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Current view: top level - include/llvm/Analysis - ScalarEvolutionExpander.h (source / functions) Hit Total Coverage
Test: llvm-toolchain.info Lines: 33 33 100.0 %
Date: 2018-05-20 00:06:23 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 anywhere their operands are
      31             :   /// defined.
      32             :   bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
      33             : 
      34             :   /// Return true if the given expression is safe to expand in the sense that
      35             :   /// all materialized values are defined and safe to speculate at the specified
      36             :   /// location and their operands are defined at this location.
      37             :   bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint,
      38             :                         ScalarEvolution &SE);
      39             : 
      40             :   /// This class uses information about analyze scalars to rewrite expressions
      41             :   /// in canonical form.
      42             :   ///
      43             :   /// Clients should create an instance of this class when rewriting is needed,
      44             :   /// and destroy it when finished to allow the release of the associated
      45             :   /// memory.
      46             :   class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> {
      47             :     ScalarEvolution &SE;
      48             :     const DataLayout &DL;
      49             : 
      50             :     // New instructions receive a name to identify them with the current pass.
      51             :     const char* IVName;
      52             : 
      53             :     // InsertedExpressions caches Values for reuse, so must track RAUW.
      54             :     DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
      55             :         InsertedExpressions;
      56             : 
      57             :     // InsertedValues only flags inserted instructions so needs no RAUW.
      58             :     DenseSet<AssertingVH<Value>> InsertedValues;
      59             :     DenseSet<AssertingVH<Value>> InsertedPostIncValues;
      60             : 
      61             :     /// A memoization of the "relevant" loop for a given SCEV.
      62             :     DenseMap<const SCEV *, const Loop *> RelevantLoops;
      63             : 
      64             :     /// Addrecs referring to any of the given loops are expanded in post-inc
      65             :     /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
      66             :     /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
      67             :     /// phi starting at 1. This is only supported in non-canonical mode.
      68             :     PostIncLoopSet PostIncLoops;
      69             : 
      70             :     /// When this is non-null, addrecs expanded in the loop it indicates should
      71             :     /// be inserted with increments at IVIncInsertPos.
      72             :     const Loop *IVIncInsertLoop;
      73             : 
      74             :     /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
      75             :     /// increment at this position.
      76             :     Instruction *IVIncInsertPos;
      77             : 
      78             :     /// Phis that complete an IV chain. Reuse
      79             :     DenseSet<AssertingVH<PHINode>> ChainedPhis;
      80             : 
      81             :     /// When true, expressions are expanded in "canonical" form. In particular,
      82             :     /// addrecs are expanded as arithmetic based on a canonical induction
      83             :     /// variable. When false, expression are expanded in a more literal form.
      84             :     bool CanonicalMode;
      85             : 
      86             :     /// When invoked from LSR, the expander is in "strength reduction" mode. The
      87             :     /// only difference is that phi's are only reused if they are already in
      88             :     /// "expanded" form.
      89             :     bool LSRMode;
      90             : 
      91             :     typedef IRBuilder<TargetFolder> BuilderType;
      92             :     BuilderType Builder;
      93             : 
      94             :     // RAII object that stores the current insertion point and restores it when
      95             :     // the object is destroyed. This includes the debug location.  Duplicated
      96             :     // from InsertPointGuard to add SetInsertPoint() which is used to updated
      97             :     // InsertPointGuards stack when insert points are moved during SCEV
      98             :     // expansion.
      99             :     class SCEVInsertPointGuard {
     100             :       IRBuilderBase &Builder;
     101             :       AssertingVH<BasicBlock> Block;
     102             :       BasicBlock::iterator Point;
     103             :       DebugLoc DbgLoc;
     104             :       SCEVExpander *SE;
     105             : 
     106             :       SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
     107             :       SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
     108             : 
     109             :     public:
     110       96142 :       SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
     111       96142 :           : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
     112      288426 :             DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
     113       96142 :         SE->InsertPointGuards.push_back(this);
     114       96142 :       }
     115             : 
     116      192284 :       ~SCEVInsertPointGuard() {
     117             :         // These guards should always created/destroyed in FIFO order since they
     118             :         // are used to guard lexically scoped blocks of code in
     119             :         // ScalarEvolutionExpander.
     120             :         assert(SE->InsertPointGuards.back() == this);
     121       96142 :         SE->InsertPointGuards.pop_back();
     122       96142 :         Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
     123      192284 :         Builder.SetCurrentDebugLocation(DbgLoc);
     124       96142 :       }
     125             : 
     126             :       BasicBlock::iterator GetInsertPoint() const { return Point; }
     127           1 :       void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
     128             :     };
     129             : 
     130             :     /// Stack of pointers to saved insert points, used to keep insert points
     131             :     /// consistent when instructions are moved.
     132             :     SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
     133             : 
     134             : #ifndef NDEBUG
     135             :     const char *DebugType;
     136             : #endif
     137             : 
     138             :     friend struct SCEVVisitor<SCEVExpander, Value*>;
     139             : 
     140             :   public:
     141             :     /// Construct a SCEVExpander in "canonical" mode.
     142       21073 :     explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
     143             :                           const char *name)
     144       21073 :         : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
     145             :           IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
     146       84292 :           Builder(se.getContext(), TargetFolder(DL)) {
     147             : #ifndef NDEBUG
     148             :       DebugType = "";
     149             : #endif
     150       21073 :     }
     151             : 
     152       63219 :     ~SCEVExpander() {
     153             :       // Make sure the insert point guard stack is consistent.
     154             :       assert(InsertPointGuards.empty());
     155       21073 :     }
     156             : 
     157             : #ifndef NDEBUG
     158             :     void setDebugType(const char* s) { DebugType = s; }
     159             : #endif
     160             : 
     161             :     /// Erase the contents of the InsertedExpressions map so that users trying
     162             :     /// to expand the same expression into multiple BasicBlocks or different
     163             :     /// places within the same BasicBlock can do so.
     164        7484 :     void clear() {
     165        7484 :       InsertedExpressions.clear();
     166             :       InsertedValues.clear();
     167             :       InsertedPostIncValues.clear();
     168             :       ChainedPhis.clear();
     169        7484 :     }
     170             : 
     171             :     /// Return true for expressions that may incur non-trivial cost to evaluate
     172             :     /// at runtime.
     173             :     ///
     174             :     /// At is an optional parameter which specifies point in code where user is
     175             :     /// going to expand this expression. Sometimes this knowledge can lead to a
     176             :     /// more accurate cost estimation.
     177        2087 :     bool isHighCostExpansion(const SCEV *Expr, Loop *L,
     178             :                              const Instruction *At = nullptr) {
     179             :       SmallPtrSet<const SCEV *, 8> Processed;
     180        4174 :       return isHighCostExpansionHelper(Expr, L, At, Processed);
     181             :     }
     182             : 
     183             :     /// This method returns the canonical induction variable of the specified
     184             :     /// type for the specified loop (inserting one if there is none).  A
     185             :     /// canonical induction variable starts at zero and steps by one on each
     186             :     /// iteration.
     187             :     PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
     188             : 
     189             :     /// Return the induction variable increment's IV operand.
     190             :     Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
     191             :                                  bool allowScale);
     192             : 
     193             :     /// Utility for hoisting an IV increment.
     194             :     bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
     195             : 
     196             :     /// replace congruent phis with their most canonical representative. Return
     197             :     /// the number of phis eliminated.
     198             :     unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
     199             :                                  SmallVectorImpl<WeakTrackingVH> &DeadInsts,
     200             :                                  const TargetTransformInfo *TTI = nullptr);
     201             : 
     202             :     /// Insert code to directly compute the specified SCEV expression into the
     203             :     /// program.  The inserted code is inserted into the specified block.
     204             :     Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
     205             : 
     206             :     /// Insert code to directly compute the specified SCEV expression into the
     207             :     /// program.  The inserted code is inserted into the SCEVExpander's current
     208             :     /// insertion point. If a type is specified, the result will be expanded to
     209             :     /// have that type, with a cast if necessary.
     210             :     Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
     211             : 
     212             : 
     213             :     /// Generates a code sequence that evaluates this predicate.  The inserted
     214             :     /// instructions will be at position \p Loc.  The result will be of type i1
     215             :     /// and will have a value of 0 when the predicate is false and 1 otherwise.
     216             :     Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
     217             : 
     218             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     219             :     /// we are expanding code for a SCEVEqualPredicate.
     220             :     Value *expandEqualPredicate(const SCEVEqualPredicate *Pred,
     221             :                                 Instruction *Loc);
     222             : 
     223             :     /// Generates code that evaluates if the \p AR expression will overflow.
     224             :     Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
     225             :                                  bool Signed);
     226             : 
     227             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     228             :     /// we are expanding code for a SCEVWrapPredicate.
     229             :     Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
     230             : 
     231             :     /// A specialized variant of expandCodeForPredicate, handling the case when
     232             :     /// we are expanding code for a SCEVUnionPredicate.
     233             :     Value *expandUnionPredicate(const SCEVUnionPredicate *Pred,
     234             :                                 Instruction *Loc);
     235             : 
     236             :     /// Set the current IV increment loop and position.
     237             :     void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
     238             :       assert(!CanonicalMode &&
     239             :              "IV increment positions are not supported in CanonicalMode");
     240        3201 :       IVIncInsertLoop = L;
     241        3201 :       IVIncInsertPos = Pos;
     242             :     }
     243             : 
     244             :     /// Enable post-inc expansion for addrecs referring to the given
     245             :     /// loops. Post-inc expansion is only supported in non-canonical mode.
     246             :     void setPostInc(const PostIncLoopSet &L) {
     247             :       assert(!CanonicalMode &&
     248             :              "Post-inc expansion is not supported in CanonicalMode");
     249       12459 :       PostIncLoops = L;
     250             :     }
     251             : 
     252             :     /// Disable all post-inc expansion.
     253             :     void clearPostInc() {
     254       13577 :       PostIncLoops.clear();
     255             : 
     256             :       // When we change the post-inc loop set, cached expansions may no
     257             :       // longer be valid.
     258             :       InsertedPostIncValues.clear();
     259             :     }
     260             : 
     261             :     /// Disable the behavior of expanding expressions in canonical form rather
     262             :     /// than in a more literal form. Non-canonical mode is useful for late
     263             :     /// optimization passes.
     264        7246 :     void disableCanonicalMode() { CanonicalMode = false; }
     265             : 
     266        3201 :     void enableLSRMode() { LSRMode = true; }
     267             : 
     268             :     /// Set the current insertion point. This is useful if multiple calls to
     269             :     /// expandCodeFor() are going to be made with the same insert point and the
     270             :     /// insert point may be moved during one of the expansions (e.g. if the
     271             :     /// insert point is not a block terminator).
     272             :     void setInsertPoint(Instruction *IP) {
     273             :       assert(IP);
     274       30017 :       Builder.SetInsertPoint(IP);
     275             :     }
     276             : 
     277             :     /// Clear the current insertion point. This is useful if the instruction
     278             :     /// that had been serving as the insertion point may have been deleted.
     279             :     void clearInsertPoint() {
     280             :       Builder.ClearInsertionPoint();
     281             :     }
     282             : 
     283             :     /// Return true if the specified instruction was inserted by the code
     284             :     /// rewriter.  If so, the client should not modify the instruction.
     285       43383 :     bool isInsertedInstruction(Instruction *I) const {
     286       43383 :       return InsertedValues.count(I) || InsertedPostIncValues.count(I);
     287             :     }
     288             : 
     289         241 :     void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
     290             : 
     291             :     /// Try to find existing LLVM IR value for S available at the point At.
     292             :     Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
     293             :                                      Loop *L);
     294             : 
     295             :     /// Try to find the ValueOffsetPair for S. The function is mainly used to
     296             :     /// check whether S can be expanded cheaply.  If this returns a non-None
     297             :     /// value, we know we can codegen the `ValueOffsetPair` into a suitable
     298             :     /// expansion identical with S so that S can be expanded cheaply.
     299             :     ///
     300             :     /// L is a hint which tells in which loop to look for the suitable value.
     301             :     /// On success return value which is equivalent to the expanded S at point
     302             :     /// At. Return nullptr if value was not found.
     303             :     ///
     304             :     /// Note that this function does not perform an exhaustive search. I.e if it
     305             :     /// didn't find any value it does not mean that there is no such value.
     306             :     ///
     307             :     Optional<ScalarEvolution::ValueOffsetPair>
     308             :     getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
     309             : 
     310             :   private:
     311             :     LLVMContext &getContext() const { return SE.getContext(); }
     312             : 
     313             :     /// Recursive helper function for isHighCostExpansion.
     314             :     bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
     315             :                                    const Instruction *At,
     316             :                                    SmallPtrSetImpl<const SCEV *> &Processed);
     317             : 
     318             :     /// Insert the specified binary operator, doing a small amount of work to
     319             :     /// avoid inserting an obviously redundant operation.
     320             :     Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
     321             : 
     322             :     /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
     323             :     /// cast if a suitable one exists, moving an existing cast if a suitable one
     324             :     /// exists but isn't in the right place, or creating a new one.
     325             :     Value *ReuseOrCreateCast(Value *V, Type *Ty,
     326             :                              Instruction::CastOps Op,
     327             :                              BasicBlock::iterator IP);
     328             : 
     329             :     /// Insert a cast of V to the specified type, which must be possible with a
     330             :     /// noop cast, doing what we can to share the casts.
     331             :     Value *InsertNoopCastOfTo(Value *V, Type *Ty);
     332             : 
     333             :     /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
     334             :     /// ptrtoint+arithmetic+inttoptr.
     335             :     Value *expandAddToGEP(const SCEV *const *op_begin,
     336             :                           const SCEV *const *op_end,
     337             :                           PointerType *PTy, Type *Ty, Value *V);
     338             : 
     339             :     /// Find a previous Value in ExprValueMap for expand.
     340             :     ScalarEvolution::ValueOffsetPair
     341             :     FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);
     342             : 
     343             :     Value *expand(const SCEV *S);
     344             : 
     345             :     /// Determine the most "relevant" loop for the given SCEV.
     346             :     const Loop *getRelevantLoop(const SCEV *);
     347             : 
     348             :     Value *visitConstant(const SCEVConstant *S) {
     349       13645 :       return S->getValue();
     350             :     }
     351             : 
     352             :     Value *visitTruncateExpr(const SCEVTruncateExpr *S);
     353             : 
     354             :     Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
     355             : 
     356             :     Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
     357             : 
     358             :     Value *visitAddExpr(const SCEVAddExpr *S);
     359             : 
     360             :     Value *visitMulExpr(const SCEVMulExpr *S);
     361             : 
     362             :     Value *visitUDivExpr(const SCEVUDivExpr *S);
     363             : 
     364             :     Value *visitAddRecExpr(const SCEVAddRecExpr *S);
     365             : 
     366             :     Value *visitSMaxExpr(const SCEVSMaxExpr *S);
     367             : 
     368             :     Value *visitUMaxExpr(const SCEVUMaxExpr *S);
     369             : 
     370             :     Value *visitUnknown(const SCEVUnknown *S) {
     371             :       return S->getValue();
     372             :     }
     373             : 
     374             :     void rememberInstruction(Value *I);
     375             : 
     376             :     bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
     377             : 
     378             :     bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
     379             : 
     380             :     Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
     381             :     PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
     382             :                                        const Loop *L,
     383             :                                        Type *ExpandTy,
     384             :                                        Type *IntTy,
     385             :                                        Type *&TruncTy,
     386             :                                        bool &InvertStep);
     387             :     Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
     388             :                        Type *ExpandTy, Type *IntTy, bool useSubtract);
     389             : 
     390             :     void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
     391             :                         Instruction *Pos, PHINode *LoopPhi);
     392             : 
     393             :     void fixupInsertPoints(Instruction *I);
     394             :   };
     395             : }
     396             : 
     397             : #endif

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