| //===-- llvm/Analysis/DemandedBits.h - Determine demanded bits --*- C++ -*-===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass implements a demanded bits analysis. A demanded bit is one that |
| // contributes to a result; bits that are not demanded can be either zero or |
| // one without affecting control or data flow. For example in this sequence: |
| // |
| // %1 = add i32 %x, %y |
| // %2 = trunc i32 %1 to i16 |
| // |
| // Only the lowest 16 bits of %1 are demanded; the rest are removed by the |
| // trunc. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef LLVM_ANALYSIS_DEMANDED_BITS_H |
| #define LLVM_ANALYSIS_DEMANDED_BITS_H |
| |
| #include "llvm/Pass.h" |
| #include "llvm/ADT/APInt.h" |
| #include "llvm/ADT/DenseMap.h" |
| #include "llvm/ADT/SmallPtrSet.h" |
| |
| namespace llvm { |
| |
| class FunctionPass; |
| class Function; |
| class Instruction; |
| class DominatorTree; |
| class AssumptionCache; |
| |
| struct DemandedBits : public FunctionPass { |
| static char ID; // Pass identification, replacement for typeid |
| DemandedBits(); |
| |
| bool runOnFunction(Function& F) override; |
| void getAnalysisUsage(AnalysisUsage& AU) const override; |
| void print(raw_ostream &OS, const Module *M) const override; |
| |
| /// Return the bits demanded from instruction I. |
| APInt getDemandedBits(Instruction *I); |
| |
| /// Return true if, during analysis, I could not be reached. |
| bool isInstructionDead(Instruction *I); |
| |
| private: |
| void performAnalysis(); |
| void determineLiveOperandBits(const Instruction *UserI, |
| const Instruction *I, unsigned OperandNo, |
| const APInt &AOut, APInt &AB, |
| APInt &KnownZero, APInt &KnownOne, |
| APInt &KnownZero2, APInt &KnownOne2); |
| |
| AssumptionCache *AC; |
| DominatorTree *DT; |
| Function *F; |
| bool Analyzed; |
| |
| // The set of visited instructions (non-integer-typed only). |
| SmallPtrSet<Instruction*, 128> Visited; |
| DenseMap<Instruction *, APInt> AliveBits; |
| }; |
| |
| /// Create a demanded bits analysis pass. |
| FunctionPass *createDemandedBitsPass(); |
| |
| } // End llvm namespace |
| |
| #endif |