EIC code displayed by LXR master/​include/​llvm/​Transforms/​Utils/​ScalarEvolutionExpander.h	Source navigation Diff markup Identifier search General search
	Version: master test Revert   Change

File indexing completed on 2026-05-10 08:44:44

 //===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the classes used to generate code from scalar expressions.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
 #define LLVM_TRANSFORMS_UTILS_SCALAREVOLUTIONEXPANDER_H
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/Analysis/InstSimplifyFolder.h"
 #include "llvm/Analysis/ScalarEvolutionExpressions.h"
 #include "llvm/Analysis/ScalarEvolutionNormalization.h"
 #include "llvm/Analysis/TargetTransformInfo.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/ValueHandle.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InstructionCost.h"
 
 namespace llvm {
 extern cl::opt<unsigned> SCEVCheapExpansionBudget;
 
 /// struct for holding enough information to help calculate the cost of the
 /// given SCEV when expanded into IR.
 struct SCEVOperand {
   explicit SCEVOperand(unsigned Opc, int Idx, const SCEV *S) :
     ParentOpcode(Opc), OperandIdx(Idx), S(S) { }
   /// LLVM instruction opcode that uses the operand.
   unsigned ParentOpcode;
   /// The use index of an expanded instruction.
   int OperandIdx;
   /// The SCEV operand to be costed.
   const SCEV* S;
 };
 
 struct PoisonFlags {
   unsigned NUW : 1;
   unsigned NSW : 1;
   unsigned Exact : 1;
   unsigned Disjoint : 1;
   unsigned NNeg : 1;
   unsigned SameSign : 1;
   GEPNoWrapFlags GEPNW;
 
   PoisonFlags(const Instruction *I);
   void apply(Instruction *I);
 };
 
 /// This class uses information about analyze scalars to rewrite expressions
 /// in canonical form.
 ///
 /// Clients should create an instance of this class when rewriting is needed,
 /// and destroy it when finished to allow the release of the associated
 /// memory.
 class SCEVExpander : public SCEVVisitor<SCEVExpander, Value *> {
   friend class SCEVExpanderCleaner;
 
   ScalarEvolution &SE;
   const DataLayout &DL;
 
   // New instructions receive a name to identify them with the current pass.
   const char *IVName;
 
   /// Indicates whether LCSSA phis should be created for inserted values.
   bool PreserveLCSSA;
 
   // InsertedExpressions caches Values for reuse, so must track RAUW.
   DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>>
       InsertedExpressions;
 
   // InsertedValues only flags inserted instructions so needs no RAUW.
   DenseSet<AssertingVH<Value>> InsertedValues;
   DenseSet<AssertingVH<Value>> InsertedPostIncValues;
 
   /// Keep track of the existing IR values re-used during expansion.
   /// FIXME: Ideally re-used instructions would not be added to
   /// InsertedValues/InsertedPostIncValues.
   SmallPtrSet<Value *, 16> ReusedValues;
 
   /// Original flags of instructions for which they were modified. Used
   /// by SCEVExpanderCleaner to undo changes.
   DenseMap<PoisoningVH<Instruction>, PoisonFlags> OrigFlags;
 
   // The induction variables generated.
   SmallVector<WeakVH, 2> InsertedIVs;
 
   /// A memoization of the "relevant" loop for a given SCEV.
   DenseMap<const SCEV *, const Loop *> RelevantLoops;
 
   /// Addrecs referring to any of the given loops are expanded in post-inc
   /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add
   /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new
   /// phi starting at 1. This is only supported in non-canonical mode.
   PostIncLoopSet PostIncLoops;
 
   /// When this is non-null, addrecs expanded in the loop it indicates should
   /// be inserted with increments at IVIncInsertPos.
   const Loop *IVIncInsertLoop;
 
   /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV
   /// increment at this position.
   Instruction *IVIncInsertPos;
 
   /// Phis that complete an IV chain. Reuse
   DenseSet<AssertingVH<PHINode>> ChainedPhis;
 
   /// When true, SCEVExpander tries to expand expressions in "canonical" form.
   /// When false, expressions are expanded in a more literal form.
   ///
   /// In "canonical" form addrecs are expanded as arithmetic based on a
   /// canonical induction variable. Note that CanonicalMode doesn't guarantee
   /// that all expressions are expanded in "canonical" form. For some
   /// expressions literal mode can be preferred.
   bool CanonicalMode;
 
   /// When invoked from LSR, the expander is in "strength reduction" mode. The
   /// only difference is that phi's are only reused if they are already in
   /// "expanded" form.
   bool LSRMode;
 
   /// When true, rewrite any divisors of UDiv expressions that may be 0 to
   /// umax(Divisor, 1) to avoid introducing UB. If the divisor may be poison,
   /// freeze it first.
   bool SafeUDivMode = false;
 
   typedef IRBuilder<InstSimplifyFolder, IRBuilderCallbackInserter> BuilderType;
   BuilderType Builder;
 
   // RAII object that stores the current insertion point and restores it when
   // the object is destroyed. This includes the debug location.  Duplicated
   // from InsertPointGuard to add SetInsertPoint() which is used to updated
   // InsertPointGuards stack when insert points are moved during SCEV
   // expansion.
   class SCEVInsertPointGuard {
     IRBuilderBase &Builder;
     AssertingVH<BasicBlock> Block;
     BasicBlock::iterator Point;
     DebugLoc DbgLoc;
     SCEVExpander *SE;
 
     SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete;
     SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete;
 
   public:
     SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE)
         : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()),
           DbgLoc(B.getCurrentDebugLocation()), SE(SE) {
       SE->InsertPointGuards.push_back(this);
     }
 
     ~SCEVInsertPointGuard() {
       // These guards should always created/destroyed in FIFO order since they
       // are used to guard lexically scoped blocks of code in
       // ScalarEvolutionExpander.
       assert(SE->InsertPointGuards.back() == this);
       SE->InsertPointGuards.pop_back();
       Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point));
       Builder.SetCurrentDebugLocation(DbgLoc);
     }
 
     BasicBlock::iterator GetInsertPoint() const { return Point; }
     void SetInsertPoint(BasicBlock::iterator I) { Point = I; }
   };
 
   /// Stack of pointers to saved insert points, used to keep insert points
   /// consistent when instructions are moved.
   SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards;
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   const char *DebugType;
 #endif
 
   friend struct SCEVVisitor<SCEVExpander, Value *>;
 
 public:
   /// Construct a SCEVExpander in "canonical" mode.
   explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL,
                         const char *name, bool PreserveLCSSA = true)
       : SE(se), DL(DL), IVName(name), PreserveLCSSA(PreserveLCSSA),
         IVIncInsertLoop(nullptr), IVIncInsertPos(nullptr), CanonicalMode(true),
         LSRMode(false),
         Builder(se.getContext(), InstSimplifyFolder(DL),
                 IRBuilderCallbackInserter(
                     [this](Instruction *I) { rememberInstruction(I); })) {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
     DebugType = "";
 #endif
   }
 
   ~SCEVExpander() {
     // Make sure the insert point guard stack is consistent.
     assert(InsertPointGuards.empty());
   }
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   void setDebugType(const char *s) { DebugType = s; }
 #endif
 
   /// Erase the contents of the InsertedExpressions map so that users trying
   /// to expand the same expression into multiple BasicBlocks or different
   /// places within the same BasicBlock can do so.
   void clear() {
     InsertedExpressions.clear();
     InsertedValues.clear();
     InsertedPostIncValues.clear();
     ReusedValues.clear();
     OrigFlags.clear();
     ChainedPhis.clear();
     InsertedIVs.clear();
   }
 
   ScalarEvolution *getSE() { return &SE; }
   const SmallVectorImpl<WeakVH> &getInsertedIVs() const { return InsertedIVs; }
 
   /// Return a vector containing all instructions inserted during expansion.
   SmallVector<Instruction *, 32> getAllInsertedInstructions() const {
     SmallVector<Instruction *, 32> Result;
     for (const auto &VH : InsertedValues) {
       Value *V = VH;
       if (ReusedValues.contains(V))
         continue;
       if (auto *Inst = dyn_cast<Instruction>(V))
         Result.push_back(Inst);
     }
     for (const auto &VH : InsertedPostIncValues) {
       Value *V = VH;
       if (ReusedValues.contains(V))
         continue;
       if (auto *Inst = dyn_cast<Instruction>(V))
         Result.push_back(Inst);
     }
 
     return Result;
   }
 
   /// Return true for expressions that can't be evaluated at runtime
   /// within given \b Budget.
   ///
   /// \p At is a parameter which specifies point in code where user is going to
   /// expand these expressions. Sometimes this knowledge can lead to
   /// a less pessimistic cost estimation.
   bool isHighCostExpansion(ArrayRef<const SCEV *> Exprs, Loop *L,
                            unsigned Budget, const TargetTransformInfo *TTI,
                            const Instruction *At) {
     assert(TTI && "This function requires TTI to be provided.");
     assert(At && "This function requires At instruction to be provided.");
     if (!TTI)      // In assert-less builds, avoid crashing
       return true; // by always claiming to be high-cost.
     SmallVector<SCEVOperand, 8> Worklist;
     SmallPtrSet<const SCEV *, 8> Processed;
     InstructionCost Cost = 0;
     unsigned ScaledBudget = Budget * TargetTransformInfo::TCC_Basic;
     for (auto *Expr : Exprs)
       Worklist.emplace_back(-1, -1, Expr);
     while (!Worklist.empty()) {
       const SCEVOperand WorkItem = Worklist.pop_back_val();
       if (isHighCostExpansionHelper(WorkItem, L, *At, Cost, ScaledBudget, *TTI,
                                     Processed, Worklist))
         return true;
     }
     assert(Cost <= ScaledBudget && "Should have returned from inner loop.");
     return false;
   }
 
   /// Return the induction variable increment's IV operand.
   Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
                                bool allowScale);
 
   /// Utility for hoisting \p IncV (with all subexpressions requried for its
   /// computation) before \p InsertPos. If \p RecomputePoisonFlags is set, drops
   /// all poison-generating flags from instructions being hoisted and tries to
   /// re-infer them in the new location. It should be used when we are going to
   /// introduce a new use in the new position that didn't exist before, and may
   /// trigger new UB in case of poison.
   bool hoistIVInc(Instruction *IncV, Instruction *InsertPos,
                   bool RecomputePoisonFlags = false);
 
   /// Return true if both increments directly increment the corresponding IV PHI
   /// nodes and have the same opcode. It is not safe to re-use the flags from
   /// the original increment, if it is more complex and SCEV expansion may have
   /// yielded a more simplified wider increment.
   static bool canReuseFlagsFromOriginalIVInc(PHINode *OrigPhi, PHINode *WidePhi,
                                              Instruction *OrigInc,
                                              Instruction *WideInc);
 
   /// replace congruent phis with their most canonical representative. Return
   /// the number of phis eliminated.
   unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT,
                                SmallVectorImpl<WeakTrackingVH> &DeadInsts,
                                const TargetTransformInfo *TTI = nullptr);
 
   /// Return true if the given expression is safe to expand in the sense that
   /// all materialized values are safe to speculate anywhere their operands are
   /// defined, and the expander is capable of expanding the expression.
   bool isSafeToExpand(const SCEV *S) const;
 
   /// Return true if the given expression is safe to expand in the sense that
   /// all materialized values are defined and safe to speculate at the specified
   /// location and their operands are defined at this location.
   bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint) const;
 
   /// Insert code to directly compute the specified SCEV expression into the
   /// program.  The code is inserted into the specified block.
   Value *expandCodeFor(const SCEV *SH, Type *Ty, BasicBlock::iterator I);
   Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I) {
     return expandCodeFor(SH, Ty, I->getIterator());
   }
 
   /// Insert code to directly compute the specified SCEV expression into the
   /// program.  The code is inserted into the SCEVExpander's current
   /// insertion point. If a type is specified, the result will be expanded to
   /// have that type, with a cast if necessary.
   Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr);
 
   /// Generates a code sequence that evaluates this predicate.  The inserted
   /// instructions will be at position \p Loc.  The result will be of type i1
   /// and will have a value of 0 when the predicate is false and 1 otherwise.
   Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc);
 
   /// A specialized variant of expandCodeForPredicate, handling the case when
   /// we are expanding code for a SCEVComparePredicate.
   Value *expandComparePredicate(const SCEVComparePredicate *Pred,
                                 Instruction *Loc);
 
   /// Generates code that evaluates if the \p AR expression will overflow.
   Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc,
                                bool Signed);
 
   /// A specialized variant of expandCodeForPredicate, handling the case when
   /// we are expanding code for a SCEVWrapPredicate.
   Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc);
 
   /// A specialized variant of expandCodeForPredicate, handling the case when
   /// we are expanding code for a SCEVUnionPredicate.
   Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, Instruction *Loc);
 
   /// Set the current IV increment loop and position.
   void setIVIncInsertPos(const Loop *L, Instruction *Pos) {
     assert(!CanonicalMode &&
            "IV increment positions are not supported in CanonicalMode");
     IVIncInsertLoop = L;
     IVIncInsertPos = Pos;
   }
 
   /// Enable post-inc expansion for addrecs referring to the given
   /// loops. Post-inc expansion is only supported in non-canonical mode.
   void setPostInc(const PostIncLoopSet &L) {
     assert(!CanonicalMode &&
            "Post-inc expansion is not supported in CanonicalMode");
     PostIncLoops = L;
   }
 
   /// Disable all post-inc expansion.
   void clearPostInc() {
     PostIncLoops.clear();
 
     // When we change the post-inc loop set, cached expansions may no
     // longer be valid.
     InsertedPostIncValues.clear();
   }
 
   /// Disable the behavior of expanding expressions in canonical form rather
   /// than in a more literal form. Non-canonical mode is useful for late
   /// optimization passes.
   void disableCanonicalMode() { CanonicalMode = false; }
 
   void enableLSRMode() { LSRMode = true; }
 
   /// Set the current insertion point. This is useful if multiple calls to
   /// expandCodeFor() are going to be made with the same insert point and the
   /// insert point may be moved during one of the expansions (e.g. if the
   /// insert point is not a block terminator).
   void setInsertPoint(Instruction *IP) {
     assert(IP);
     Builder.SetInsertPoint(IP);
   }
 
   void setInsertPoint(BasicBlock::iterator IP) {
     Builder.SetInsertPoint(IP->getParent(), IP);
   }
 
   /// Clear the current insertion point. This is useful if the instruction
   /// that had been serving as the insertion point may have been deleted.
   void clearInsertPoint() { Builder.ClearInsertionPoint(); }
 
   /// Set location information used by debugging information.
   void SetCurrentDebugLocation(DebugLoc L) {
     Builder.SetCurrentDebugLocation(std::move(L));
   }
 
   /// Get location information used by debugging information.
   DebugLoc getCurrentDebugLocation() const {
     return Builder.getCurrentDebugLocation();
   }
 
   /// Return true if the specified instruction was inserted by the code
   /// rewriter.  If so, the client should not modify the instruction. Note that
   /// this also includes instructions re-used during expansion.
   bool isInsertedInstruction(Instruction *I) const {
     return InsertedValues.count(I) || InsertedPostIncValues.count(I);
   }
 
   void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
 
   /// Determine whether there is an existing expansion of S that can be reused.
   /// This is used to check whether S can be expanded cheaply.
   ///
   /// L is a hint which tells in which loop to look for the suitable value.
   ///
   /// Note that this function does not perform an exhaustive search. I.e if it
   /// didn't find any value it does not mean that there is no such value.
   bool hasRelatedExistingExpansion(const SCEV *S, const Instruction *At,
                                    Loop *L);
 
   /// Returns a suitable insert point after \p I, that dominates \p
   /// MustDominate. Skips instructions inserted by the expander.
   BasicBlock::iterator findInsertPointAfter(Instruction *I,
                                             Instruction *MustDominate) const;
 
 private:
   LLVMContext &getContext() const { return SE.getContext(); }
 
   /// Recursive helper function for isHighCostExpansion.
   bool isHighCostExpansionHelper(const SCEVOperand &WorkItem, Loop *L,
                                  const Instruction &At, InstructionCost &Cost,
                                  unsigned Budget,
                                  const TargetTransformInfo &TTI,
                                  SmallPtrSetImpl<const SCEV *> &Processed,
                                  SmallVectorImpl<SCEVOperand> &Worklist);
 
   /// Insert the specified binary operator, doing a small amount of work to
   /// avoid inserting an obviously redundant operation, and hoisting to an
   /// outer loop when the opportunity is there and it is safe.
   Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS,
                      SCEV::NoWrapFlags Flags, bool IsSafeToHoist);
 
   /// We want to cast \p V. What would be the best place for such a cast?
   BasicBlock::iterator GetOptimalInsertionPointForCastOf(Value *V) const;
 
   /// Arrange for there to be a cast of V to Ty at IP, reusing an existing
   /// cast if a suitable one exists, moving an existing cast if a suitable one
   /// exists but isn't in the right place, or creating a new one.
   Value *ReuseOrCreateCast(Value *V, Type *Ty, Instruction::CastOps Op,
                            BasicBlock::iterator IP);
 
   /// Insert a cast of V to the specified type, which must be possible with a
   /// noop cast, doing what we can to share the casts.
   Value *InsertNoopCastOfTo(Value *V, Type *Ty);
 
   /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using
   /// ptrtoint+arithmetic+inttoptr.
   Value *expandAddToGEP(const SCEV *Op, Value *V, SCEV::NoWrapFlags Flags);
 
   /// Find a previous Value in ExprValueMap for expand.
   /// DropPoisonGeneratingInsts is populated with instructions for which
   /// poison-generating flags must be dropped if the value is reused.
   Value *FindValueInExprValueMap(
       const SCEV *S, const Instruction *InsertPt,
       SmallVectorImpl<Instruction *> &DropPoisonGeneratingInsts);
 
   Value *expand(const SCEV *S);
   Value *expand(const SCEV *S, BasicBlock::iterator I) {
     setInsertPoint(I);
     return expand(S);
   }
   Value *expand(const SCEV *S, Instruction *I) {
     setInsertPoint(I);
     return expand(S);
   }
 
   /// Determine the most "relevant" loop for the given SCEV.
   const Loop *getRelevantLoop(const SCEV *);
 
   Value *expandMinMaxExpr(const SCEVNAryExpr *S, Intrinsic::ID IntrinID,
                           Twine Name, bool IsSequential = false);
 
   Value *visitConstant(const SCEVConstant *S) { return S->getValue(); }
 
   Value *visitVScale(const SCEVVScale *S);
 
   Value *visitPtrToIntExpr(const SCEVPtrToIntExpr *S);
 
   Value *visitTruncateExpr(const SCEVTruncateExpr *S);
 
   Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S);
 
   Value *visitSignExtendExpr(const SCEVSignExtendExpr *S);
 
   Value *visitAddExpr(const SCEVAddExpr *S);
 
   Value *visitMulExpr(const SCEVMulExpr *S);
 
   Value *visitUDivExpr(const SCEVUDivExpr *S);
 
   Value *visitAddRecExpr(const SCEVAddRecExpr *S);
 
   Value *visitSMaxExpr(const SCEVSMaxExpr *S);
 
   Value *visitUMaxExpr(const SCEVUMaxExpr *S);
 
   Value *visitSMinExpr(const SCEVSMinExpr *S);
 
   Value *visitUMinExpr(const SCEVUMinExpr *S);
 
   Value *visitSequentialUMinExpr(const SCEVSequentialUMinExpr *S);
 
   Value *visitUnknown(const SCEVUnknown *S) { return S->getValue(); }
 
   void rememberInstruction(Value *I);
 
   void rememberFlags(Instruction *I);
 
   bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
 
   bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L);
 
   Value *expandAddRecExprLiterally(const SCEVAddRecExpr *);
   PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
                                      const Loop *L, Type *&TruncTy,
                                      bool &InvertStep);
   Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
                      bool useSubtract);
 
   void fixupInsertPoints(Instruction *I);
 
   /// Create LCSSA PHIs for \p V, if it is required for uses at the Builder's
   /// current insertion point.
   Value *fixupLCSSAFormFor(Value *V);
 
   /// Replace congruent phi increments with their most canonical representative.
   /// May swap \p Phi and \p OrigPhi, if \p Phi is more canonical, due to its
   /// increment.
   void replaceCongruentIVInc(PHINode *&Phi, PHINode *&OrigPhi, Loop *L,
                              const DominatorTree *DT,
                              SmallVectorImpl<WeakTrackingVH> &DeadInsts);
 };
 
 /// Helper to remove instructions inserted during SCEV expansion, unless they
 /// are marked as used.
 class SCEVExpanderCleaner {
   SCEVExpander &Expander;
 
   /// Indicates whether the result of the expansion is used. If false, the
   /// instructions added during expansion are removed.
   bool ResultUsed;
 
 public:
   SCEVExpanderCleaner(SCEVExpander &Expander)
       : Expander(Expander), ResultUsed(false) {}
 
   ~SCEVExpanderCleaner() { cleanup(); }
 
   /// Indicate that the result of the expansion is used.
   void markResultUsed() { ResultUsed = true; }
 
   void cleanup();
 };
 } // namespace llvm
 
 #endif

This page was automatically generated by the 2.3.7 LXR engine. The LXR team