GISelValueTracking.h

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//===- llvm/CodeGen/GlobalISel/GISelValueTracking.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
//
//===----------------------------------------------------------------------===//
/// \file
/// Provides analysis for querying information about KnownBits during GISel
/// passes.
///
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_CODEGEN_GLOBALISEL_GISELVALUETRACKING_H
#define LLVM_CODEGEN_GLOBALISEL_GISELVALUETRACKING_H
 
#include "llvm/ADT/APFloat.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/CodeGen/GlobalISel/GISelChangeObserver.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/IR/InstrTypes.h"
#include "llvm/IR/PassManager.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/KnownFPClass.h"
 
namespace llvm {
 
class TargetLowering;
class DataLayout;
 
class LLVM_ABI GISelValueTracking : public GISelChangeObserver {
  MachineFunction &MF;
  MachineRegisterInfo &MRI;
  const TargetLowering &TL;
  const DataLayout &DL;
  unsigned MaxDepth;
 
  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);
 
  void computeKnownFPClass(Register R, KnownFPClass &Known,
                           FPClassTest InterestedClasses, unsigned Depth);
 
  void computeKnownFPClassForFPTrunc(const MachineInstr &MI,
                                     const APInt &DemandedElts,
                                     FPClassTest InterestedClasses,
                                     KnownFPClass &Known, unsigned Depth);
 
  void computeKnownFPClass(Register R, const APInt &DemandedElts,
                           FPClassTest InterestedClasses, KnownFPClass &Known,
                           unsigned Depth);
 
public:
  GISelValueTracking(MachineFunction &MF, unsigned MaxDepth = 6);
  ~GISelValueTracking() override = default;
 
  const MachineFunction &getMachineFunction() const { return MF; }
 
  const DataLayout &getDataLayout() const { return DL; }
 
  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);
 
  /// Return true if the value defined by \p R is provably never zero.
  ///
  /// \p DemandedElts selects the vector elements that must be proven nonzero.
  /// For scalar values this is a one-bit mask. The overload without
  /// \p DemandedElts demands every fixed-vector element, or the scalar value to
  /// be non-zero.
  bool isKnownNeverZero(Register R, unsigned Depth = 0);
  bool isKnownNeverZero(Register R, const APInt &DemandedElts,
                        unsigned Depth = 0);
 
  static void computeKnownBitsForAlignment(KnownBits &Known, Align Alignment) {
    // The low bits are known zero if the pointer is aligned.
    Known.Zero.setLowBits(Log2(Alignment));
  }
 
  /// \return The known alignment for the pointer-like value \p R.
  Align computeKnownAlignment(Register R, unsigned Depth = 0);
 
  /// If a G_SHL/G_ASHR/G_LSHR node with shift operand \p R has shift amounts
  /// that are all less than the element bit-width of the shift node, return the
  /// valid constant range.
  std::optional<ConstantRange>
  getValidShiftAmountRange(Register R, const APInt &DemandedElts,
                           unsigned Depth);
 
  /// If a G_SHL/G_ASHR/G_LSHR node with shift operand \p R has shift amounts
  /// that are all less than the element bit-width of the shift node, return the
  /// minimum possible value.
  std::optional<uint64_t> getValidMinimumShiftAmount(Register R,
                                                     const APInt &DemandedElts,
                                                     unsigned Depth = 0);
 
  /// Determine which floating-point classes are valid for \p V, and return them
  /// in KnownFPClass bit sets.
  ///
  /// This function is defined on values with floating-point type, values
  /// vectors of floating-point type, and arrays of floating-point type.
 
  /// \p InterestedClasses is a compile time optimization hint for which
  /// floating point classes should be queried. Queries not specified in \p
  /// InterestedClasses should be reliable if they are determined during the
  /// query.
  KnownFPClass computeKnownFPClass(Register R, const APInt &DemandedElts,
                                   FPClassTest InterestedClasses,
                                   unsigned Depth);
 
  KnownFPClass computeKnownFPClass(Register R,
                                   FPClassTest InterestedClasses = fcAllFlags,
                                   unsigned Depth = 0);
 
  /// Wrapper to account for known fast math flags at the use instruction.
  KnownFPClass computeKnownFPClass(Register R, const APInt &DemandedElts,
                                   uint32_t Flags,
                                   FPClassTest InterestedClasses,
                                   unsigned Depth);
 
  KnownFPClass computeKnownFPClass(Register R, uint32_t Flags,
                                   FPClassTest InterestedClasses,
                                   unsigned Depth);
 
  /// Returns true if \p Val can be assumed to never be a NaN. If \p SNaN is
  /// true, this returns whether \p Val can be assumed to never be a signaling
  /// NaN.
  bool isKnownNeverNaN(Register Val, bool SNaN = false);
 
  /// Returns true if \p Val can be assumed to never be a signaling NaN.
  bool isKnownNeverSNaN(Register Val) { return isKnownNeverNaN(Val, true); }
 
  // 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 MaxDepth; }
};
 
/// To use KnownBitsInfo analysis in a pass,
/// KnownBitsInfo &Info = getAnalysis<GISelValueTrackingInfoAnalysis>().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 GISelValueTracking
/// and override computeKnownBitsImpl.
class LLVM_ABI GISelValueTrackingAnalysisLegacy : public MachineFunctionPass {
  std::unique_ptr<GISelValueTracking> Info;
 
public:
  static char ID;
  GISelValueTrackingAnalysisLegacy() : MachineFunctionPass(ID) {}
  GISelValueTracking &get(MachineFunction &MF);
  void getAnalysisUsage(AnalysisUsage &AU) const override;
  bool runOnMachineFunction(MachineFunction &MF) override;
  void releaseMemory() override { Info.reset(); }
};
 
class GISelValueTrackingAnalysis
    : public AnalysisInfoMixin<GISelValueTrackingAnalysis> {
  friend AnalysisInfoMixin<GISelValueTrackingAnalysis>;
  LLVM_ABI static AnalysisKey Key;
 
public:
  using Result = GISelValueTracking;
 
  LLVM_ABI Result run(MachineFunction &MF,
                      MachineFunctionAnalysisManager &MFAM);
};
 
class GISelValueTrackingPrinterPass
    : public RequiredPassInfoMixin<GISelValueTrackingPrinterPass> {
  raw_ostream &OS;
 
public:
  GISelValueTrackingPrinterPass(raw_ostream &OS) : OS(OS) {}
 
  LLVM_ABI PreservedAnalyses run(MachineFunction &MF,
                                 MachineFunctionAnalysisManager &MFAM);
};
} // namespace llvm
 
#endif // LLVM_CODEGEN_GLOBALISEL_GISELVALUETRACKING_H