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Current view: top level - include/llvm/Analysis - ScalarEvolutionExpander.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 40 40 100.0 %
Date: 2017-09-14 15:23:50 Functions: 7 7 100.0 %
Legend: Lines: hit not hit

          Line data    Source code
       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/ADT/DenseMap.h"
      18             : #include "llvm/ADT/DenseSet.h"
      19             : #include "llvm/ADT/Optional.h"
      20             : #include "llvm/Analysis/ScalarEvolutionExpressions.h"
      21             : #include "llvm/Analysis/ScalarEvolutionNormalization.h"
      22             : #include "llvm/Analysis/TargetFolder.h"
      23             : #include "llvm/IR/IRBuilder.h"
      24             : #include "llvm/IR/ValueHandle.h"
      25             : 
      26             : namespace llvm {
      27             :   class TargetTransformInfo;
      28             : 
      29             :   /// Return true if the given expression is safe to expand in the sense that
      30             :   /// all materialized values are safe to speculate.
      31             :   bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
      32             : 
      33             :   /// This class uses information about analyze scalars to rewrite expressions
      34             :   /// in canonical form.
      35             :   ///
      36             :   /// Clients should create an instance of this class when rewriting is needed,
      37             :   /// and destroy it when finished to allow the release of the associated
      38             :   /// memory.
      39             :   class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
      40             :     ScalarEvolution &SE;
      41             :     const DataLayout &DL;
      42             : 
      43             :     // New instructions receive a name to identifies them with the current pass.
      44             :     const char* IVName;
      45             : 
      46             :     // InsertedExpressions caches Values for reuse, so must track RAUW.
      47             :     DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
      48             :         InsertedExpressions;
      49             : 
      50             :     // InsertedValues only flags inserted instructions so needs no RAUW.
      51             :     DenseSet<AssertingVH<Value>> InsertedValues;
      52             :     DenseSet<AssertingVH<Value>> InsertedPostIncValues;
      53             : 
      54             :     /// A memoization of the "relevant" loop for a given SCEV.
      55             :     DenseMap<const SCEV *, const Loop *> RelevantLoops;
      56             : 
      57             :     /// Addrecs referring to any of the given loops are expanded in post-inc
      58             :     /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
      59             :     /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
      60             :     /// phi starting at 1. This is only supported in non-canonical mode.
      61             :     PostIncLoopSet PostIncLoops;
      62             : 
      63             :     /// When this is non-null, addrecs expanded in the loop it indicates should
      64             :     /// be inserted with increments at IVIncInsertPos.
      65             :     const Loop *IVIncInsertLoop;
      66             : 
      67             :     /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
      68             :     /// increment at this position.
      69             :     Instruction *IVIncInsertPos;
      70             : 
      71             :     /// Phis that complete an IV chain. Reuse
      72             :     DenseSet<AssertingVH<PHINode>> ChainedPhis;
      73             : 
      74             :     /// When true, expressions are expanded in "canonical" form. In particular,
      75             :     /// addrecs are expanded as arithmetic based on a canonical induction
      76             :     /// variable. When false, expression are expanded in a more literal form.
      77             :     bool CanonicalMode;
      78             : 
      79             :     /// When invoked from LSR, the expander is in "strength reduction" mode. The
      80             :     /// only difference is that phi's are only reused if they are already in
      81             :     /// "expanded" form.
      82             :     bool LSRMode;
      83             : 
      84             :     typedef IRBuilder<TargetFolder> BuilderType;
      85             :     BuilderType Builder;
      86             : 
      87             :     // RAII object that stores the current insertion point and restores it when
      88             :     // the object is destroyed. This includes the debug location.  Duplicated
      89             :     // from InsertPointGuard to add SetInsertPoint() which is used to updated
      90             :     // InsertPointGuards stack when insert points are moved during SCEV
      91             :     // expansion.
      92             :     class SCEVInsertPointGuard {
      93             :       IRBuilderBase &Builder;
      94             :       AssertingVH<BasicBlock> Block;
      95             :       BasicBlock::iterator Point;
      96             :       DebugLoc DbgLoc;
      97             :       SCEVExpander *SE;
      98             : 
      99             :       SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
     100             :       SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
     101             : 
     102             :     public:
     103       69587 :       SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
     104       69587 :           : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
     105      208761 :             DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
     106       69587 :         SE->InsertPointGuards.push_back(this);
     107       69587 :       }
     108             : 
     109      208761 :       ~SCEVInsertPointGuard() {
     110             :         // These guards should always created/destroyed in FIFO order since they
     111             :         // are used to guard lexically scoped blocks of code in
     112             :         // ScalarEvolutionExpander.
     113             :         assert(SE->InsertPointGuards.back() == this);
     114      139174 :         SE->InsertPointGuards.pop_back();
     115      208761 :         Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
     116      278348 :         Builder.SetCurrentDebugLocation(DbgLoc);
     117       69587 :       }
     118             : 
     119             :       BasicBlock::iterator GetInsertPoint() const { return Point; }
     120           1 :       void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
     121             :     };
     122             : 
     123             :     /// Stack of pointers to saved insert points, used to keep insert points
     124             :     /// consistent when instructions are moved.
     125             :     SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
     126             : 
     127             : #ifndef NDEBUG
     128             :     const char *DebugType;
     129             : #endif
     130             : 
     131             :     friend struct SCEVVisitor<SCEVExpander, Value*>;
     132             : 
     133             :   public:
     134             :     /// Construct a SCEVExpander in "canonical" mode.
     135       18419 :     explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
     136             :                           const char *name)
     137       18419 :         : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
     138             :           IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
     139      184190 :           Builder(se.getContext(), TargetFolder(DL)) {
     140             : #ifndef NDEBUG
     141             :       DebugType = "";
     142             : #endif
     143       18419 :     }
     144             : 
     145      165771 :     ~SCEVExpander() {
     146             :       // Make sure the insert point guard stack is consistent.
     147             :       assert(InsertPointGuards.empty());
     148       18419 :     }
     149             : 
     150             : #ifndef NDEBUG
     151             :     void setDebugType(const char* s) { DebugType = s; }
     152             : #endif
     153             : 
     154             :     /// Erase the contents of the InsertedExpressions map so that users trying
     155             :     /// to expand the same expression into multiple BasicBlocks or different
     156             :     /// places within the same BasicBlock can do so.
     157        6432 :     void clear() {
     158        6432 :       InsertedExpressions.clear();
     159       12864 :       InsertedValues.clear();
     160       12864 :       InsertedPostIncValues.clear();
     161       12864 :       ChainedPhis.clear();
     162        6432 :     }
     163             : 
     164             :     /// Return true for expressions that may incur non-trivial cost to evaluate
     165             :     /// at runtime.
     166             :     ///
     167             :     /// At is an optional parameter which specifies point in code where user is
     168             :     /// going to expand this expression. Sometimes this knowledge can lead to a
     169             :     /// more accurate cost estimation.
     170        1840 :     bool isHighCostExpansion(const SCEV *Expr, Loop *L,
     171             :                              const Instruction *At = nullptr) {
     172        3680 :       SmallPtrSet<const SCEV *, 8> Processed;
     173        3680 :       return isHighCostExpansionHelper(Expr, L, At, Processed);
     174             :     }
     175             : 
     176             :     /// This method returns the canonical induction variable of the specified
     177             :     /// type for the specified loop (inserting one if there is none).  A
     178             :     /// canonical induction variable starts at zero and steps by one on each
     179             :     /// iteration.
     180             :     PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
     181             : 
     182             :     /// Return the induction variable increment's IV operand.
     183             :     Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
     184             :                                  bool allowScale);
     185             : 
     186             :     /// Utility for hoisting an IV increment.
     187             :     bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
     188             : 
     189             :     /// replace congruent phis with their most canonical representative. Return
     190             :     /// the number of phis eliminated.
     191             :     unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
     192             :                                  SmallVectorImpl<WeakTrackingVH> &DeadInsts,
     193             :                                  const TargetTransformInfo *TTI = nullptr);
     194             : 
     195             :     /// Insert code to directly compute the specified SCEV expression into the
     196             :     /// program.  The inserted code is inserted into the specified block.
     197             :     Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
     198             : 
     199             :     /// Insert code to directly compute the specified SCEV expression into the
     200             :     /// program.  The inserted code is inserted into the SCEVExpander's current
     201             :     /// insertion point. If a type is specified, the result will be expanded to
     202             :     /// have that type, with a cast if necessary.
     203             :     Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
     204             : 
     205             : 
     206             :     /// Generates a code sequence that evaluates this predicate.  The inserted
     207             :     /// instructions will be at position \p Loc.  The result will be of type i1
     208             :     /// and will have a value of 0 when the predicate is false and 1 otherwise.
     209             :     Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
     210             : 
     211             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     212             :     /// we are expanding code for a SCEVEqualPredicate.
     213             :     Value *expandEqualPredicate(const SCEVEqualPredicate *Pred,
     214             :                                 Instruction *Loc);
     215             : 
     216             :     /// Generates code that evaluates if the \p AR expression will overflow.
     217             :     Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
     218             :                                  bool Signed);
     219             : 
     220             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     221             :     /// we are expanding code for a SCEVWrapPredicate.
     222             :     Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
     223             : 
     224             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     225             :     /// we are expanding code for a SCEVUnionPredicate.
     226             :     Value *expandUnionPredicate(const SCEVUnionPredicate *Pred,
     227             :                                 Instruction *Loc);
     228             : 
     229             :     /// Set the current IV increment loop and position.
     230             :     void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
     231             :       assert(!CanonicalMode &&
     232             :              "IV increment positions are not supported in CanonicalMode");
     233        2618 :       IVIncInsertLoop = L;
     234        2618 :       IVIncInsertPos = Pos;
     235             :     }
     236             : 
     237             :     /// Enable post-inc expansion for addrecs referring to the given
     238             :     /// loops. Post-inc expansion is only supported in non-canonical mode.
     239             :     void setPostInc(const PostIncLoopSet &L) {
     240             :       assert(!CanonicalMode &&
     241             :              "Post-inc expansion is not supported in CanonicalMode");
     242       18206 :       PostIncLoops = L;
     243             :     }
     244             : 
     245             :     /// Disable all post-inc expansion.
     246             :     void clearPostInc() {
     247        9949 :       PostIncLoops.clear();
     248             : 
     249             :       // When we change the post-inc loop set, cached expansions may no
     250             :       // longer be valid.
     251       19898 :       InsertedPostIncValues.clear();
     252             :     }
     253             : 
     254             :     /// Disable the behavior of expanding expressions in canonical form rather
     255             :     /// than in a more literal form. Non-canonical mode is useful for late
     256             :     /// optimization passes.
     257        6281 :     void disableCanonicalMode() { CanonicalMode = false; }
     258             : 
     259        2618 :     void enableLSRMode() { LSRMode = true; }
     260             : 
     261             :     /// Set the current insertion point. This is useful if multiple calls to
     262             :     /// expandCodeFor() are going to be made with the same insert point and the
     263             :     /// insert point may be moved during one of the expansions (e.g. if the
     264             :     /// insert point is not a block terminator).
     265             :     void setInsertPoint(Instruction *IP) {
     266             :       assert(IP);
     267       23328 :       Builder.SetInsertPoint(IP);
     268             :     }
     269             : 
     270             :     /// Clear the current insertion point. This is useful if the instruction
     271             :     /// that had been serving as the insertion point may have been deleted.
     272             :     void clearInsertPoint() {
     273        2670 :       Builder.ClearInsertionPoint();
     274             :     }
     275             : 
     276             :     /// Return true if the specified instruction was inserted by the code
     277             :     /// rewriter.  If so, the client should not modify the instruction.
     278       24792 :     bool isInsertedInstruction(Instruction *I) const {
     279      116366 :       return InsertedValues.count(I) || InsertedPostIncValues.count(I);
     280             :     }
     281             : 
     282         549 :     void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
     283             : 
     284             :     /// Try to find existing LLVM IR value for S available at the point At.
     285             :     Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
     286             :                                      Loop *L);
     287             : 
     288             :     /// Try to find the ValueOffsetPair for S. The function is mainly used to
     289             :     /// check whether S can be expanded cheaply.  If this returns a non-None
     290             :     /// value, we know we can codegen the `ValueOffsetPair` into a suitable
     291             :     /// expansion identical with S so that S can be expanded cheaply.
     292             :     ///
     293             :     /// L is a hint which tells in which loop to look for the suitable value.
     294             :     /// On success return value which is equivalent to the expanded S at point
     295             :     /// At. Return nullptr if value was not found.
     296             :     ///
     297             :     /// Note that this function does not perform an exhaustive search. I.e if it
     298             :     /// didn't find any value it does not mean that there is no such value.
     299             :     ///
     300             :     Optional<ScalarEvolution::ValueOffsetPair>
     301             :     getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
     302             : 
     303             :   private:
     304             :     LLVMContext &getContext() const { return SE.getContext(); }
     305             : 
     306             :     /// Recursive helper function for isHighCostExpansion.
     307             :     bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
     308             :                                    const Instruction *At,
     309             :                                    SmallPtrSetImpl<const SCEV *> &Processed);
     310             : 
     311             :     /// Insert the specified binary operator, doing a small amount of work to
     312             :     /// avoid inserting an obviously redundant operation.
     313             :     Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
     314             : 
     315             :     /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
     316             :     /// cast if a suitable one exists, moving an existing cast if a suitable one
     317             :     /// exists but isn't in the right place, or or creating a new one.
     318             :     Value *ReuseOrCreateCast(Value *V, Type *Ty,
     319             :                              Instruction::CastOps Op,
     320             :                              BasicBlock::iterator IP);
     321             : 
     322             :     /// Insert a cast of V to the specified type, which must be possible with a
     323             :     /// noop cast, doing what we can to share the casts.
     324             :     Value *InsertNoopCastOfTo(Value *V, Type *Ty);
     325             : 
     326             :     /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
     327             :     /// ptrtoint+arithmetic+inttoptr.
     328             :     Value *expandAddToGEP(const SCEV *const *op_begin,
     329             :                           const SCEV *const *op_end,
     330             :                           PointerType *PTy, Type *Ty, Value *V);
     331             : 
     332             :     /// Find a previous Value in ExprValueMap for expand.
     333             :     ScalarEvolution::ValueOffsetPair
     334             :     FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);
     335             : 
     336             :     Value *expand(const SCEV *S);
     337             : 
     338             :     /// Determine the most "relevant" loop for the given SCEV.
     339             :     const Loop *getRelevantLoop(const SCEV *);
     340             : 
     341             :     Value *visitConstant(const SCEVConstant *S) {
     342       10382 :       return S->getValue();
     343             :     }
     344             : 
     345             :     Value *visitTruncateExpr(const SCEVTruncateExpr *S);
     346             : 
     347             :     Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
     348             : 
     349             :     Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
     350             : 
     351             :     Value *visitAddExpr(const SCEVAddExpr *S);
     352             : 
     353             :     Value *visitMulExpr(const SCEVMulExpr *S);
     354             : 
     355             :     Value *visitUDivExpr(const SCEVUDivExpr *S);
     356             : 
     357             :     Value *visitAddRecExpr(const SCEVAddRecExpr *S);
     358             : 
     359             :     Value *visitSMaxExpr(const SCEVSMaxExpr *S);
     360             : 
     361             :     Value *visitUMaxExpr(const SCEVUMaxExpr *S);
     362             : 
     363             :     Value *visitUnknown(const SCEVUnknown *S) {
     364       24597 :       return S->getValue();
     365             :     }
     366             : 
     367             :     void rememberInstruction(Value *I);
     368             : 
     369             :     bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
     370             : 
     371             :     bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
     372             : 
     373             :     Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
     374             :     PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
     375             :                                        const Loop *L,
     376             :                                        Type *ExpandTy,
     377             :                                        Type *IntTy,
     378             :                                        Type *&TruncTy,
     379             :                                        bool &InvertStep);
     380             :     Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
     381             :                        Type *ExpandTy, Type *IntTy, bool useSubtract);
     382             : 
     383             :     void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
     384             :                         Instruction *Pos, PHINode *LoopPhi);
     385             : 
     386             :     void fixupInsertPoints(Instruction *I);
     387             :   };
     388             : }
     389             : 
     390             : #endif

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