Index: llvm/trunk/include/llvm/Support/Threading.h
===================================================================
--- llvm/trunk/include/llvm/Support/Threading.h
+++ llvm/trunk/include/llvm/Support/Threading.h
@@ -115,6 +115,10 @@
     TsanHappensAfter(&flag);
 #endif
   }
+
+  /// Get the amount of currency based on physical cores, if available for the
+  /// host system, otherwise falls back to thread::hardware_concurrency().
+  unsigned hardware_physical_concurrency();
 }
 
 #endif
Index: llvm/trunk/lib/Support/Threading.cpp
===================================================================
--- llvm/trunk/lib/Support/Threading.cpp
+++ llvm/trunk/lib/Support/Threading.cpp
@@ -15,6 +15,7 @@
 #include "llvm/Support/Threading.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/Atomic.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/Mutex.h"
 #include "llvm/Support/thread.h"
 #include <cassert>
@@ -116,3 +117,10 @@
 }
 
 #endif
+
+unsigned llvm::hardware_physical_concurrency() {
+  int NumPhysical = sys::getHostNumPhysicalCores();
+  if (NumPhysical == -1)
+    return thread::hardware_concurrency();
+  return NumPhysical;
+}
Index: llvm/trunk/unittests/Support/CMakeLists.txt
===================================================================
--- llvm/trunk/unittests/Support/CMakeLists.txt
+++ llvm/trunk/unittests/Support/CMakeLists.txt
@@ -40,6 +40,7 @@
   StringPool.cpp
   SwapByteOrderTest.cpp
   TargetParserTest.cpp
+  Threading.cpp
   ThreadLocalTest.cpp
   ThreadPool.cpp
   TimerTest.cpp
Index: llvm/trunk/unittests/Support/Threading.cpp
===================================================================
--- llvm/trunk/unittests/Support/Threading.cpp
+++ llvm/trunk/unittests/Support/Threading.cpp
@@ -0,0 +1,25 @@
+//===- unittests/Threading.cpp - Thread tests -----------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Threading.h"
+#include "llvm/Support/thread.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(Threading, PhysicalConcurrency) {
+  auto Num = hardware_physical_concurrency();
+  // Since Num is unsigned this will also catch us trying to
+  // return -1.
+  ASSERT_LE(Num, thread::hardware_concurrency());
+}
+
+} // end anon namespace