV* getUMaxExpr(SmallVectorImpl<const SCEV*> &Operands);
422    const SCEV* getSMinExpr(const SCEV* LHS, const SCEV* RHS);
423    const SCEV* getUMinExpr(const SCEV* LHS, const SCEV* RHS);
424    const SCEV* getUnknown(Value *V);
425    const SCEV* getCouldNotCompute();
426
427    /// getNegativeSCEV - Return the SCEV object corresponding to -V.
428    ///
429    const SCEV* getNegativeSCEV(const SCEV* V);
430
431    /// getNotSCEV - Return the SCEV object corresponding to ~V.
432    ///
433    const SCEV* getNotSCEV(const SCEV* V);
434
435    /// getMinusSCEV - Return LHS-RHS.
436    ///
437    const SCEV* getMinusSCEV(const SCEV* LHS,
438                            const SCEV* RHS);
439
440    /// getTruncateOrZeroExtend - 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 zero extended.
443    const SCEV* getTruncateOrZeroExtend(const SCEV* V, const Type *Ty);
444
445    /// getTruncateOrSignExtend - Return a SCEV corresponding to a conversion
446    /// of the input value to the specified type.  If the type must be
447    /// extended, it is sign extended.
448    const SCEV* getTruncateOrSignExtend(const SCEV* V, const Type *Ty);
449
450    /// getNoopOrZeroExtend - Return a SCEV corresponding to a conversion of
451    /// the input value to the specified type.  If the type must be extended,
452    /// it is zero extended.  The conversion must not be narrowing.
453    const SCEV* getNoopOrZeroExtend(const SCEV* V, const Type *Ty);
454
455    /// getNoopOrSignExtend - Return a SCEV corresponding to a conversion of
456    /// the input value to the specified type.  If the type must be extended,
457    /// it is sign extended.  The conversion must not be narrowing.
458    const SCEV* getNoopOrSignExtend(const SCEV* V, const Type *Ty);
459
460    /// getNoopOrAnyExtend - Return a SCEV corresponding to a conversion of
461    /// the input value to the specified type. If the type must be extended,
462    /// it is extended with unspecified bits. The conversion must not be
463    /// narrowing.
464    const SCEV* getNoopOrAnyExtend(const SCEV* V, const Type *Ty);
465
466    /// getTruncateOrNoop - Return a SCEV corresponding to a conversion of the
467    /// input value to the specified type.  The conversion must not be
468    /// widening.
469    const SCEV* getTruncateOrNoop(const SCEV* V, const Type *Ty);
470
471    /// getIntegerSCEV - Given a SCEVable type, create a constant for the
472    /// specified signed integer value and return a SCEV for the constant.
473    const SCEV* getIntegerSCEV(int Val, const Type *Ty);
474
475    /// getUMaxFromMismatchedTypes - Promote the operands to the wider of
476    /// the types using zero-extension, and then perform a umax operation
477    /// with them.
478    const SCEV* getUMaxFromMismatchedTypes(const SCEV* LHS,
479                                          const SCEV* RHS);
480
481    /// getUMinFromMismatchedTypes - Promote the operands to the wider of
482    /// the types using zero-extension, and then perform a umin operation
483    /// with them.
484    const SCEV* getUMinFromMismatchedTypes(const SCEV* LHS,
485                                           const SCEV* RHS);
486
487    /// hasSCEV - Return true if the SCEV for this value has already been
488    /// computed.
489    bool hasSCEV(Value *V) const;
490
491    /// setSCEV - Insert the specified SCEV into the map of current SCEVs for
492    /// the specified value.
493    void setSCEV(Value *V, const SCEV* H);
494
495    /// getSCEVAtScope - Return a SCEV expression handle for the specified value
496    /// at the specified scope in the program.  The L value specifies a loop
497    /// nest to evaluate the expression at, where null is the top-level or a
498    /// specified loop is immediately inside of the loop.
499    ///
500    /// This method can be used to compute the exit value for a variable defined
501    /// in a loop by querying what the value will hold in the parent loop.
502    ///
503    /// In the case that a relevant loop exit value cannot be computed, the
504    /// original value V is returned.
505    const SCEV* getSCEVAtScope(const SCEV *S, const Loop *L);
506
507    /// getSCEVAtScope - This is a convenience function which does
508    /// getSCEVAtScope(getSCEV(V), L).
509    const SCEV* getSCEVAtScope(Value *V, const Loop *L);
510
511    /// isLoopGuardedByCond - Test whether entry to the loop is protected by
512    /// a conditional between LHS and RHS.  This is used to help avoid max
513    /// expressions in loop trip counts.
514    bool isLoopGuardedByCond(const Loop *L, ICmpInst::Predicate Pred,
515                             const SCEV *LHS, const SCEV *RHS);
516
517    /// getBackedgeTakenCount - If the specified loop has a predictable
518    /// backedge-taken count, return it, otherwise return a SCEVCouldNotCompute
519    /// object. The backedge-taken count is the number of times the loop header
520    /// will be branched to from within the loop. This is one less than the
521    /// trip count of the loop, since it doesn't count the first iteration,
522    /// when the header is branched to from outside the loop.
523    ///
524    /// Note that it is not valid to call this method on a loop without a
525    /// loop-invariant backedge-taken count (see
526    /// hasLoopInvariantBackedgeTakenCount).
527    ///
528    const SCEV* getBackedgeTakenCount(const Loop *L);
529
530    /// getMaxBackedgeTakenCount - Similar to getBackedgeTakenCount, except
531    /// return the least SCEV value that is known never to be less than the
532    /// actual backedge taken count.
533    const SCEV* getMaxBackedgeTakenCount(const Loop *L);
534
535    /// hasLoopInvariantBackedgeTakenCount - Return true if the specified loop
536    /// has an analyzable loop-invariant backedge-taken count.
537    bool hasLoopInvariantBackedgeTakenCount(const Loop *L);
538
539    /// forgetLoopBackedgeTakenCount - This method should be called by the
540    /// client when it has changed a loop in a way that may effect
541    /// ScalarEvolution's ability to compute a trip count, or if the loop
542    /// is deleted.
543    void forgetLoopBackedgeTakenCount(const Loop *L);
544
545    /// GetMinTrailingZeros - Determine the minimum number of zero bits that S is
546    /// guaranteed to end in (at every loop iteration).  It is, at the same time,
547    /// the minimum number of times S is divisible by 2.  For example, given {4,+,8}
548    /// it returns 2.  If S is guaranteed to be 0, it returns the bitwidth of S.
549    uint32_t GetMinTrailingZeros(const SCEV* S);
550
551    /// GetMinLeadingZeros - Determine the minimum number of zero bits that S is
552    /// guaranteed to begin with (at every loop iteration).
553    uint32_t GetMinLeadingZeros(const SCEV* S);
554
555    /// GetMinSignBits - Determine the minimum number of sign bits that S is
556    /// guaranteed to begin with.
557    uint32_t GetMinSignBits(const SCEV* S);
558
559    virtual bool runOnFunction(Function &F);
560    virtual void releaseMemory();
561    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
562    void print(raw_ostream &OS, const Module* = 0) const;
563    virtual void print(std::ostream &OS, const Module* = 0) const;
564    void print(std::ostream *OS, const Module* M = 0) const {
565      if (OS) print(*OS, M);
566    }
567
568  private:
569    // Uniquing tables.
570    std::map<ConstantInt*, SCEVConstant*> SCEVConstants;
571    std::map<std::pair<const SCEV*, const Type*>,
572             SCEVTruncateExpr*> SCEVTruncates;
573    std::map<std::pair<const SCEV*, const Type*>,
574             SCEVZeroExtendExpr*> SCEVZeroExtends;
575    std::map<std::pair<unsigned, std::vector<const SCEV*> >,
576             SCEVCommutativeExpr*> SCEVCommExprs;
577    std::map<std::pair<const SCEV*, const SCEV*>,
578             SCEVUDivExpr*> SCEVUDivs;
579    std::map<std::pair<const SCEV*, const Type*>,
580             SCEVSignExtendExpr*> SCEVSignExtends;
581    std::map<std::pair<const Loop *, std::vector<const SCEV*> >,
582             SCEVAddRecExpr*> SCEVAddRecExprs;
583    std::map<Value*, SCEVUnknown*> SCEVUnknowns;
584  };
585}
586
587#endif
588