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//===- llvm/CodeGen/GlobalISel/GISelKnownBits.h ---------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
/// \file
/// Provides analysis for querying information about KnownBits during GISel
/// passes.
#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/InitializePasses.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;
unsigned MaxDepth;
/// Cache maintained during a computeKnownBits request.
SmallDenseMap<Register, KnownBits, 16> ComputeKnownBitsCache;
void computeKnownBitsMin(Register Src0, Register Src1, KnownBits &Known,
const APInt &DemandedElts,
unsigned Depth = 0);
unsigned computeNumSignBitsMin(Register Src0, Register Src1,
const APInt &DemandedElts, unsigned Depth = 0);
GISelKnownBits(MachineFunction &MF, unsigned MaxDepth = 6);
virtual ~GISelKnownBits() = default;
const MachineFunction &getMachineFunction() const {
return MF;
const DataLayout &getDataLayout() const {
return DL;
virtual void computeKnownBitsImpl(Register R, KnownBits &Known,
const APInt &DemandedElts,
unsigned Depth = 0);
unsigned computeNumSignBits(Register R, const APInt &DemandedElts,
unsigned Depth = 0);
unsigned computeNumSignBits(Register R, unsigned Depth = 0);
// KnownBitsAPI
KnownBits getKnownBits(Register R);
KnownBits getKnownBits(Register R, const APInt &DemandedElts,
unsigned Depth = 0);
// 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);
static void computeKnownBitsForAlignment(KnownBits &Known,
Align Alignment) {
// The low bits are known zero if the pointer is aligned.
/// \return The known alignment for the pointer-like value \p R.
Align computeKnownAlignment(Register R, unsigned Depth = 0);
// 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{};
unsigned getMaxDepth() const { return MaxDepth; }
/// 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;
static char ID;
GISelKnownBitsAnalysis() : MachineFunctionPass(ID) {
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