AMDGPUMCExpr.cpp

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//===- AMDGPUMCExpr.cpp - AMDGPU specific MC expression classes -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "AMDGPUMCExpr.h"
#include "GCNSubtarget.h"
#include "Utils/AMDGPUBaseInfo.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/MC/MCAssembler.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCStreamer.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/MC/MCValue.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include <optional>
 
using namespace llvm;
using namespace llvm::AMDGPU;
 
AMDGPUMCExpr::AMDGPUMCExpr(VariantKind Kind, ArrayRef<const MCExpr *> Args,
                           MCContext &Ctx)
    : Kind(Kind), Ctx(Ctx) {
  assert(Args.size() >= 1 && "Needs a minimum of one expression.");
  assert(Kind != AGVK_None && "Cannot construct AMDGPUMCExpr of kind none.");
 
  // Allocating the variadic arguments through the same allocation mechanism
  // that the object itself is allocated with so they end up in the same memory.
  //
  // Will result in an asan failure if allocated on the heap through standard
  // allocation (e.g., through SmallVector's grow).
  RawArgs = static_cast<const MCExpr **>(
      Ctx.allocate(sizeof(const MCExpr *) * Args.size()));
  llvm::uninitialized_copy(Args, RawArgs);
  this->Args = ArrayRef<const MCExpr *>(RawArgs, Args.size());
}
 
AMDGPUMCExpr::~AMDGPUMCExpr() { Ctx.deallocate(RawArgs); }
 
const AMDGPUMCExpr *AMDGPUMCExpr::create(VariantKind Kind,
                                         ArrayRef<const MCExpr *> Args,
                                         MCContext &Ctx) {
  return new (Ctx) AMDGPUMCExpr(Kind, Args, Ctx);
}
 
const MCExpr *AMDGPUMCExpr::getSubExpr(size_t Index) const {
  assert(Index < Args.size() && "Indexing out of bounds AMDGPUMCExpr sub-expr");
  return Args[Index];
}
 
void AMDGPUMCExpr::printImpl(raw_ostream &OS, const MCAsmInfo *MAI) const {
  switch (Kind) {
  default:
    llvm_unreachable("Unknown AMDGPUMCExpr kind.");
  case AGVK_Or:
    OS << "or(";
    break;
  case AGVK_Max:
    OS << "max(";
    break;
  case AGVK_ExtraSGPRs:
    OS << "extrasgprs(";
    break;
  case AGVK_TotalNumVGPRs:
    OS << "totalnumvgprs(";
    break;
  case AGVK_AlignTo:
    OS << "alignto(";
    break;
  case AGVK_Occupancy:
    OS << "occupancy(";
    break;
  case AGVK_Lit:
    OS << "lit(";
    break;
  case AGVK_Lit64:
    OS << "lit64(";
    break;
  }
  for (const auto *It = Args.begin(); It != Args.end(); ++It) {
    MAI->printExpr(OS, **It);
    if ((It + 1) != Args.end())
      OS << ", ";
  }
  OS << ')';
}
 
static int64_t op(AMDGPUMCExpr::VariantKind Kind, int64_t Arg1, int64_t Arg2) {
  switch (Kind) {
  default:
    llvm_unreachable("Unknown AMDGPUMCExpr kind.");
  case AMDGPUMCExpr::AGVK_Max:
    return std::max(Arg1, Arg2);
  case AMDGPUMCExpr::AGVK_Or:
    return Arg1 | Arg2;
  }
}
 
bool AMDGPUMCExpr::evaluateExtraSGPRs(MCValue &Res,
                                      const MCAssembler *Asm) const {
  auto TryGetMCExprValue = [&](const MCExpr *Arg, uint64_t &ConstantValue) {
    MCValue MCVal;
    if (!Arg->evaluateAsRelocatable(MCVal, Asm) || !MCVal.isAbsolute())
      return false;
 
    ConstantValue = MCVal.getConstant();
    return true;
  };
 
  assert(Args.size() == 3 &&
         "AMDGPUMCExpr Argument count incorrect for ExtraSGPRs");
  const MCSubtargetInfo *STI = Ctx.getSubtargetInfo();
  uint64_t VCCUsed = 0, FlatScrUsed = 0, XNACKUsed = 0;
 
  bool Success = TryGetMCExprValue(Args[2], XNACKUsed);
 
  assert(Success && "Arguments 3 for ExtraSGPRs should be a known constant");
  if (!Success || !TryGetMCExprValue(Args[0], VCCUsed) ||
      !TryGetMCExprValue(Args[1], FlatScrUsed))
    return false;
 
  uint64_t ExtraSGPRs = IsaInfo::getNumExtraSGPRs(
      STI, (bool)VCCUsed, (bool)FlatScrUsed, (bool)XNACKUsed);
  Res = MCValue::get(ExtraSGPRs);
  return true;
}
 
bool AMDGPUMCExpr::evaluateTotalNumVGPR(MCValue &Res,
                                        const MCAssembler *Asm) const {
  auto TryGetMCExprValue = [&](const MCExpr *Arg, uint64_t &ConstantValue) {
    MCValue MCVal;
    if (!Arg->evaluateAsRelocatable(MCVal, Asm) || !MCVal.isAbsolute())
      return false;
 
    ConstantValue = MCVal.getConstant();
    return true;
  };
  assert(Args.size() == 2 &&
         "AMDGPUMCExpr Argument count incorrect for TotalNumVGPRs");
  const MCSubtargetInfo *STI = Ctx.getSubtargetInfo();
  uint64_t NumAGPR = 0, NumVGPR = 0;
 
  bool Has90AInsts = AMDGPU::isGFX90A(*STI);
 
  if (!TryGetMCExprValue(Args[0], NumAGPR) ||
      !TryGetMCExprValue(Args[1], NumVGPR))
    return false;
 
  uint64_t TotalNum = Has90AInsts && NumAGPR ? alignTo(NumVGPR, 4) + NumAGPR
                                             : std::max(NumVGPR, NumAGPR);
  Res = MCValue::get(TotalNum);
  return true;
}
 
bool AMDGPUMCExpr::evaluateAlignTo(MCValue &Res, const MCAssembler *Asm) const {
  auto TryGetMCExprValue = [&](const MCExpr *Arg, uint64_t &ConstantValue) {
    MCValue MCVal;
    if (!Arg->evaluateAsRelocatable(MCVal, Asm) || !MCVal.isAbsolute())
      return false;
 
    ConstantValue = MCVal.getConstant();
    return true;
  };
 
  assert(Args.size() == 2 &&
         "AMDGPUMCExpr Argument count incorrect for AlignTo");
  uint64_t Value = 0, Align = 0;
  if (!TryGetMCExprValue(Args[0], Value) || !TryGetMCExprValue(Args[1], Align))
    return false;
 
  Res = MCValue::get(alignTo(Value, Align));
  return true;
}
 
bool AMDGPUMCExpr::evaluateOccupancy(MCValue &Res,
                                     const MCAssembler *Asm) const {
  auto TryGetMCExprValue = [&](const MCExpr *Arg, uint64_t &ConstantValue) {
    MCValue MCVal;
    if (!Arg->evaluateAsRelocatable(MCVal, Asm) || !MCVal.isAbsolute())
      return false;
 
    ConstantValue = MCVal.getConstant();
    return true;
  };
  assert(Args.size() == 7 &&
         "AMDGPUMCExpr Argument count incorrect for Occupancy");
  uint64_t InitOccupancy, MaxWaves, Granule, TargetTotalNumVGPRs, Generation,
      NumSGPRs, NumVGPRs;
 
  bool Success = true;
  Success &= TryGetMCExprValue(Args[0], MaxWaves);
  Success &= TryGetMCExprValue(Args[1], Granule);
  Success &= TryGetMCExprValue(Args[2], TargetTotalNumVGPRs);
  Success &= TryGetMCExprValue(Args[3], Generation);
  Success &= TryGetMCExprValue(Args[4], InitOccupancy);
 
  assert(Success && "Arguments 1 to 5 for Occupancy should be known constants");
 
  if (!Success || !TryGetMCExprValue(Args[5], NumSGPRs) ||
      !TryGetMCExprValue(Args[6], NumVGPRs))
    return false;
 
  unsigned Occupancy = InitOccupancy;
  if (NumSGPRs)
    Occupancy = std::min(
        Occupancy, IsaInfo::getOccupancyWithNumSGPRs(
                       NumSGPRs, MaxWaves,
                       static_cast<AMDGPUSubtarget::Generation>(Generation)));
  if (NumVGPRs)
    Occupancy = std::min(Occupancy,
                         IsaInfo::getNumWavesPerEUWithNumVGPRs(
                             NumVGPRs, Granule, MaxWaves, TargetTotalNumVGPRs));
 
  Res = MCValue::get(Occupancy);
  return true;
}
 
bool AMDGPUMCExpr::isSymbolUsedInExpression(const MCSymbol *Sym,
                                            const MCExpr *E) {
  switch (E->getKind()) {
  case MCExpr::Constant:
    return false;
  case MCExpr::Unary:
    return isSymbolUsedInExpression(
        Sym, static_cast<const MCUnaryExpr *>(E)->getSubExpr());
  case MCExpr::Binary: {
    const MCBinaryExpr *BE = static_cast<const MCBinaryExpr *>(E);
    return isSymbolUsedInExpression(Sym, BE->getLHS()) ||
           isSymbolUsedInExpression(Sym, BE->getRHS());
  }
  case MCExpr::SymbolRef: {
    const MCSymbol &S = static_cast<const MCSymbolRefExpr *>(E)->getSymbol();
    if (S.isVariable())
      return isSymbolUsedInExpression(Sym, S.getVariableValue());
    return &S == Sym;
  }
  case MCExpr::Specifier:
  case MCExpr::Target: {
    auto *TE = static_cast<const AMDGPUMCExpr *>(E);
    for (const MCExpr *E : TE->getArgs())
      if (isSymbolUsedInExpression(Sym, E))
        return true;
    return false;
  }
  }
  llvm_unreachable("Unknown expr kind!");
}
 
bool AMDGPUMCExpr::evaluateAsRelocatableImpl(MCValue &Res,
                                             const MCAssembler *Asm) const {
  std::optional<int64_t> Total;
  switch (Kind) {
  default:
    break;
  case AGVK_ExtraSGPRs:
    return evaluateExtraSGPRs(Res, Asm);
  case AGVK_AlignTo:
    return evaluateAlignTo(Res, Asm);
  case AGVK_TotalNumVGPRs:
    return evaluateTotalNumVGPR(Res, Asm);
  case AGVK_Occupancy:
    return evaluateOccupancy(Res, Asm);
  case AGVK_Lit:
  case AGVK_Lit64:
    return Args[0]->evaluateAsRelocatable(Res, Asm);
  }
 
  for (const MCExpr *Arg : Args) {
    MCValue ArgRes;
    if (!Arg->evaluateAsRelocatable(ArgRes, Asm) || !ArgRes.isAbsolute())
      return false;
 
    if (!Total.has_value())
      Total = ArgRes.getConstant();
    Total = op(Kind, *Total, ArgRes.getConstant());
  }
 
  Res = MCValue::get(*Total);
  return true;
}
 
void AMDGPUMCExpr::visitUsedExpr(MCStreamer &Streamer) const {
  for (const MCExpr *Arg : Args)
    Streamer.visitUsedExpr(*Arg);
}
 
MCFragment *AMDGPUMCExpr::findAssociatedFragment() const {
  for (const MCExpr *Arg : Args) {
    if (Arg->findAssociatedFragment())
      return Arg->findAssociatedFragment();
  }
  return nullptr;
}
 
/// Allow delayed MCExpr resolve of ExtraSGPRs (in case VCCUsed or FlatScrUsed
/// are unresolvable but needed for further MCExprs). Derived from
/// implementation of IsaInfo::getNumExtraSGPRs in AMDGPUBaseInfo.cpp.
///
const AMDGPUMCExpr *AMDGPUMCExpr::createExtraSGPRs(const MCExpr *VCCUsed,
                                                   const MCExpr *FlatScrUsed,
                                                   bool XNACKUsed,
                                                   MCContext &Ctx) {
 
  return create(AGVK_ExtraSGPRs,
                {VCCUsed, FlatScrUsed, MCConstantExpr::create(XNACKUsed, Ctx)},
                Ctx);
}
 
const AMDGPUMCExpr *AMDGPUMCExpr::createTotalNumVGPR(const MCExpr *NumAGPR,
                                                     const MCExpr *NumVGPR,
                                                     MCContext &Ctx) {
  return create(AGVK_TotalNumVGPRs, {NumAGPR, NumVGPR}, Ctx);
}
 
/// Mimics GCNSubtarget::computeOccupancy for MCExpr.
///
/// Remove dependency on GCNSubtarget and depend only only the necessary values
/// for said occupancy computation. Should match computeOccupancy implementation
/// without passing \p STM on.
const AMDGPUMCExpr *AMDGPUMCExpr::createOccupancy(
    unsigned InitOcc, const MCExpr *NumSGPRs, const MCExpr *NumVGPRs,
    unsigned DynamicVGPRBlockSize, const GCNSubtarget &STM, MCContext &Ctx) {
  unsigned MaxWaves = IsaInfo::getMaxWavesPerEU(&STM);
  unsigned Granule = IsaInfo::getVGPRAllocGranule(&STM, DynamicVGPRBlockSize);
  unsigned TargetTotalNumVGPRs = IsaInfo::getTotalNumVGPRs(&STM);
  unsigned Generation = STM.getGeneration();
 
  auto CreateExpr = [&Ctx](unsigned Value) {
    return MCConstantExpr::create(Value, Ctx);
  };
 
  return create(AGVK_Occupancy,
                {CreateExpr(MaxWaves), CreateExpr(Granule),
                 CreateExpr(TargetTotalNumVGPRs), CreateExpr(Generation),
                 CreateExpr(InitOcc), NumSGPRs, NumVGPRs},
                Ctx);
}
 
const AMDGPUMCExpr *AMDGPUMCExpr::createLit(LitModifier Lit, int64_t Value,
                                            MCContext &Ctx) {
  assert(Lit == LitModifier::Lit || Lit == LitModifier::Lit64);
  return create(Lit == LitModifier::Lit ? VariantKind::AGVK_Lit
                                        : VariantKind::AGVK_Lit64,
                {MCConstantExpr::create(Value, Ctx, /*PrintInHex=*/true)}, Ctx);
}
 
static KnownBits fromOptionalToKnownBits(std::optional<bool> CompareResult) {
  static constexpr unsigned BitWidth = 64;
  const APInt True(BitWidth, 1);
  const APInt False(BitWidth, 0);
  if (CompareResult) {
    return *CompareResult ? KnownBits::makeConstant(True)
                          : KnownBits::makeConstant(False);
  }
 
  KnownBits UnknownBool(/*BitWidth=*/1);
  return UnknownBool.zext(BitWidth);
}
 
using KnownBitsMap = DenseMap<const MCExpr *, KnownBits>;
static void knownBitsMapHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                               unsigned Depth = 0);
 
static void binaryOpKnownBitsMapHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                                       unsigned Depth) {
  static constexpr unsigned BitWidth = 64;
  const MCBinaryExpr *BExpr = cast<MCBinaryExpr>(Expr);
  const MCExpr *LHS = BExpr->getLHS();
  const MCExpr *RHS = BExpr->getRHS();
 
  knownBitsMapHelper(LHS, KBM, Depth + 1);
  knownBitsMapHelper(RHS, KBM, Depth + 1);
  KnownBits LHSKnown = KBM[LHS];
  KnownBits RHSKnown = KBM[RHS];
 
  switch (BExpr->getOpcode()) {
  default:
    KBM[Expr] = KnownBits(BitWidth);
    return;
  case MCBinaryExpr::Opcode::Add:
    KBM[Expr] = KnownBits::add(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::And:
    KBM[Expr] = LHSKnown & RHSKnown;
    return;
  case MCBinaryExpr::Opcode::Div:
    KBM[Expr] = KnownBits::sdiv(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::EQ: {
    std::optional<bool> CompareRes = KnownBits::eq(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::NE: {
    std::optional<bool> CompareRes = KnownBits::ne(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::GT: {
    std::optional<bool> CompareRes = KnownBits::sgt(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::GTE: {
    std::optional<bool> CompareRes = KnownBits::sge(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::LAnd: {
    std::optional<bool> CompareRes;
    const APInt False(BitWidth, 0);
    std::optional<bool> LHSBool =
        KnownBits::ne(LHSKnown, KnownBits::makeConstant(False));
    std::optional<bool> RHSBool =
        KnownBits::ne(RHSKnown, KnownBits::makeConstant(False));
    if (LHSBool && RHSBool)
      CompareRes = *LHSBool && *RHSBool;
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::LOr: {
    const APInt False(BitWidth, 0);
    KnownBits Bits = LHSKnown | RHSKnown;
    std::optional<bool> CompareRes =
        KnownBits::ne(Bits, KnownBits::makeConstant(False));
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::LT: {
    std::optional<bool> CompareRes = KnownBits::slt(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::LTE: {
    std::optional<bool> CompareRes = KnownBits::sle(LHSKnown, RHSKnown);
    KBM[Expr] = fromOptionalToKnownBits(CompareRes);
    return;
  }
  case MCBinaryExpr::Opcode::Mod:
    KBM[Expr] = KnownBits::srem(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::Mul:
    KBM[Expr] = KnownBits::mul(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::Or:
    KBM[Expr] = LHSKnown | RHSKnown;
    return;
  case MCBinaryExpr::Opcode::Shl:
    KBM[Expr] = KnownBits::shl(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::AShr:
    KBM[Expr] = KnownBits::ashr(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::LShr:
    KBM[Expr] = KnownBits::lshr(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::Sub:
    KBM[Expr] = KnownBits::sub(LHSKnown, RHSKnown);
    return;
  case MCBinaryExpr::Opcode::Xor:
    KBM[Expr] = LHSKnown ^ RHSKnown;
    return;
  }
}
 
static void unaryOpKnownBitsMapHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                                      unsigned Depth) {
  static constexpr unsigned BitWidth = 64;
  const MCUnaryExpr *UExpr = cast<MCUnaryExpr>(Expr);
  knownBitsMapHelper(UExpr->getSubExpr(), KBM, Depth + 1);
  KnownBits KB = KBM[UExpr->getSubExpr()];
 
  switch (UExpr->getOpcode()) {
  default:
    KBM[Expr] = KnownBits(BitWidth);
    return;
  case MCUnaryExpr::Opcode::Minus: {
    KB.makeNegative();
    KBM[Expr] = KB;
    return;
  }
  case MCUnaryExpr::Opcode::Not: {
    KnownBits AllOnes(BitWidth);
    AllOnes.setAllOnes();
    KBM[Expr] = KB ^ AllOnes;
    return;
  }
  case MCUnaryExpr::Opcode::Plus: {
    KB.makeNonNegative();
    KBM[Expr] = KB;
    return;
  }
  }
}
 
static void targetOpKnownBitsMapHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                                       unsigned Depth) {
  static constexpr unsigned BitWidth = 64;
  const AMDGPUMCExpr *AGVK = cast<AMDGPUMCExpr>(Expr);
 
  switch (AGVK->getKind()) {
  default:
    KBM[Expr] = KnownBits(BitWidth);
    return;
  case AMDGPUMCExpr::VariantKind::AGVK_Or: {
    knownBitsMapHelper(AGVK->getSubExpr(0), KBM, Depth + 1);
    KnownBits KB = KBM[AGVK->getSubExpr(0)];
    for (const MCExpr *Arg : AGVK->getArgs()) {
      knownBitsMapHelper(Arg, KBM, Depth + 1);
      KB |= KBM[Arg];
    }
    KBM[Expr] = KB;
    return;
  }
  case AMDGPUMCExpr::VariantKind::AGVK_Max: {
    knownBitsMapHelper(AGVK->getSubExpr(0), KBM, Depth + 1);
    KnownBits KB = KBM[AGVK->getSubExpr(0)];
    for (const MCExpr *Arg : AGVK->getArgs()) {
      knownBitsMapHelper(Arg, KBM, Depth + 1);
      KB = KnownBits::umax(KB, KBM[Arg]);
    }
    KBM[Expr] = KB;
    return;
  }
  case AMDGPUMCExpr::VariantKind::AGVK_ExtraSGPRs:
  case AMDGPUMCExpr::VariantKind::AGVK_TotalNumVGPRs:
  case AMDGPUMCExpr::VariantKind::AGVK_AlignTo:
  case AMDGPUMCExpr::VariantKind::AGVK_Occupancy:
  case AMDGPUMCExpr::VariantKind::AGVK_Lit:
  case AMDGPUMCExpr::VariantKind::AGVK_Lit64: {
    int64_t Val;
    if (AGVK->evaluateAsAbsolute(Val)) {
      APInt APValue(BitWidth, Val);
      KBM[Expr] = KnownBits::makeConstant(APValue);
      return;
    }
    KBM[Expr] = KnownBits(BitWidth);
    return;
  }
  }
}
 
static void knownBitsMapHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                               unsigned Depth) {
  static constexpr unsigned BitWidth = 64;
 
  int64_t Val;
  if (Expr->evaluateAsAbsolute(Val)) {
    APInt APValue(BitWidth, Val, /*isSigned=*/true);
    KBM[Expr] = KnownBits::makeConstant(APValue);
    return;
  }
 
  if (Depth == 16) {
    KBM[Expr] = KnownBits(BitWidth);
    return;
  }
 
  switch (Expr->getKind()) {
  case MCExpr::ExprKind::Binary: {
    binaryOpKnownBitsMapHelper(Expr, KBM, Depth);
    return;
  }
  case MCExpr::ExprKind::Constant: {
    const MCConstantExpr *CE = cast<MCConstantExpr>(Expr);
    APInt APValue(BitWidth, CE->getValue(), /*isSigned=*/true);
    KBM[Expr] = KnownBits::makeConstant(APValue);
    return;
  }
  case MCExpr::ExprKind::SymbolRef: {
    const MCSymbolRefExpr *RExpr = cast<MCSymbolRefExpr>(Expr);
    const MCSymbol &Sym = RExpr->getSymbol();
    if (!Sym.isVariable()) {
      KBM[Expr] = KnownBits(BitWidth);
      return;
    }
 
    // Variable value retrieval is not for actual use but only for knownbits
    // analysis.
    const MCExpr *SymVal = Sym.getVariableValue();
    knownBitsMapHelper(SymVal, KBM, Depth + 1);
 
    // Explicitly copy-construct so that there exists a local KnownBits in case
    // KBM[SymVal] gets invalidated after a potential growth through KBM[Expr].
    KBM[Expr] = KnownBits(KBM[SymVal]);
    return;
  }
  case MCExpr::ExprKind::Unary: {
    unaryOpKnownBitsMapHelper(Expr, KBM, Depth);
    return;
  }
  case MCExpr::ExprKind::Target: {
    targetOpKnownBitsMapHelper(Expr, KBM, Depth);
    return;
  case MCExpr::Specifier:
    llvm_unreachable("unused by this backend");
  }
  }
}
 
static const MCExpr *tryFoldHelper(const MCExpr *Expr, KnownBitsMap &KBM,
                                   MCContext &Ctx) {
  if (!KBM.count(Expr))
    return Expr;
 
  auto ValueCheckKnownBits = [](KnownBits &KB, unsigned Value) -> bool {
    if (!KB.isConstant())
      return false;
 
    return Value == KB.getConstant();
  };
 
  if (Expr->getKind() == MCExpr::ExprKind::Constant)
    return Expr;
 
  // Resolving unary operations to constants may make the value more ambiguous.
  // For example, `~62` becomes `-63`; however, to me it's more ambiguous if a
  // bit mask value is represented through a negative number.
  if (Expr->getKind() != MCExpr::ExprKind::Unary) {
    if (KBM[Expr].isConstant()) {
      APInt ConstVal = KBM[Expr].getConstant();
      return MCConstantExpr::create(ConstVal.getSExtValue(), Ctx);
    }
 
    int64_t EvalValue;
    if (Expr->evaluateAsAbsolute(EvalValue))
      return MCConstantExpr::create(EvalValue, Ctx);
  }
 
  switch (Expr->getKind()) {
  default:
    return Expr;
  case MCExpr::ExprKind::Binary: {
    const MCBinaryExpr *BExpr = cast<MCBinaryExpr>(Expr);
    const MCExpr *LHS = BExpr->getLHS();
    const MCExpr *RHS = BExpr->getRHS();
 
    switch (BExpr->getOpcode()) {
    default:
      return Expr;
    case MCBinaryExpr::Opcode::Sub: {
      if (ValueCheckKnownBits(KBM[RHS], 0))
        return tryFoldHelper(LHS, KBM, Ctx);
      break;
    }
    case MCBinaryExpr::Opcode::Add:
    case MCBinaryExpr::Opcode::Or: {
      if (ValueCheckKnownBits(KBM[LHS], 0))
        return tryFoldHelper(RHS, KBM, Ctx);
      if (ValueCheckKnownBits(KBM[RHS], 0))
        return tryFoldHelper(LHS, KBM, Ctx);
      break;
    }
    case MCBinaryExpr::Opcode::Mul: {
      if (ValueCheckKnownBits(KBM[LHS], 1))
        return tryFoldHelper(RHS, KBM, Ctx);
      if (ValueCheckKnownBits(KBM[RHS], 1))
        return tryFoldHelper(LHS, KBM, Ctx);
      break;
    }
    case MCBinaryExpr::Opcode::Shl:
    case MCBinaryExpr::Opcode::AShr:
    case MCBinaryExpr::Opcode::LShr: {
      if (ValueCheckKnownBits(KBM[RHS], 0))
        return tryFoldHelper(LHS, KBM, Ctx);
      if (ValueCheckKnownBits(KBM[LHS], 0))
        return MCConstantExpr::create(0, Ctx);
      break;
    }
    case MCBinaryExpr::Opcode::And: {
      if (ValueCheckKnownBits(KBM[LHS], 0) || ValueCheckKnownBits(KBM[RHS], 0))
        return MCConstantExpr::create(0, Ctx);
      break;
    }
    }
    const MCExpr *NewLHS = tryFoldHelper(LHS, KBM, Ctx);
    const MCExpr *NewRHS = tryFoldHelper(RHS, KBM, Ctx);
    if (NewLHS != LHS || NewRHS != RHS)
      return MCBinaryExpr::create(BExpr->getOpcode(), NewLHS, NewRHS, Ctx,
                                  BExpr->getLoc());
    return Expr;
  }
  case MCExpr::ExprKind::Unary: {
    const MCUnaryExpr *UExpr = cast<MCUnaryExpr>(Expr);
    const MCExpr *SubExpr = UExpr->getSubExpr();
    const MCExpr *NewSubExpr = tryFoldHelper(SubExpr, KBM, Ctx);
    if (SubExpr != NewSubExpr)
      return MCUnaryExpr::create(UExpr->getOpcode(), NewSubExpr, Ctx,
                                 UExpr->getLoc());
    return Expr;
  }
  case MCExpr::ExprKind::Target: {
    const AMDGPUMCExpr *AGVK = cast<AMDGPUMCExpr>(Expr);
    SmallVector<const MCExpr *, 8> NewArgs;
    bool Changed = false;
    for (const MCExpr *Arg : AGVK->getArgs()) {
      const MCExpr *NewArg = tryFoldHelper(Arg, KBM, Ctx);
      NewArgs.push_back(NewArg);
      Changed |= Arg != NewArg;
    }
    return Changed ? AMDGPUMCExpr::create(AGVK->getKind(), NewArgs, Ctx) : Expr;
  }
  }
  return Expr;
}
 
const MCExpr *llvm::AMDGPU::foldAMDGPUMCExpr(const MCExpr *Expr,
                                             MCContext &Ctx) {
  KnownBitsMap KBM;
  knownBitsMapHelper(Expr, KBM);
  const MCExpr *NewExpr = tryFoldHelper(Expr, KBM, Ctx);
 
  return Expr != NewExpr ? NewExpr : Expr;
}
 
void llvm::AMDGPU::printAMDGPUMCExpr(const MCExpr *Expr, raw_ostream &OS,
                                     const MCAsmInfo *MAI) {
  int64_t Val;
  if (Expr->evaluateAsAbsolute(Val)) {
    OS << Val;
    return;
  }
 
  MAI->printExpr(OS, *Expr);
}
 
bool AMDGPU::isLitExpr(const MCExpr *Expr) {
  const auto *E = dyn_cast<AMDGPUMCExpr>(Expr);
  return E && (E->getKind() == AMDGPUMCExpr::AGVK_Lit ||
               E->getKind() == AMDGPUMCExpr::AGVK_Lit64);
}
 
int64_t AMDGPU::getLitValue(const MCExpr *Expr) {
  assert(isLitExpr(Expr));
  return cast<MCConstantExpr>(cast<AMDGPUMCExpr>(Expr)->getArgs()[0])
      ->getValue();
}