1//===---- llvm/Analysis/ScalarEvolutionExpander.h - SCEV Exprs --*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file defines the classes used to generate code from scalar expressions. 11// 12//===----------------------------------------------------------------------===// 13 14#ifndef LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H 15#define LLVM_ANALYSIS_SCALAREVOLUTIONEXPANDER_H 16 17#include "llvm/ADT/DenseMap.h" 18#include "llvm/ADT/DenseSet.h" 19#include "llvm/ADT/Optional.h" 20#include "llvm/Analysis/ScalarEvolutionExpressions.h" 21#include "llvm/Analysis/ScalarEvolutionNormalization.h" 22#include "llvm/Analysis/TargetFolder.h" 23#include "llvm/IR/IRBuilder.h" 24#include "llvm/IR/ValueHandle.h" 25 26namespace llvm { 27 class TargetTransformInfo; 28 29 /// Return true if the given expression is safe to expand in the sense that 30 /// all materialized values are safe to speculate. 31 bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE); 32 33 /// This class uses information about analyze scalars to rewrite expressions 34 /// in canonical form. 35 /// 36 /// Clients should create an instance of this class when rewriting is needed, 37 /// and destroy it when finished to allow the release of the associated 38 /// memory. 39 class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> { 40 ScalarEvolution &SE; 41 const DataLayout &DL; 42 43 // New instructions receive a name to identifies them with the current pass. 44 const char* IVName; 45 46 // InsertedExpressions caches Values for reuse, so must track RAUW. 47 DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>> 48 InsertedExpressions; 49 50 // InsertedValues only flags inserted instructions so needs no RAUW. 51 DenseSet<AssertingVH<Value>> InsertedValues; 52 DenseSet<AssertingVH<Value>> InsertedPostIncValues; 53 54 /// A memoization of the "relevant" loop for a given SCEV. 55 DenseMap<const SCEV *, const Loop *> RelevantLoops; 56 57 /// Addrecs referring to any of the given loops are expanded in post-inc 58 /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add 59 /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new 60 /// phi starting at 1. This is only supported in non-canonical mode. 61 PostIncLoopSet PostIncLoops; 62 63 /// When this is non-null, addrecs expanded in the loop it indicates should 64 /// be inserted with increments at IVIncInsertPos. 65 const Loop *IVIncInsertLoop; 66 67 /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV 68 /// increment at this position. 69 Instruction *IVIncInsertPos; 70 71 /// Phis that complete an IV chain. Reuse 72 DenseSet<AssertingVH<PHINode>> ChainedPhis; 73 74 /// When true, expressions are expanded in "canonical" form. In particular, 75 /// addrecs are expanded as arithmetic based on a canonical induction 76 /// variable. When false, expression are expanded in a more literal form. 77 bool CanonicalMode; 78 79 /// When invoked from LSR, the expander is in "strength reduction" mode. The 80 /// only difference is that phi's are only reused if they are already in 81 /// "expanded" form. 82 bool LSRMode; 83 84 typedef IRBuilder<TargetFolder> BuilderType; 85 BuilderType Builder; 86 87 // RAII object that stores the current insertion point and restores it when 88 // the object is destroyed. This includes the debug location. Duplicated 89 // from InsertPointGuard to add SetInsertPoint() which is used to updated 90 // InsertPointGuards stack when insert points are moved during SCEV 91 // expansion. 92 class SCEVInsertPointGuard { 93 IRBuilderBase &Builder; 94 AssertingVH<BasicBlock> Block; 95 BasicBlock::iterator Point; 96 DebugLoc DbgLoc; 97 SCEVExpander *SE; 98 99 SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete; 100 SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete; 101 102 public: 103 SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE) 104 : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()), 105 DbgLoc(B.getCurrentDebugLocation()), SE(SE) { 106 SE->InsertPointGuards.push_back(this); 107 } 108 109 ~SCEVInsertPointGuard() { 110 // These guards should always created/destroyed in FIFO order since they 111 // are used to guard lexically scoped blocks of code in 112 // ScalarEvolutionExpander. 113 assert(SE->InsertPointGuards.back() == this); 114 SE->InsertPointGuards.pop_back(); 115 Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point)); 116 Builder.SetCurrentDebugLocation(DbgLoc); 117 } 118 119 BasicBlock::iterator GetInsertPoint() const { return Point; } 120 void SetInsertPoint(BasicBlock::iterator I) { Point = I; } 121 }; 122 123 /// Stack of pointers to saved insert points, used to keep insert points 124 /// consistent when instructions are moved. 125 SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards; 126 127#ifndef NDEBUG 128 const char *DebugType; 129#endif 130 131 friend struct SCEVVisitor<SCEVExpander, Value*>; 132 133 public: 134 /// Construct a SCEVExpander in "canonical" mode. 135 explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL, 136 const char *name) 137 : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr), 138 IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false), 139 Builder(se.getContext(), TargetFolder(DL)) { 140#ifndef NDEBUG 141 DebugType = ""; 142#endif 143 } 144 145 ~SCEVExpander() { 146 // Make sure the insert point guard stack is consistent. 147 assert(InsertPointGuards.empty()); 148 } 149 150#ifndef NDEBUG 151 void setDebugType(const char* s) { DebugType = s; } 152#endif 153 154 /// Erase the contents of the InsertedExpressions map so that users trying 155 /// to expand the same expression into multiple BasicBlocks or different 156 /// places within the same BasicBlock can do so. 157 void clear() { 158 InsertedExpressions.clear(); 159 InsertedValues.clear(); 160 InsertedPostIncValues.clear(); 161 ChainedPhis.clear(); 162 } 163 164 /// Return true for expressions that may incur non-trivial cost to evaluate 165 /// at runtime. 166 /// 167 /// At is an optional parameter which specifies point in code where user is 168 /// going to expand this expression. Sometimes this knowledge can lead to a 169 /// more accurate cost estimation. 170 bool isHighCostExpansion(const SCEV *Expr, Loop *L, 171 const Instruction *At = nullptr) { 172 SmallPtrSet<const SCEV *, 8> Processed; 173 return isHighCostExpansionHelper(Expr, L, At, Processed); 174 } 175 176 /// This method returns the canonical induction variable of the specified 177 /// type for the specified loop (inserting one if there is none). A 178 /// canonical induction variable starts at zero and steps by one on each 179 /// iteration. 180 PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty); 181 182 /// Return the induction variable increment's IV operand. 183 Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos, 184 bool allowScale); 185 186 /// Utility for hoisting an IV increment. 187 bool hoistIVInc(Instruction *IncV, Instruction *InsertPos); 188 189 /// replace congruent phis with their most canonical representative. Return 190 /// the number of phis eliminated. 191 unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT, 192 SmallVectorImpl<WeakTrackingVH> &DeadInsts, 193 const TargetTransformInfo *TTI = nullptr); 194 195 /// Insert code to directly compute the specified SCEV expression into the 196 /// program. The inserted code is inserted into the specified block. 197 Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I); 198 199 /// Insert code to directly compute the specified SCEV expression into the 200 /// program. The inserted code is inserted into the SCEVExpander's current 201 /// insertion point. If a type is specified, the result will be expanded to 202 /// have that type, with a cast if necessary. 203 Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr); 204 205 206 /// Generates a code sequence that evaluates this predicate. The inserted 207 /// instructions will be at position \p Loc. The result will be of type i1 208 /// and will have a value of 0 when the predicate is false and 1 otherwise. 209 Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc); 210 211 /// A specialized variant of expandCodeForPredicate, handling the case when 212 /// we are expanding code for a SCEVEqualPredicate. 213 Value *expandEqualPredicate(const SCEVEqualPredicate *Pred, 214 Instruction *Loc); 215 216 /// Generates code that evaluates if the \p AR expression will overflow. 217 Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc, 218 bool Signed); 219 220 /// A specialized variant of expandCodeForPredicate, handling the case when 221 /// we are expanding code for a SCEVWrapPredicate. 222 Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc); 223 224 /// A specialized variant of expandCodeForPredicate, handling the case when 225 /// we are expanding code for a SCEVUnionPredicate. 226 Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, 227 Instruction *Loc); 228 229 /// Set the current IV increment loop and position. 230 void setIVIncInsertPos(const Loop *L, Instruction *Pos) { 231 assert(!CanonicalMode && 232 "IV increment positions are not supported in CanonicalMode"); 233 IVIncInsertLoop = L; 234 IVIncInsertPos = Pos; 235 } 236 237 /// Enable post-inc expansion for addrecs referring to the given 238 /// loops. Post-inc expansion is only supported in non-canonical mode. 239 void setPostInc(const PostIncLoopSet &L) { 240 assert(!CanonicalMode && 241 "Post-inc expansion is not supported in CanonicalMode"); 242 PostIncLoops = L; 243 } 244 245 /// Disable all post-inc expansion. 246 void clearPostInc() { 247 PostIncLoops.clear(); 248 249 // When we change the post-inc loop set, cached expansions may no 250 // longer be valid. 251 InsertedPostIncValues.clear(); 252 } 253 254 /// Disable the behavior of expanding expressions in canonical form rather 255 /// than in a more literal form. Non-canonical mode is useful for late 256 /// optimization passes. 257 void disableCanonicalMode() { CanonicalMode = false; } 258 259 void enableLSRMode() { LSRMode = true; } 260 261 /// Set the current insertion point. This is useful if multiple calls to 262 /// expandCodeFor() are going to be made with the same insert point and the 263 /// insert point may be moved during one of the expansions (e.g. if the 264 /// insert point is not a block terminator). 265 void setInsertPoint(Instruction *IP) { 266 assert(IP); 267 Builder.SetInsertPoint(IP); 268 } 269 270 /// Clear the current insertion point. This is useful if the instruction 271 /// that had been serving as the insertion point may have been deleted. 272 void clearInsertPoint() { 273 Builder.ClearInsertionPoint(); 274 } 275 276 /// Return true if the specified instruction was inserted by the code 277 /// rewriter. If so, the client should not modify the instruction. 278 bool isInsertedInstruction(Instruction *I) const { 279 return InsertedValues.count(I) || InsertedPostIncValues.count(I); 280 } 281 282 void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); } 283 284 /// Try to find existing LLVM IR value for S available at the point At. 285 Value *getExactExistingExpansion(const SCEV *S, const Instruction *At, 286 Loop *L); 287 288 /// Try to find the ValueOffsetPair for S. The function is mainly used to 289 /// check whether S can be expanded cheaply. If this returns a non-None 290 /// value, we know we can codegen the `ValueOffsetPair` into a suitable 291 /// expansion identical with S so that S can be expanded cheaply. 292 /// 293 /// L is a hint which tells in which loop to look for the suitable value. 294 /// On success return value which is equivalent to the expanded S at point 295 /// At. Return nullptr if value was not found. 296 /// 297 /// Note that this function does not perform an exhaustive search. I.e if it 298 /// didn't find any value it does not mean that there is no such value. 299 /// 300 Optional<ScalarEvolution::ValueOffsetPair> 301 getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L); 302 303 private: 304 LLVMContext &getContext() const { return SE.getContext(); } 305 306 /// Recursive helper function for isHighCostExpansion. 307 bool isHighCostExpansionHelper(const SCEV *S, Loop *L, 308 const Instruction *At, 309 SmallPtrSetImpl<const SCEV *> &Processed); 310 311 /// Insert the specified binary operator, doing a small amount of work to 312 /// avoid inserting an obviously redundant operation. 313 Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS); 314 315 /// Arrange for there to be a cast of V to Ty at IP, reusing an existing 316 /// cast if a suitable one exists, moving an existing cast if a suitable one 317 /// exists but isn't in the right place, or or creating a new one. 318 Value *ReuseOrCreateCast(Value *V, Type *Ty, 319 Instruction::CastOps Op, 320 BasicBlock::iterator IP); 321 322 /// Insert a cast of V to the specified type, which must be possible with a 323 /// noop cast, doing what we can to share the casts. 324 Value *InsertNoopCastOfTo(Value *V, Type *Ty); 325 326 /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using 327 /// ptrtoint+arithmetic+inttoptr. 328 Value *expandAddToGEP(const SCEV *const *op_begin, 329 const SCEV *const *op_end, 330 PointerType *PTy, Type *Ty, Value *V); 331 332 /// Find a previous Value in ExprValueMap for expand. 333 ScalarEvolution::ValueOffsetPair 334 FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt); 335 336 Value *expand(const SCEV *S); 337 338 /// Determine the most "relevant" loop for the given SCEV. 339 const Loop *getRelevantLoop(const SCEV *); 340 341 Value *visitConstant(const SCEVConstant *S) { 342 return S->getValue(); 343 } 344 345 Value *visitTruncateExpr(const SCEVTruncateExpr *S); 346 347 Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S); 348 349 Value *visitSignExtendExpr(const SCEVSignExtendExpr *S); 350 351 Value *visitAddExpr(const SCEVAddExpr *S); 352 353 Value *visitMulExpr(const SCEVMulExpr *S); 354 355 Value *visitUDivExpr(const SCEVUDivExpr *S); 356 357 Value *visitAddRecExpr(const SCEVAddRecExpr *S); 358 359 Value *visitSMaxExpr(const SCEVSMaxExpr *S); 360 361 Value *visitUMaxExpr(const SCEVUMaxExpr *S); 362 363 Value *visitUnknown(const SCEVUnknown *S) { 364 return S->getValue(); 365 } 366 367 void rememberInstruction(Value *I); 368 369 bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 370 371 bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 372 373 Value *expandAddRecExprLiterally(const SCEVAddRecExpr *); 374 PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized, 375 const Loop *L, 376 Type *ExpandTy, 377 Type *IntTy, 378 Type *&TruncTy, 379 bool &InvertStep); 380 Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L, 381 Type *ExpandTy, Type *IntTy, bool useSubtract); 382 383 void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist, 384 Instruction *Pos, PHINode *LoopPhi); 385 386 void fixupInsertPoints(Instruction *I); 387 }; 388} 389 390#endif 391