include/llvm/Transforms/Scalar/GVN.h

   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/PostOrderIterator.h"
  21 #include "llvm/ADT/SetVector.h"
  22 #include "llvm/ADT/SmallVector.h"
  23 #include "llvm/Analysis/AliasAnalysis.h"
  24 #include "llvm/Analysis/InstructionPrecedenceTracking.h"
  25 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
  26 #include "llvm/IR/Dominators.h"
  27 #include "llvm/IR/InstrTypes.h"
  28 #include "llvm/IR/PassManager.h"
  29 #include "llvm/IR/ValueHandle.h"
  30 #include "llvm/Support/Allocator.h"
  31 #include "llvm/Support/Compiler.h"
  32 #include <cstdint>
  33 #include <utility>
  34 #include <vector>
  35
  36 namespace llvm {
  37
  38 class AssumptionCache;
  39 class BasicBlock;
  40 class BranchInst;
  41 class CallInst;
  42 class Constant;
  43 class ExtractValueInst;
  44 class Function;
  45 class FunctionPass;
  46 class IntrinsicInst;
  47 class LoadInst;
  48 class LoopInfo;
  49 class OptimizationRemarkEmitter;
  50 class PHINode;
  51 class TargetLibraryInfo;
  52 class Value;
  53
  54 /// A private "module" namespace for types and utilities used by GVN. These
  55 /// are implementation details and should not be used by clients.
  56 namespace gvn LLVM_LIBRARY_VISIBILITY {
  57
  58 struct AvailableValue;
  59 struct AvailableValueInBlock;
  60 class GVNLegacyPass;
  61
  62 } // end namespace gvn
  63
  64 /// The core GVN pass object.
  65 ///
  66 /// FIXME: We should have a good summary of the GVN algorithm implemented by
  67 /// this particular pass here.
  68 class GVN : public PassInfoMixin<GVN> {
  69 public:
  70   struct Expression;
  71
  72   /// Run the pass over the function.
  73   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
  74
  75   /// This removes the specified instruction from
  76   /// our various maps and marks it for deletion.
  77   void markInstructionForDeletion(Instruction *I) {
  78     VN.erase(I);
  79     InstrsToErase.push_back(I);
  80   }
  81
  82   DominatorTree &getDominatorTree() const { return *DT; }
  83   AliasAnalysis *getAliasAnalysis() const { return VN.getAliasAnalysis(); }
  84   MemoryDependenceResults &getMemDep() const { return *MD; }
  85
  86   /// This class holds the mapping between values and value numbers.  It is used
  87   /// as an efficient mechanism to determine the expression-wise equivalence of
  88   /// two values.
  89   class ValueTable {
  90     DenseMap<Value *, uint32_t> valueNumbering;
  91     DenseMap<Expression, uint32_t> expressionNumbering;
  92
  93     // Expressions is the vector of Expression. ExprIdx is the mapping from
  94     // value number to the index of Expression in Expressions. We use it
  95     // instead of a DenseMap because filling such mapping is faster than
  96     // filling a DenseMap and the compile time is a little better.
  97     uint32_t nextExprNumber;
  98
  99     std::vector<Expression> Expressions;
 100     std::vector<uint32_t> ExprIdx;
 101
 102     // Value number to PHINode mapping. Used for phi-translate in scalarpre.
 103     DenseMap<uint32_t, PHINode *> NumberingPhi;
 104
 105     // Cache for phi-translate in scalarpre.
 106     using PhiTranslateMap =
 107         DenseMap<std::pair<uint32_t, const BasicBlock *>, uint32_t>;
 108     PhiTranslateMap PhiTranslateTable;
 109
 110     AliasAnalysis *AA;
 111     MemoryDependenceResults *MD;
 112     DominatorTree *DT;
 113
 114     uint32_t nextValueNumber = 1;
 115
 116     Expression createExpr(Instruction *I);
 117     Expression createCmpExpr(unsigned Opcode, CmpInst::Predicate Predicate,
 118                              Value *LHS, Value *RHS);
 119     Expression createExtractvalueExpr(ExtractValueInst *EI);
 120     uint32_t lookupOrAddCall(CallInst *C);
 121     uint32_t phiTranslateImpl(const BasicBlock *BB, const BasicBlock *PhiBlock,
 122                               uint32_t Num, GVN &Gvn);
 123     std::pair<uint32_t, bool> assignExpNewValueNum(Expression &exp);
 124     bool areAllValsInBB(uint32_t num, const BasicBlock *BB, GVN &Gvn);
 125
 126   public:
 127     ValueTable();
 128     ValueTable(const ValueTable &Arg);
 129     ValueTable(ValueTable &&Arg);
 130     ~ValueTable();
 131
 132     uint32_t lookupOrAdd(Value *V);
 133     uint32_t lookup(Value *V, bool Verify = true) const;
 134     uint32_t lookupOrAddCmp(unsigned Opcode, CmpInst::Predicate Pred,
 135                             Value *LHS, Value *RHS);
 136     uint32_t phiTranslate(const BasicBlock *BB, const BasicBlock *PhiBlock,
 137                           uint32_t Num, GVN &Gvn);
 138     void eraseTranslateCacheEntry(uint32_t Num, const BasicBlock &CurrBlock);
 139     bool exists(Value *V) const;
 140     void add(Value *V, uint32_t num);
 141     void clear();
 142     void erase(Value *v);
 143     void setAliasAnalysis(AliasAnalysis *A) { AA = A; }
 144     AliasAnalysis *getAliasAnalysis() const { return AA; }
 145     void setMemDep(MemoryDependenceResults *M) { MD = M; }
 146     void setDomTree(DominatorTree *D) { DT = D; }
 147     uint32_t getNextUnusedValueNumber() { return nextValueNumber; }
 148     void verifyRemoved(const Value *) const;
 149   };
 150
 151 private:
 152   friend class gvn::GVNLegacyPass;
 153   friend struct DenseMapInfo<Expression>;
 154
 155   MemoryDependenceResults *MD;
 156   DominatorTree *DT;
 157   const TargetLibraryInfo *TLI;
 158   AssumptionCache *AC;
 159   SetVector<BasicBlock *> DeadBlocks;
 160   OptimizationRemarkEmitter *ORE;
 161   ImplicitControlFlowTracking *ICF;
 162
 163   ValueTable VN;
 164
 165   /// A mapping from value numbers to lists of Value*'s that
 166   /// have that value number.  Use findLeader to query it.
 167   struct LeaderTableEntry {
 168     Value *Val;
 169     const BasicBlock *BB;
 170     LeaderTableEntry *Next;
 171   };
 172   DenseMap<uint32_t, LeaderTableEntry> LeaderTable;
 173   BumpPtrAllocator TableAllocator;
 174
 175   // Block-local map of equivalent values to their leader, does not
 176   // propagate to any successors. Entries added mid-block are applied
 177   // to the remaining instructions in the block.
 178   SmallMapVector<Value *, Constant *, 4> ReplaceWithConstMap;
 179   SmallVector<Instruction *, 8> InstrsToErase;
 180
 181   // Map the block to reversed postorder traversal number. It is used to
 182   // find back edge easily.
 183   DenseMap<AssertingVH<BasicBlock>, uint32_t> BlockRPONumber;
 184
 185   // This is set 'true' initially and also when new blocks have been added to
 186   // the function being analyzed. This boolean is used to control the updating
 187   // of BlockRPONumber prior to accessing the contents of BlockRPONumber.
 188   bool InvalidBlockRPONumbers = true;
 189
 190   using LoadDepVect = SmallVector<NonLocalDepResult, 64>;
 191   using AvailValInBlkVect = SmallVector<gvn::AvailableValueInBlock, 64>;
 192   using UnavailBlkVect = SmallVector<BasicBlock *, 64>;
 193
 194   bool runImpl(Function &F, AssumptionCache &RunAC, DominatorTree &RunDT,
 195                const TargetLibraryInfo &RunTLI, AAResults &RunAA,
 196                MemoryDependenceResults *RunMD, LoopInfo *LI,
 197                OptimizationRemarkEmitter *ORE);
 198
 199   /// Push a new Value to the LeaderTable onto the list for its value number.
 200   void addToLeaderTable(uint32_t N, Value *V, const BasicBlock *BB) {
 201     LeaderTableEntry &Curr = LeaderTable[N];
 202     if (!Curr.Val) {
 203       Curr.Val = V;
 204       Curr.BB = BB;
 205       return;
 206     }
 207
 208     LeaderTableEntry *Node = TableAllocator.Allocate<LeaderTableEntry>();
 209     Node->Val = V;
 210     Node->BB = BB;
 211     Node->Next = Curr.Next;
 212     Curr.Next = Node;
 213   }
 214
 215   /// Scan the list of values corresponding to a given
 216   /// value number, and remove the given instruction if encountered.
 217   void removeFromLeaderTable(uint32_t N, Instruction *I, BasicBlock *BB) {
 218     LeaderTableEntry *Prev = nullptr;
 219     LeaderTableEntry *Curr = &LeaderTable[N];
 220
 221     while (Curr && (Curr->Val != I || Curr->BB != BB)) {
 222       Prev = Curr;
 223       Curr = Curr->Next;
 224     }
 225
 226     if (!Curr)
 227       return;
 228
 229     if (Prev) {
 230       Prev->Next = Curr->Next;
 231     } else {
 232       if (!Curr->Next) {
 233         Curr->Val = nullptr;
 234         Curr->BB = nullptr;
 235       } else {
 236         LeaderTableEntry *Next = Curr->Next;
 237         Curr->Val = Next->Val;
 238         Curr->BB = Next->BB;
 239         Curr->Next = Next->Next;
 240       }
 241     }
 242   }
 243
 244   // List of critical edges to be split between iterations.
 245   SmallVector<std::pair<Instruction *, unsigned>, 4> toSplit;
 246
 247   // Helper functions of redundant load elimination
 248   bool processLoad(LoadInst *L);
 249   bool processNonLocalLoad(LoadInst *L);
 250   bool processAssumeIntrinsic(IntrinsicInst *II);
 251
 252   /// Given a local dependency (Def or Clobber) determine if a value is
 253   /// available for the load.  Returns true if an value is known to be
 254   /// available and populates Res.  Returns false otherwise.
 255   bool AnalyzeLoadAvailability(LoadInst *LI, MemDepResult DepInfo,
 256                                Value *Address, gvn::AvailableValue &Res);
 257
 258   /// Given a list of non-local dependencies, determine if a value is
 259   /// available for the load in each specified block.  If it is, add it to
 260   /// ValuesPerBlock.  If not, add it to UnavailableBlocks.
 261   void AnalyzeLoadAvailability(LoadInst *LI, LoadDepVect &Deps,
 262                                AvailValInBlkVect &ValuesPerBlock,
 263                                UnavailBlkVect &UnavailableBlocks);
 264
 265   bool PerformLoadPRE(LoadInst *LI, AvailValInBlkVect &ValuesPerBlock,
 266                       UnavailBlkVect &UnavailableBlocks);
 267
 268   // Other helper routines
 269   bool processInstruction(Instruction *I);
 270   bool processBlock(BasicBlock *BB);
 271   void dump(DenseMap<uint32_t, Value *> &d) const;
 272   bool iterateOnFunction(Function &F);
 273   bool performPRE(Function &F);
 274   bool performScalarPRE(Instruction *I);
 275   bool performScalarPREInsertion(Instruction *Instr, BasicBlock *Pred,
 276                                  BasicBlock *Curr, unsigned int ValNo);
 277   Value *findLeader(const BasicBlock *BB, uint32_t num);
 278   void cleanupGlobalSets();
 279   void fillImplicitControlFlowInfo(BasicBlock *BB);
 280   void verifyRemoved(const Instruction *I) const;
 281   bool splitCriticalEdges();
 282   BasicBlock *splitCriticalEdges(BasicBlock *Pred, BasicBlock *Succ);
 283   bool replaceOperandsWithConsts(Instruction *I) const;
 284   bool propagateEquality(Value *LHS, Value *RHS, const BasicBlockEdge &Root,
 285                          bool DominatesByEdge);
 286   bool processFoldableCondBr(BranchInst *BI);
 287   void addDeadBlock(BasicBlock *BB);
 288   void assignValNumForDeadCode();
 289   void assignBlockRPONumber(Function &F);
 290 };
 291
 292 /// Create a legacy GVN pass. This also allows parameterizing whether or not
 293 /// loads are eliminated by the pass.
 294 FunctionPass *createGVNPass(bool NoLoads = false);
 295
 296 /// A simple and fast domtree-based GVN pass to hoist common expressions
 297 /// from sibling branches.
 298 struct GVNHoistPass : PassInfoMixin<GVNHoistPass> {
 299   /// Run the pass over the function.
 300   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 301 };
 302
 303 /// Uses an "inverted" value numbering to decide the similarity of
 304 /// expressions and sinks similar expressions into successors.
 305 struct GVNSinkPass : PassInfoMixin<GVNSinkPass> {
 306   /// Run the pass over the function.
 307   PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
 308 };
 309
 310 } // end namespace llvm
 311
 312 #endif // LLVM_TRANSFORMS_SCALAR_GVN_H