MCSubtargetInfo.cpp

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//===- MCSubtargetInfo.cpp - Subtarget Information ------------------------===//
//
// 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 "llvm/MC/MCSubtargetInfo.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/Twine.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/MC/MCSchedule.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/TargetParser/SubtargetFeature.h"
#include <algorithm>
#include <cassert>
#include <cstring>
#include <optional>
 
using namespace llvm;
 
/// Find KV in array using binary search.
template <typename T>
static const T *Find(StringRef S, ArrayRef<T> A) {
  // Binary search the array
  auto F = llvm::lower_bound(A, S);
  // If not found then return NULL
  if (F == A.end() || StringRef(F->key()) != S)
    return nullptr;
  // Return the found array item
  return F;
}
 
/// For each feature that is (transitively) implied by this feature, set it.
static void SetImpliedBits(FeatureBitset &Bits, FeatureBitset Implies,
                           ArrayRef<SubtargetFeatureKV> FeatureTable) {
  // Transitively set all features implied. We don't assume that the features in
  // Bits have already had their implied features set.
  FeatureBitset NewBits = Implies;
  while (Implies.any()) {
    FeatureBitset Implied;
    for (const SubtargetFeatureKV &FE : FeatureTable) {
      if (Implies.test(FE.Value))
        Implied |= FE.Implies.getAsBitset();
    }
 
    // Only continue for bits that haven't been set yet.
    Implies = Implied & ~NewBits;
    NewBits |= Implies;
  }
  Bits |= NewBits;
}
 
/// For each feature that (transitively) implies this feature, clear it.
static
void ClearImpliedBits(FeatureBitset &Bits, unsigned Value,
                      ArrayRef<SubtargetFeatureKV> FeatureTable) {
  for (const SubtargetFeatureKV &FE : FeatureTable) {
    if (FE.Implies.getAsBitset().test(Value)) {
      Bits.reset(FE.Value);
      ClearImpliedBits(Bits, FE.Value, FeatureTable);
    }
  }
}
 
static void ApplyFeatureFlag(FeatureBitset &Bits, StringRef Feature,
                             ArrayRef<SubtargetFeatureKV> FeatureTable) {
  assert(SubtargetFeatures::hasFlag(Feature) &&
         "Feature flags should start with '+' or '-'");
 
  // Find feature in table.
  const SubtargetFeatureKV *FeatureEntry =
      Find(SubtargetFeatures::StripFlag(Feature), FeatureTable);
  // If there is a match
  if (FeatureEntry) {
    // Enable/disable feature in bits
    if (SubtargetFeatures::isEnabled(Feature)) {
      Bits.set(FeatureEntry->Value);
 
      // For each feature that this implies, set it.
      SetImpliedBits(Bits, FeatureEntry->Implies.getAsBitset(), FeatureTable);
    } else {
      Bits.reset(FeatureEntry->Value);
 
      // For each feature that implies this, clear it.
      ClearImpliedBits(Bits, FeatureEntry->Value, FeatureTable);
    }
  } else {
    errs() << "'" << Feature << "' is not a recognized feature for this target"
           << " (ignoring feature)\n";
  }
}
 
/// Return the length of the longest entry in the table.
static size_t getLongestEntryLength(ArrayRef<SubtargetFeatureKV> Table) {
  size_t MaxLen = 0;
  for (auto &I : Table)
    MaxLen = std::max(MaxLen, std::strlen(I.key()));
  return MaxLen;
}
 
static size_t getLongestEntryLength(StringTable Table) {
  size_t MaxLen = 0;
  for (StringRef I : Table)
    MaxLen = std::max(MaxLen, I.size());
  return MaxLen;
}
 
/// Display help for feature and mcpu choices.
static void Help(StringTable CPUNames, ArrayRef<SubtargetFeatureKV> FeatTable) {
  // the static variable ensures that the help information only gets
  // printed once even though a target machine creates multiple subtargets
  static bool PrintOnce = false;
  if (PrintOnce) {
    return;
  }
 
  // Determine the length of the longest CPU and Feature entries.
  unsigned MaxCPULen = getLongestEntryLength(CPUNames);
  unsigned MaxFeatLen = getLongestEntryLength(FeatTable);
 
  // Print the CPU table.
  errs() << "Available CPUs for this target:\n\n";
  for (auto &CPUName : CPUNames) {
    // Skip apple-latest, as that's only meant to be used in
    // disassemblers/debuggers, and we don't want normal code to be built with
    // it as an -mcpu=
    if (CPUName == "apple-latest")
      continue;
    errs() << format("  %-*s - Select the %s processor.\n", MaxCPULen,
                     CPUName.str().c_str(), CPUName.str().c_str());
  }
  errs() << '\n';
 
  // Print the Feature table.
  errs() << "Available features for this target:\n\n";
  for (auto &Feature : FeatTable)
    errs() << format("  %-*s - %s.\n", MaxFeatLen, Feature.key(),
                     Feature.desc());
  errs() << '\n';
 
  errs() << "Use +feature to enable a feature, or -feature to disable it.\n"
            "For example, llc -mcpu=mycpu -mattr=+feature1,-feature2\n";
 
  PrintOnce = true;
}
 
/// Display help for mcpu choices only
static void cpuHelp(StringTable CPUNames) {
  // the static variable ensures that the help information only gets
  // printed once even though a target machine creates multiple subtargets
  static bool PrintOnce = false;
  if (PrintOnce) {
    return;
  }
 
  // Print the CPU table.
  errs() << "Available CPUs for this target:\n\n";
  for (auto &CPU : CPUNames) {
    // Skip apple-latest, as that's only meant to be used in
    // disassemblers/debuggers, and we don't want normal code to be built with
    // it as an -mcpu=
    if (CPU == "apple-latest")
      continue;
    errs() << "\t" << CPU << "\n";
  }
  errs() << '\n';
 
  errs() << "Use -mcpu or -mtune to specify the target's processor.\n"
            "For example, clang --target=aarch64-unknown-linux-gnu "
            "-mcpu=cortex-a35\n";
 
  PrintOnce = true;
}
 
static FeatureBitset getFeatures(MCSubtargetInfo &STI, StringRef CPU,
                                 StringRef TuneCPU, StringRef FS,
                                 StringTable ProcNames,
                                 ArrayRef<SubtargetSubTypeKV> ProcDesc,
                                 ArrayRef<SubtargetFeatureKV> ProcFeatures) {
  SubtargetFeatures Features(FS);
 
  if (ProcDesc.empty() || ProcFeatures.empty())
    return FeatureBitset();
 
  assert(llvm::is_sorted(ProcDesc) && "CPU table is not sorted");
  assert(llvm::is_sorted(ProcFeatures) && "CPU features table is not sorted");
  // Resulting bits
  FeatureBitset Bits;
 
  // Check if help is needed
  if (CPU == "help")
    Help(ProcNames, ProcFeatures);
 
  // Find CPU entry if CPU name is specified.
  else if (!CPU.empty()) {
    const SubtargetSubTypeKV *CPUEntry = STI.resolveCPU(CPU);
 
    // If there is a match
    if (CPUEntry) {
      // Set the features implied by this CPU feature, if any.
      SetImpliedBits(Bits, CPUEntry->Implies.getAsBitset(), ProcFeatures);
    } else {
      errs() << "'" << CPU << "' is not a recognized processor for this target"
             << " (ignoring processor)\n";
    }
  }
 
  if (!TuneCPU.empty()) {
    const SubtargetSubTypeKV *CPUEntry = STI.resolveCPU(TuneCPU);
 
    // If there is a match
    if (CPUEntry) {
      // Set the features implied by this CPU feature, if any.
      SetImpliedBits(Bits, CPUEntry->TuneImplies.getAsBitset(), ProcFeatures);
    } else if (TuneCPU != CPU) {
      errs() << "'" << TuneCPU << "' is not a recognized processor for this "
             << "target (ignoring processor)\n";
    }
  }
 
  // Iterate through each feature
  for (const std::string &Feature : Features.getFeatures()) {
    // Check for help
    if (Feature == "+help")
      Help(ProcNames, ProcFeatures);
    else if (Feature == "+cpuhelp")
      cpuHelp(ProcNames);
    else
      ApplyFeatureFlag(Bits, Feature, ProcFeatures);
  }
 
  return Bits;
}
 
void MCSubtargetInfo::InitMCProcessorInfo(StringRef CPU, StringRef TuneCPU,
                                          StringRef FS) {
  FeatureBits =
      getFeatures(*this, CPU, TuneCPU, FS, ProcNames, ProcDesc, ProcFeatures);
  FeatureString = std::string(FS);
 
  if (!TuneCPU.empty())
    CPUSchedModel = &getSchedModelForCPU(TuneCPU);
  else
    CPUSchedModel = &MCSchedModel::Default;
}
 
void MCSubtargetInfo::setDefaultFeatures(StringRef CPU, StringRef TuneCPU,
                                         StringRef FS) {
  FeatureBits =
      getFeatures(*this, CPU, TuneCPU, FS, ProcNames, ProcDesc, ProcFeatures);
  FeatureString = std::string(FS);
}
 
MCSubtargetInfo::MCSubtargetInfo(
    const Triple &TT, StringRef C, StringRef TC, StringRef FS, StringTable PN,
    ArrayRef<SubtargetFeatureKV> PF, ArrayRef<SubtargetSubTypeKV> PD,
    ArrayRef<SubtargetSubTypeAliasKV> PA, const MCSchedModel *PSM,
    const MCWriteProcResEntry *WPR, const MCWriteLatencyEntry *WL,
    const MCReadAdvanceEntry *RA, const InstrStage *IS, const unsigned *OC,
    const unsigned *FP)
    : TargetTriple(TT), CPU(std::string(C)), TuneCPU(std::string(TC)),
      ProcNames(PN), ProcFeatures(PF), ProcDesc(PD), ProcAliases(PA),
      ProcSchedModels(PSM), WriteProcResTable(WPR), WriteLatencyTable(WL),
      ReadAdvanceTable(RA), Stages(IS), OperandCycles(OC), ForwardingPaths(FP) {
  InitMCProcessorInfo(CPU, TuneCPU, FS);
}
 
const FeatureBitset &MCSubtargetInfo::ToggleFeature(uint64_t FB) {
  FeatureBits.flip(FB);
  return FeatureBits;
}
 
const FeatureBitset &MCSubtargetInfo::ToggleFeature(const FeatureBitset &FB) {
  FeatureBits ^= FB;
  return FeatureBits;
}
 
const FeatureBitset &
MCSubtargetInfo::SetFeatureBitsTransitively(const FeatureBitset &FB) {
  SetImpliedBits(FeatureBits, FB, ProcFeatures);
  return FeatureBits;
}
 
const FeatureBitset &
MCSubtargetInfo::ClearFeatureBitsTransitively(const FeatureBitset &FB) {
  for (unsigned I = 0, E = FB.size(); I < E; I++) {
    if (FB[I]) {
      FeatureBits.reset(I);
      ClearImpliedBits(FeatureBits, I, ProcFeatures);
    }
  }
  return FeatureBits;
}
 
const FeatureBitset &MCSubtargetInfo::ToggleFeature(StringRef Feature) {
  // Find feature in table.
  const SubtargetFeatureKV *FeatureEntry =
      Find(SubtargetFeatures::StripFlag(Feature), ProcFeatures);
  // If there is a match
  if (FeatureEntry) {
    if (FeatureBits.test(FeatureEntry->Value)) {
      FeatureBits.reset(FeatureEntry->Value);
      // For each feature that implies this, clear it.
      ClearImpliedBits(FeatureBits, FeatureEntry->Value, ProcFeatures);
    } else {
      FeatureBits.set(FeatureEntry->Value);
 
      // For each feature that this implies, set it.
      SetImpliedBits(FeatureBits, FeatureEntry->Implies.getAsBitset(),
                     ProcFeatures);
    }
  } else {
    errs() << "'" << Feature << "' is not a recognized feature for this target"
           << " (ignoring feature)\n";
  }
 
  return FeatureBits;
}
 
const FeatureBitset &MCSubtargetInfo::ApplyFeatureFlag(StringRef FS) {
  ::ApplyFeatureFlag(FeatureBits, FS, ProcFeatures);
  return FeatureBits;
}
 
bool MCSubtargetInfo::checkFeatures(StringRef FS) const {
  SubtargetFeatures T(FS);
  return all_of(T.getFeatures(), [this](const std::string &F) {
    assert(SubtargetFeatures::hasFlag(F) &&
           "Feature flags should start with '+' or '-'");
    const SubtargetFeatureKV *FeatureEntry =
        Find(SubtargetFeatures::StripFlag(F), ProcFeatures);
    if (!FeatureEntry) {
      reportFatalInternalError(Twine("'") + F +
                               "' is not a recognized feature for this target");
    }
 
    return FeatureBits.test(FeatureEntry->Value) ==
           SubtargetFeatures::isEnabled(F);
  });
}
 
static bool hasFeature(StringRef Feature, const FeatureBitset &FeatureBits,
                       ArrayRef<SubtargetFeatureKV> ProcFeatures) {
  bool ShouldBeEnabled = true;
  if (!Feature.consume_front("+") && Feature.consume_front("-"))
    ShouldBeEnabled = false;
 
  const SubtargetFeatureKV *FeatureEntry = Find(Feature, ProcFeatures);
  if (!FeatureEntry) {
    reportFatalInternalError(Twine("'") + Feature +
                             "' is not a recognized feature for this target");
  }
 
  return FeatureBits.test(FeatureEntry->Value) == ShouldBeEnabled;
}
 
namespace {
class FeatureExpressionParser {
  StringRef Expr;
  const FeatureBitset &FeatureBits;
  ArrayRef<SubtargetFeatureKV> ProcFeatures;
  size_t Pos = 0;
 
public:
  FeatureExpressionParser(StringRef Expr, const FeatureBitset &FeatureBits,
                          ArrayRef<SubtargetFeatureKV> ProcFeatures)
      : Expr(Expr), FeatureBits(FeatureBits), ProcFeatures(ProcFeatures) {}
 
  bool parse() {
    bool Result = parseOr();
    if (Pos != Expr.size())
      reportFatalInternalError("malformed target feature expression");
    return Result;
  }
 
private:
  bool consume(char C) {
    if (Pos == Expr.size() || Expr[Pos] != C)
      return false;
    ++Pos;
    return true;
  }
 
  bool parseOr() {
    bool Result = parseAnd();
    while (consume('|')) {
      bool RHS = parseAnd();
      Result |= RHS;
    }
    return Result;
  }
 
  bool parseAnd() {
    bool Result = parsePrimary();
    while (consume(',')) {
      bool RHS = parsePrimary();
      Result &= RHS;
    }
    return Result;
  }
 
  bool parsePrimary() {
    if (consume('(')) {
      bool Result = parseOr();
      if (!consume(')'))
        reportFatalInternalError("malformed target feature expression");
      return Result;
    }
 
    size_t Start = Pos;
    Pos = Expr.find_first_of(",|()", Pos);
    if (Pos == StringRef::npos)
      Pos = Expr.size();
 
    if (Start == Pos)
      reportFatalInternalError("malformed target feature expression");
 
    return hasFeature(Expr.slice(Start, Pos), FeatureBits, ProcFeatures);
  }
};
} // namespace
 
bool MCSubtargetInfo::checkFeatureExpression(StringRef FeatureExpr) const {
  if (FeatureExpr.empty())
    return true;
  if (FeatureExpr.contains(' ')) {
    reportFatalInternalError(
        "spaces are not allowed in target feature expressions");
  }
  FeatureExpressionParser Parser(FeatureExpr, FeatureBits, ProcFeatures);
  return Parser.parse();
}
 
const SubtargetSubTypeKV *MCSubtargetInfo::resolveCPU(StringRef CPU) const {
  if (const SubtargetSubTypeKV *CPUEntry = Find(CPU, ProcDesc))
    return CPUEntry;
 
  // Not a canonical processor name; check whether it is a known alias.
  if (const SubtargetSubTypeAliasKV *Alias = Find(CPU, ProcAliases))
    return &ProcDesc[Alias->SubTypeIdx];
 
  return nullptr;
}
 
const MCSchedModel &MCSubtargetInfo::getSchedModelForCPU(StringRef CPU) const {
  assert(llvm::is_sorted(ProcDesc) &&
         "Processor machine model table is not sorted");
 
  // Find entry
  const SubtargetSubTypeKV *CPUEntry = resolveCPU(CPU);
 
  if (!CPUEntry) {
    if (CPU != "help") // Don't error if the user asked for help.
      errs() << "'" << CPU
             << "' is not a recognized processor for this target"
             << " (ignoring processor)\n";
    return MCSchedModel::Default;
  }
  return ProcSchedModels[CPUEntry->SchedModelIdx];
}
 
InstrItineraryData
MCSubtargetInfo::getInstrItineraryForCPU(StringRef CPU) const {
  const MCSchedModel &SchedModel = getSchedModelForCPU(CPU);
  return InstrItineraryData(SchedModel, Stages, OperandCycles, ForwardingPaths);
}
 
void MCSubtargetInfo::initInstrItins(InstrItineraryData &InstrItins) const {
  InstrItins = InstrItineraryData(getSchedModel(), Stages, OperandCycles,
                                  ForwardingPaths);
}
 
std::vector<const SubtargetFeatureKV *>
MCSubtargetInfo::getEnabledProcessorFeatures() const {
  std::vector<const SubtargetFeatureKV *> EnabledFeatures;
  for (const SubtargetFeatureKV &FeatureKV : ProcFeatures)
    if (FeatureBits.test(FeatureKV.Value))
      EnabledFeatures.push_back(&FeatureKV);
  return EnabledFeatures;
}
 
std::optional<unsigned> MCSubtargetInfo::getCacheSize(unsigned Level) const {
  return std::nullopt;
}
 
std::optional<unsigned>
MCSubtargetInfo::getCacheAssociativity(unsigned Level) const {
  return std::nullopt;
}
 
std::optional<unsigned>
MCSubtargetInfo::getCacheLineSize(unsigned Level) const {
  return std::nullopt;
}
 
unsigned MCSubtargetInfo::getPrefetchDistance() const {
  return 0;
}
 
unsigned MCSubtargetInfo::getMaxPrefetchIterationsAhead() const {
  return UINT_MAX;
}
 
bool MCSubtargetInfo::enableWritePrefetching() const {
  return false;
}
 
unsigned MCSubtargetInfo::getMinPrefetchStride(unsigned NumMemAccesses,
                                               unsigned NumStridedMemAccesses,
                                               unsigned NumPrefetches,
                                               bool HasCall) const {
  return 1;
}
 
bool MCSubtargetInfo::shouldPrefetchAddressSpace(unsigned AS) const {
  return !AS;
}