1 //===-- llvm/Analysis/DemandedBits.h - Determine demanded bits --*- 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 pass implements a demanded bits analysis. A demanded bit is one that 11 // contributes to a result; bits that are not demanded can be either zero or 12 // one without affecting control or data flow. For example in this sequence: 13 // 14 // %1 = add i32 %x, %y 15 // %2 = trunc i32 %1 to i16 16 // 17 // Only the lowest 16 bits of %1 are demanded; the rest are removed by the 18 // trunc. 19 // 20 //===----------------------------------------------------------------------===// 21 22 #ifndef LLVM_ANALYSIS_DEMANDED_BITS_H 23 #define LLVM_ANALYSIS_DEMANDED_BITS_H 24 25 #include "llvm/Pass.h" 26 #include "llvm/ADT/APInt.h" 27 #include "llvm/ADT/DenseMap.h" 28 #include "llvm/ADT/SmallPtrSet.h" 29 #include "llvm/IR/PassManager.h" 30 31 namespace llvm { 32 33 class FunctionPass; 34 class Function; 35 class Instruction; 36 class DominatorTree; 37 class AssumptionCache; 38 39 class DemandedBits { 40 public: DemandedBits(Function & F,AssumptionCache & AC,DominatorTree & DT)41 DemandedBits(Function &F, AssumptionCache &AC, DominatorTree &DT) : 42 F(F), AC(AC), DT(DT), Analyzed(false) {} 43 44 /// Return the bits demanded from instruction I. 45 APInt getDemandedBits(Instruction *I); 46 47 /// Return true if, during analysis, I could not be reached. 48 bool isInstructionDead(Instruction *I); 49 50 void print(raw_ostream &OS); 51 52 private: 53 Function &F; 54 AssumptionCache &AC; 55 DominatorTree &DT; 56 57 void performAnalysis(); 58 void determineLiveOperandBits(const Instruction *UserI, 59 const Instruction *I, unsigned OperandNo, 60 const APInt &AOut, APInt &AB, 61 APInt &KnownZero, APInt &KnownOne, 62 APInt &KnownZero2, APInt &KnownOne2); 63 64 bool Analyzed; 65 66 // The set of visited instructions (non-integer-typed only). 67 SmallPtrSet<Instruction*, 32> Visited; 68 DenseMap<Instruction *, APInt> AliveBits; 69 }; 70 71 class DemandedBitsWrapperPass : public FunctionPass { 72 private: 73 mutable Optional<DemandedBits> DB; 74 public: 75 static char ID; // Pass identification, replacement for typeid 76 DemandedBitsWrapperPass(); 77 78 bool runOnFunction(Function &F) override; 79 void getAnalysisUsage(AnalysisUsage &AU) const override; 80 81 /// Clean up memory in between runs 82 void releaseMemory() override; 83 getDemandedBits()84 DemandedBits &getDemandedBits() { return *DB; } 85 86 void print(raw_ostream &OS, const Module *M) const override; 87 }; 88 89 /// An analysis that produces \c DemandedBits for a function. 90 class DemandedBitsAnalysis : public AnalysisInfoMixin<DemandedBitsAnalysis> { 91 friend AnalysisInfoMixin<DemandedBitsAnalysis>; 92 static char PassID; 93 94 public: 95 /// \brief Provide the result typedef for this analysis pass. 96 typedef DemandedBits Result; 97 98 /// \brief Run the analysis pass over a function and produce demanded bits 99 /// information. 100 DemandedBits run(Function &F, AnalysisManager<Function> &AM); 101 }; 102 103 /// \brief Printer pass for DemandedBits 104 class DemandedBitsPrinterPass : public PassInfoMixin<DemandedBitsPrinterPass> { 105 raw_ostream &OS; 106 107 public: DemandedBitsPrinterPass(raw_ostream & OS)108 explicit DemandedBitsPrinterPass(raw_ostream &OS) : OS(OS) {} 109 PreservedAnalyses run(Function &F, AnalysisManager<Function> &AM); 110 }; 111 112 /// Create a demanded bits analysis pass. 113 FunctionPass *createDemandedBitsWrapperPass(); 114 115 } // End llvm namespace 116 117 #endif 118