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118 lines
3.3 KiB
C++
118 lines
3.3 KiB
C++
//===-- llvm/Analysis/DemandedBits.h - Determine demanded bits --*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass implements a demanded bits analysis. A demanded bit is one that
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// contributes to a result; bits that are not demanded can be either zero or
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// one without affecting control or data flow. For example in this sequence:
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//
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// %1 = add i32 %x, %y
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// %2 = trunc i32 %1 to i16
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//
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// Only the lowest 16 bits of %1 are demanded; the rest are removed by the
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// trunc.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_ANALYSIS_DEMANDED_BITS_H
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#define LLVM_ANALYSIS_DEMANDED_BITS_H
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#include "llvm/Pass.h"
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#include "llvm/ADT/APInt.h"
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#include "llvm/ADT/DenseMap.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/IR/PassManager.h"
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namespace llvm {
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class FunctionPass;
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class Function;
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class Instruction;
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class DominatorTree;
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class AssumptionCache;
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class DemandedBits {
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public:
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DemandedBits(Function &F, AssumptionCache &AC, DominatorTree &DT) :
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F(F), AC(AC), DT(DT), Analyzed(false) {}
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/// Return the bits demanded from instruction I.
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APInt getDemandedBits(Instruction *I);
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/// Return true if, during analysis, I could not be reached.
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bool isInstructionDead(Instruction *I);
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void print(raw_ostream &OS);
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private:
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Function &F;
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AssumptionCache ∾
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DominatorTree &DT;
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void performAnalysis();
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void determineLiveOperandBits(const Instruction *UserI,
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const Instruction *I, unsigned OperandNo,
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const APInt &AOut, APInt &AB,
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APInt &KnownZero, APInt &KnownOne,
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APInt &KnownZero2, APInt &KnownOne2);
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bool Analyzed;
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// The set of visited instructions (non-integer-typed only).
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SmallPtrSet<Instruction*, 32> Visited;
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DenseMap<Instruction *, APInt> AliveBits;
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};
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class DemandedBitsWrapperPass : public FunctionPass {
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private:
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mutable Optional<DemandedBits> DB;
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public:
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static char ID; // Pass identification, replacement for typeid
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DemandedBitsWrapperPass();
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bool runOnFunction(Function &F) override;
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void getAnalysisUsage(AnalysisUsage &AU) const override;
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/// Clean up memory in between runs
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void releaseMemory() override;
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DemandedBits &getDemandedBits() { return *DB; }
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void print(raw_ostream &OS, const Module *M) const override;
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};
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/// An analysis that produces \c DemandedBits for a function.
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class DemandedBitsAnalysis : public AnalysisInfoMixin<DemandedBitsAnalysis> {
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friend AnalysisInfoMixin<DemandedBitsAnalysis>;
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static char PassID;
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public:
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/// \brief Provide the result typedef for this analysis pass.
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typedef DemandedBits Result;
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/// \brief Run the analysis pass over a function and produce demanded bits
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/// information.
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DemandedBits run(Function &F, AnalysisManager<Function> &AM);
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};
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/// \brief Printer pass for DemandedBits
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class DemandedBitsPrinterPass : public PassInfoMixin<DemandedBitsPrinterPass> {
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raw_ostream &OS;
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public:
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explicit DemandedBitsPrinterPass(raw_ostream &OS) : OS(OS) {}
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PreservedAnalyses run(Function &F, AnalysisManager<Function> &AM);
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};
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/// Create a demanded bits analysis pass.
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FunctionPass *createDemandedBitsWrapperPass();
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} // End llvm namespace
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#endif
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