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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_SCALAREVOLUTIONEXPANDER_H
     15 #define LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
     16 
     17 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
     18 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
     19 #include "llvm/Analysis/TargetFolder.h"
     20 #include "llvm/IR/IRBuilder.h"
     21 #include "llvm/IR/ValueHandle.h"
     22 #include <set>
     23 
     24 namespace llvm {
     25   class TargetTransformInfo;
     26 
     27   /// Return true if the given expression is safe to expand in the sense that
     28   /// all materialized values are safe to speculate.
     29   bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
     30 
     31   /// SCEVExpander - This class uses information about analyze scalars to
     32   /// rewrite expressions in canonical form.
     33   ///
     34   /// Clients should create an instance of this class when rewriting is needed,
     35   /// and destroy it when finished to allow the release of the associated
     36   /// memory.
     37   class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
     38     ScalarEvolution &SE;
     39 
     40     // New instructions receive a name to identifies them with the current pass.
     41     const char* IVName;
     42 
     43     // InsertedExpressions caches Values for reuse, so must track RAUW.
     44     std::map<std::pair<const SCEV *, Instruction *>, TrackingVH<Value> >
     45       InsertedExpressions;
     46     // InsertedValues only flags inserted instructions so needs no RAUW.
     47     std::set<AssertingVH<Value> > InsertedValues;
     48     std::set<AssertingVH<Value> > InsertedPostIncValues;
     49 
     50     /// RelevantLoops - A memoization of the "relevant" loop for a given SCEV.
     51     DenseMap<const SCEV *, const Loop *> RelevantLoops;
     52 
     53     /// PostIncLoops - Addrecs referring to any of the given loops are expanded
     54     /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode
     55     /// returns the add instruction that adds one to the phi for {0,+,1}<L>,
     56     /// as opposed to a new phi starting at 1. This is only supported in
     57     /// non-canonical mode.
     58     PostIncLoopSet PostIncLoops;
     59 
     60     /// IVIncInsertPos - When this is non-null, addrecs expanded in the
     61     /// loop it indicates should be inserted with increments at
     62     /// IVIncInsertPos.
     63     const Loop *IVIncInsertLoop;
     64 
     65     /// IVIncInsertPos - When expanding addrecs in the IVIncInsertLoop loop,
     66     /// insert the IV increment at this position.
     67     Instruction *IVIncInsertPos;
     68 
     69     /// Phis that complete an IV chain. Reuse
     70     std::set<AssertingVH<PHINode> > ChainedPhis;
     71 
     72     /// CanonicalMode - When true, expressions are expanded in "canonical"
     73     /// form. In particular, addrecs are expanded as arithmetic based on
     74     /// a canonical induction variable. When false, expression are expanded
     75     /// in a more literal form.
     76     bool CanonicalMode;
     77 
     78     /// When invoked from LSR, the expander is in "strength reduction" mode. The
     79     /// only difference is that phi's are only reused if they are already in
     80     /// "expanded" form.
     81     bool LSRMode;
     82 
     83     typedef IRBuilder<true, TargetFolder> BuilderType;
     84     BuilderType Builder;
     85 
     86 #ifndef NDEBUG
     87     const char *DebugType;
     88 #endif
     89 
     90     friend struct SCEVVisitor<SCEVExpander, Value*>;
     91 
     92   public:
     93     /// SCEVExpander - Construct a SCEVExpander in "canonical" mode.
     94     explicit SCEVExpander(ScalarEvolution &se, const char *name)
     95       : SE(se), IVName(name), IVIncInsertLoop(nullptr), IVIncInsertPos(nullptr),
     96         CanonicalMode(true), LSRMode(false),
     97         Builder(se.getContext(), TargetFolder(se.DL)) {
     98 #ifndef NDEBUG
     99       DebugType = "";
    100 #endif
    101     }
    102 
    103 #ifndef NDEBUG
    104     void setDebugType(const char* s) { DebugType = s; }
    105 #endif
    106 
    107     /// clear - Erase the contents of the InsertedExpressions map so that users
    108     /// trying to expand the same expression into multiple BasicBlocks or
    109     /// different places within the same BasicBlock can do so.
    110     void clear() {
    111       InsertedExpressions.clear();
    112       InsertedValues.clear();
    113       InsertedPostIncValues.clear();
    114       ChainedPhis.clear();
    115     }
    116 
    117     /// getOrInsertCanonicalInductionVariable - This method returns the
    118     /// canonical induction variable of the specified type for the specified
    119     /// loop (inserting one if there is none).  A canonical induction variable
    120     /// starts at zero and steps by one on each iteration.
    121     PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
    122 
    123     /// getIVIncOperand - Return the induction variable increment's IV operand.
    124     Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
    125                                  bool allowScale);
    126 
    127     /// hoistIVInc - Utility for hoisting an IV increment.
    128     bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
    129 
    130     /// replaceCongruentIVs - replace congruent phis with their most canonical
    131     /// representative. Return the number of phis eliminated.
    132     unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
    133                                  SmallVectorImpl<WeakVH> &DeadInsts,
    134                                  const TargetTransformInfo *TTI = nullptr);
    135 
    136     /// expandCodeFor - Insert code to directly compute the specified SCEV
    137     /// expression into the program.  The inserted code is inserted into the
    138     /// specified block.
    139     Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
    140 
    141     /// setIVIncInsertPos - Set the current IV increment loop and position.
    142     void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
    143       assert(!CanonicalMode &&
    144              "IV increment positions are not supported in CanonicalMode");
    145       IVIncInsertLoop = L;
    146       IVIncInsertPos = Pos;
    147     }
    148 
    149     /// setPostInc - Enable post-inc expansion for addrecs referring to the
    150     /// given loops. Post-inc expansion is only supported in non-canonical
    151     /// mode.
    152     void setPostInc(const PostIncLoopSet &L) {
    153       assert(!CanonicalMode &&
    154              "Post-inc expansion is not supported in CanonicalMode");
    155       PostIncLoops = L;
    156     }
    157 
    158     /// clearPostInc - Disable all post-inc expansion.
    159     void clearPostInc() {
    160       PostIncLoops.clear();
    161 
    162       // When we change the post-inc loop set, cached expansions may no
    163       // longer be valid.
    164       InsertedPostIncValues.clear();
    165     }
    166 
    167     /// disableCanonicalMode - Disable the behavior of expanding expressions in
    168     /// canonical form rather than in a more literal form. Non-canonical mode
    169     /// is useful for late optimization passes.
    170     void disableCanonicalMode() { CanonicalMode = false; }
    171 
    172     void enableLSRMode() { LSRMode = true; }
    173 
    174     /// clearInsertPoint - Clear the current insertion point. This is useful
    175     /// if the instruction that had been serving as the insertion point may
    176     /// have been deleted.
    177     void clearInsertPoint() {
    178       Builder.ClearInsertionPoint();
    179     }
    180 
    181     /// isInsertedInstruction - Return true if the specified instruction was
    182     /// inserted by the code rewriter.  If so, the client should not modify the
    183     /// instruction.
    184     bool isInsertedInstruction(Instruction *I) const {
    185       return InsertedValues.count(I) || InsertedPostIncValues.count(I);
    186     }
    187 
    188     void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
    189 
    190   private:
    191     LLVMContext &getContext() const { return SE.getContext(); }
    192 
    193     /// InsertBinop - Insert the specified binary operator, doing a small amount
    194     /// of work to avoid inserting an obviously redundant operation.
    195     Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
    196 
    197     /// ReuseOrCreateCast - Arange for there to be a cast of V to Ty at IP,
    198     /// reusing an existing cast if a suitable one exists, moving an existing
    199     /// cast if a suitable one exists but isn't in the right place, or
    200     /// or creating a new one.
    201     Value *ReuseOrCreateCast(Value *V, Type *Ty,
    202                              Instruction::CastOps Op,
    203                              BasicBlock::iterator IP);
    204 
    205     /// InsertNoopCastOfTo - Insert a cast of V to the specified type,
    206     /// which must be possible with a noop cast, doing what we can to
    207     /// share the casts.
    208     Value *InsertNoopCastOfTo(Value *V, Type *Ty);
    209 
    210     /// expandAddToGEP - Expand a SCEVAddExpr with a pointer type into a GEP
    211     /// instead of using ptrtoint+arithmetic+inttoptr.
    212     Value *expandAddToGEP(const SCEV *const *op_begin,
    213                           const SCEV *const *op_end,
    214                           PointerType *PTy, Type *Ty, Value *V);
    215 
    216     Value *expand(const SCEV *S);
    217 
    218     /// expandCodeFor - Insert code to directly compute the specified SCEV
    219     /// expression into the program.  The inserted code is inserted into the
    220     /// SCEVExpander's current insertion point. If a type is specified, the
    221     /// result will be expanded to have that type, with a cast if necessary.
    222     Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
    223 
    224     /// getRelevantLoop - Determine the most "relevant" loop for the given SCEV.
    225     const Loop *getRelevantLoop(const SCEV *);
    226 
    227     Value *visitConstant(const SCEVConstant *S) {
    228       return S->getValue();
    229     }
    230 
    231     Value *visitTruncateExpr(const SCEVTruncateExpr *S);
    232 
    233     Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
    234 
    235     Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
    236 
    237     Value *visitAddExpr(const SCEVAddExpr *S);
    238 
    239     Value *visitMulExpr(const SCEVMulExpr *S);
    240 
    241     Value *visitUDivExpr(const SCEVUDivExpr *S);
    242 
    243     Value *visitAddRecExpr(const SCEVAddRecExpr *S);
    244 
    245     Value *visitSMaxExpr(const SCEVSMaxExpr *S);
    246 
    247     Value *visitUMaxExpr(const SCEVUMaxExpr *S);
    248 
    249     Value *visitUnknown(const SCEVUnknown *S) {
    250       return S->getValue();
    251     }
    252 
    253     void rememberInstruction(Value *I);
    254 
    255     bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
    256 
    257     bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
    258 
    259     Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
    260     PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
    261                                        const Loop *L,
    262                                        Type *ExpandTy,
    263                                        Type *IntTy,
    264                                        Type *&TruncTy,
    265                                        bool &InvertStep);
    266     Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
    267                        Type *ExpandTy, Type *IntTy, bool useSubtract);
    268   };
    269 }
    270 
    271 #endif
    272