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//===---- 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;

};

/// 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 *> {

  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;

  // 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;

  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;

#ifdef 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); })) {

#ifdef LLVM_ENABLE_ABI_BREAKING_CHECKS

    DebugType = "";

#endif

  }

  ~SCEVExpander() {

    // Make sure the insert point guard stack is consistent.

    assert(InsertPointGuards.empty());

  }

#ifdef 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();

    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);

  /// 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, Instruction *I) {

    return expandCodeForImpl(SH, Ty, I);

  }

  /// 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) {

    return expandCodeForImpl(SH, Ty);

  }

  /// 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);

  }

  /// 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); }

  /// Try to find the ValueOffsetPair for S. The function is mainly used to

  /// check whether S can be expanded cheaply.  If this returns a non-None

  /// value, we know we can codegen the `ValueOffsetPair` into a suitable

  /// expansion identical with S so that S can be expanded cheaply.

  ///

  /// L is a hint which tells in which loop to look for the suitable value.

  /// On success return value which is equivalent to the expanded S at point

  /// At. Return nullptr if value was not found.

  ///

  /// 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.

  ///

  Value *getRelatedExistingExpansion(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(); }

  /// 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. If \p Root is true, this

  /// indicates that \p SH is the top-level expression to expand passed from

  /// an external client call.

  Value *expandCodeForImpl(const SCEV *SH, Type *Ty);

  /// Insert code to directly compute the specified SCEV expression into the

  /// program. The code is inserted into the specified block. If \p

  /// Root is true, this indicates that \p SH is the top-level expression to

  /// expand passed from an external client call.

  Value *expandCodeForImpl(const SCEV *SH, Type *Ty, Instruction *I);

  /// 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 *const *op_begin, const SCEV *const *op_end,

                        PointerType *PTy, Type *Ty, Value *V);

  Value *expandAddToGEP(const SCEV *Op, PointerType *PTy, Type *Ty, Value *V);

  /// Find a previous Value in ExprValueMap for expand.

  Value *FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt);

  Value *expand(const SCEV *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 *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);

  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 *ExpandTy, Type *IntTy,

                                     Type *&TruncTy, bool &InvertStep);

  Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L, Type *ExpandTy,

                     Type *IntTy, 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);

};

/// 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