Add computeHostNumPhysicalCores() implementation for Darwin

[tejohnson]

lib/Support/Host.cpp

1237

Is this true only for x86?

[mehdi_amini]

lib/Support/Host.cpp

1237

The syscall should work on every Apple Darwin platform, but I haven't a build of LLVM that runs on a device to validate it right now, I can ifdef on X86 as well for now.

[mehdi_amini]

Haven't tested other platform than x86_64 right now, add this as conditional compilation.

[tejohnson]

LGTM Thanks!

lib/Support/Host.cpp

for (auto &Line : strs) {
     if (CurPhysicalId != -1 && CurCoreId != -1) {
       UniqueItems.insert(std::make_pair(CurPhysicalId, CurCoreId));
       CurPhysicalId = -1;
       CurCoreId = -1;
     }
   }
   return UniqueItems.size();
 }
+#elif defined(__APPLE__) && defined(__x86_64__)
+#include <sys/param.h>
+#include <sys/sysctl.h>
+
+// Gets the number of *physical cores* on the machine.
+static 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;
+}
 #else
 // On other systems, return -1 to indicate unknown.
 static int computeHostNumPhysicalCores() { return -1; }
 #endif
 
 int sys::getHostNumPhysicalCores() {
   static int NumCores = computeHostNumPhysicalCores();
   return NumCores;

unittests/Support/Host.cpp

bool isSupportedArchAndOS() {
 
     return false;
   }
 
   HostTest() {
     Host.setTriple(Triple::normalize(sys::getProcessTriple()));
 
     // Initially this is only testing detection of the number of
-    // physical cores, which is currently only supported for
-    // x86_64 Linux.
+    // physical cores, which is currently only supported/tested for
+    // x86_64 Linux and Darwin.
     SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::Linux));
+    SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::Darwin));
   }
 };
 
 TEST_F(HostTest, NumPhysicalCores) {
   int Num = sys::getHostNumPhysicalCores();
 
   if (isSupportedArchAndOS())
     ASSERT_GT(Num, 0);
   else
     ASSERT_EQ(Num, -1);
 }