LLVM API Documentation

ScalarEvolution.h

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00001 //===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- C++ -*-===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // The ScalarEvolution class is an LLVM pass which can be used to analyze and
00011 // catagorize scalar expressions in loops.  It specializes in recognizing
00012 // general induction variables, representing them with the abstract and opaque
00013 // SCEV class.  Given this analysis, trip counts of loops and other important
00014 // properties can be obtained.
00015 //
00016 // This analysis is primarily useful for induction variable substitution and
00017 // strength reduction.
00018 //
00019 //===----------------------------------------------------------------------===//
00020 
00021 #ifndef LLVM_ANALYSIS_SCALAREVOLUTION_H
00022 #define LLVM_ANALYSIS_SCALAREVOLUTION_H
00023 
00024 #include "llvm/Pass.h"
00025 #include <set>
00026 
00027 namespace llvm {
00028   class Instruction;
00029   class Type;
00030   class ConstantRange;
00031   class Loop;
00032   class LoopInfo;
00033   class SCEVHandle;
00034 
00035   /// SCEV - This class represent an analyzed expression in the program.  These
00036   /// are reference counted opaque objects that the client is not allowed to
00037   /// do much with directly.
00038   ///
00039   class SCEV {
00040     const unsigned SCEVType;      // The SCEV baseclass this node corresponds to
00041     mutable unsigned RefCount;
00042 
00043     friend class SCEVHandle;
00044     void addRef() const { ++RefCount; }
00045     void dropRef() const {
00046       if (--RefCount == 0)
00047         delete this;
00048     }
00049 
00050     SCEV(const SCEV &);            // DO NOT IMPLEMENT
00051     void operator=(const SCEV &);  // DO NOT IMPLEMENT
00052   protected:
00053     virtual ~SCEV();
00054   public:
00055     SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {}
00056 
00057     /// getNegativeSCEV - Return the SCEV object corresponding to -V.
00058     ///
00059     static SCEVHandle getNegativeSCEV(const SCEVHandle &V);
00060 
00061     /// getMinusSCEV - Return LHS-RHS.
00062     ///
00063     static SCEVHandle getMinusSCEV(const SCEVHandle &LHS,
00064                                    const SCEVHandle &RHS);
00065 
00066 
00067     unsigned getSCEVType() const { return SCEVType; }
00068 
00069     /// getValueRange - Return the tightest constant bounds that this value is
00070     /// known to have.  This method is only valid on integer SCEV objects.
00071     virtual ConstantRange getValueRange() const;
00072 
00073     /// isLoopInvariant - Return true if the value of this SCEV is unchanging in
00074     /// the specified loop.
00075     virtual bool isLoopInvariant(const Loop *L) const = 0;
00076 
00077     /// hasComputableLoopEvolution - Return true if this SCEV changes value in a
00078     /// known way in the specified loop.  This property being true implies that
00079     /// the value is variant in the loop AND that we can emit an expression to
00080     /// compute the value of the expression at any particular loop iteration.
00081     virtual bool hasComputableLoopEvolution(const Loop *L) const = 0;
00082 
00083     /// getType - Return the LLVM type of this SCEV expression.
00084     ///
00085     virtual const Type *getType() const = 0;
00086 
00087     /// replaceSymbolicValuesWithConcrete - If this SCEV internally references
00088     /// the symbolic value "Sym", construct and return a new SCEV that produces
00089     /// the same value, but which uses the concrete value Conc instead of the
00090     /// symbolic value.  If this SCEV does not use the symbolic value, it
00091     /// returns itself.
00092     virtual SCEVHandle
00093     replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
00094                                       const SCEVHandle &Conc) const = 0;
00095 
00096     /// print - Print out the internal representation of this scalar to the
00097     /// specified stream.  This should really only be used for debugging
00098     /// purposes.
00099     virtual void print(std::ostream &OS) const = 0;
00100 
00101     /// dump - This method is used for debugging.
00102     ///
00103     void dump() const;
00104   };
00105 
00106   inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
00107     S.print(OS);
00108     return OS;
00109   }
00110 
00111   /// SCEVCouldNotCompute - An object of this class is returned by queries that
00112   /// could not be answered.  For example, if you ask for the number of
00113   /// iterations of a linked-list traversal loop, you will get one of these.
00114   /// None of the standard SCEV operations are valid on this class, it is just a
00115   /// marker.
00116   struct SCEVCouldNotCompute : public SCEV {
00117     SCEVCouldNotCompute();
00118 
00119     // None of these methods are valid for this object.
00120     virtual bool isLoopInvariant(const Loop *L) const;
00121     virtual const Type *getType() const;
00122     virtual bool hasComputableLoopEvolution(const Loop *L) const;
00123     virtual void print(std::ostream &OS) const;
00124     virtual SCEVHandle
00125     replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
00126                                       const SCEVHandle &Conc) const;
00127 
00128     /// Methods for support type inquiry through isa, cast, and dyn_cast:
00129     static inline bool classof(const SCEVCouldNotCompute *S) { return true; }
00130     static bool classof(const SCEV *S);
00131   };
00132 
00133   /// SCEVHandle - This class is used to maintain the SCEV object's refcounts,
00134   /// freeing the objects when the last reference is dropped.
00135   class SCEVHandle {
00136     SCEV *S;
00137     SCEVHandle();  // DO NOT IMPLEMENT
00138   public:
00139     SCEVHandle(const SCEV *s) : S(const_cast<SCEV*>(s)) {
00140       assert(S && "Cannot create a handle to a null SCEV!");
00141       S->addRef();
00142     }
00143     SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) {
00144       S->addRef();
00145     }
00146     ~SCEVHandle() { S->dropRef(); }
00147 
00148     operator SCEV*() const { return S; }
00149 
00150     SCEV &operator*() const { return *S; }
00151     SCEV *operator->() const { return S; }
00152 
00153     bool operator==(SCEV *RHS) const { return S == RHS; }
00154     bool operator!=(SCEV *RHS) const { return S != RHS; }
00155 
00156     const SCEVHandle &operator=(SCEV *RHS) {
00157       if (S != RHS) {
00158         S->dropRef();
00159         S = RHS;
00160         S->addRef();
00161       }
00162       return *this;
00163     }
00164 
00165     const SCEVHandle &operator=(const SCEVHandle &RHS) {
00166       if (S != RHS.S) {
00167         S->dropRef();
00168         S = RHS.S;
00169         S->addRef();
00170       }
00171       return *this;
00172     }
00173   };
00174 
00175   template<typename From> struct simplify_type;
00176   template<> struct simplify_type<const SCEVHandle> {
00177     typedef SCEV* SimpleType;
00178     static SimpleType getSimplifiedValue(const SCEVHandle &Node) {
00179       return Node;
00180     }
00181   };
00182   template<> struct simplify_type<SCEVHandle>
00183     : public simplify_type<const SCEVHandle> {};
00184 
00185   /// ScalarEvolution - This class is the main scalar evolution driver.  Because
00186   /// client code (intentionally) can't do much with the SCEV objects directly,
00187   /// they must ask this class for services.
00188   ///
00189   class ScalarEvolution : public FunctionPass {
00190     void *Impl;    // ScalarEvolution uses the pimpl pattern
00191   public:
00192     ScalarEvolution() : Impl(0) {}
00193 
00194     /// getSCEV - Return a SCEV expression handle for the full generality of the
00195     /// specified expression.
00196     SCEVHandle getSCEV(Value *V) const;
00197 
00198     /// hasSCEV - Return true if the SCEV for this value has already been
00199     /// computed.
00200     bool hasSCEV(Value *V) const;
00201 
00202     /// setSCEV - Insert the specified SCEV into the map of current SCEVs for
00203     /// the specified value.
00204     void setSCEV(Value *V, const SCEVHandle &H);
00205 
00206     /// getSCEVAtScope - Return a SCEV expression handle for the specified value
00207     /// at the specified scope in the program.  The L value specifies a loop
00208     /// nest to evaluate the expression at, where null is the top-level or a
00209     /// specified loop is immediately inside of the loop.
00210     ///
00211     /// This method can be used to compute the exit value for a variable defined
00212     /// in a loop by querying what the value will hold in the parent loop.
00213     ///
00214     /// If this value is not computable at this scope, a SCEVCouldNotCompute
00215     /// object is returned.
00216     SCEVHandle getSCEVAtScope(Value *V, const Loop *L) const;
00217 
00218     /// getIterationCount - If the specified loop has a predictable iteration
00219     /// count, return it, otherwise return a SCEVCouldNotCompute object.
00220     SCEVHandle getIterationCount(const Loop *L) const;
00221 
00222     /// hasLoopInvariantIterationCount - Return true if the specified loop has
00223     /// an analyzable loop-invariant iteration count.
00224     bool hasLoopInvariantIterationCount(const Loop *L) const;
00225 
00226     /// deleteInstructionFromRecords - This method should be called by the
00227     /// client before it removes an instruction from the program, to make sure
00228     /// that no dangling references are left around.
00229     void deleteInstructionFromRecords(Instruction *I) const;
00230 
00231     virtual bool runOnFunction(Function &F);
00232     virtual void releaseMemory();
00233     virtual void getAnalysisUsage(AnalysisUsage &AU) const;
00234     virtual void print(std::ostream &OS, const Module* = 0) const;
00235   };
00236 }
00237 
00238 #endif