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      1 //===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- 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 // This file defines the classes used to generate code from scalar expressions.
     11 //
     12 //===----------------------------------------------------------------------===//
     13 
     14 #ifndef LLVM_ANALYSIS_SCALAREVOLUTION_EXPANDER_H
     15 #define LLVM_ANALYSIS_SCALAREVOLUTION_EXPANDER_H
     16 
     17 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
     18 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
     19 #include "llvm/Support/IRBuilder.h"
     20 #include "llvm/Support/TargetFolder.h"
     21 #include "llvm/Support/ValueHandle.h"
     22 #include <set>
     23 
     24 namespace llvm {
     25   /// SCEVExpander - This class uses information about analyze scalars to
     26   /// rewrite expressions in canonical form.
     27   ///
     28   /// Clients should create an instance of this class when rewriting is needed,
     29   /// and destroy it when finished to allow the release of the associated
     30   /// memory.
     31   class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
     32     ScalarEvolution &SE;
     33 
     34     // New instructions receive a name to identifies them with the current pass.
     35     const char* IVName;
     36 
     37     std::map<std::pair<const SCEV *, Instruction *>, AssertingVH<Value> >
     38       InsertedExpressions;
     39     std::set<AssertingVH<Value> > InsertedValues;
     40     std::set<AssertingVH<Value> > InsertedPostIncValues;
     41 
     42     /// RelevantLoops - A memoization of the "relevant" loop for a given SCEV.
     43     DenseMap<const SCEV *, const Loop *> RelevantLoops;
     44 
     45     /// PostIncLoops - Addrecs referring to any of the given loops are expanded
     46     /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
     47     /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
     48     /// as opposed to a new phi starting at 1. This is only supported in
     49     /// non-canonical mode.
     50     PostIncLoopSet PostIncLoops;
     51 
     52     /// IVIncInsertPos - When this is non-null, addrecs expanded in the
     53     /// loop it indicates should be inserted with increments at
     54     /// IVIncInsertPos.
     55     const Loop *IVIncInsertLoop;
     56 
     57     /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
     58     /// insert the IV increment at this position.
     59     Instruction *IVIncInsertPos;
     60 
     61     /// CanonicalMode - When true, expressions are expanded in "canonical"
     62     /// form. In particular, addrecs are expanded as arithmetic based on
     63     /// a canonical induction variable. When false, expression are expanded
     64     /// in a more literal form.
     65     bool CanonicalMode;
     66 
     67     typedef IRBuilder<true, TargetFolder> BuilderType;
     68     BuilderType Builder;
     69 
     70     friend struct SCEVVisitor<SCEVExpander, Value*>;
     71 
     72   public:
     73     /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
     74     explicit SCEVExpander(ScalarEvolution &se, const char *name)
     75       : SE(se), IVName(name), IVIncInsertLoop(0), IVIncInsertPos(0),
     76         CanonicalMode(true), Builder(se.getContext(), TargetFolder(se.TD)) {}
     77 
     78     /// clear - Erase the contents of the InsertedExpressions map so that users
     79     /// trying to expand the same expression into multiple BasicBlocks or
     80     /// different places within the same BasicBlock can do so.
     81     void clear() {
     82       InsertedExpressions.clear();
     83       InsertedValues.clear();
     84       InsertedPostIncValues.clear();
     85     }
     86 
     87     /// getOrInsertCanonicalInductionVariable - This method returns the
     88     /// canonical induction variable of the specified type for the specified
     89     /// loop (inserting one if there is none).  A canonical induction variable
     90     /// starts at zero and steps by one on each iteration.
     91     PHINode *getOrInsertCanonicalInductionVariable(const Loop *L,
     92                                                    Type *Ty);
     93 
     94     /// expandCodeFor - Insert code to directly compute the specified SCEV
     95     /// expression into the program.  The inserted code is inserted into the
     96     /// specified block.
     97     Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
     98 
     99     /// setIVIncInsertPos - Set the current IV increment loop and position.
    100     void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
    101       assert(!CanonicalMode &&
    102              "IV increment positions are not supported in CanonicalMode");
    103       IVIncInsertLoop = L;
    104       IVIncInsertPos = Pos;
    105     }
    106 
    107     /// setPostInc - Enable post-inc expansion for addrecs referring to the
    108     /// given loops. Post-inc expansion is only supported in non-canonical
    109     /// mode.
    110     void setPostInc(const PostIncLoopSet &L) {
    111       assert(!CanonicalMode &&
    112              "Post-inc expansion is not supported in CanonicalMode");
    113       PostIncLoops = L;
    114     }
    115 
    116     /// clearPostInc - Disable all post-inc expansion.
    117     void clearPostInc() {
    118       PostIncLoops.clear();
    119 
    120       // When we change the post-inc loop set, cached expansions may no
    121       // longer be valid.
    122       InsertedPostIncValues.clear();
    123     }
    124 
    125     /// disableCanonicalMode - Disable the behavior of expanding expressions in
    126     /// canonical form rather than in a more literal form. Non-canonical mode
    127     /// is useful for late optimization passes.
    128     void disableCanonicalMode() { CanonicalMode = false; }
    129 
    130     /// clearInsertPoint - Clear the current insertion point. This is useful
    131     /// if the instruction that had been serving as the insertion point may
    132     /// have been deleted.
    133     void clearInsertPoint() {
    134       Builder.ClearInsertionPoint();
    135     }
    136 
    137   private:
    138     LLVMContext &getContext() const { return SE.getContext(); }
    139 
    140     /// InsertBinop - Insert the specified binary operator, doing a small amount
    141     /// of work to avoid inserting an obviously redundant operation.
    142     Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
    143 
    144     /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
    145     /// reusing an existing cast if a suitable one exists, moving an existing
    146     /// cast if a suitable one exists but isn't in the right place, or
    147     /// or creating a new one.
    148     Value *ReuseOrCreateCast(Value *V, Type *Ty,
    149                              Instruction::CastOps Op,
    150                              BasicBlock::iterator IP);
    151 
    152     /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
    153     /// which must be possible with a noop cast, doing what we can to
    154     /// share the casts.
    155     Value *InsertNoopCastOfTo(Value *V, Type *Ty);
    156 
    157     /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
    158     /// instead of using ptrtoint+arithmetic+inttoptr.
    159     Value *expandAddToGEP(const SCEV *const *op_begin,
    160                           const SCEV *const *op_end,
    161                           PointerType *PTy, Type *Ty, Value *V);
    162 
    163     Value *expand(const SCEV *S);
    164 
    165     /// expandCodeFor - Insert code to directly compute the specified SCEV
    166     /// expression into the program.  The inserted code is inserted into the
    167     /// SCEVExpander's current insertion point. If a type is specified, the
    168     /// result will be expanded to have that type, with a cast if necessary.
    169     Value *expandCodeFor(const SCEV *SH, Type *Ty = 0);
    170 
    171     /// isInsertedInstruction - Return true if the specified instruction was
    172     /// inserted by the code rewriter.  If so, the client should not modify the
    173     /// instruction.
    174     bool isInsertedInstruction(Instruction *I) const {
    175       return InsertedValues.count(I) || InsertedPostIncValues.count(I);
    176     }
    177 
    178     /// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
    179     const Loop *getRelevantLoop(const SCEV *);
    180 
    181     Value *visitConstant(const SCEVConstant *S) {
    182       return S->getValue();
    183     }
    184 
    185     Value *visitTruncateExpr(const SCEVTruncateExpr *S);
    186 
    187     Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
    188 
    189     Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
    190 
    191     Value *visitAddExpr(const SCEVAddExpr *S);
    192 
    193     Value *visitMulExpr(const SCEVMulExpr *S);
    194 
    195     Value *visitUDivExpr(const SCEVUDivExpr *S);
    196 
    197     Value *visitAddRecExpr(const SCEVAddRecExpr *S);
    198 
    199     Value *visitSMaxExpr(const SCEVSMaxExpr *S);
    200 
    201     Value *visitUMaxExpr(const SCEVUMaxExpr *S);
    202 
    203     Value *visitUnknown(const SCEVUnknown *S) {
    204       return S->getValue();
    205     }
    206 
    207     void rememberInstruction(Value *I);
    208 
    209     void restoreInsertPoint(BasicBlock *BB, BasicBlock::iterator I);
    210 
    211     Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
    212     PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
    213                                        const Loop *L,
    214                                        Type *ExpandTy,
    215                                        Type *IntTy);
    216   };
    217 }
    218 
    219 #endif
    220