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 26 namespace 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 anywhere their operands are 31 /// defined. 32 bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE); 33 34 /// Return true if the given expression is safe to expand in the sense that 35 /// all materialized values are defined and safe to speculate at the specified 36 /// location and their operands are defined at this location. 37 bool isSafeToExpandAt(const SCEV *S, const Instruction *InsertionPoint, 38 ScalarEvolution &SE); 39 40 /// This class uses information about analyze scalars to rewrite expressions 41 /// in canonical form. 42 /// 43 /// Clients should create an instance of this class when rewriting is needed, 44 /// and destroy it when finished to allow the release of the associated 45 /// memory. 46 class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> { 47 ScalarEvolution &SE; 48 const DataLayout &DL; 49 50 // New instructions receive a name to identify them with the current pass. 51 const char* IVName; 52 53 // InsertedExpressions caches Values for reuse, so must track RAUW. 54 DenseMap<std::pair<const SCEV *, Instruction *>, TrackingVH<Value>> 55 InsertedExpressions; 56 57 // InsertedValues only flags inserted instructions so needs no RAUW. 58 DenseSet<AssertingVH<Value>> InsertedValues; 59 DenseSet<AssertingVH<Value>> InsertedPostIncValues; 60 61 /// A memoization of the "relevant" loop for a given SCEV. 62 DenseMap<const SCEV *, const Loop *> RelevantLoops; 63 64 /// Addrecs referring to any of the given loops are expanded in post-inc 65 /// mode. For example, expanding {1,+,1}<L> in post-inc mode returns the add 66 /// instruction that adds one to the phi for {0,+,1}<L>, as opposed to a new 67 /// phi starting at 1. This is only supported in non-canonical mode. 68 PostIncLoopSet PostIncLoops; 69 70 /// When this is non-null, addrecs expanded in the loop it indicates should 71 /// be inserted with increments at IVIncInsertPos. 72 const Loop *IVIncInsertLoop; 73 74 /// When expanding addrecs in the IVIncInsertLoop loop, insert the IV 75 /// increment at this position. 76 Instruction *IVIncInsertPos; 77 78 /// Phis that complete an IV chain. Reuse 79 DenseSet<AssertingVH<PHINode>> ChainedPhis; 80 81 /// When true, expressions are expanded in "canonical" form. In particular, 82 /// addrecs are expanded as arithmetic based on a canonical induction 83 /// variable. When false, expression are expanded in a more literal form. 84 bool CanonicalMode; 85 86 /// When invoked from LSR, the expander is in "strength reduction" mode. The 87 /// only difference is that phi's are only reused if they are already in 88 /// "expanded" form. 89 bool LSRMode; 90 91 typedef IRBuilder<TargetFolder> BuilderType; 92 BuilderType Builder; 93 94 // RAII object that stores the current insertion point and restores it when 95 // the object is destroyed. This includes the debug location. Duplicated 96 // from InsertPointGuard to add SetInsertPoint() which is used to updated 97 // InsertPointGuards stack when insert points are moved during SCEV 98 // expansion. 99 class SCEVInsertPointGuard { 100 IRBuilderBase &Builder; 101 AssertingVH<BasicBlock> Block; 102 BasicBlock::iterator Point; 103 DebugLoc DbgLoc; 104 SCEVExpander *SE; 105 106 SCEVInsertPointGuard(const SCEVInsertPointGuard &) = delete; 107 SCEVInsertPointGuard &operator=(const SCEVInsertPointGuard &) = delete; 108 109 public: SCEVInsertPointGuard(IRBuilderBase & B,SCEVExpander * SE)110 SCEVInsertPointGuard(IRBuilderBase &B, SCEVExpander *SE) 111 : Builder(B), Block(B.GetInsertBlock()), Point(B.GetInsertPoint()), 112 DbgLoc(B.getCurrentDebugLocation()), SE(SE) { 113 SE->InsertPointGuards.push_back(this); 114 } 115 ~SCEVInsertPointGuard()116 ~SCEVInsertPointGuard() { 117 // These guards should always created/destroyed in FIFO order since they 118 // are used to guard lexically scoped blocks of code in 119 // ScalarEvolutionExpander. 120 assert(SE->InsertPointGuards.back() == this); 121 SE->InsertPointGuards.pop_back(); 122 Builder.restoreIP(IRBuilderBase::InsertPoint(Block, Point)); 123 Builder.SetCurrentDebugLocation(DbgLoc); 124 } 125 GetInsertPoint()126 BasicBlock::iterator GetInsertPoint() const { return Point; } SetInsertPoint(BasicBlock::iterator I)127 void SetInsertPoint(BasicBlock::iterator I) { Point = I; } 128 }; 129 130 /// Stack of pointers to saved insert points, used to keep insert points 131 /// consistent when instructions are moved. 132 SmallVector<SCEVInsertPointGuard *, 8> InsertPointGuards; 133 134 #ifndef NDEBUG 135 const char *DebugType; 136 #endif 137 138 friend struct SCEVVisitor<SCEVExpander, Value*>; 139 140 public: 141 /// Construct a SCEVExpander in "canonical" mode. 142 explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL, 143 const char *name) 144 : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr), 145 IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false), 146 Builder(se.getContext(), TargetFolder(DL)) { 147 #ifndef NDEBUG 148 DebugType = ""; 149 #endif 150 } 151 152 ~SCEVExpander() { 153 // Make sure the insert point guard stack is consistent. 154 assert(InsertPointGuards.empty()); 155 } 156 157 #ifndef NDEBUG 158 void setDebugType(const char* s) { DebugType = s; } 159 #endif 160 161 /// Erase the contents of the InsertedExpressions map so that users trying 162 /// to expand the same expression into multiple BasicBlocks or different 163 /// places within the same BasicBlock can do so. 164 void clear() { 165 InsertedExpressions.clear(); 166 InsertedValues.clear(); 167 InsertedPostIncValues.clear(); 168 ChainedPhis.clear(); 169 } 170 171 /// Return true for expressions that may incur non-trivial cost to evaluate 172 /// at runtime. 173 /// 174 /// At is an optional parameter which specifies point in code where user is 175 /// going to expand this expression. Sometimes this knowledge can lead to a 176 /// more accurate cost estimation. 177 bool isHighCostExpansion(const SCEV *Expr, Loop *L, 178 const Instruction *At = nullptr) { 179 SmallPtrSet<const SCEV *, 8> Processed; 180 return isHighCostExpansionHelper(Expr, L, At, Processed); 181 } 182 183 /// This method returns the canonical induction variable of the specified 184 /// type for the specified loop (inserting one if there is none). A 185 /// canonical induction variable starts at zero and steps by one on each 186 /// iteration. 187 PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty); 188 189 /// Return the induction variable increment's IV operand. 190 Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos, 191 bool allowScale); 192 193 /// Utility for hoisting an IV increment. 194 bool hoistIVInc(Instruction *IncV, Instruction *InsertPos); 195 196 /// replace congruent phis with their most canonical representative. Return 197 /// the number of phis eliminated. 198 unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT, 199 SmallVectorImpl<WeakTrackingVH> &DeadInsts, 200 const TargetTransformInfo *TTI = nullptr); 201 202 /// Insert code to directly compute the specified SCEV expression into the 203 /// program. The inserted code is inserted into the specified block. 204 Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I); 205 206 /// Insert code to directly compute the specified SCEV expression into the 207 /// program. The inserted code is inserted into the SCEVExpander's current 208 /// insertion point. If a type is specified, the result will be expanded to 209 /// have that type, with a cast if necessary. 210 Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr); 211 212 213 /// Generates a code sequence that evaluates this predicate. The inserted 214 /// instructions will be at position \p Loc. The result will be of type i1 215 /// and will have a value of 0 when the predicate is false and 1 otherwise. 216 Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc); 217 218 /// A specialized variant of expandCodeForPredicate, handling the case when 219 /// we are expanding code for a SCEVEqualPredicate. 220 Value *expandEqualPredicate(const SCEVEqualPredicate *Pred, 221 Instruction *Loc); 222 223 /// Generates code that evaluates if the \p AR expression will overflow. 224 Value *generateOverflowCheck(const SCEVAddRecExpr *AR, Instruction *Loc, 225 bool Signed); 226 227 /// A specialized variant of expandCodeForPredicate, handling the case when 228 /// we are expanding code for a SCEVWrapPredicate. 229 Value *expandWrapPredicate(const SCEVWrapPredicate *P, Instruction *Loc); 230 231 /// A specialized variant of expandCodeForPredicate, handling the case when 232 /// we are expanding code for a SCEVUnionPredicate. 233 Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, 234 Instruction *Loc); 235 236 /// Set the current IV increment loop and position. 237 void setIVIncInsertPos(const Loop *L, Instruction *Pos) { 238 assert(!CanonicalMode && 239 "IV increment positions are not supported in CanonicalMode"); 240 IVIncInsertLoop = L; 241 IVIncInsertPos = Pos; 242 } 243 244 /// Enable post-inc expansion for addrecs referring to the given 245 /// loops. Post-inc expansion is only supported in non-canonical mode. 246 void setPostInc(const PostIncLoopSet &L) { 247 assert(!CanonicalMode && 248 "Post-inc expansion is not supported in CanonicalMode"); 249 PostIncLoops = L; 250 } 251 252 /// Disable all post-inc expansion. 253 void clearPostInc() { 254 PostIncLoops.clear(); 255 256 // When we change the post-inc loop set, cached expansions may no 257 // longer be valid. 258 InsertedPostIncValues.clear(); 259 } 260 261 /// Disable the behavior of expanding expressions in canonical form rather 262 /// than in a more literal form. Non-canonical mode is useful for late 263 /// optimization passes. 264 void disableCanonicalMode() { CanonicalMode = false; } 265 266 void enableLSRMode() { LSRMode = true; } 267 268 /// Set the current insertion point. This is useful if multiple calls to 269 /// expandCodeFor() are going to be made with the same insert point and the 270 /// insert point may be moved during one of the expansions (e.g. if the 271 /// insert point is not a block terminator). 272 void setInsertPoint(Instruction *IP) { 273 assert(IP); 274 Builder.SetInsertPoint(IP); 275 } 276 277 /// Clear the current insertion point. This is useful if the instruction 278 /// that had been serving as the insertion point may have been deleted. 279 void clearInsertPoint() { 280 Builder.ClearInsertionPoint(); 281 } 282 283 /// Return true if the specified instruction was inserted by the code 284 /// rewriter. If so, the client should not modify the instruction. 285 bool isInsertedInstruction(Instruction *I) const { 286 return InsertedValues.count(I) || InsertedPostIncValues.count(I); 287 } 288 289 void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); } 290 291 /// Try to find existing LLVM IR value for S available at the point At. 292 Value *getExactExistingExpansion(const SCEV *S, const Instruction *At, 293 Loop *L); 294 295 /// Try to find the ValueOffsetPair for S. The function is mainly used to 296 /// check whether S can be expanded cheaply. If this returns a non-None 297 /// value, we know we can codegen the `ValueOffsetPair` into a suitable 298 /// expansion identical with S so that S can be expanded cheaply. 299 /// 300 /// L is a hint which tells in which loop to look for the suitable value. 301 /// On success return value which is equivalent to the expanded S at point 302 /// At. Return nullptr if value was not found. 303 /// 304 /// Note that this function does not perform an exhaustive search. I.e if it 305 /// didn't find any value it does not mean that there is no such value. 306 /// 307 Optional<ScalarEvolution::ValueOffsetPair> 308 getRelatedExistingExpansion(const SCEV *S, const Instruction *At, Loop *L); 309 310 private: 311 LLVMContext &getContext() const { return SE.getContext(); } 312 313 /// Recursive helper function for isHighCostExpansion. 314 bool isHighCostExpansionHelper(const SCEV *S, Loop *L, 315 const Instruction *At, 316 SmallPtrSetImpl<const SCEV *> &Processed); 317 318 /// Insert the specified binary operator, doing a small amount of work to 319 /// avoid inserting an obviously redundant operation. 320 Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS); 321 322 /// Arrange for there to be a cast of V to Ty at IP, reusing an existing 323 /// cast if a suitable one exists, moving an existing cast if a suitable one 324 /// exists but isn't in the right place, or creating a new one. 325 Value *ReuseOrCreateCast(Value *V, Type *Ty, 326 Instruction::CastOps Op, 327 BasicBlock::iterator IP); 328 329 /// Insert a cast of V to the specified type, which must be possible with a 330 /// noop cast, doing what we can to share the casts. 331 Value *InsertNoopCastOfTo(Value *V, Type *Ty); 332 333 /// Expand a SCEVAddExpr with a pointer type into a GEP instead of using 334 /// ptrtoint+arithmetic+inttoptr. 335 Value *expandAddToGEP(const SCEV *const *op_begin, 336 const SCEV *const *op_end, 337 PointerType *PTy, Type *Ty, Value *V); 338 Value *expandAddToGEP(const SCEV *Op, PointerType *PTy, Type *Ty, Value *V); 339 340 /// Find a previous Value in ExprValueMap for expand. 341 ScalarEvolution::ValueOffsetPair 342 FindValueInExprValueMap(const SCEV *S, const Instruction *InsertPt); 343 344 Value *expand(const SCEV *S); 345 346 /// Determine the most "relevant" loop for the given SCEV. 347 const Loop *getRelevantLoop(const SCEV *); 348 349 Value *visitConstant(const SCEVConstant *S) { 350 return S->getValue(); 351 } 352 353 Value *visitTruncateExpr(const SCEVTruncateExpr *S); 354 355 Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S); 356 357 Value *visitSignExtendExpr(const SCEVSignExtendExpr *S); 358 359 Value *visitAddExpr(const SCEVAddExpr *S); 360 361 Value *visitMulExpr(const SCEVMulExpr *S); 362 363 Value *visitUDivExpr(const SCEVUDivExpr *S); 364 365 Value *visitAddRecExpr(const SCEVAddRecExpr *S); 366 367 Value *visitSMaxExpr(const SCEVSMaxExpr *S); 368 369 Value *visitUMaxExpr(const SCEVUMaxExpr *S); 370 371 Value *visitUnknown(const SCEVUnknown *S) { 372 return S->getValue(); 373 } 374 375 void rememberInstruction(Value *I); 376 377 bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 378 379 bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 380 381 Value *expandAddRecExprLiterally(const SCEVAddRecExpr *); 382 PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized, 383 const Loop *L, 384 Type *ExpandTy, 385 Type *IntTy, 386 Type *&TruncTy, 387 bool &InvertStep); 388 Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L, 389 Type *ExpandTy, Type *IntTy, bool useSubtract); 390 391 void hoistBeforePos(DominatorTree *DT, Instruction *InstToHoist, 392 Instruction *Pos, PHINode *LoopPhi); 393 394 void fixupInsertPoints(Instruction *I); 395 }; 396 } 397 398 #endif 399