clang-r370808b/include/llvm/CodeGen/GlobalISel/GISelKnownBits.h

//===- llvm/CodeGen/GlobalISel/GISelKnownBits.h ---------------*- C++ -*-===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
/// Provides analysis for querying information about KnownBits during GISel
/// passes.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_GLOBALISEL_KNOWNBITSINFO_H
#define LLVM_CODEGEN_GLOBALISEL_KNOWNBITSINFO_H

#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/KnownBits.h"

namespace llvm {

class TargetLowering;
class DataLayout;

class GISelKnownBits : public GISelChangeObserver {
  MachineFunction &MF;
  MachineRegisterInfo &MRI;
  const TargetLowering &TL;
  const DataLayout &DL;

public:
  GISelKnownBits(MachineFunction &MF);
  virtual ~GISelKnownBits() = default;
  void setMF(MachineFunction &MF);
  virtual void computeKnownBitsImpl(Register R, KnownBits &Known,
                                    const APInt &DemandedElts,
                                    unsigned Depth = 0);

  // KnownBitsAPI
  KnownBits getKnownBits(Register R);
  // Calls getKnownBits for first operand def of MI.
  KnownBits getKnownBits(MachineInstr &MI);
  APInt getKnownZeroes(Register R);
  APInt getKnownOnes(Register R);

  /// \return true if 'V & Mask' is known to be zero in DemandedElts. We use
  /// this predicate to simplify operations downstream.
  /// Mask is known to be zero for bits that V cannot have.
  bool maskedValueIsZero(Register Val, const APInt &Mask) {
    return Mask.isSubsetOf(getKnownBits(Val).Zero);
  }

  /// \return true if the sign bit of Op is known to be zero.  We use this
  /// predicate to simplify operations downstream.
  bool signBitIsZero(Register Op);

  // FIXME: Is this the right place for G_FRAME_INDEX? Should it be in
  // TargetLowering?
  void computeKnownBitsForFrameIndex(Register R, KnownBits &Known,
                                     const APInt &DemandedElts,
                                     unsigned Depth = 0);
  static unsigned inferAlignmentForFrameIdx(int FrameIdx, int Offset,
                                            const MachineFunction &MF);
  static void computeKnownBitsForAlignment(KnownBits &Known, unsigned Align);

  // Try to infer alignment for MI.
  static unsigned inferPtrAlignment(const MachineInstr &MI);

  // Observer API. No-op for non-caching implementation.
  void erasingInstr(MachineInstr &MI) override{};
  void createdInstr(MachineInstr &MI) override{};
  void changingInstr(MachineInstr &MI) override{};
  void changedInstr(MachineInstr &MI) override{};

protected:
  unsigned getMaxDepth() const { return 6; }
};

/// To use KnownBitsInfo analysis in a pass,
/// KnownBitsInfo &Info = getAnalysis<GISelKnownBitsInfoAnalysis>().get(MF);
/// Add to observer if the Info is caching.
/// WrapperObserver.addObserver(Info);

/// Eventually add other features such as caching/ser/deserializing
/// to MIR etc. Those implementations can derive from GISelKnownBits
/// and override computeKnownBitsImpl.
class GISelKnownBitsAnalysis : public MachineFunctionPass {
  std::unique_ptr<GISelKnownBits> Info;

public:
  static char ID;
  GISelKnownBitsAnalysis() : MachineFunctionPass(ID) {
    initializeGISelKnownBitsAnalysisPass(*PassRegistry::getPassRegistry());
  }
  GISelKnownBits &get(MachineFunction &MF) {
    if (!Info)
      Info = std::make_unique<GISelKnownBits>(MF);
    return *Info.get();
  }
  void getAnalysisUsage(AnalysisUsage &AU) const override;
  bool runOnMachineFunction(MachineFunction &MF) override;
  void releaseMemory() override { Info.reset(); }
};
} // namespace llvm

#endif // ifdef