Fix arch version detection/checking on ARM/AArch64

The code was using two different `std::pair` types to pass this info around
as remnant of an earlier version and the auto conversion between the two types
does not retain the meaning we want...

Use a custom struct to hold the info to guard against this kind of errors in the future.

src/processor_arm.cpp

@@ -763,10 +763,20 @@ static CPU get_cpu_name(CPUID cpuid)
  }
 }
 
-static std::pair<int,char> get_elf_arch(void)
+namespace {
+
+struct arm_arch {
+ int version;
+ char klass;
+ constexpr bool mclass() const { return klass == 'M'; }
+};
+
+}
+
+static arm_arch get_elf_arch(void)
 {
 #ifdef _CPU_AARCH64_
- return std::make_pair(8, 'A');
+ return {8, 'A'};
 #else
  int ver = 0;
  char profile = 0;
@@ -792,7 +802,7 @@ static std::pair<int,char> get_elf_arch(void)
 # if __ARM_ARCH > 6 && defined(__ARM_ARCH_PROFILE)
  profile = __ARM_ARCH_PROFILE;
 # endif
- return std::make_pair(ver, profile);
+ return {ver, profile};
 #endif
 }
 
@@ -811,30 +821,45 @@ static inline const char *find_cpu_name(uint32_t cpu)
  return ::find_cpu_name(cpu, cpus, ncpu_names);
 }
 
-static std::pair<int,bool> feature_arch_version(const FeatureList<feature_sz> &feature)
+static arm_arch feature_arch_version(const FeatureList<feature_sz> &feature)
 {
 #ifdef _CPU_AARCH64_
- return std::make_pair(8, false);
+ return {8, 'A'};
 #else
- if (test_nbit(feature, Feature::v8))
- return std::make_pair(8, test_nbit(feature, Feature::mclass));
- if (test_nbit(feature, Feature::v7))
- return std::make_pair(7, test_nbit(feature, Feature::mclass));
- return std::make_pair(6, false);
+ int ver;
+ if (test_nbit(feature, Feature::v8)) {
+ ver = 8;
+ }
+ else if (test_nbit(feature, Feature::v7)) {
+ ver = 7;
+ }
+ else {
+ return {6, 0};
+ }
+ if (test_nbit(feature, Feature::mclass)) {
+ return {ver, 'M'};
+ }
+ else if (test_nbit(feature, Feature::rclass)) {
+ return {ver, 'R'};
+ }
+ else if (test_nbit(feature, Feature::aclass)) {
+ return {ver, 'A'};
+ }
+ return {ver, 0};
 #endif
 }
 
-static CPU generic_for_arch(std::pair<int,bool> arch)
+static CPU generic_for_arch(arm_arch arch)
 {
 #ifdef _CPU_AARCH64_
  return CPU::generic;
 #else
 # if defined(__ARM_ARCH_PROFILE)
  char klass = __ARM_ARCH_PROFILE;
 # else
- char klass = arch.second ? 'M' : 'A';
+ char klass = arch.klass;
 # endif
- if (arch.first >= 8) {
+ if (arch.version >= 8) {
  if (klass == 'M') {
  return CPU::armv8_m_base;
  }
@@ -845,7 +870,7 @@ static CPU generic_for_arch(std::pair<int,bool> arch)
  return CPU::armv8_a;
  }
  }
- else if (arch.first == 7) {
+ else if (arch.version == 7) {
  if (klass == 'M') {
  return CPU::armv7_m;
  }
@@ -860,16 +885,16 @@ static CPU generic_for_arch(std::pair<int,bool> arch)
 #endif
 }
 
-static bool check_cpu_arch_ver(uint32_t cpu, std::pair<int,bool> arch)
+static bool check_cpu_arch_ver(uint32_t cpu, arm_arch arch)
 {
  auto spec = find_cpu(cpu);
  // This happens on AArch64 and indicates that the cpu name isn't a valid aarch64 CPU
  if (!spec)
  return false;
- auto cpu_arch = feature_arch_version(spec->features);
- if (arch.second != cpu_arch.second)
+ auto feature_arch = feature_arch_version(spec->features);
+ if (arch.mclass() != feature_arch.mclass())
  return false;
- if (arch.first > cpu_arch.first)
+ if (arch.version > feature_arch.version)
  return false;
  return true;
 }
@@ -911,18 +936,18 @@ static NOINLINE std::pair<uint32_t,FeatureList<feature_sz>> _get_host_cpu()
  auto cpuinfo = get_cpuinfo();
  auto arch = get_elf_arch();
 #ifdef _CPU_ARM_
- if (arch.first >= 7) {
- if (arch.second == 'M') {
+ if (arch.version >= 7) {
+ if (arch.klass == 'M') {
  set_bit(features, Feature::mclass, true);
  }
- else if (arch.second == 'R') {
+ else if (arch.klass == 'R') {
  set_bit(features, Feature::rclass, true);
  }
- else if (arch.second == 'A') {
+ else if (arch.klass == 'A') {
  set_bit(features, Feature::aclass, true);
  }
  }
- switch (arch.first) {
+ switch (arch.version) {
  case 8:
  set_bit(features, Feature::v8, true);
  JL_FALLTHROUGH;
@@ -1309,18 +1334,18 @@ static FeatureList<feature_sz> get_max_feature(void)
 #ifdef _CPU_ARM_
  auto arch = get_elf_arch();
  auto features = real_feature_masks;
- if (arch.second == 0)
- arch.second = 'A';
+ if (arch.klass == 0)
+ arch.klass = 'A';
  set_bit(features, Feature::v7, true);
  set_bit(features, Feature::v8, true);
- if (arch.second == 'M') {
+ if (arch.klass == 'M') {
  set_bit(features, Feature::mclass, true);
  set_bit(features, Feature::v8_m_main, true);
  }
- else if (arch.second == 'R') {
+ else if (arch.klass == 'R') {
  set_bit(features, Feature::rclass, true);
  }
- else if (arch.second == 'A') {
+ else if (arch.klass == 'A') {
  set_bit(features, Feature::aclass, true);
  set_bit(features, Feature::v8_1a, true);
  set_bit(features, Feature::v8_2a, true);