SIRegisterInfo.h

Go to the documentation of this file.

//===-- SIRegisterInfo.h - SI Register Info Interface ----------*- 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
/// Interface definition for SIRegisterInfo
//
//===----------------------------------------------------------------------===//
 
#ifndef LLVM_LIB_TARGET_AMDGPU_SIREGISTERINFO_H
#define LLVM_LIB_TARGET_AMDGPU_SIREGISTERINFO_H
 
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveRegMatrix.h"
#include "llvm/CodeGen/Register.h"
#include "llvm/CodeGen/VirtRegMap.h"
#include "llvm/MC/MCRegister.h"
 
#define GET_REGINFO_HEADER
#include "AMDGPUGenRegisterInfo.inc"
 
#include "SIDefines.h"
 
namespace llvm {
 
class GCNSubtarget;
class LiveIntervals;
class LiveRegUnits;
class MachineInstrBuilder;
class RegisterBank;
struct SGPRSpillBuilder;
 
/// Register allocation hint types. Helps eliminate unneeded COPY with True16
namespace AMDGPURI {
 
enum { Size16 = 1, Size32 = 2 };
 
} // end namespace AMDGPURI
 
class SIRegisterInfo final : public AMDGPUGenRegisterInfo {
private:
  const GCNSubtarget &ST;
  bool SpillSGPRToVGPR;
  bool isWave32;
  BitVector RegPressureIgnoredUnits;
 
  /// Sub reg indexes for getRegSplitParts.
  /// First index represents subreg size from 1 to 32 Half DWORDS.
  /// The inner vector is sorted by bit offset.
  /// Provided a register can be fully split with given subregs,
  /// all elements of the inner vector combined give a full lane mask.
  static std::array<std::vector<int16_t>, 32> RegSplitParts;
 
  // Table representing sub reg of given width and offset.
  // First index is subreg size: 32, 64, 96, 128, 160, 192, 224, 256, 512.
  // Second index is 32 different dword offsets.
  static std::array<std::array<uint16_t, 32>, 9> SubRegFromChannelTable;
 
  void reserveRegisterTuples(BitVector &, MCRegister Reg) const;
 
  /// True if assigning Reg would fit in the current occupancy VGPR budget.
  bool isRegWithinOccupancyBudget(MCPhysReg Reg, unsigned NumVGPRs,
                                  unsigned NumAGPRs,
                                  unsigned MaxVGPRsForCurrentOccupancy) const;
 
public:
  SIRegisterInfo(const GCNSubtarget &ST);
 
  struct SpilledReg {
    Register VGPR;
    int Lane = -1;
 
    SpilledReg() = default;
    SpilledReg(Register R, int L) : VGPR(R), Lane(L) {}
 
    bool hasLane() { return Lane != -1; }
    bool hasReg() { return VGPR != 0; }
  };
 
  /// \returns the sub reg enum value for the given \p Channel
  /// (e.g. getSubRegFromChannel(0) -> AMDGPU::sub0)
  static unsigned getSubRegFromChannel(unsigned Channel, unsigned NumRegs = 1);
 
  bool spillSGPRToVGPR() const {
    return SpillSGPRToVGPR;
  }
 
  bool isCFISavedRegsSpillEnabled() const;
 
  /// Return the largest available SGPR aligned to \p Align for the register
  /// class \p RC.
  MCRegister getAlignedHighSGPRForRC(const MachineFunction &MF,
                                     const unsigned Align,
                                     const TargetRegisterClass *RC) const;
 
  /// Return the end register initially reserved for the scratch buffer in case
  /// spilling is needed.
  MCRegister reservedPrivateSegmentBufferReg(const MachineFunction &MF) const;
 
  BitVector getReservedRegs(const MachineFunction &MF) const override;
  bool isAsmClobberable(const MachineFunction &MF,
                        MCRegister PhysReg) const override;
 
  const MCPhysReg *getCalleeSavedRegs(const MachineFunction *MF) const override;
  const MCPhysReg *getCalleeSavedRegsViaCopy(const MachineFunction *MF) const;
  const uint32_t *getCallPreservedMask(const MachineFunction &MF,
                                       CallingConv::ID) const override;
  const uint32_t *getNoPreservedMask() const override;
 
  // Functions with the amdgpu_cs_chain or amdgpu_cs_chain_preserve calling
  // conventions are free to use certain VGPRs without saving and restoring any
  // lanes (not even inactive ones).
  static bool isChainScratchRegister(Register VGPR);
 
  unsigned getCSRFirstUseCost(const MachineFunction &) const override {
    // The cost of 27 balances multiple factors that influence CSR cost:
    // - Saving a SGPR CSR to VGPR lanes is relatively cheap.
    // - In cases where this is not possible, stack access is very expensive.
    // - CSRs are also the high registers, and we want to minimize the number of
    //   used registers as it impacts occupancy.
    // Note: Register allocation only applies these cost to callee-save
    // registers according to getCalleeSavedRegs, so handling of calling
    // conventions with no CSR is handled there.
    return 27;
  }
 
  // When building a block VGPR load, we only really transfer a subset of the
  // registers in the block, based on a mask. Liveness analysis is not aware of
  // the mask, so it might consider that any register in the block is available
  // before the load and may therefore be scavenged. This is not ok for CSRs
  // that are not clobbered, since the caller will expect them to be preserved.
  // This method will add artificial implicit uses for those registers on the
  // load instruction, so liveness analysis knows they're unavailable.
  void addImplicitUsesForBlockCSRLoad(MachineInstrBuilder &MIB,
                                      Register BlockReg) const;
 
  // Iterate over all VGPRs in the given BlockReg and emit CFI for each VGPR
  // as-needed depending on the (statically known) mask, relative to the given
  // base Offset.
  void buildCFIForBlockCSRStore(MachineBasicBlock &MBB,
                                MachineBasicBlock::iterator MBBI,
                                Register BlockReg, int64_t Offset) const;
 
  const TargetRegisterClass *
  getLargestLegalSuperClass(const TargetRegisterClass *RC,
                            const MachineFunction &MF) const override;
 
  Register getFrameRegister(const MachineFunction &MF) const override;
 
  bool hasBasePointer(const MachineFunction &MF) const;
  Register getBaseRegister() const;
 
  bool shouldRealignStack(const MachineFunction &MF) const override;
  bool requiresRegisterScavenging(const MachineFunction &Fn) const override;
 
  bool requiresFrameIndexScavenging(const MachineFunction &MF) const override;
  bool requiresFrameIndexReplacementScavenging(
    const MachineFunction &MF) const override;
  bool requiresVirtualBaseRegisters(const MachineFunction &Fn) const override;
 
  int64_t getScratchInstrOffset(const MachineInstr *MI) const;
 
  int64_t getFrameIndexInstrOffset(const MachineInstr *MI,
                                   int Idx) const override;
 
  bool needsFrameBaseReg(MachineInstr *MI, int64_t Offset) const override;
 
  Register materializeFrameBaseRegister(MachineBasicBlock *MBB, int FrameIdx,
                                        int64_t Offset) const override;
 
  void resolveFrameIndex(MachineInstr &MI, Register BaseReg,
                         int64_t Offset) const override;
 
  bool isFrameOffsetLegal(const MachineInstr *MI, Register BaseReg,
                          int64_t Offset) const override;
 
  /// Returns a legal register class to copy a register in the specified class
  /// to or from. If it is possible to copy the register directly without using
  /// a cross register class copy, return the specified RC. Returns NULL if it
  /// is not possible to copy between two registers of the specified class.
  const TargetRegisterClass *
  getCrossCopyRegClass(const TargetRegisterClass *RC) const override;
 
  const TargetRegisterClass *
  getRegClassForBlockOp(const MachineFunction &MF) const {
    return &AMDGPU::VReg_1024RegClass;
  }
 
  void buildVGPRSpillLoadStore(SGPRSpillBuilder &SB, int Index, int Offset,
                               bool IsLoad, bool IsKill = true) const;
 
  /// If \p OnlyToVGPR is true, this will only succeed if this manages to find a
  /// free VGPR lane to spill.
  bool spillSGPR(MachineBasicBlock::iterator MI, int FI, RegScavenger *RS,
                 SlotIndexes *Indexes = nullptr, LiveIntervals *LIS = nullptr,
                 bool OnlyToVGPR = false, bool SpillToPhysVGPRLane = false,
                 bool NeedsCFI = false) const;
 
  bool restoreSGPR(MachineBasicBlock::iterator MI, int FI, RegScavenger *RS,
                   SlotIndexes *Indexes = nullptr, LiveIntervals *LIS = nullptr,
                   bool OnlyToVGPR = false,
                   bool SpillToPhysVGPRLane = false) const;
 
  bool spillEmergencySGPR(MachineBasicBlock::iterator MI,
                          MachineBasicBlock &RestoreMBB, Register SGPR,
                          RegScavenger *RS) const;
 
  bool eliminateFrameIndex(MachineBasicBlock::iterator MI, int SPAdj,
                           unsigned FIOperandNum,
                           RegScavenger *RS) const override;
 
  bool eliminateSGPRToVGPRSpillFrameIndex(
      MachineBasicBlock::iterator MI, int FI, RegScavenger *RS,
      SlotIndexes *Indexes = nullptr, LiveIntervals *LIS = nullptr,
      bool SpillToPhysVGPRLane = false) const;
 
  StringRef getRegAsmName(MCRegister Reg) const override;
 
  // Pseudo regs are not allowed
  unsigned getHWRegIndex(MCRegister Reg) const;
 
  LLVM_READONLY
  const TargetRegisterClass *getVGPRClassForBitWidth(unsigned BitWidth) const;
 
  LLVM_READONLY const TargetRegisterClass *
  getAlignedLo256VGPRClassForBitWidth(unsigned BitWidth) const;
 
  LLVM_READONLY
  const TargetRegisterClass *getAGPRClassForBitWidth(unsigned BitWidth) const;
 
  LLVM_READONLY
  const TargetRegisterClass *
  getVectorSuperClassForBitWidth(unsigned BitWidth) const;
 
  LLVM_READONLY
  const TargetRegisterClass *
  getDefaultVectorSuperClassForBitWidth(unsigned BitWidth) const;
 
  LLVM_READONLY
  static const TargetRegisterClass *getSGPRClassForBitWidth(unsigned BitWidth);
 
  /// \returns true if this class contains only SGPR registers
  static bool isSGPRClass(const TargetRegisterClass *RC) {
    return hasSGPRs(RC) && !hasVGPRs(RC) && !hasAGPRs(RC);
  }
 
  /// \returns true if this class ID contains only SGPR registers
  bool isSGPRClassID(unsigned RCID) const {
    return isSGPRClass(getRegClass(RCID));
  }
 
  bool isSGPRReg(const MachineRegisterInfo &MRI, Register Reg) const;
  bool isSGPRPhysReg(Register Reg) const {
    return isSGPRClass(getPhysRegBaseClass(Reg));
  }
 
  bool isVGPRPhysReg(Register Reg) const {
    return isVGPRClass(getPhysRegBaseClass(Reg));
  }
 
  /// \returns true if this class contains only VGPR registers
  static bool isVGPRClass(const TargetRegisterClass *RC) {
    return hasVGPRs(RC) && !hasAGPRs(RC) && !hasSGPRs(RC);
  }
 
  /// \returns true if this class contains only AGPR registers
  static bool isAGPRClass(const TargetRegisterClass *RC) {
    return hasAGPRs(RC) && !hasVGPRs(RC) && !hasSGPRs(RC);
  }
 
  /// \returns true only if this class contains both VGPR and AGPR registers
  bool isVectorSuperClass(const TargetRegisterClass *RC) const {
    return hasVGPRs(RC) && hasAGPRs(RC) && !hasSGPRs(RC);
  }
 
  /// \returns true only if this class contains both VGPR and SGPR registers
  bool isVSSuperClass(const TargetRegisterClass *RC) const {
    return hasVGPRs(RC) && hasSGPRs(RC) && !hasAGPRs(RC);
  }
 
  /// \returns true if this class contains VGPR registers.
  static bool hasVGPRs(const TargetRegisterClass *RC) {
    return RC->TSFlags & SIRCFlags::HasVGPR;
  }
 
  /// \returns true if this class contains AGPR registers.
  static bool hasAGPRs(const TargetRegisterClass *RC) {
    return RC->TSFlags & SIRCFlags::HasAGPR;
  }
 
  /// \returns true if this class contains SGPR registers.
  static bool hasSGPRs(const TargetRegisterClass *RC) {
    return RC->TSFlags & SIRCFlags::HasSGPR;
  }
 
  /// \returns true if this class contains any vector registers.
  static bool hasVectorRegisters(const TargetRegisterClass *RC) {
    return hasVGPRs(RC) || hasAGPRs(RC);
  }
 
  /// \returns A VGPR reg class with the same width as \p SRC
  const TargetRegisterClass *
  getEquivalentVGPRClass(const TargetRegisterClass *SRC) const;
 
  /// \returns An AGPR reg class with the same width as \p SRC
  const TargetRegisterClass *
  getEquivalentAGPRClass(const TargetRegisterClass *SRC) const;
 
  /// \returns An AGPR+VGPR super reg class with the same width as \p SRC
  const TargetRegisterClass *
  getEquivalentAVClass(const TargetRegisterClass *SRC) const;
 
  /// \returns A SGPR reg class with the same width as \p SRC
  const TargetRegisterClass *
  getEquivalentSGPRClass(const TargetRegisterClass *VRC) const;
 
  /// Returns a register class which is compatible with \p SuperRC, such that a
  /// subregister exists with class \p SubRC with subregister index \p
  /// SubIdx. If this is impossible (e.g., an unaligned subregister index within
  /// a register tuple), return null.
  const TargetRegisterClass *
  getCompatibleSubRegClass(const TargetRegisterClass *SuperRC,
                           const TargetRegisterClass *SubRC,
                           unsigned SubIdx) const;
 
  /// \returns True if operands defined with this operand type can accept
  /// a literal constant (i.e. any 32-bit immediate).
  bool opCanUseLiteralConstant(unsigned OpType) const;
 
  /// \returns True if operands defined with this operand type can accept
  /// an inline constant. i.e. An integer value in the range (-16, 64) or
  /// -4.0f, -2.0f, -1.0f, -0.5f, 0.0f, 0.5f, 1.0f, 2.0f, 4.0f.
  bool opCanUseInlineConstant(unsigned OpType) const;
 
  MCRegister findUnusedRegister(const MachineRegisterInfo &MRI,
                                const TargetRegisterClass *RC,
                                const MachineFunction &MF,
                                bool ReserveHighestVGPR = false) const;
 
  const TargetRegisterClass *getRegClassForReg(const MachineRegisterInfo &MRI,
                                               Register Reg) const;
  const TargetRegisterClass *
  getRegClassForOperandReg(const MachineRegisterInfo &MRI,
                           const MachineOperand &MO) const;
 
  bool isVGPR(const MachineRegisterInfo &MRI, Register Reg) const;
  bool isAGPR(const MachineRegisterInfo &MRI, Register Reg) const;
  bool isVectorRegister(const MachineRegisterInfo &MRI, Register Reg) const {
    return isVGPR(MRI, Reg) || isAGPR(MRI, Reg);
  }
 
  // FIXME: SGPRs are assumed to be uniform, but this is not true for i1 SGPRs
  // (such as VCC) which hold a wave-wide vector of boolean values. Examining
  // just the register class is not suffcient; it needs to be combined with a
  // value type. The next predicate isUniformReg() does this correctly.
  bool isDivergentRegClass(const TargetRegisterClass *RC) const override {
    return !isSGPRClass(RC);
  }
 
  bool isUniformReg(const MachineRegisterInfo &MRI, const RegisterBankInfo &RBI,
                    Register Reg) const override;
 
  ArrayRef<int16_t> getRegSplitParts(const TargetRegisterClass *RC,
                                     unsigned EltSize) const;
 
  unsigned getRegPressureLimit(const TargetRegisterClass *RC,
                               MachineFunction &MF) const override;
 
  unsigned getRegPressureSetLimit(const MachineFunction &MF,
                                  unsigned Idx) const override;
 
  bool getRegAllocationHints(Register VirtReg, ArrayRef<MCPhysReg> Order,
                             SmallSetVector<MCPhysReg, 16> &Hints,
                             const MachineFunction &MF, const VirtRegMap *VRM,
                             const LiveRegMatrix *Matrix) const override;
 
  bool shouldApplyAntiHints(const MachineFunction &MF,
                            unsigned NumAllocatedVGPRs,
                            unsigned &MaxVGPRsForCurrentOccupancy) const;
 
  void filterAndSortForAntiHintedRegs(
      Register VirtReg, MutableArrayRef<MCPhysReg> CustomOrder,
      const BitVector &AntiHintedRegUnits, const MachineFunction &MF,
      const LiveRegMatrix *Matrix = nullptr,
      const RegisterClassInfo *RegClassInfo = nullptr) const override;
 
  const int *getRegUnitPressureSets(MCRegUnit RegUnit) const override;
 
  MCRegister getReturnAddressReg(const MachineFunction &MF) const;
 
  const TargetRegisterClass *
  getRegClassForSizeOnBank(unsigned Size, const RegisterBank &Bank) const;
 
  const TargetRegisterClass *
  getRegClassForTypeOnBank(LLT Ty, const RegisterBank &Bank) const {
    return getRegClassForSizeOnBank(Ty.getSizeInBits(), Bank);
  }
 
  const TargetRegisterClass *
  getConstrainedRegClassForReg(Register Reg,
                               const MachineRegisterInfo &MRI) const override;
 
  const TargetRegisterClass *getBoolRC() const {
    return isWave32 ? &AMDGPU::SReg_32RegClass
                    : &AMDGPU::SReg_64RegClass;
  }
 
  const TargetRegisterClass *getWaveMaskRegClass() const {
    return isWave32 ? &AMDGPU::SReg_32_XM0_XEXECRegClass
                    : &AMDGPU::SReg_64_XEXECRegClass;
  }
 
  // Return the appropriate register class to use for 64-bit VGPRs for the
  // subtarget.
  const TargetRegisterClass *getVGPR64Class() const;
 
  MCRegister getVCC() const;
 
  MCRegister getExec() const;
 
  // Find reaching register definition
  MachineInstr *findReachingDef(Register Reg, unsigned SubReg,
                                MachineInstr &Use,
                                MachineRegisterInfo &MRI,
                                LiveIntervals *LIS) const;
 
  const uint32_t *getAllVGPRRegMask() const;
  const uint32_t *getAllAGPRRegMask() const;
  const uint32_t *getAllVectorRegMask() const;
  const uint32_t *getAllAllocatableSRegMask() const;
 
  // \returns number of 32 bit registers covered by a \p LM
  static unsigned getNumCoveredRegs(LaneBitmask LM) {
    // The assumption is that every lo16 subreg is an even bit and every hi16
    // is an adjacent odd bit or vice versa.
    uint64_t Mask = LM.getAsInteger();
    uint64_t Even = Mask & 0xAAAAAAAAAAAAAAAAULL;
    Mask = (Even >> 1) | Mask;
    uint64_t Odd = Mask & 0x5555555555555555ULL;
    return llvm::popcount(Odd);
  }
 
  // \returns a DWORD offset of a \p SubReg
  unsigned getChannelFromSubReg(unsigned SubReg) const {
    return SubReg ? (getSubRegIdxOffset(SubReg) + 31) / 32 : 0;
  }
 
  // \returns a DWORD size of a \p SubReg
  unsigned getNumChannelsFromSubReg(unsigned SubReg) const {
    return getNumCoveredRegs(getSubRegIndexLaneMask(SubReg));
  }
 
  // For a given 16 bit \p Reg \returns a 32 bit register holding it.
  // \returns \p Reg otherwise.
  MCPhysReg get32BitRegister(MCPhysReg Reg) const;
 
  // Returns true if a given register class is properly aligned for
  // the subtarget.
  bool isProperlyAlignedRC(const TargetRegisterClass &RC) const;
 
  /// Return all SGPR128 which satisfy the waves per execution unit requirement
  /// of the subtarget.
  ArrayRef<MCPhysReg> getAllSGPR128(const MachineFunction &MF) const;
 
  /// Return all SGPR64 which satisfy the waves per execution unit requirement
  /// of the subtarget.
  ArrayRef<MCPhysReg> getAllSGPR64(const MachineFunction &MF) const;
 
  /// Return all SGPR32 which satisfy the waves per execution unit requirement
  /// of the subtarget.
  ArrayRef<MCPhysReg> getAllSGPR32(const MachineFunction &MF) const;
 
  // Insert spill or restore instructions.
  // When lowering spill pseudos, the RegScavenger should be set.
  // For creating spill instructions during frame lowering, where no scavenger
  // is available, LiveUnits can be used.
  void buildSpillLoadStore(MachineBasicBlock &MBB,
                           MachineBasicBlock::iterator MI, const DebugLoc &DL,
                           unsigned LoadStoreOp, int Index, Register ValueReg,
                           bool ValueIsKill, MCRegister ScratchOffsetReg,
                           int64_t InstrOffset, MachineMemOperand *MMO,
                           RegScavenger *RS, LiveRegUnits *LiveUnits = nullptr,
                           bool NeedsCFI = false) const;
 
  // Return alignment in register file of first register in a register tuple.
  unsigned getRegClassAlignmentNumBits(const TargetRegisterClass *RC) const {
    return (RC->TSFlags & SIRCFlags::RegTupleAlignUnitsMask) * 32;
  }
 
  // Check if register class RC has required alignment.
  bool isRegClassAligned(const TargetRegisterClass *RC,
                         unsigned AlignNumBits) const {
    assert(AlignNumBits != 0);
    unsigned RCAlign = getRegClassAlignmentNumBits(RC);
    return RCAlign == AlignNumBits ||
           (RCAlign > AlignNumBits && (RCAlign % AlignNumBits) == 0);
  }
 
  // Return alignment of a SubReg relative to start of a register in RC class.
  // No check if the subreg is supported by the current RC is made.
  unsigned getSubRegAlignmentNumBits(const TargetRegisterClass *RC,
                                     unsigned SubReg) const;
 
  // \returns a number of registers of a given \p RC used in a function.
  // Does not go inside function calls. If \p IncludeCalls is true, it will
  // include registers that may be clobbered by calls.
  unsigned getNumUsedPhysRegs(const MachineRegisterInfo &MRI,
                              const TargetRegisterClass &RC,
                              bool IncludeCalls = true) const;
 
  std::optional<uint8_t> getVRegFlagValue(StringRef Name) const override {
    return Name == "WWM_REG" ? AMDGPU::VirtRegFlag::WWM_REG
                             : std::optional<uint8_t>{};
  }
 
  SmallVector<StringLiteral>
  getVRegFlagsOfReg(Register Reg, const MachineFunction &MF) const override;
 
  float
  getSpillWeightScaleFactor(const TargetRegisterClass *RC) const override {
    // Prioritize VGPR_32_Lo256 over other classes which may occupy registers
    // beyond v256.
    return AMDGPUGenRegisterInfo::getSpillWeightScaleFactor(RC) *
           ((RC == &AMDGPU::VGPR_32_Lo256RegClass ||
             RC == &AMDGPU::VReg_64_Lo256_Align2RegClass)
                ? 2.0
                : 1.0);
  }
};
 
} // End namespace llvm
 
#endif