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/Analysis/ScalarEvolutionExpressions.h" 18 #include "llvm/Analysis/ScalarEvolutionNormalization.h" 19 #include "llvm/Analysis/TargetFolder.h" 20 #include "llvm/IR/IRBuilder.h" 21 #include "llvm/IR/ValueHandle.h" 22 #include <set> 23 24 namespace llvm { 25 class TargetTransformInfo; 26 27 /// Return true if the given expression is safe to expand in the sense that 28 /// all materialized values are safe to speculate. 29 bool isSafeToExpand(const SCEV *S, ScalarEvolution &SE); 30 31 /// This class uses information about analyze scalars to 32 /// rewrite expressions in canonical form. 33 /// 34 /// Clients should create an instance of this class when rewriting is needed, 35 /// and destroy it when finished to allow the release of the associated 36 /// memory. 37 class SCEVExpander : public SCEVVisitor<SCEVExpander, Value*> { 38 ScalarEvolution &SE; 39 const DataLayout &DL; 40 41 // New instructions receive a name to identifies them with the current pass. 42 const char* IVName; 43 44 // InsertedExpressions caches Values for reuse, so must track RAUW. 45 std::map<std::pair<const SCEV *, Instruction *>, TrackingVH<Value> > 46 InsertedExpressions; 47 // InsertedValues only flags inserted instructions so needs no RAUW. 48 std::set<AssertingVH<Value> > InsertedValues; 49 std::set<AssertingVH<Value> > InsertedPostIncValues; 50 51 /// A memoization of the "relevant" loop for a given SCEV. 52 DenseMap<const SCEV *, const Loop *> RelevantLoops; 53 54 /// \brief Addrecs referring to any of the given loops are expanded 55 /// in post-inc mode. For example, expanding {1,+,1}<L> in post-inc mode 56 /// returns the add instruction that adds one to the phi for {0,+,1}<L>, 57 /// as opposed to a new phi starting at 1. This is only supported in 58 /// non-canonical mode. 59 PostIncLoopSet PostIncLoops; 60 61 /// \brief When this is non-null, addrecs expanded in the loop it indicates 62 /// should be inserted with increments at IVIncInsertPos. 63 const Loop *IVIncInsertLoop; 64 65 /// \brief When expanding addrecs in the IVIncInsertLoop loop, insert the IV 66 /// increment at this position. 67 Instruction *IVIncInsertPos; 68 69 /// \brief Phis that complete an IV chain. Reuse 70 std::set<AssertingVH<PHINode> > ChainedPhis; 71 72 /// \brief When true, expressions are expanded in "canonical" form. In 73 /// particular, addrecs are expanded as arithmetic based on a canonical 74 /// induction variable. When false, expression are expanded in a more 75 /// literal form. 76 bool CanonicalMode; 77 78 /// \brief When invoked from LSR, the expander is in "strength reduction" 79 /// mode. The only difference is that phi's are only reused if they are 80 /// already in "expanded" form. 81 bool LSRMode; 82 83 typedef IRBuilder<true, TargetFolder> BuilderType; 84 BuilderType Builder; 85 86 #ifndef NDEBUG 87 const char *DebugType; 88 #endif 89 90 friend struct SCEVVisitor<SCEVExpander, Value*>; 91 92 public: 93 /// \brief Construct a SCEVExpander in "canonical" mode. 94 explicit SCEVExpander(ScalarEvolution &se, const DataLayout &DL, 95 const char *name) 96 : SE(se), DL(DL), IVName(name), IVIncInsertLoop(nullptr), 97 IVIncInsertPos(nullptr), CanonicalMode(true), LSRMode(false), 98 Builder(se.getContext(), TargetFolder(DL)) { 99 #ifndef NDEBUG 100 DebugType = ""; 101 #endif 102 } 103 104 #ifndef NDEBUG 105 void setDebugType(const char* s) { DebugType = s; } 106 #endif 107 108 /// \brief Erase the contents of the InsertedExpressions map so that users 109 /// trying to expand the same expression into multiple BasicBlocks or 110 /// different places within the same BasicBlock can do so. 111 void clear() { 112 InsertedExpressions.clear(); 113 InsertedValues.clear(); 114 InsertedPostIncValues.clear(); 115 ChainedPhis.clear(); 116 } 117 118 /// \brief Return true for expressions that may incur non-trivial cost to 119 /// evaluate at runtime. 120 /// 121 /// At is an optional parameter which specifies point in code where user is 122 /// going to expand this expression. Sometimes this knowledge can lead to a 123 /// more accurate cost estimation. 124 bool isHighCostExpansion(const SCEV *Expr, Loop *L, 125 const Instruction *At = nullptr) { 126 SmallPtrSet<const SCEV *, 8> Processed; 127 return isHighCostExpansionHelper(Expr, L, At, Processed); 128 } 129 130 /// \brief This method returns the canonical induction variable of the 131 /// specified type for the specified loop (inserting one if there is none). 132 /// A canonical induction variable starts at zero and steps by one on each 133 /// iteration. 134 PHINode *getOrInsertCanonicalInductionVariable(const Loop *L, Type *Ty); 135 136 /// \brief Return the induction variable increment's IV operand. 137 Instruction *getIVIncOperand(Instruction *IncV, Instruction *InsertPos, 138 bool allowScale); 139 140 /// \brief Utility for hoisting an IV increment. 141 bool hoistIVInc(Instruction *IncV, Instruction *InsertPos); 142 143 /// \brief replace congruent phis with their most canonical 144 /// representative. Return the number of phis eliminated. 145 unsigned replaceCongruentIVs(Loop *L, const DominatorTree *DT, 146 SmallVectorImpl<WeakVH> &DeadInsts, 147 const TargetTransformInfo *TTI = nullptr); 148 149 /// \brief Insert code to directly compute the specified SCEV expression 150 /// into the program. The inserted code is inserted into the specified 151 /// block. 152 Value *expandCodeFor(const SCEV *SH, Type *Ty, Instruction *I); 153 154 /// \brief Generates a code sequence that evaluates this predicate. 155 /// The inserted instructions will be at position \p Loc. 156 /// The result will be of type i1 and will have a value of 0 when the 157 /// predicate is false and 1 otherwise. 158 Value *expandCodeForPredicate(const SCEVPredicate *Pred, Instruction *Loc); 159 160 /// \brief A specialized variant of expandCodeForPredicate, handling the 161 /// case when we are expanding code for a SCEVEqualPredicate. 162 Value *expandEqualPredicate(const SCEVEqualPredicate *Pred, 163 Instruction *Loc); 164 165 /// \brief A specialized variant of expandCodeForPredicate, handling the 166 /// case when we are expanding code for a SCEVUnionPredicate. 167 Value *expandUnionPredicate(const SCEVUnionPredicate *Pred, 168 Instruction *Loc); 169 170 /// \brief Set the current IV increment loop and position. 171 void setIVIncInsertPos(const Loop *L, Instruction *Pos) { 172 assert(!CanonicalMode && 173 "IV increment positions are not supported in CanonicalMode"); 174 IVIncInsertLoop = L; 175 IVIncInsertPos = Pos; 176 } 177 178 /// \brief Enable post-inc expansion for addrecs referring to the given 179 /// loops. Post-inc expansion is only supported in non-canonical mode. 180 void setPostInc(const PostIncLoopSet &L) { 181 assert(!CanonicalMode && 182 "Post-inc expansion is not supported in CanonicalMode"); 183 PostIncLoops = L; 184 } 185 186 /// \brief Disable all post-inc expansion. 187 void clearPostInc() { 188 PostIncLoops.clear(); 189 190 // When we change the post-inc loop set, cached expansions may no 191 // longer be valid. 192 InsertedPostIncValues.clear(); 193 } 194 195 /// \brief Disable the behavior of expanding expressions in canonical form 196 /// rather than in a more literal form. Non-canonical mode is useful for 197 /// late optimization passes. 198 void disableCanonicalMode() { CanonicalMode = false; } 199 200 void enableLSRMode() { LSRMode = true; } 201 202 /// \brief Clear the current insertion point. This is useful if the 203 /// instruction that had been serving as the insertion point may have been 204 /// deleted. 205 void clearInsertPoint() { 206 Builder.ClearInsertionPoint(); 207 } 208 209 /// \brief Return true if the specified instruction was inserted by the code 210 /// rewriter. If so, the client should not modify the instruction. 211 bool isInsertedInstruction(Instruction *I) const { 212 return InsertedValues.count(I) || InsertedPostIncValues.count(I); 213 } 214 215 void setChainedPhi(PHINode *PN) { ChainedPhis.insert(PN); } 216 217 /// \brief Try to find LLVM IR value for S available at the point At. 218 /// 219 /// L is a hint which tells in which loop to look for the suitable value. 220 /// On success return value which is equivalent to the expanded S at point 221 /// At. Return nullptr if value was not found. 222 /// 223 /// Note that this function does not perform an exhaustive search. I.e if it 224 /// didn't find any value it does not mean that there is no such value. 225 Value *findExistingExpansion(const SCEV *S, const Instruction *At, Loop *L); 226 227 private: 228 LLVMContext &getContext() const { return SE.getContext(); } 229 230 /// \brief Recursive helper function for isHighCostExpansion. 231 bool isHighCostExpansionHelper(const SCEV *S, Loop *L, 232 const Instruction *At, 233 SmallPtrSetImpl<const SCEV *> &Processed); 234 235 /// \brief Insert the specified binary operator, doing a small amount 236 /// of work to avoid inserting an obviously redundant operation. 237 Value *InsertBinop(Instruction::BinaryOps Opcode, Value *LHS, Value *RHS); 238 239 /// \brief Arrange for there to be a cast of V to Ty at IP, reusing an 240 /// existing cast if a suitable one exists, moving an existing cast if a 241 /// suitable one exists but isn't in the right place, or or creating a new 242 /// one. 243 Value *ReuseOrCreateCast(Value *V, Type *Ty, 244 Instruction::CastOps Op, 245 BasicBlock::iterator IP); 246 247 /// \brief Insert a cast of V to the specified type, which must be possible 248 /// with a noop cast, doing what we can to share the casts. 249 Value *InsertNoopCastOfTo(Value *V, Type *Ty); 250 251 /// \brief Expand a SCEVAddExpr with a pointer type into a GEP 252 /// instead of using ptrtoint+arithmetic+inttoptr. 253 Value *expandAddToGEP(const SCEV *const *op_begin, 254 const SCEV *const *op_end, 255 PointerType *PTy, Type *Ty, Value *V); 256 257 Value *expand(const SCEV *S); 258 259 /// \brief Insert code to directly compute the specified SCEV expression 260 /// into the program. The inserted code is inserted into the SCEVExpander's 261 /// current insertion point. If a type is specified, the result will be 262 /// expanded to have that type, with a cast if necessary. 263 Value *expandCodeFor(const SCEV *SH, Type *Ty = nullptr); 264 265 /// \brief Determine the most "relevant" loop for the given SCEV. 266 const Loop *getRelevantLoop(const SCEV *); 267 268 Value *visitConstant(const SCEVConstant *S) { 269 return S->getValue(); 270 } 271 272 Value *visitTruncateExpr(const SCEVTruncateExpr *S); 273 274 Value *visitZeroExtendExpr(const SCEVZeroExtendExpr *S); 275 276 Value *visitSignExtendExpr(const SCEVSignExtendExpr *S); 277 278 Value *visitAddExpr(const SCEVAddExpr *S); 279 280 Value *visitMulExpr(const SCEVMulExpr *S); 281 282 Value *visitUDivExpr(const SCEVUDivExpr *S); 283 284 Value *visitAddRecExpr(const SCEVAddRecExpr *S); 285 286 Value *visitSMaxExpr(const SCEVSMaxExpr *S); 287 288 Value *visitUMaxExpr(const SCEVUMaxExpr *S); 289 290 Value *visitUnknown(const SCEVUnknown *S) { 291 return S->getValue(); 292 } 293 294 void rememberInstruction(Value *I); 295 296 bool isNormalAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 297 298 bool isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV, const Loop *L); 299 300 Value *expandAddRecExprLiterally(const SCEVAddRecExpr *); 301 PHINode *getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized, 302 const Loop *L, 303 Type *ExpandTy, 304 Type *IntTy, 305 Type *&TruncTy, 306 bool &InvertStep); 307 Value *expandIVInc(PHINode *PN, Value *StepV, const Loop *L, 308 Type *ExpandTy, Type *IntTy, bool useSubtract); 309 }; 310 } 311 312 #endif 313
