1 //===- GVN.h - Eliminate redundant values and loads -------------*- 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 /// \file 9 /// This file provides the interface for LLVM's Global Value Numbering pass 10 /// which eliminates fully redundant instructions. It also does somewhat Ad-Hoc 11 /// PRE and dead load elimination. 12 /// 13 //===----------------------------------------------------------------------===// 14 15 #ifndef LLVM_TRANSFORMS_SCALAR_GVN_H 16 #define LLVM_TRANSFORMS_SCALAR_GVN_H 17 18 #include "llvm/ADT/DenseMap.h" 19 #include "llvm/ADT/MapVector.h" 20 #include "llvm/ADT/SetVector.h" 21 #include "llvm/ADT/SmallVector.h" 22 #include "llvm/IR/Dominators.h" 23 #include "llvm/IR/InstrTypes.h" 24 #include "llvm/IR/PassManager.h" 25 #include "llvm/IR/ValueHandle.h" 26 #include "llvm/Support/Allocator.h" 27 #include "llvm/Support/Compiler.h" 28 #include <cstdint> 29 #include <utility> 30 #include <vector> 31 32 namespace llvm { 33 34 class AAResults; 35 class AssumeInst; 36 class AssumptionCache; 37 class BasicBlock; 38 class BranchInst; 39 class CallInst; 40 class ExtractValueInst; 41 class Function; 42 class FunctionPass; 43 class GetElementPtrInst; 44 class ImplicitControlFlowTracking; 45 class LoadInst; 46 class LoopInfo; 47 class MemDepResult; 48 class MemoryDependenceResults; 49 class MemorySSA; 50 class MemorySSAUpdater; 51 class NonLocalDepResult; 52 class OptimizationRemarkEmitter; 53 class PHINode; 54 class TargetLibraryInfo; 55 class Value; 56 /// A private "module" namespace for types and utilities used by GVN. These 57 /// are implementation details and should not be used by clients. 58 namespace gvn LLVM_LIBRARY_VISIBILITY { 59 60 struct AvailableValue; 61 struct AvailableValueInBlock; 62 class GVNLegacyPass; 63 64 } // end namespace gvn 65 66 /// A set of parameters to control various transforms performed by GVN pass. 67 // Each of the optional boolean parameters can be set to: 68 /// true - enabling the transformation. 69 /// false - disabling the transformation. 70 /// None - relying on a global default. 71 /// Intended use is to create a default object, modify parameters with 72 /// additional setters and then pass it to GVN. 73 struct GVNOptions { 74 Optional<bool> AllowPRE = None; 75 Optional<bool> AllowLoadPRE = None; 76 Optional<bool> AllowLoadInLoopPRE = None; 77 Optional<bool> AllowLoadPRESplitBackedge = None; 78 Optional<bool> AllowMemDep = None; 79 80 GVNOptions() = default; 81 82 /// Enables or disables PRE in GVN. 83 GVNOptions &setPRE(bool PRE) { 84 AllowPRE = PRE; 85 return *this; 86 } 87 88 /// Enables or disables PRE of loads in GVN. 89 GVNOptions &setLoadPRE(bool LoadPRE) { 90 AllowLoadPRE = LoadPRE; 91 return *this; 92 } 93 94 GVNOptions &setLoadInLoopPRE(bool LoadInLoopPRE) { 95 AllowLoadInLoopPRE = LoadInLoopPRE; 96 return *this; 97 } 98 99 /// Enables or disables PRE of loads in GVN. 100 GVNOptions &setLoadPRESplitBackedge(bool LoadPRESplitBackedge) { 101 AllowLoadPRESplitBackedge = LoadPRESplitBackedge; 102 return *this; 103 } 104 105 /// Enables or disables use of MemDepAnalysis. 106 GVNOptions &setMemDep(bool MemDep) { 107 AllowMemDep = MemDep; 108 return *this; 109 } 110 }; 111 112 /// The core GVN pass object. 113 /// 114 /// FIXME: We should have a good summary of the GVN algorithm implemented by 115 /// this particular pass here. 116 class GVNPass : public PassInfoMixin<GVNPass> { 117 GVNOptions Options; 118 119 public: 120 struct Expression; 121 122 GVNPass(GVNOptions Options = {}) : Options(Options) {} 123 124 /// Run the pass over the function. 125 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 126 127 void printPipeline(raw_ostream &OS, 128 function_ref<StringRef(StringRef)> MapClassName2PassName); 129 130 /// This removes the specified instruction from 131 /// our various maps and marks it for deletion. 132 void markInstructionForDeletion(Instruction *I) { 133 VN.erase(I); 134 InstrsToErase.push_back(I); 135 } 136 137 DominatorTree &getDominatorTree() const { return *DT; } 138 AAResults *getAliasAnalysis() const { return VN.getAliasAnalysis(); } 139 MemoryDependenceResults &getMemDep() const { return *MD; } 140 141 bool isPREEnabled() const; 142 bool isLoadPREEnabled() const; 143 bool isLoadInLoopPREEnabled() const; 144 bool isLoadPRESplitBackedgeEnabled() const; 145 bool isMemDepEnabled() const; 146 147 /// This class holds the mapping between values and value numbers. It is used 148 /// as an efficient mechanism to determine the expression-wise equivalence of 149 /// two values. 150 class ValueTable { 151 DenseMap<Value *, uint32_t> valueNumbering; 152 DenseMap<Expression, uint32_t> expressionNumbering; 153 154 // Expressions is the vector of Expression. ExprIdx is the mapping from 155 // value number to the index of Expression in Expressions. We use it 156 // instead of a DenseMap because filling such mapping is faster than 157 // filling a DenseMap and the compile time is a little better. 158 uint32_t nextExprNumber = 0; 159 160 std::vector<Expression> Expressions; 161 std::vector<uint32_t> ExprIdx; 162 163 // Value number to PHINode mapping. Used for phi-translate in scalarpre. 164 DenseMap<uint32_t, PHINode *> NumberingPhi; 165 166 // Cache for phi-translate in scalarpre. 167 using PhiTranslateMap = 168 DenseMap<std::pair<uint32_t, const BasicBlock *>, uint32_t>; 169 PhiTranslateMap PhiTranslateTable; 170 171 AAResults *AA = nullptr; 172 MemoryDependenceResults *MD = nullptr; 173 DominatorTree *DT = nullptr; 174 175 uint32_t nextValueNumber = 1; 176 177 Expression createExpr(Instruction *I); 178 Expression createCmpExpr(unsigned Opcode, CmpInst::Predicate Predicate, 179 Value *LHS, Value *RHS); 180 Expression createExtractvalueExpr(ExtractValueInst *EI); 181 Expression createGEPExpr(GetElementPtrInst *GEP); 182 uint32_t lookupOrAddCall(CallInst *C); 183 uint32_t phiTranslateImpl(const BasicBlock *BB, const BasicBlock *PhiBlock, 184 uint32_t Num, GVNPass &Gvn); 185 bool areCallValsEqual(uint32_t Num, uint32_t NewNum, const BasicBlock *Pred, 186 const BasicBlock *PhiBlock, GVNPass &Gvn); 187 std::pair<uint32_t, bool> assignExpNewValueNum(Expression &exp); 188 bool areAllValsInBB(uint32_t num, const BasicBlock *BB, GVNPass &Gvn); 189 190 public: 191 ValueTable(); 192 ValueTable(const ValueTable &Arg); 193 ValueTable(ValueTable &&Arg); 194 ~ValueTable(); 195 ValueTable &operator=(const ValueTable &Arg); 196 197 uint32_t lookupOrAdd(Value *V); 198 uint32_t lookup(Value *V, bool Verify = true) const; 199 uint32_t lookupOrAddCmp(unsigned Opcode, CmpInst::Predicate Pred, 200 Value *LHS, Value *RHS); 201 uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock, 202 uint32_t Num, GVNPass &Gvn); 203 void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock); 204 bool exists(Value *V) const; 205 void add(Value *V, uint32_t num); 206 void clear(); 207 void erase(Value *v); 208 void setAliasAnalysis(AAResults *A) { AA = A; } 209 AAResults *getAliasAnalysis() const { return AA; } 210 void setMemDep(MemoryDependenceResults *M) { MD = M; } 211 void setDomTree(DominatorTree *D) { DT = D; } 212 uint32_t getNextUnusedValueNumber() { return nextValueNumber; } 213 void verifyRemoved(const Value *) const; 214 }; 215 216 private: 217 friend class gvn::GVNLegacyPass; 218 friend struct DenseMapInfo<Expression>; 219 220 MemoryDependenceResults *MD = nullptr; 221 DominatorTree *DT = nullptr; 222 const TargetLibraryInfo *TLI = nullptr; 223 AssumptionCache *AC = nullptr; 224 SetVector<BasicBlock *> DeadBlocks; 225 OptimizationRemarkEmitter *ORE = nullptr; 226 ImplicitControlFlowTracking *ICF = nullptr; 227 LoopInfo *LI = nullptr; 228 MemorySSAUpdater *MSSAU = nullptr; 229 230 ValueTable VN; 231 232 /// A mapping from value numbers to lists of Value*'s that 233 /// have that value number. Use findLeader to query it. 234 struct LeaderTableEntry { 235 Value *Val; 236 const BasicBlock *BB; 237 LeaderTableEntry *Next; 238 }; 239 DenseMap<uint32_t, LeaderTableEntry> LeaderTable; 240 BumpPtrAllocator TableAllocator; 241 242 // Block-local map of equivalent values to their leader, does not 243 // propagate to any successors. Entries added mid-block are applied 244 // to the remaining instructions in the block. 245 SmallMapVector<Value *, Value *, 4> ReplaceOperandsWithMap; 246 SmallVector<Instruction *, 8> InstrsToErase; 247 248 // Map the block to reversed postorder traversal number. It is used to 249 // find back edge easily. 250 DenseMap<AssertingVH<BasicBlock>, uint32_t> BlockRPONumber; 251 252 // This is set 'true' initially and also when new blocks have been added to 253 // the function being analyzed. This boolean is used to control the updating 254 // of BlockRPONumber prior to accessing the contents of BlockRPONumber. 255 bool InvalidBlockRPONumbers = true; 256 257 using LoadDepVect = SmallVector<NonLocalDepResult, 64>; 258 using AvailValInBlkVect = SmallVector<gvn::AvailableValueInBlock, 64>; 259 using UnavailBlkVect = SmallVector<BasicBlock *, 64>; 260 261 bool runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT, 262 const TargetLibraryInfo &RunTLI, AAResults &RunAA, 263 MemoryDependenceResults *RunMD, LoopInfo *LI, 264 OptimizationRemarkEmitter *ORE, MemorySSA *MSSA = nullptr); 265 266 /// Push a new Value to the LeaderTable onto the list for its value number. 267 void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) { 268 LeaderTableEntry &Curr = LeaderTable[N]; 269 if (!Curr.Val) { 270 Curr.Val = V; 271 Curr.BB = BB; 272 return; 273 } 274 275 LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>(); 276 Node->Val = V; 277 Node->BB = BB; 278 Node->Next = Curr.Next; 279 Curr.Next = Node; 280 } 281 282 /// Scan the list of values corresponding to a given 283 /// value number, and remove the given instruction if encountered. 284 void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) { 285 LeaderTableEntry *Prev = nullptr; 286 LeaderTableEntry *Curr = &LeaderTable[N]; 287 288 while (Curr && (Curr->Val != I || Curr->BB != BB)) { 289 Prev = Curr; 290 Curr = Curr->Next; 291 } 292 293 if (!Curr) 294 return; 295 296 if (Prev) { 297 Prev->Next = Curr->Next; 298 } else { 299 if (!Curr->Next) { 300 Curr->Val = nullptr; 301 Curr->BB = nullptr; 302 } else { 303 LeaderTableEntry *Next = Curr->Next; 304 Curr->Val = Next->Val; 305 Curr->BB = Next->BB; 306 Curr->Next = Next->Next; 307 } 308 } 309 } 310 311 // List of critical edges to be split between iterations. 312 SmallVector<std::pair<Instruction *, unsigned>, 4> toSplit; 313 314 // Helper functions of redundant load elimination 315 bool processLoad(LoadInst *L); 316 bool processNonLocalLoad(LoadInst *L); 317 bool processAssumeIntrinsic(AssumeInst *II); 318 319 /// Given a local dependency (Def or Clobber) determine if a value is 320 /// available for the load. Returns true if an value is known to be 321 /// available and populates Res. Returns false otherwise. 322 bool AnalyzeLoadAvailability(LoadInst *Load, MemDepResult DepInfo, 323 Value *Address, gvn::AvailableValue &Res); 324 325 /// Given a list of non-local dependencies, determine if a value is 326 /// available for the load in each specified block. If it is, add it to 327 /// ValuesPerBlock. If not, add it to UnavailableBlocks. 328 void AnalyzeLoadAvailability(LoadInst *Load, LoadDepVect &Deps, 329 AvailValInBlkVect &ValuesPerBlock, 330 UnavailBlkVect &UnavailableBlocks); 331 332 bool PerformLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock, 333 UnavailBlkVect &UnavailableBlocks); 334 335 /// Try to replace a load which executes on each loop iteraiton with Phi 336 /// translation of load in preheader and load(s) in conditionally executed 337 /// paths. 338 bool performLoopLoadPRE(LoadInst *Load, AvailValInBlkVect &ValuesPerBlock, 339 UnavailBlkVect &UnavailableBlocks); 340 341 /// Eliminates partially redundant \p Load, replacing it with \p 342 /// AvailableLoads (connected by Phis if needed). 343 void eliminatePartiallyRedundantLoad( 344 LoadInst *Load, AvailValInBlkVect &ValuesPerBlock, 345 MapVector<BasicBlock *, Value *> &AvailableLoads); 346 347 // Other helper routines 348 bool processInstruction(Instruction *I); 349 bool processBlock(BasicBlock *BB); 350 void dump(DenseMap<uint32_t, Value *> &d) const; 351 bool iterateOnFunction(Function &F); 352 bool performPRE(Function &F); 353 bool performScalarPRE(Instruction *I); 354 bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred, 355 BasicBlock *Curr, unsigned int ValNo); 356 Value *findLeader(const BasicBlock *BB, uint32_t num); 357 void cleanupGlobalSets(); 358 void verifyRemoved(const Instruction *I) const; 359 bool splitCriticalEdges(); 360 BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ); 361 bool replaceOperandsForInBlockEquality(Instruction *I) const; 362 bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root, 363 bool DominatesByEdge); 364 bool processFoldableCondBr(BranchInst *BI); 365 void addDeadBlock(BasicBlock *BB); 366 void assignValNumForDeadCode(); 367 void assignBlockRPONumber(Function &F); 368 }; 369 370 /// Create a legacy GVN pass. This also allows parameterizing whether or not 371 /// MemDep is enabled. 372 FunctionPass *createGVNPass(bool NoMemDepAnalysis = false); 373 374 /// A simple and fast domtree-based GVN pass to hoist common expressions 375 /// from sibling branches. 376 struct GVNHoistPass : PassInfoMixin<GVNHoistPass> { 377 /// Run the pass over the function. 378 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 379 }; 380 381 /// Uses an "inverted" value numbering to decide the similarity of 382 /// expressions and sinks similar expressions into successors. 383 struct GVNSinkPass : PassInfoMixin<GVNSinkPass> { 384 /// Run the pass over the function. 385 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 386 }; 387 388 } // end namespace llvm 389 390 #endif // LLVM_TRANSFORMS_SCALAR_GVN_H 391