src/cpu-features.cc

// Copyright 2018, VIXL authors
// All rights reserved.
//
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// modification, are permitted provided that the following conditions are met:
//
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//     this list of conditions and the following disclaimer.
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//     used to endorse or promote products derived from this software without
//     specific prior written permission.
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#include <ostream>

#include "cpu-features.h"
#include "globals-vixl.h"
#include "utils-vixl.h"

#if defined(__aarch64__) && defined(VIXL_INCLUDE_TARGET_AARCH64)
#include "aarch64/cpu-aarch64.h"
#define VIXL_USE_AARCH64_CPU_HELPERS
#endif

namespace vixl {

static uint64_t MakeFeatureMask(CPUFeatures::Feature feature) {
  if (feature == CPUFeatures::kNone) {
    return 0;
  } else {
    // Check that the shift is well-defined, and that the feature is valid.
    VIXL_STATIC_ASSERT(CPUFeatures::kNumberOfFeatures <=
                       (sizeof(uint64_t) * 8));
    VIXL_ASSERT(feature < CPUFeatures::kNumberOfFeatures);
    return UINT64_C(1) << feature;
  }
}

CPUFeatures::CPUFeatures(Feature feature0,
                         Feature feature1,
                         Feature feature2,
                         Feature feature3)
    : features_(0) {
  Combine(feature0, feature1, feature2, feature3);
}

CPUFeatures CPUFeatures::All() {
  CPUFeatures all;
  // Check that the shift is well-defined.
  VIXL_STATIC_ASSERT(CPUFeatures::kNumberOfFeatures < (sizeof(uint64_t) * 8));
  all.features_ = (UINT64_C(1) << kNumberOfFeatures) - 1;
  return all;
}

CPUFeatures CPUFeatures::InferFromIDRegisters() {
  // This function assumes that kIDRegisterEmulation is available.
  CPUFeatures features(CPUFeatures::kIDRegisterEmulation);
#ifdef VIXL_USE_AARCH64_CPU_HELPERS
  // Note that the Linux kernel filters these values during emulation, so the
  // results may not exactly match the expected hardware support.
  features.Combine(aarch64::CPU::InferCPUFeaturesFromIDRegisters());
#endif
  return features;
}

CPUFeatures CPUFeatures::InferFromOS(QueryIDRegistersOption option) {
#ifdef VIXL_USE_AARCH64_CPU_HELPERS
  return aarch64::CPU::InferCPUFeaturesFromOS(option);
#else
  USE(option);
  return CPUFeatures();
#endif
}

void CPUFeatures::Combine(const CPUFeatures& other) {
  features_ |= other.features_;
}

void CPUFeatures::Combine(Feature feature0,
                          Feature feature1,
                          Feature feature2,
                          Feature feature3) {
  features_ |= MakeFeatureMask(feature0);
  features_ |= MakeFeatureMask(feature1);
  features_ |= MakeFeatureMask(feature2);
  features_ |= MakeFeatureMask(feature3);
}

void CPUFeatures::Remove(const CPUFeatures& other) {
  features_ &= ~other.features_;
}

void CPUFeatures::Remove(Feature feature0,
                         Feature feature1,
                         Feature feature2,
                         Feature feature3) {
  features_ &= ~MakeFeatureMask(feature0);
  features_ &= ~MakeFeatureMask(feature1);
  features_ &= ~MakeFeatureMask(feature2);
  features_ &= ~MakeFeatureMask(feature3);
}

CPUFeatures CPUFeatures::With(const CPUFeatures& other) const {
  CPUFeatures f(*this);
  f.Combine(other);
  return f;
}

CPUFeatures CPUFeatures::With(Feature feature0,
                              Feature feature1,
                              Feature feature2,
                              Feature feature3) const {
  CPUFeatures f(*this);
  f.Combine(feature0, feature1, feature2, feature3);
  return f;
}

CPUFeatures CPUFeatures::Without(const CPUFeatures& other) const {
  CPUFeatures f(*this);
  f.Remove(other);
  return f;
}

CPUFeatures CPUFeatures::Without(Feature feature0,
                                 Feature feature1,
                                 Feature feature2,
                                 Feature feature3) const {
  CPUFeatures f(*this);
  f.Remove(feature0, feature1, feature2, feature3);
  return f;
}

bool CPUFeatures::Has(const CPUFeatures& other) const {
  return (features_ & other.features_) == other.features_;
}

bool CPUFeatures::Has(Feature feature0,
                      Feature feature1,
                      Feature feature2,
                      Feature feature3) const {
  uint64_t mask = MakeFeatureMask(feature0) | MakeFeatureMask(feature1) |
                  MakeFeatureMask(feature2) | MakeFeatureMask(feature3);
  return (features_ & mask) == mask;
}

size_t CPUFeatures::Count() const { return CountSetBits(features_); }

std::ostream& operator<<(std::ostream& os, CPUFeatures::Feature feature) {
  // clang-format off
  switch (feature) {
#define VIXL_FORMAT_FEATURE(SYMBOL, NAME, CPUINFO) \
    case CPUFeatures::SYMBOL:                      \
      return os << NAME;
VIXL_CPU_FEATURE_LIST(VIXL_FORMAT_FEATURE)
#undef VIXL_FORMAT_FEATURE
    case CPUFeatures::kNone:
      return os << "none";
    case CPUFeatures::kNumberOfFeatures:
      VIXL_UNREACHABLE();
  }
  // clang-format on
  VIXL_UNREACHABLE();
  return os;
}

CPUFeatures::const_iterator CPUFeatures::begin() const {
  // For iterators in general, it's undefined to increment `end()`, but here we
  // control the implementation and it is safe to do this.
  return ++end();
}

CPUFeatures::const_iterator CPUFeatures::end() const {
  return const_iterator(this, kNone);
}

std::ostream& operator<<(std::ostream& os, const CPUFeatures& features) {
  bool need_separator = false;
  for (CPUFeatures::Feature feature : features) {
    if (need_separator) os << ", ";
    need_separator = true;
    os << feature;
  }
  return os;
}

bool CPUFeaturesConstIterator::operator==(
    const CPUFeaturesConstIterator& other) const {
  VIXL_ASSERT(IsValid());
  return (cpu_features_ == other.cpu_features_) && (feature_ == other.feature_);
}

CPUFeaturesConstIterator& CPUFeaturesConstIterator::operator++() {  // Prefix
  VIXL_ASSERT(IsValid());
  do {
    // Find the next feature. The order is unspecified.
    feature_ = static_cast<CPUFeatures::Feature>(feature_ + 1);
    if (feature_ == CPUFeatures::kNumberOfFeatures) {
      feature_ = CPUFeatures::kNone;
      VIXL_STATIC_ASSERT(CPUFeatures::kNone == -1);
    }
    VIXL_ASSERT(CPUFeatures::kNone <= feature_);
    VIXL_ASSERT(feature_ < CPUFeatures::kNumberOfFeatures);
    // cpu_features_->Has(kNone) is always true, so this will terminate even if
    // the features list is empty.
  } while (!cpu_features_->Has(feature_));
  return *this;
}

CPUFeaturesConstIterator CPUFeaturesConstIterator::operator++(int) {  // Postfix
  CPUFeaturesConstIterator result = *this;
  ++(*this);
  return result;
}

}  // namespace vixl