include/llvm/Analysis/ScalarEvolutionExpressions.h

   1 //===- llvm/Analysis/ScalarEvolutionExpressions.h - SCEV Exprs --*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file defines the classes used to represent and build scalar expressions.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_ANALYSIS_SCALAREVOLUTIONEXPRESSIONS_H
  14 #define LLVM_ANALYSIS_SCALAREVOLUTIONEXPRESSIONS_H
  15
  16 #include "llvm/ADT/DenseMap.h"
  17 #include "llvm/ADT/FoldingSet.h"
  18 #include "llvm/ADT/SmallPtrSet.h"
  19 #include "llvm/ADT/SmallVector.h"
  20 #include "llvm/ADT/iterator_range.h"
  21 #include "llvm/Analysis/ScalarEvolution.h"
  22 #include "llvm/IR/Constants.h"
  23 #include "llvm/IR/Value.h"
  24 #include "llvm/IR/ValueHandle.h"
  25 #include "llvm/Support/Casting.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include <cassert>
  28 #include <cstddef>
  29
  30 namespace llvm {
  31
  32 class APInt;
  33 class Constant;
  34 class ConstantRange;
  35 class Loop;
  36 class Type;
  37
  38   enum SCEVTypes {
  39     // These should be ordered in terms of increasing complexity to make the
  40     // folders simpler.
  41     scConstant, scTruncate, scZeroExtend, scSignExtend, scAddExpr, scMulExpr,
  42     scUDivExpr, scAddRecExpr, scUMaxExpr, scSMaxExpr,
  43     scUnknown, scCouldNotCompute
  44   };
  45
  46   /// This class represents a constant integer value.
  47   class SCEVConstant : public SCEV {
  48     friend class ScalarEvolution;
  49
  50     ConstantInt *V;
  51
  52     SCEVConstant(const FoldingSetNodeIDRef ID, ConstantInt *v) :
  53       SCEV(ID, scConstant, 1), V(v) {}
  54
  55   public:
  56     ConstantInt *getValue() const { return V; }
  57     const APInt &getAPInt() const { return getValue()->getValue(); }
  58
  59     Type *getType() const { return V->getType(); }
  60
  61     /// Methods for support type inquiry through isa, cast, and dyn_cast:
  62     static bool classof(const SCEV *S) {
  63       return S->getSCEVType() == scConstant;
  64     }
  65   };
  66
  67   static unsigned short computeExpressionSize(ArrayRef<const SCEV *> Args) {
  68     APInt Size(16, 1);
  69     for (auto *Arg : Args)
  70       Size = Size.uadd_sat(APInt(16, Arg->getExpressionSize()));
  71     return (unsigned short)Size.getZExtValue();
  72   }
  73
  74   /// This is the base class for unary cast operator classes.
  75   class SCEVCastExpr : public SCEV {
  76   protected:
  77     const SCEV *Op;
  78     Type *Ty;
  79
  80     SCEVCastExpr(const FoldingSetNodeIDRef ID,
  81                  unsigned SCEVTy, const SCEV *op, Type *ty);
  82
  83   public:
  84     const SCEV *getOperand() const { return Op; }
  85     Type *getType() const { return Ty; }
  86
  87     /// Methods for support type inquiry through isa, cast, and dyn_cast:
  88     static bool classof(const SCEV *S) {
  89       return S->getSCEVType() == scTruncate ||
  90              S->getSCEVType() == scZeroExtend ||
  91              S->getSCEVType() == scSignExtend;
  92     }
  93   };
  94
  95   /// This class represents a truncation of an integer value to a
  96   /// smaller integer value.
  97   class SCEVTruncateExpr : public SCEVCastExpr {
  98     friend class ScalarEvolution;
  99
 100     SCEVTruncateExpr(const FoldingSetNodeIDRef ID,
 101                      const SCEV *op, Type *ty);
 102
 103   public:
 104     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 105     static bool classof(const SCEV *S) {
 106       return S->getSCEVType() == scTruncate;
 107     }
 108   };
 109
 110   /// This class represents a zero extension of a small integer value
 111   /// to a larger integer value.
 112   class SCEVZeroExtendExpr : public SCEVCastExpr {
 113     friend class ScalarEvolution;
 114
 115     SCEVZeroExtendExpr(const FoldingSetNodeIDRef ID,
 116                        const SCEV *op, Type *ty);
 117
 118   public:
 119     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 120     static bool classof(const SCEV *S) {
 121       return S->getSCEVType() == scZeroExtend;
 122     }
 123   };
 124
 125   /// This class represents a sign extension of a small integer value
 126   /// to a larger integer value.
 127   class SCEVSignExtendExpr : public SCEVCastExpr {
 128     friend class ScalarEvolution;
 129
 130     SCEVSignExtendExpr(const FoldingSetNodeIDRef ID,
 131                        const SCEV *op, Type *ty);
 132
 133   public:
 134     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 135     static bool classof(const SCEV *S) {
 136       return S->getSCEVType() == scSignExtend;
 137     }
 138   };
 139
 140   /// This node is a base class providing common functionality for
 141   /// n'ary operators.
 142   class SCEVNAryExpr : public SCEV {
 143   protected:
 144     // Since SCEVs are immutable, ScalarEvolution allocates operand
 145     // arrays with its SCEVAllocator, so this class just needs a simple
 146     // pointer rather than a more elaborate vector-like data structure.
 147     // This also avoids the need for a non-trivial destructor.
 148     const SCEV *const *Operands;
 149     size_t NumOperands;
 150
 151     SCEVNAryExpr(const FoldingSetNodeIDRef ID, enum SCEVTypes T,
 152                  const SCEV *const *O, size_t N)
 153         : SCEV(ID, T, computeExpressionSize(makeArrayRef(O, N))), Operands(O),
 154           NumOperands(N) {}
 155
 156   public:
 157     size_t getNumOperands() const { return NumOperands; }
 158
 159     const SCEV *getOperand(unsigned i) const {
 160       assert(i < NumOperands && "Operand index out of range!");
 161       return Operands[i];
 162     }
 163
 164     using op_iterator = const SCEV *const *;
 165     using op_range = iterator_range<op_iterator>;
 166
 167     op_iterator op_begin() const { return Operands; }
 168     op_iterator op_end() const { return Operands + NumOperands; }
 169     op_range operands() const {
 170       return make_range(op_begin(), op_end());
 171     }
 172
 173     Type *getType() const { return getOperand(0)->getType(); }
 174
 175     NoWrapFlags getNoWrapFlags(NoWrapFlags Mask = NoWrapMask) const {
 176       return (NoWrapFlags)(SubclassData & Mask);
 177     }
 178
 179     bool hasNoUnsignedWrap() const {
 180       return getNoWrapFlags(FlagNUW) != FlagAnyWrap;
 181     }
 182
 183     bool hasNoSignedWrap() const {
 184       return getNoWrapFlags(FlagNSW) != FlagAnyWrap;
 185     }
 186
 187     bool hasNoSelfWrap() const {
 188       return getNoWrapFlags(FlagNW) != FlagAnyWrap;
 189     }
 190
 191     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 192     static bool classof(const SCEV *S) {
 193       return S->getSCEVType() == scAddExpr ||
 194              S->getSCEVType() == scMulExpr ||
 195              S->getSCEVType() == scSMaxExpr ||
 196              S->getSCEVType() == scUMaxExpr ||
 197              S->getSCEVType() == scAddRecExpr;
 198     }
 199   };
 200
 201   /// This node is the base class for n'ary commutative operators.
 202   class SCEVCommutativeExpr : public SCEVNAryExpr {
 203   protected:
 204     SCEVCommutativeExpr(const FoldingSetNodeIDRef ID,
 205                         enum SCEVTypes T, const SCEV *const *O, size_t N)
 206       : SCEVNAryExpr(ID, T, O, N) {}
 207
 208   public:
 209     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 210     static bool classof(const SCEV *S) {
 211       return S->getSCEVType() == scAddExpr ||
 212              S->getSCEVType() == scMulExpr ||
 213              S->getSCEVType() == scSMaxExpr ||
 214              S->getSCEVType() == scUMaxExpr;
 215     }
 216
 217     /// Set flags for a non-recurrence without clearing previously set flags.
 218     void setNoWrapFlags(NoWrapFlags Flags) {
 219       SubclassData |= Flags;
 220     }
 221   };
 222
 223   /// This node represents an addition of some number of SCEVs.
 224   class SCEVAddExpr : public SCEVCommutativeExpr {
 225     friend class ScalarEvolution;
 226
 227     SCEVAddExpr(const FoldingSetNodeIDRef ID,
 228                 const SCEV *const *O, size_t N)
 229       : SCEVCommutativeExpr(ID, scAddExpr, O, N) {}
 230
 231   public:
 232     Type *getType() const {
 233       // Use the type of the last operand, which is likely to be a pointer
 234       // type, if there is one. This doesn't usually matter, but it can help
 235       // reduce casts when the expressions are expanded.
 236       return getOperand(getNumOperands() - 1)->getType();
 237     }
 238
 239     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 240     static bool classof(const SCEV *S) {
 241       return S->getSCEVType() == scAddExpr;
 242     }
 243   };
 244
 245   /// This node represents multiplication of some number of SCEVs.
 246   class SCEVMulExpr : public SCEVCommutativeExpr {
 247     friend class ScalarEvolution;
 248
 249     SCEVMulExpr(const FoldingSetNodeIDRef ID,
 250                 const SCEV *const *O, size_t N)
 251       : SCEVCommutativeExpr(ID, scMulExpr, O, N) {}
 252
 253   public:
 254     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 255     static bool classof(const SCEV *S) {
 256       return S->getSCEVType() == scMulExpr;
 257     }
 258   };
 259
 260   /// This class represents a binary unsigned division operation.
 261   class SCEVUDivExpr : public SCEV {
 262     friend class ScalarEvolution;
 263
 264     const SCEV *LHS;
 265     const SCEV *RHS;
 266
 267     SCEVUDivExpr(const FoldingSetNodeIDRef ID, const SCEV *lhs, const SCEV *rhs)
 268         : SCEV(ID, scUDivExpr, computeExpressionSize({lhs, rhs})), LHS(lhs),
 269           RHS(rhs) {}
 270
 271   public:
 272     const SCEV *getLHS() const { return LHS; }
 273     const SCEV *getRHS() const { return RHS; }
 274
 275     Type *getType() const {
 276       // In most cases the types of LHS and RHS will be the same, but in some
 277       // crazy cases one or the other may be a pointer. ScalarEvolution doesn't
 278       // depend on the type for correctness, but handling types carefully can
 279       // avoid extra casts in the SCEVExpander. The LHS is more likely to be
 280       // a pointer type than the RHS, so use the RHS' type here.
 281       return getRHS()->getType();
 282     }
 283
 284     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 285     static bool classof(const SCEV *S) {
 286       return S->getSCEVType() == scUDivExpr;
 287     }
 288   };
 289
 290   /// This node represents a polynomial recurrence on the trip count
 291   /// of the specified loop.  This is the primary focus of the
 292   /// ScalarEvolution framework; all the other SCEV subclasses are
 293   /// mostly just supporting infrastructure to allow SCEVAddRecExpr
 294   /// expressions to be created and analyzed.
 295   ///
 296   /// All operands of an AddRec are required to be loop invariant.
 297   ///
 298   class SCEVAddRecExpr : public SCEVNAryExpr {
 299     friend class ScalarEvolution;
 300
 301     const Loop *L;
 302
 303     SCEVAddRecExpr(const FoldingSetNodeIDRef ID,
 304                    const SCEV *const *O, size_t N, const Loop *l)
 305       : SCEVNAryExpr(ID, scAddRecExpr, O, N), L(l) {}
 306
 307   public:
 308     const SCEV *getStart() const { return Operands[0]; }
 309     const Loop *getLoop() const { return L; }
 310
 311     /// Constructs and returns the recurrence indicating how much this
 312     /// expression steps by.  If this is a polynomial of degree N, it
 313     /// returns a chrec of degree N-1.  We cannot determine whether
 314     /// the step recurrence has self-wraparound.
 315     const SCEV *getStepRecurrence(ScalarEvolution &SE) const {
 316       if (isAffine()) return getOperand(1);
 317       return SE.getAddRecExpr(SmallVector<const SCEV *, 3>(op_begin()+1,
 318                                                            op_end()),
 319                               getLoop(), FlagAnyWrap);
 320     }
 321
 322     /// Return true if this represents an expression A + B*x where A
 323     /// and B are loop invariant values.
 324     bool isAffine() const {
 325       // We know that the start value is invariant.  This expression is thus
 326       // affine iff the step is also invariant.
 327       return getNumOperands() == 2;
 328     }
 329
 330     /// Return true if this represents an expression A + B*x + C*x^2
 331     /// where A, B and C are loop invariant values.  This corresponds
 332     /// to an addrec of the form {L,+,M,+,N}
 333     bool isQuadratic() const {
 334       return getNumOperands() == 3;
 335     }
 336
 337     /// Set flags for a recurrence without clearing any previously set flags.
 338     /// For AddRec, either NUW or NSW implies NW. Keep track of this fact here
 339     /// to make it easier to propagate flags.
 340     void setNoWrapFlags(NoWrapFlags Flags) {
 341       if (Flags & (FlagNUW | FlagNSW))
 342         Flags = ScalarEvolution::setFlags(Flags, FlagNW);
 343       SubclassData |= Flags;
 344     }
 345
 346     /// Return the value of this chain of recurrences at the specified
 347     /// iteration number.
 348     const SCEV *evaluateAtIteration(const SCEV *It, ScalarEvolution &SE) const;
 349
 350     /// Return the number of iterations of this loop that produce
 351     /// values in the specified constant range.  Another way of
 352     /// looking at this is that it returns the first iteration number
 353     /// where the value is not in the condition, thus computing the
 354     /// exit count.  If the iteration count can't be computed, an
 355     /// instance of SCEVCouldNotCompute is returned.
 356     const SCEV *getNumIterationsInRange(const ConstantRange &Range,
 357                                         ScalarEvolution &SE) const;
 358
 359     /// Return an expression representing the value of this expression
 360     /// one iteration of the loop ahead.
 361     const SCEVAddRecExpr *getPostIncExpr(ScalarEvolution &SE) const;
 362
 363     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 364     static bool classof(const SCEV *S) {
 365       return S->getSCEVType() == scAddRecExpr;
 366     }
 367   };
 368
 369   /// This class represents a signed maximum selection.
 370   class SCEVSMaxExpr : public SCEVCommutativeExpr {
 371     friend class ScalarEvolution;
 372
 373     SCEVSMaxExpr(const FoldingSetNodeIDRef ID,
 374                  const SCEV *const *O, size_t N)
 375       : SCEVCommutativeExpr(ID, scSMaxExpr, O, N) {
 376       // Max never overflows.
 377       setNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW));
 378     }
 379
 380   public:
 381     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 382     static bool classof(const SCEV *S) {
 383       return S->getSCEVType() == scSMaxExpr;
 384     }
 385   };
 386
 387   /// This class represents an unsigned maximum selection.
 388   class SCEVUMaxExpr : public SCEVCommutativeExpr {
 389     friend class ScalarEvolution;
 390
 391     SCEVUMaxExpr(const FoldingSetNodeIDRef ID,
 392                  const SCEV *const *O, size_t N)
 393       : SCEVCommutativeExpr(ID, scUMaxExpr, O, N) {
 394       // Max never overflows.
 395       setNoWrapFlags((NoWrapFlags)(FlagNUW | FlagNSW));
 396     }
 397
 398   public:
 399     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 400     static bool classof(const SCEV *S) {
 401       return S->getSCEVType() == scUMaxExpr;
 402     }
 403   };
 404
 405   /// This means that we are dealing with an entirely unknown SCEV
 406   /// value, and only represent it as its LLVM Value.  This is the
 407   /// "bottom" value for the analysis.
 408   class SCEVUnknown final : public SCEV, private CallbackVH {
 409     friend class ScalarEvolution;
 410
 411     /// The parent ScalarEvolution value. This is used to update the
 412     /// parent's maps when the value associated with a SCEVUnknown is
 413     /// deleted or RAUW'd.
 414     ScalarEvolution *SE;
 415
 416     /// The next pointer in the linked list of all SCEVUnknown
 417     /// instances owned by a ScalarEvolution.
 418     SCEVUnknown *Next;
 419
 420     SCEVUnknown(const FoldingSetNodeIDRef ID, Value *V,
 421                 ScalarEvolution *se, SCEVUnknown *next) :
 422       SCEV(ID, scUnknown, 1), CallbackVH(V), SE(se), Next(next) {}
 423
 424     // Implement CallbackVH.
 425     void deleted() override;
 426     void allUsesReplacedWith(Value *New) override;
 427
 428   public:
 429     Value *getValue() const { return getValPtr(); }
 430
 431     /// @{
 432     /// Test whether this is a special constant representing a type
 433     /// size, alignment, or field offset in a target-independent
 434     /// manner, and hasn't happened to have been folded with other
 435     /// operations into something unrecognizable. This is mainly only
 436     /// useful for pretty-printing and other situations where it isn't
 437     /// absolutely required for these to succeed.
 438     bool isSizeOf(Type *&AllocTy) const;
 439     bool isAlignOf(Type *&AllocTy) const;
 440     bool isOffsetOf(Type *&STy, Constant *&FieldNo) const;
 441     /// @}
 442
 443     Type *getType() const { return getValPtr()->getType(); }
 444
 445     /// Methods for support type inquiry through isa, cast, and dyn_cast:
 446     static bool classof(const SCEV *S) {
 447       return S->getSCEVType() == scUnknown;
 448     }
 449   };
 450
 451   /// This class defines a simple visitor class that may be used for
 452   /// various SCEV analysis purposes.
 453   template<typename SC, typename RetVal=void>
 454   struct SCEVVisitor {
 455     RetVal visit(const SCEV *S) {
 456       switch (S->getSCEVType()) {
 457       case scConstant:
 458         return ((SC*)this)->visitConstant((const SCEVConstant*)S);
 459       case scTruncate:
 460         return ((SC*)this)->visitTruncateExpr((const SCEVTruncateExpr*)S);
 461       case scZeroExtend:
 462         return ((SC*)this)->visitZeroExtendExpr((const SCEVZeroExtendExpr*)S);
 463       case scSignExtend:
 464         return ((SC*)this)->visitSignExtendExpr((const SCEVSignExtendExpr*)S);
 465       case scAddExpr:
 466         return ((SC*)this)->visitAddExpr((const SCEVAddExpr*)S);
 467       case scMulExpr:
 468         return ((SC*)this)->visitMulExpr((const SCEVMulExpr*)S);
 469       case scUDivExpr:
 470         return ((SC*)this)->visitUDivExpr((const SCEVUDivExpr*)S);
 471       case scAddRecExpr:
 472         return ((SC*)this)->visitAddRecExpr((const SCEVAddRecExpr*)S);
 473       case scSMaxExpr:
 474         return ((SC*)this)->visitSMaxExpr((const SCEVSMaxExpr*)S);
 475       case scUMaxExpr:
 476         return ((SC*)this)->visitUMaxExpr((const SCEVUMaxExpr*)S);
 477       case scUnknown:
 478         return ((SC*)this)->visitUnknown((const SCEVUnknown*)S);
 479       case scCouldNotCompute:
 480         return ((SC*)this)->visitCouldNotCompute((const SCEVCouldNotCompute*)S);
 481       default:
 482         llvm_unreachable("Unknown SCEV type!");
 483       }
 484     }
 485
 486     RetVal visitCouldNotCompute(const SCEVCouldNotCompute *S) {
 487       llvm_unreachable("Invalid use of SCEVCouldNotCompute!");
 488     }
 489   };
 490
 491   /// Visit all nodes in the expression tree using worklist traversal.
 492   ///
 493   /// Visitor implements:
 494   ///   // return true to follow this node.
 495   ///   bool follow(const SCEV *S);
 496   ///   // return true to terminate the search.
 497   ///   bool isDone();
 498   template<typename SV>
 499   class SCEVTraversal {
 500     SV &Visitor;
 501     SmallVector<const SCEV *, 8> Worklist;
 502     SmallPtrSet<const SCEV *, 8> Visited;
 503
 504     void push(const SCEV *S) {
 505       if (Visited.insert(S).second && Visitor.follow(S))
 506         Worklist.push_back(S);
 507     }
 508
 509   public:
 510     SCEVTraversal(SV& V): Visitor(V) {}
 511
 512     void visitAll(const SCEV *Root) {
 513       push(Root);
 514       while (!Worklist.empty() && !Visitor.isDone()) {
 515         const SCEV *S = Worklist.pop_back_val();
 516
 517         switch (S->getSCEVType()) {
 518         case scConstant:
 519         case scUnknown:
 520           break;
 521         case scTruncate:
 522         case scZeroExtend:
 523         case scSignExtend:
 524           push(cast<SCEVCastExpr>(S)->getOperand());
 525           break;
 526         case scAddExpr:
 527         case scMulExpr:
 528         case scSMaxExpr:
 529         case scUMaxExpr:
 530         case scAddRecExpr:
 531           for (const auto *Op : cast<SCEVNAryExpr>(S)->operands())
 532             push(Op);
 533           break;
 534         case scUDivExpr: {
 535           const SCEVUDivExpr *UDiv = cast<SCEVUDivExpr>(S);
 536           push(UDiv->getLHS());
 537           push(UDiv->getRHS());
 538           break;
 539         }
 540         case scCouldNotCompute:
 541           llvm_unreachable("Attempt to use a SCEVCouldNotCompute object!");
 542         default:
 543           llvm_unreachable("Unknown SCEV kind!");
 544         }
 545       }
 546     }
 547   };
 548
 549   /// Use SCEVTraversal to visit all nodes in the given expression tree.
 550   template<typename SV>
 551   void visitAll(const SCEV *Root, SV& Visitor) {
 552     SCEVTraversal<SV> T(Visitor);
 553     T.visitAll(Root);
 554   }
 555
 556   /// Return true if any node in \p Root satisfies the predicate \p Pred.
 557   template <typename PredTy>
 558   bool SCEVExprContains(const SCEV *Root, PredTy Pred) {
 559     struct FindClosure {
 560       bool Found = false;
 561       PredTy Pred;
 562
 563       FindClosure(PredTy Pred) : Pred(Pred) {}
 564
 565       bool follow(const SCEV *S) {
 566         if (!Pred(S))
 567           return true;
 568
 569         Found = true;
 570         return false;
 571       }
 572
 573       bool isDone() const { return Found; }
 574     };
 575
 576     FindClosure FC(Pred);
 577     visitAll(Root, FC);
 578     return FC.Found;
 579   }
 580
 581   /// This visitor recursively visits a SCEV expression and re-writes it.
 582   /// The result from each visit is cached, so it will return the same
 583   /// SCEV for the same input.
 584   template<typename SC>
 585   class SCEVRewriteVisitor : public SCEVVisitor<SC, const SCEV *> {
 586   protected:
 587     ScalarEvolution &SE;
 588     // Memoize the result of each visit so that we only compute once for
 589     // the same input SCEV. This is to avoid redundant computations when
 590     // a SCEV is referenced by multiple SCEVs. Without memoization, this
 591     // visit algorithm would have exponential time complexity in the worst
 592     // case, causing the compiler to hang on certain tests.
 593     DenseMap<const SCEV *, const SCEV *> RewriteResults;
 594
 595   public:
 596     SCEVRewriteVisitor(ScalarEvolution &SE) : SE(SE) {}
 597
 598     const SCEV *visit(const SCEV *S) {
 599       auto It = RewriteResults.find(S);
 600       if (It != RewriteResults.end())
 601         return It->second;
 602       auto* Visited = SCEVVisitor<SC, const SCEV *>::visit(S);
 603       auto Result = RewriteResults.try_emplace(S, Visited);
 604       assert(Result.second && "Should insert a new entry");
 605       return Result.first->second;
 606     }
 607
 608     const SCEV *visitConstant(const SCEVConstant *Constant) {
 609       return Constant;
 610     }
 611
 612     const SCEV *visitTruncateExpr(const SCEVTruncateExpr *Expr) {
 613       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
 614       return Operand == Expr->getOperand()
 615                  ? Expr
 616                  : SE.getTruncateExpr(Operand, Expr->getType());
 617     }
 618
 619     const SCEV *visitZeroExtendExpr(const SCEVZeroExtendExpr *Expr) {
 620       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
 621       return Operand == Expr->getOperand()
 622                  ? Expr
 623                  : SE.getZeroExtendExpr(Operand, Expr->getType());
 624     }
 625
 626     const SCEV *visitSignExtendExpr(const SCEVSignExtendExpr *Expr) {
 627       const SCEV *Operand = ((SC*)this)->visit(Expr->getOperand());
 628       return Operand == Expr->getOperand()
 629                  ? Expr
 630                  : SE.getSignExtendExpr(Operand, Expr->getType());
 631     }
 632
 633     const SCEV *visitAddExpr(const SCEVAddExpr *Expr) {
 634       SmallVector<const SCEV *, 2> Operands;
 635       bool Changed = false;
 636       for (auto *Op : Expr->operands()) {
 637         Operands.push_back(((SC*)this)->visit(Op));
 638         Changed |= Op != Operands.back();
 639       }
 640       return !Changed ? Expr : SE.getAddExpr(Operands);
 641     }
 642
 643     const SCEV *visitMulExpr(const SCEVMulExpr *Expr) {
 644       SmallVector<const SCEV *, 2> Operands;
 645       bool Changed = false;
 646       for (auto *Op : Expr->operands()) {
 647         Operands.push_back(((SC*)this)->visit(Op));
 648         Changed |= Op != Operands.back();
 649       }
 650       return !Changed ? Expr : SE.getMulExpr(Operands);
 651     }
 652
 653     const SCEV *visitUDivExpr(const SCEVUDivExpr *Expr) {
 654       auto *LHS = ((SC *)this)->visit(Expr->getLHS());
 655       auto *RHS = ((SC *)this)->visit(Expr->getRHS());
 656       bool Changed = LHS != Expr->getLHS() || RHS != Expr->getRHS();
 657       return !Changed ? Expr : SE.getUDivExpr(LHS, RHS);
 658     }
 659
 660     const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
 661       SmallVector<const SCEV *, 2> Operands;
 662       bool Changed = false;
 663       for (auto *Op : Expr->operands()) {
 664         Operands.push_back(((SC*)this)->visit(Op));
 665         Changed |= Op != Operands.back();
 666       }
 667       return !Changed ? Expr
 668                       : SE.getAddRecExpr(Operands, Expr->getLoop(),
 669                                          Expr->getNoWrapFlags());
 670     }
 671
 672     const SCEV *visitSMaxExpr(const SCEVSMaxExpr *Expr) {
 673       SmallVector<const SCEV *, 2> Operands;
 674       bool Changed = false;
 675       for (auto *Op : Expr->operands()) {
 676         Operands.push_back(((SC *)this)->visit(Op));
 677         Changed |= Op != Operands.back();
 678       }
 679       return !Changed ? Expr : SE.getSMaxExpr(Operands);
 680     }
 681
 682     const SCEV *visitUMaxExpr(const SCEVUMaxExpr *Expr) {
 683       SmallVector<const SCEV *, 2> Operands;
 684       bool Changed = false;
 685       for (auto *Op : Expr->operands()) {
 686         Operands.push_back(((SC*)this)->visit(Op));
 687         Changed |= Op != Operands.back();
 688       }
 689       return !Changed ? Expr : SE.getUMaxExpr(Operands);
 690     }
 691
 692     const SCEV *visitUnknown(const SCEVUnknown *Expr) {
 693       return Expr;
 694     }
 695
 696     const SCEV *visitCouldNotCompute(const SCEVCouldNotCompute *Expr) {
 697       return Expr;
 698     }
 699   };
 700
 701   using ValueToValueMap = DenseMap<const Value *, Value *>;
 702
 703   /// The SCEVParameterRewriter takes a scalar evolution expression and updates
 704   /// the SCEVUnknown components following the Map (Value -> Value).
 705   class SCEVParameterRewriter : public SCEVRewriteVisitor<SCEVParameterRewriter> {
 706   public:
 707     static const SCEV *rewrite(const SCEV *Scev, ScalarEvolution &SE,
 708                                ValueToValueMap &Map,
 709                                bool InterpretConsts = false) {
 710       SCEVParameterRewriter Rewriter(SE, Map, InterpretConsts);
 711       return Rewriter.visit(Scev);
 712     }
 713
 714     SCEVParameterRewriter(ScalarEvolution &SE, ValueToValueMap &M, bool C)
 715       : SCEVRewriteVisitor(SE), Map(M), InterpretConsts(C) {}
 716
 717     const SCEV *visitUnknown(const SCEVUnknown *Expr) {
 718       Value *V = Expr->getValue();
 719       if (Map.count(V)) {
 720         Value *NV = Map[V];
 721         if (InterpretConsts && isa<ConstantInt>(NV))
 722           return SE.getConstant(cast<ConstantInt>(NV));
 723         return SE.getUnknown(NV);
 724       }
 725       return Expr;
 726     }
 727
 728   private:
 729     ValueToValueMap &Map;
 730     bool InterpretConsts;
 731   };
 732
 733   using LoopToScevMapT = DenseMap<const Loop *, const SCEV *>;
 734
 735   /// The SCEVLoopAddRecRewriter takes a scalar evolution expression and applies
 736   /// the Map (Loop -> SCEV) to all AddRecExprs.
 737   class SCEVLoopAddRecRewriter
 738       : public SCEVRewriteVisitor<SCEVLoopAddRecRewriter> {
 739   public:
 740     SCEVLoopAddRecRewriter(ScalarEvolution &SE, LoopToScevMapT &M)
 741         : SCEVRewriteVisitor(SE), Map(M) {}
 742
 743     static const SCEV *rewrite(const SCEV *Scev, LoopToScevMapT &Map,
 744                                ScalarEvolution &SE) {
 745       SCEVLoopAddRecRewriter Rewriter(SE, Map);
 746       return Rewriter.visit(Scev);
 747     }
 748
 749     const SCEV *visitAddRecExpr(const SCEVAddRecExpr *Expr) {
 750       SmallVector<const SCEV *, 2> Operands;
 751       for (const SCEV *Op : Expr->operands())
 752         Operands.push_back(visit(Op));
 753
 754       const Loop *L = Expr->getLoop();
 755       const SCEV *Res = SE.getAddRecExpr(Operands, L, Expr->getNoWrapFlags());
 756
 757       if (0 == Map.count(L))
 758         return Res;
 759
 760       const SCEVAddRecExpr *Rec = cast<SCEVAddRecExpr>(Res);
 761       return Rec->evaluateAtIteration(Map[L], SE);
 762     }
 763
 764   private:
 765     LoopToScevMapT &Map;
 766   };
 767
 768 } // end namespace llvm
 769
 770 #endif // LLVM_ANALYSIS_SCALAREVOLUTIONEXPRESSIONS_H