1 //===- JumpThreading.h - thread control through conditional BBs -*- 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 // 9 /// \file 10 /// See the comments on JumpThreadingPass. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H 15 #define LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H 16 17 #include "llvm/ADT/ArrayRef.h" 18 #include "llvm/ADT/DenseSet.h" 19 #include "llvm/ADT/SmallSet.h" 20 #include "llvm/ADT/SmallVector.h" 21 #include "llvm/Analysis/BlockFrequencyInfo.h" 22 #include "llvm/Analysis/BranchProbabilityInfo.h" 23 #include "llvm/Analysis/DomTreeUpdater.h" 24 #include "llvm/IR/ValueHandle.h" 25 #include "llvm/Transforms/Utils/ValueMapper.h" 26 #include <optional> 27 #include <utility> 28 29 namespace llvm { 30 31 class AAResults; 32 class BasicBlock; 33 class BinaryOperator; 34 class BranchInst; 35 class CmpInst; 36 class Constant; 37 class Function; 38 class Instruction; 39 class IntrinsicInst; 40 class LazyValueInfo; 41 class LoadInst; 42 class PHINode; 43 class SelectInst; 44 class SwitchInst; 45 class TargetLibraryInfo; 46 class TargetTransformInfo; 47 class Value; 48 49 /// A private "module" namespace for types and utilities used by 50 /// JumpThreading. 51 /// These are implementation details and should not be used by clients. 52 namespace jumpthreading { 53 54 // These are at global scope so static functions can use them too. 55 using PredValueInfo = SmallVectorImpl<std::pair<Constant *, BasicBlock *>>; 56 using PredValueInfoTy = SmallVector<std::pair<Constant *, BasicBlock *>, 8>; 57 58 // This is used to keep track of what kind of constant we're currently hoping 59 // to find. 60 enum ConstantPreference { WantInteger, WantBlockAddress }; 61 62 } // end namespace jumpthreading 63 64 /// This pass performs 'jump threading', which looks at blocks that have 65 /// multiple predecessors and multiple successors. If one or more of the 66 /// predecessors of the block can be proven to always jump to one of the 67 /// successors, we forward the edge from the predecessor to the successor by 68 /// duplicating the contents of this block. 69 /// 70 /// An example of when this can occur is code like this: 71 /// 72 /// if () { ... 73 /// X = 4; 74 /// } 75 /// if (X < 3) { 76 /// 77 /// In this case, the unconditional branch at the end of the first if can be 78 /// revectored to the false side of the second if. 79 class JumpThreadingPass : public PassInfoMixin<JumpThreadingPass> { 80 Function *F = nullptr; 81 FunctionAnalysisManager *FAM = nullptr; 82 TargetLibraryInfo *TLI = nullptr; 83 TargetTransformInfo *TTI = nullptr; 84 LazyValueInfo *LVI = nullptr; 85 AAResults *AA = nullptr; 86 std::unique_ptr<DomTreeUpdater> DTU; 87 std::optional<BlockFrequencyInfo *> BFI; 88 std::optional<BranchProbabilityInfo *> BPI; 89 bool ChangedSinceLastAnalysisUpdate = false; 90 bool HasGuards = false; 91 #ifndef LLVM_ENABLE_ABI_BREAKING_CHECKS 92 SmallPtrSet<const BasicBlock *, 16> LoopHeaders; 93 #else 94 SmallSet<AssertingVH<const BasicBlock>, 16> LoopHeaders; 95 #endif 96 97 unsigned BBDupThreshold; 98 unsigned DefaultBBDupThreshold; 99 100 public: 101 JumpThreadingPass(int T = -1); 102 103 // Glue for old PM. 104 bool runImpl(Function &F, FunctionAnalysisManager *FAM, 105 TargetLibraryInfo *TLI, TargetTransformInfo *TTI, 106 LazyValueInfo *LVI, AAResults *AA, 107 std::unique_ptr<DomTreeUpdater> DTU, 108 std::optional<BlockFrequencyInfo *> BFI, 109 std::optional<BranchProbabilityInfo *> BPI); 110 111 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM); 112 113 DomTreeUpdater *getDomTreeUpdater() const { return DTU.get(); } 114 void findLoopHeaders(Function &F); 115 bool processBlock(BasicBlock *BB); 116 bool maybeMergeBasicBlockIntoOnlyPred(BasicBlock *BB); 117 void updateSSA(BasicBlock *BB, BasicBlock *NewBB, 118 ValueToValueMapTy &ValueMapping); 119 void cloneInstructions(ValueToValueMapTy &ValueMapping, 120 BasicBlock::iterator BI, BasicBlock::iterator BE, 121 BasicBlock *NewBB, BasicBlock *PredBB); 122 bool tryThreadEdge(BasicBlock *BB, 123 const SmallVectorImpl<BasicBlock *> &PredBBs, 124 BasicBlock *SuccBB); 125 void threadEdge(BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs, 126 BasicBlock *SuccBB); 127 bool duplicateCondBranchOnPHIIntoPred( 128 BasicBlock *BB, const SmallVectorImpl<BasicBlock *> &PredBBs); 129 130 bool computeValueKnownInPredecessorsImpl( 131 Value *V, BasicBlock *BB, jumpthreading::PredValueInfo &Result, 132 jumpthreading::ConstantPreference Preference, 133 SmallPtrSet<Value *, 4> &RecursionSet, Instruction *CxtI = nullptr); 134 bool 135 computeValueKnownInPredecessors(Value *V, BasicBlock *BB, 136 jumpthreading::PredValueInfo &Result, 137 jumpthreading::ConstantPreference Preference, 138 Instruction *CxtI = nullptr) { 139 SmallPtrSet<Value *, 4> RecursionSet; 140 return computeValueKnownInPredecessorsImpl(V, BB, Result, Preference, 141 RecursionSet, CxtI); 142 } 143 144 Constant *evaluateOnPredecessorEdge(BasicBlock *BB, BasicBlock *PredPredBB, 145 Value *cond, const DataLayout &DL); 146 bool maybethreadThroughTwoBasicBlocks(BasicBlock *BB, Value *Cond); 147 void threadThroughTwoBasicBlocks(BasicBlock *PredPredBB, BasicBlock *PredBB, 148 BasicBlock *BB, BasicBlock *SuccBB); 149 bool processThreadableEdges(Value *Cond, BasicBlock *BB, 150 jumpthreading::ConstantPreference Preference, 151 Instruction *CxtI = nullptr); 152 153 bool processBranchOnPHI(PHINode *PN); 154 bool processBranchOnXOR(BinaryOperator *BO); 155 bool processImpliedCondition(BasicBlock *BB); 156 157 bool simplifyPartiallyRedundantLoad(LoadInst *LI); 158 void unfoldSelectInstr(BasicBlock *Pred, BasicBlock *BB, SelectInst *SI, 159 PHINode *SIUse, unsigned Idx); 160 161 bool tryToUnfoldSelect(CmpInst *CondCmp, BasicBlock *BB); 162 bool tryToUnfoldSelect(SwitchInst *SI, BasicBlock *BB); 163 bool tryToUnfoldSelectInCurrBB(BasicBlock *BB); 164 165 bool processGuards(BasicBlock *BB); 166 bool threadGuard(BasicBlock *BB, IntrinsicInst *Guard, BranchInst *BI); 167 168 private: 169 BasicBlock *splitBlockPreds(BasicBlock *BB, ArrayRef<BasicBlock *> Preds, 170 const char *Suffix); 171 void updateBlockFreqAndEdgeWeight(BasicBlock *PredBB, BasicBlock *BB, 172 BasicBlock *NewBB, BasicBlock *SuccBB, 173 BlockFrequencyInfo *BFI, 174 BranchProbabilityInfo *BPI, 175 bool HasProfile); 176 /// Check if the block has profile metadata for its outgoing edges. 177 bool doesBlockHaveProfileData(BasicBlock *BB); 178 179 /// Returns analysis preserved by the pass. 180 PreservedAnalyses getPreservedAnalysis() const; 181 182 /// Helper function to run "external" analysis in the middle of JumpThreading. 183 /// It takes care of updating/invalidating other existing analysis 184 /// before/after running the "external" one. 185 template <typename AnalysisT> 186 typename AnalysisT::Result *runExternalAnalysis(); 187 188 /// Returns an existing instance of BPI if any, otherwise nullptr. By 189 /// "existing" we mean either cached result provided by FunctionAnalysisManger 190 /// or created by preceding call to 'getOrCreateBPI'. 191 BranchProbabilityInfo *getBPI(); 192 193 /// Returns an existing instance of BFI if any, otherwise nullptr. By 194 /// "existing" we mean either cached result provided by FunctionAnalysisManger 195 /// or created by preceding call to 'getOrCreateBFI'. 196 BlockFrequencyInfo *getBFI(); 197 198 /// Returns an existing instance of BPI if any, otherwise: 199 /// if 'HasProfile' is true creates new instance through 200 /// FunctionAnalysisManager, otherwise nullptr. 201 BranchProbabilityInfo *getOrCreateBPI(bool Force = false); 202 203 /// Returns an existing instance of BFI if any, otherwise: 204 /// if 'HasProfile' is true creates new instance through 205 /// FunctionAnalysisManager, otherwise nullptr. 206 BlockFrequencyInfo *getOrCreateBFI(bool Force = false); 207 }; 208 209 } // end namespace llvm 210 211 #endif // LLVM_TRANSFORMS_SCALAR_JUMPTHREADING_H 212