[Support] Get correct number of physical cores on Apple Silicon

[steven_wu]

Summary

Fix a bug that computeHostNumPhysicalCores is fallback to default
unknown when building for Apple Silicon macs.

rdar://80533675

[dexonsmith]

llvm/lib/Support/Host.cpp

1407

Should this be checking if the target is for macOS? Or does is the functionality below available on all platforms?

1415

Is this available on iOS?

1420

Is this available on iOS?

[steven_wu]

llvm/lib/Support/Host.cpp

1415

Yes, they are in iOS public SDK. I checked before I apply the fix.

[dexonsmith]

llvm/lib/Support/Host.cpp

1407

Great -- I had assumed this was an intentional iOS-related carve out, but looking back:

• 7943fecee8726 added it for linux (on x86)
• db46b7d217ed4 added it for darwin (on x86)

and it seems like the "x86" part was probably just cargo-culted from the Linux side.

[steven_wu]

llvm/lib/Support/Host.cpp

1407

Let me see if I can turn on Host.cpp test for AS.

[thakis]

This breaks tests on m1 bots: http://45.33.8.238/macm1/13971/step_11.txt

Please take a look and revert for now if it takes a while to fix.

llvm/lib/Support/Host.cpp

if (sched_getaffinity(0, CPU_ALLOC_SIZE(2048), DynAffinity) == 0) {
     int NumCPUs = CPU_COUNT(DynAffinity);
     CPU_FREE(DynAffinity);
     return NumCPUs;
   }
   return -1;
 }
 #elif defined(__linux__) && defined(__s390x__)
 int computeHostNumPhysicalCores() { return sysconf(_SC_NPROCESSORS_ONLN); }
-#elif defined(__APPLE__) && defined(__x86_64__)
+#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;
     nm[1] = HW_AVAILCPU;
     sysctl(nm, 2, &count, &len, NULL, 0);
     if (count < 1)
       return -1;
   }
   return count;
 }
 #elif defined(__MVS__)
 int computeHostNumPhysicalCores() {
   enum {