[AArch64] Add support for -march=native for Apple M1 CPU

[keith]

Summary

This improves the getHostCPUName check for Apple M1 CPUs, which
previously would always be considered cyclone instead. This also enables
-march=native support when building on M1 CPUs which would previously
fail. This isn't as sophisticated as the X86 CPU feature checking which
consults the CPU via getHostCPUFeatures, but this is still better than
before. This CPU selection could also be invalid if this was run on an
iOS device instead, ideally we can improve those cases as they come up.

[keith]

Adding folks from https://reviews.llvm.org/D69597

[t.p.northover]

Things have moved on since the ARM and (especially) PPC variants of that function were written. That field (despite the name) is now more of an ABI tag and not going to be updated with each CPU.

I think the modern replacement for it is hw.cpufamily obtained from sysctl (command line or man 3 sysctl for programmatically). The potential values (CPUFAMILY_ARM_* starting with Cyclone) are listed in https://opensource.apple.com/source/xnu/xnu-4570.41.2/osfmk/mach/machine.h.auto.html (which should be in the SDK under mach/machine.h). It warns against inferring features from this, which is exactly what we'd be doing, but still probably has a better chance of being right long term.

I'd probably default to the latest known one rather than earliest too, since an unknown family is more likely to be new than old.

[t.p.northover]

Sorry, that was an old xnu version, the newest one is https://opensource.apple.com/source/xnu/xnu-7195.81.3/osfmk/mach/machine.h.auto.html which has

CPUFAMILY_ARM_CYCLONE	0x37a09642	apple-a7
CPUFAMILY_ARM_TYPHOON	0x2c91a47e	apple-a8
CPUFAMILY_ARM_TWISTER	0x92fb37c8	apple-a9
CPUFAMILY_ARM_HURRICANE	0x67ceee93	apple-a10
CPUFAMILY_ARM_MONSOON_MISTRAL	0xe81e7ef6	apple-a11
CPUFAMILY_ARM_VORTEX_TEMPEST	0x07d34b9f	apple-a12
CPUFAMILY_ARM_LIGHTNING_THUNDER	0x462504d2	apple-a13
CPUFAMILY_ARM_FIRESTORM_ICESTORM	0x1b588bb3	apple-m1 (and apple-a14)

We'll probably have to hard-code most of those because we need LLVM to be buildable on much older versions of Xcode that don't know about newer CPUs (likely Xcode 9.3 soon, but now older even than that).

[keith]

Update to read CPU from sysctl

[keith]

Thanks for the tips! I left the default as generic here, but I totally take your point on defaulting to the newest and I'm happy to update if you feel strongly, lmk what you think

[jrtc27]

llvm/lib/Support/Host.cpp

1321

ARM only calls it cyclone, AArch64 allows both but apple-a7 is the canonical name (the comment above the cyclone alias states it's for old bitcode compatibility)

1327

Not sure this should be an assert? I think other implementations will fall back on generic on errors (e.g. the things that read /proc/cpuinfo will use "" on error for the file contents and that gets parsed as generic by the various default cases).

Also technically you need to check Length is still sizeof(Family) and not smaller (the other direction is an error), but nobody ever bothers so meh.

1335

Maybe a question for AArch64 maintainers about whether apple-a14 or apple-m1 should be used... they're the same thing from the backend's perspective just with different names. Shame the naming doesn't separate out the "generation" from the specific configuration like you see for other backends (apple-aN is almost that as it omits all the bionic etc marketing name fluff, except apple-m1 comes along and ruins that).

[ab]

In D119788#3331324, @keith wrote:

Thanks for the tips! I left the default as generic here, but I totally take your point on defaulting to the newest and I'm happy to update if you feel strongly, lmk what you think

I agree with Tim, this should default to the newest known one.

generic doesn't really make sense for Darwin anyway, the "oldest" sane default would probably be cyclone, apple-a12, or apple-m1, depending on the slice and OS

llvm/lib/Support/Host.cpp

1303

Looks like we have the same includes for computeHostNumPhysicalCores. Maybe move this to the top of the file, gated with just __APPLE__?

1335

Seems fine to stick to the apple-aNN names here. (we already have a similar situation with apple-sN)

[keith]

Code review improvements

llvm/lib/Support/Host.cpp

1321

I saw this comment:

// Support cyclone as an alias for apple-a7 so we can still LTO old bitcode.
def : ProcessorModel<"cyclone", CycloneModel, ProcessorFeatures.AppleA7,
                     [TuneAppleA7]>;

And thought that implied that the a7 name would be preferred to the "old" name for this case of case, wdyt?

1335

I felt like the m1 name would be preferred here even though they're aliases just because I assume since this is for host CPUs you're more likely to hit this on an m1 machine than something that has an a14, which might lead to some user confusion. For example if you run clang -march=native -### with this change, you see apple-m1 in the invocation, I would personally be surprised if I saw a14 there on my mac, even if they're the same.

[keith]

Update default to latest known CPU

[keith]

Fix typo

[keith]

Bump, I think I've covered everything here, let me know if not!

[ab]

Reading this again, I have a feeling defaulting to newest will come back to bite us (or, well, apple folks.) But we can reevaluate if we get to that. So, LGTM, thanks!

clang/lib/Driver/ToolChains/Arch/AArch64.cpp

 static bool
 getAArch64ArchFeaturesFromMarch(const Driver &D, StringRef March,
                                 const ArgList &Args,
                                 std::vector<StringRef> &Features) {
   std::string MarchLowerCase = March.lower();
   std::pair<StringRef, StringRef> Split = StringRef(MarchLowerCase).split("+");
 
   llvm::AArch64::ArchKind ArchKind = llvm::AArch64::parseArch(Split.first);
+  if (Split.first == "native")
+    ArchKind = llvm::AArch64::getCPUArchKind(llvm::sys::getHostCPUName().str());
   if (ArchKind == llvm::AArch64::ArchKind::INVALID ||
       !llvm::AArch64::getArchFeatures(ArchKind, Features))
     return false;
 
   // Enable SVE2 by default on Armv9-A.
   // It can still be disabled if +nosve2 is present.
   // We must do this early so that DecodeAArch64Features has the correct state
   if ((ArchKind == llvm::AArch64::ArchKind::ARMV9A ||

llvm/lib/Support/Host.cpp

 #ifdef __MVS__
 #include "llvm/Support/BCD.h"
 #endif
 #if defined(__APPLE__) && (!defined(__x86_64__))
 #include <mach/host_info.h>
 #include <mach/mach.h>
 #include <mach/mach_host.h>
 #include <mach/machine.h>
+#include <sys/param.h>
+#include <sys/sysctl.h>
 #endif
 #ifdef _AIX
 #include <sys/systemcfg.h>
 #endif
 
 #define DEBUG_TYPE "host-detection"
 
 //===----------------------------------------------------------------------===//
StringRef sys::getHostCPUName() {
   // Convert number to integer.
   Id = decodePackedBCD<uint16_t>(Id, false);
   // Check for vector support. It's stored in field CVTFLAG5 (offset 244),
   // bit CVTVEF (X'80'). The facilities list is part of the PSA but the vector
   // extension can only be used if bit CVTVEF is on.
   bool HaveVectorSupport = CVT[244] & 0x80;
   return getCPUNameFromS390Model(Id, HaveVectorSupport);
 }
-#elif defined(__APPLE__) && defined(__aarch64__)
-StringRef sys::getHostCPUName() {
-  return "cyclone";
-}
-#elif defined(__APPLE__) && defined(__arm__)
-StringRef sys::getHostCPUName() {
-  host_basic_info_data_t hostInfo;
-  mach_msg_type_number_t infoCount;
+#elif defined(__APPLE__) && (defined(__arm__) || defined(__aarch64__))
+#define CPUFAMILY_ARM_SWIFT 0x1e2d6381
+#define CPUFAMILY_ARM_CYCLONE 0x37a09642
+#define CPUFAMILY_ARM_TYPHOON 0x2c91a47e
+#define CPUFAMILY_ARM_TWISTER 0x92fb37c8
+#define CPUFAMILY_ARM_HURRICANE 0x67ceee93
+#define CPUFAMILY_ARM_MONSOON_MISTRAL 0xe81e7ef6
+#define CPUFAMILY_ARM_VORTEX_TEMPEST 0x07d34b9f
+#define CPUFAMILY_ARM_LIGHTNING_THUNDER 0x462504d2
+#define CPUFAMILY_ARM_FIRESTORM_ICESTORM 0x1b588bb3
 
-  infoCount = HOST_BASIC_INFO_COUNT;
-  mach_port_t hostPort = mach_host_self();
-  host_info(hostPort, HOST_BASIC_INFO, (host_info_t)&hostInfo,
-            &infoCount);
-  mach_port_deallocate(mach_task_self(), hostPort);
+StringRef sys::getHostCPUName() {
+  uint32_t Family;
+  size_t Length = sizeof(Family);
+  sysctlbyname("hw.cpufamily", &Family, &Length, NULL, 0);
 
-  if (hostInfo.cpu_type != CPU_TYPE_ARM) {
-    assert(false && "CPUType not equal to ARM should not be possible on ARM");
-    return "generic";
-  }
-  switch (hostInfo.cpu_subtype) {
-    case CPU_SUBTYPE_ARM_V7S:
-      return "swift";
-    default:;
-    }
-
-  return "generic";
+  switch (Family) {
+  case CPUFAMILY_ARM_SWIFT:
+  case CPUFAMILY_ARM_CYCLONE:
+    return "apple-a7";
+  case CPUFAMILY_ARM_TYPHOON:
+    return "apple-a8";
+  case CPUFAMILY_ARM_TWISTER:
+    return "apple-a9";
+  case CPUFAMILY_ARM_HURRICANE:
+    return "apple-a10";
+  case CPUFAMILY_ARM_MONSOON_MISTRAL:
+    return "apple-a11";
+  case CPUFAMILY_ARM_VORTEX_TEMPEST:
+    return "apple-a12";
+  case CPUFAMILY_ARM_LIGHTNING_THUNDER:
+    return "apple-a13";
+  case CPUFAMILY_ARM_FIRESTORM_ICESTORM:
+    return "apple-m1";
+  default:
+    // Default to the newest CPU we know about.
+    return "apple-m1";
 }
 #elif defined(_AIX)
 StringRef sys::getHostCPUName() {
   switch (_system_configuration.implementation) {
   case POWER_4:
     if (_system_configuration.version == PV_4_3)
       return "970";
     return "pwr4";
if (sched_getaffinity(0, CPU_ALLOC_SIZE(2048), DynAffinity) == 0) {
     CPU_FREE(DynAffinity);
     return NumCPUs;
   }
   return -1;
 }
 #elif defined(__linux__) && defined(__s390x__)
 int computeHostNumPhysicalCores() { return sysconf(_SC_NPROCESSORS_ONLN); }
 #elif defined(__APPLE__)
-#include <sys/param.h>
-#include <sys/sysctl.h>
-
 // Gets the number of *physical cores* on the machine.
 int computeHostNumPhysicalCores() {
   uint32_t count;
   size_t len = sizeof(count);
   sysctlbyname("hw.physicalcpu", &count, &len, NULL, 0);
   if (count < 1) {
     int nm[2];
     nm[0] = CTL_HW;