ScalarEvolution.h revision 1997473cf72957d0e70322e2fe6fe2ab141c58a6 
1//===- llvm/Analysis/ScalarEvolution.h - Scalar Evolution -------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by the LLVM research group and is distributed under
6// the University of Illinois Open Source 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/Support/DataTypes.h"
26#include "llvm/Support/Streams.h"
27#include <set>
28
29namespace llvm {
30  class Instruction;
31  class Type;
32  class ConstantRange;
33  class Loop;
34  class LoopInfo;
35  class SCEVHandle;
36
37  /// SCEV - This class represent an analyzed expression in the program.  These
38  /// are reference counted opaque objects that the client is not allowed to
39  /// do much with directly.
40  ///
41  class SCEV {
42    const unsigned SCEVType;      // The SCEV baseclass this node corresponds to
43    mutable unsigned RefCount;
44
45    friend class SCEVHandle;
46    void addRef() const { ++RefCount; }
47    void dropRef() const {
48      if (--RefCount == 0)
49        delete this;
50    }
51
52    SCEV(const SCEV &);            // DO NOT IMPLEMENT
53    void operator=(const SCEV &);  // DO NOT IMPLEMENT
54  protected:
55    virtual ~SCEV();
56  public:
57    SCEV(unsigned SCEVTy) : SCEVType(SCEVTy), RefCount(0) {}
58
59    /// getNegativeSCEV - Return the SCEV object corresponding to -V.
60    ///
61    static SCEVHandle getNegativeSCEV(const SCEVHandle &V);
62
63    /// getMinusSCEV - Return LHS-RHS.
64    ///
65    static SCEVHandle getMinusSCEV(const SCEVHandle &LHS,
66                                   const SCEVHandle &RHS);
67
68
69    unsigned getSCEVType() const { return SCEVType; }
70
71    /// getValueRange - Return the tightest constant bounds that this value is
72    /// known to have.  This method is only valid on integer SCEV objects.
73    virtual ConstantRange getValueRange() const;
74
75    /// isLoopInvariant - Return true if the value of this SCEV is unchanging in
76    /// the specified loop.
77    virtual bool isLoopInvariant(const Loop *L) const = 0;
78
79    /// hasComputableLoopEvolution - Return true if this SCEV changes value in a
80    /// known way in the specified loop.  This property being true implies that
81    /// the value is variant in the loop AND that we can emit an expression to
82    /// compute the value of the expression at any particular loop iteration.
83    virtual bool hasComputableLoopEvolution(const Loop *L) const = 0;
84
85    /// getType - Return the LLVM type of this SCEV expression.
86    ///
87    virtual const Type *getType() const = 0;
88
89    /// getBitWidth - Get the bit width of the type, if it has one, 0 otherwise.
90    ///
91    uint32_t getBitWidth() const;
92
93    /// replaceSymbolicValuesWithConcrete - If this SCEV internally references
94    /// the symbolic value "Sym", construct and return a new SCEV that produces
95    /// the same value, but which uses the concrete value Conc instead of the
96    /// symbolic value.  If this SCEV does not use the symbolic value, it
97    /// returns itself.
98    virtual SCEVHandle
99    replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
100                                      const SCEVHandle &Conc) const = 0;
101
102    /// print - Print out the internal representation of this scalar to the
103    /// specified stream.  This should really only be used for debugging
104    /// purposes.
105    virtual void print(std::ostream &OS) const = 0;
106    void print(std::ostream *OS) const { if (OS) print(*OS); }
107
108    /// dump - This method is used for debugging.
109    ///
110    void dump() const;
111  };
112
113  inline std::ostream &operator<<(std::ostream &OS, const SCEV &S) {
114    S.print(OS);
115    return OS;
116  }
117
118  /// SCEVCouldNotCompute - An object of this class is returned by queries that
119  /// could not be answered.  For example, if you ask for the number of
120  /// iterations of a linked-list traversal loop, you will get one of these.
121  /// None of the standard SCEV operations are valid on this class, it is just a
122  /// marker.
123  struct SCEVCouldNotCompute : public SCEV {
124    SCEVCouldNotCompute();
125
126    // None of these methods are valid for this object.
127    virtual bool isLoopInvariant(const Loop *L) const;
128    virtual const Type *getType() const;
129    virtual bool hasComputableLoopEvolution(const Loop *L) const;
130    virtual void print(std::ostream &OS) const;
131    void print(std::ostream *OS) const { if (OS) print(*OS); }
132    virtual SCEVHandle
133    replaceSymbolicValuesWithConcrete(const SCEVHandle &Sym,
134                                      const SCEVHandle &Conc) const;
135
136    /// Methods for support type inquiry through isa, cast, and dyn_cast:
137    static inline bool classof(const SCEVCouldNotCompute *S) { return true; }
138    static bool classof(const SCEV *S);
139  };
140
141  /// SCEVHandle - This class is used to maintain the SCEV object's refcounts,
142  /// freeing the objects when the last reference is dropped.
143  class SCEVHandle {
144    SCEV *S;
145    SCEVHandle();  // DO NOT IMPLEMENT
146  public:
147    SCEVHandle(const SCEV *s) : S(const_cast<SCEV*>(s)) {
148      assert(S && "Cannot create a handle to a null SCEV!");
149      S->addRef();
150    }
151    SCEVHandle(const SCEVHandle &RHS) : S(RHS.S) {
152      S->addRef();
153    }
154    ~SCEVHandle() { S->dropRef(); }
155
156    operator SCEV*() const { return S; }
157
158    SCEV &operator*() const { return *S; }
159    SCEV *operator->() const { return S; }
160
161    bool operator==(SCEV *RHS) const { return S == RHS; }
162    bool operator!=(SCEV *RHS) const { return S != RHS; }
163
164    const SCEVHandle &operator=(SCEV *RHS) {
165      if (S != RHS) {
166        S->dropRef();
167        S = RHS;
168        S->addRef();
169      }
170      return *this;
171    }
172
173    const SCEVHandle &operator=(const SCEVHandle &RHS) {
174      if (S != RHS.S) {
175        S->dropRef();
176        S = RHS.S;
177        S->addRef();
178      }
179      return *this;
180    }
181  };
182
183  template<typename From> struct simplify_type;
184  template<> struct simplify_type<const SCEVHandle> {
185    typedef SCEV* SimpleType;
186    static SimpleType getSimplifiedValue(const SCEVHandle &Node) {
187      return Node;
188    }
189  };
190  template<> struct simplify_type<SCEVHandle>
191    : public simplify_type<const SCEVHandle> {};
192
193  /// ScalarEvolution - This class is the main scalar evolution driver.  Because
194  /// client code (intentionally) can't do much with the SCEV objects directly,
195  /// they must ask this class for services.
196  ///
197  class ScalarEvolution : public FunctionPass {
198    void *Impl;    // ScalarEvolution uses the pimpl pattern
199  public:
200    static char ID; // Pass identifcation, replacement for typeid
201    ScalarEvolution() : FunctionPass((intptr_t)&ID), Impl(0) {}
202
203    /// getSCEV - Return a SCEV expression handle for the full generality of the
204    /// specified expression.
205    SCEVHandle getSCEV(Value *V) const;
206
207    /// hasSCEV - Return true if the SCEV for this value has already been
208    /// computed.
209    bool hasSCEV(Value *V) const;
210
211    /// setSCEV - Insert the specified SCEV into the map of current SCEVs for
212    /// the specified value.
213    void setSCEV(Value *V, const SCEVHandle &H);
214
215    /// getSCEVAtScope - Return a SCEV expression handle for the specified value
216    /// at the specified scope in the program.  The L value specifies a loop
217    /// nest to evaluate the expression at, where null is the top-level or a
218    /// specified loop is immediately inside of the loop.
219    ///
220    /// This method can be used to compute the exit value for a variable defined
221    /// in a loop by querying what the value will hold in the parent loop.
222    ///
223    /// If this value is not computable at this scope, a SCEVCouldNotCompute
224    /// object is returned.
225    SCEVHandle getSCEVAtScope(Value *V, const Loop *L) const;
226
227    /// getIterationCount - If the specified loop has a predictable iteration
228    /// count, return it, otherwise return a SCEVCouldNotCompute object.
229    SCEVHandle getIterationCount(const Loop *L) const;
230
231    /// hasLoopInvariantIterationCount - Return true if the specified loop has
232    /// an analyzable loop-invariant iteration count.
233    bool hasLoopInvariantIterationCount(const Loop *L) const;
234
235    /// deleteInstructionFromRecords - This method should be called by the
236    /// client before it removes an instruction from the program, to make sure
237    /// that no dangling references are left around.
238    void deleteInstructionFromRecords(Instruction *I) const;
239
240    virtual bool runOnFunction(Function &F);
241    virtual void releaseMemory();
242    virtual void getAnalysisUsage(AnalysisUsage &AU) const;
243    virtual void print(std::ostream &OS, const Module* = 0) const;
244    void print(std::ostream *OS, const Module* M = 0) const {
245      if (OS) print(*OS, M);
246    }
247  };
248}
249
250#endif
251