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5da32b5e20
Like adds and subtracts, muls ripple only to the left so we can use the same logic. While we're here, add a print method to DemandedBits so it can be used with -analyze, which we'll use in the testcase. llvm-svn: 249686
76 lines
2.3 KiB
C++
76 lines
2.3 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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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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struct DemandedBits : public FunctionPass {
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static char ID; // Pass identification, replacement for typeid
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DemandedBits();
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bool runOnFunction(Function& F) override;
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void getAnalysisUsage(AnalysisUsage& AU) const override;
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void print(raw_ostream &OS, const Module *M) const override;
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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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private:
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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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AssumptionCache *AC;
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DominatorTree *DT;
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Function *F;
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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*, 128> Visited;
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DenseMap<Instruction *, APInt> AliveBits;
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};
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/// Create a demanded bits analysis pass.
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FunctionPass *createDemandedBitsPass();
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} // End llvm namespace
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#endif
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