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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_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
+#define LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H
+
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/Optional.h"
+#include "llvm/Analysis/ScalarEvolutionExpressions.h"
+#include "llvm/Analysis/ScalarEvolutionNormalization.h"
+#include "llvm/Analysis/TargetFolder.h"
+#include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/ValueHandle.h"
+
+namespace llvm {
+  class TargetTransformInfo;
+
+  /// 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.
+  bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE);
+
+  /// 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,
+                        ScalarEvolution &SE);
+
+  /// 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;
+
+    // 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;
+
+    /// 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, expressions are expanded in "canonical" form. In particular,
+    /// addrecs are expanded as arithmetic based on a canonical induction
+    /// variable. When false, expression are expanded in a more literal form.
+    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<TargetFolder> 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;
+
+#ifndef NDEBUG
+    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)
+        : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr),
+          IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false),
+          Builder(se.getContext(), TargetFolder(DL)) {
+#ifndef NDEBUG
+      DebugType = "";
+#endif
+    }
+
+    ~SCEVExpander() {
+      // Make sure the insert point guard stack is consistent.
+      assert(InsertPointGuards.empty());
+    }
+
+#ifndef NDEBUG
+    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();
+      ChainedPhis.clear();
+    }
+
+    /// Return true for expressions that may incur non-trivial cost to evaluate
+    /// at runtime.
+    ///
+    /// At is an optional parameter which specifies point in code where user is
+    /// going to expand this expression. Sometimes this knowledge can lead to a
+    /// more accurate cost estimation.
+    bool isHighCostExpansion(const SCEV *Expr, Loop *L,
+                             const Instruction *At = nullptr) {
+      SmallPtrSet<const SCEV *, 8> Processed;
+      return isHighCostExpansionHelper(Expr, L, At, Processed);
+    }
+
+    /// This method returns the canonical induction variable of the specified
+    /// type for the specified loop (inserting one if there is none).  A
+    /// canonical induction variable starts at zero and steps by one on each
+    /// iteration.
+    PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty);
+
+    /// Return the induction variable increment's IV operand.
+    Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos,
+                                 bool allowScale);
+
+    /// Utility for hoisting an IV increment.
+    bool hoistIVInc(Instruction *IncV, Instruction *InsertPos);
+
+    /// 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);
+
+    /// Insert code to directly compute the specified SCEV expression into the
+    /// program.  The inserted code is inserted into the specified block.
+    Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I);
+
+    /// Insert code to directly compute the specified SCEV expression into the
+    /// program.  The inserted 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 SCEVEqualPredicate.
+    Value *expandEqualPredicate(const SCEVEqualPredicate *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();
+    }
+
+    /// Return true if the specified instruction was inserted by the code
+    /// rewriter.  If so, the client should not modify the instruction.
+    bool isInsertedInstruction(Instruction *I) const {
+      return InsertedValues.count(I) || InsertedPostIncValues.count(I);
+    }
+
+    void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); }
+
+    /// Try to find existing LLVM IR value for S available at the point At.
+    Value *getExactExistingExpansion(const SCEV *S, const Instruction *At,
+                                     Loop *L);
+
+    /// 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.
+    ///
+    Optional<ScalarEvolution::ValueOffsetPair>
+    getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L);
+
+  private:
+    LLVMContext &getContext() const { return SE.getContext(); }
+
+    /// Recursive helper function for isHighCostExpansion.
+    bool isHighCostExpansionHelper(const SCEV *S, Loop *L,
+                                   const Instruction *At,
+                                   SmallPtrSetImpl<const SCEV *> &Processed);
+
+    /// Insert the specified binary operator, doing a small amount of work to
+    /// avoid inserting an obviously redundant operation.
+    Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS);
+
+    /// 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.
+    ScalarEvolution::ValueOffsetPair
+    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 *visitConstant(const SCEVConstant *S) {
+      return S->getValue();
+    }
+
+    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 *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 hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist,
+                        Instruction *Pos, PHINode *LoopPhi);
+
+    void fixupInsertPoints(Instruction *I);
+  };
+}
+
+#endif