llvm/llvm/lib/Analysis/DemandedBits.cpp

//===- DemandedBits.cpp - Determine demanded bits -------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//

#include "llvm/Analysis/DemandedBits.h"
#include "llvm/ADT/APInt.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Operator.h"
#include "llvm/IR/PassManager.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/Use.h"
#include "llvm/Support/Casting.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cstdint>

usingnamespacellvm;
usingnamespacellvm::PatternMatch;

#define DEBUG_TYPE …

static bool isAlwaysLive(Instruction *I) { … }

void DemandedBits::determineLiveOperandBits(
    const Instruction *UserI, const Value *Val, unsigned OperandNo,
    const APInt &AOut, APInt &AB, KnownBits &Known, KnownBits &Known2,
    bool &KnownBitsComputed) { … }

void DemandedBits::performAnalysis() { … }

APInt DemandedBits::getDemandedBits(Instruction *I) { … }

APInt DemandedBits::getDemandedBits(Use *U) { … }

bool DemandedBits::isInstructionDead(Instruction *I) { … }

bool DemandedBits::isUseDead(Use *U) { … }

void DemandedBits::print(raw_ostream &OS) { … }

static APInt determineLiveOperandBitsAddCarry(unsigned OperandNo,
                                              const APInt &AOut,
                                              const KnownBits &LHS,
                                              const KnownBits &RHS,
                                              bool CarryZero, bool CarryOne) { … }

APInt DemandedBits::determineLiveOperandBitsAdd(unsigned OperandNo,
                                                const APInt &AOut,
                                                const KnownBits &LHS,
                                                const KnownBits &RHS) { … }

APInt DemandedBits::determineLiveOperandBitsSub(unsigned OperandNo,
                                                const APInt &AOut,
                                                const KnownBits &LHS,
                                                const KnownBits &RHS) { … }

AnalysisKey DemandedBitsAnalysis::Key;

DemandedBits DemandedBitsAnalysis::run(Function &F,
                                             FunctionAnalysisManager &AM) { … }

PreservedAnalyses DemandedBitsPrinterPass::run(Function &F,
                                               FunctionAnalysisManager &AM) { … }