1 //===- llvm/Analysis/DemandedBits.h - Determine demanded bits ---*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
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:
14 // %1 = add i32 %x, %y
15 // %2 = trunc i32 %1 to i16
17 // Only the lowest 16 bits of %1 are demanded; the rest are removed by the
20 //===----------------------------------------------------------------------===//
22 #ifndef LLVM_ANALYSIS_DEMANDED_BITS_H
23 #define LLVM_ANALYSIS_DEMANDED_BITS_H
25 #include "llvm/ADT/APInt.h"
26 #include "llvm/ADT/DenseMap.h"
27 #include "llvm/ADT/Optional.h"
28 #include "llvm/ADT/SmallPtrSet.h"
29 #include "llvm/IR/PassManager.h"
30 #include "llvm/Pass.h"
34 class AssumptionCache;
43 DemandedBits(Function &F, AssumptionCache &AC, DominatorTree &DT) :
44 F(F), AC(AC), DT(DT) {}
46 /// Return the bits demanded from instruction I.
47 APInt getDemandedBits(Instruction *I);
49 /// Return true if, during analysis, I could not be reached.
50 bool isInstructionDead(Instruction *I);
52 void print(raw_ostream &OS);
55 void performAnalysis();
56 void determineLiveOperandBits(const Instruction *UserI,
57 const Instruction *I, unsigned OperandNo,
58 const APInt &AOut, APInt &AB,
59 KnownBits &Known, KnownBits &Known2);
65 bool Analyzed = false;
67 // The set of visited instructions (non-integer-typed only).
68 SmallPtrSet<Instruction*, 32> Visited;
69 DenseMap<Instruction *, APInt> AliveBits;
72 class DemandedBitsWrapperPass : public FunctionPass {
74 mutable Optional<DemandedBits> DB;
77 static char ID; // Pass identification, replacement for typeid
79 DemandedBitsWrapperPass();
81 bool runOnFunction(Function &F) override;
82 void getAnalysisUsage(AnalysisUsage &AU) const override;
84 /// Clean up memory in between runs
85 void releaseMemory() override;
87 DemandedBits &getDemandedBits() { return *DB; }
89 void print(raw_ostream &OS, const Module *M) const override;
92 /// An analysis that produces \c DemandedBits for a function.
93 class DemandedBitsAnalysis : public AnalysisInfoMixin<DemandedBitsAnalysis> {
94 friend AnalysisInfoMixin<DemandedBitsAnalysis>;
96 static AnalysisKey Key;
99 /// \brief Provide the result type for this analysis pass.
100 using Result = DemandedBits;
102 /// \brief Run the analysis pass over a function and produce demanded bits
104 DemandedBits run(Function &F, FunctionAnalysisManager &AM);
107 /// \brief Printer pass for DemandedBits
108 class DemandedBitsPrinterPass : public PassInfoMixin<DemandedBitsPrinterPass> {
112 explicit DemandedBitsPrinterPass(raw_ostream &OS) : OS(OS) {}
114 PreservedAnalyses run(Function &F, FunctionAnalysisManager &AM);
117 /// Create a demanded bits analysis pass.
118 FunctionPass *createDemandedBitsWrapperPass();
120 } // end namespace llvm
122 #endif // LLVM_ANALYSIS_DEMANDED_BITS_H