[Support] Move getHostNumPhysicalCores to Threading.h

This change is focussed on simplifying `Support/Host.h` to only do
target detection. In this case, this function is close in usage to
existing functions in `Support/Threading.h`, so I moved it into there.
The function is also renamed to `llvm::get_physical_cores()` to match
the style of threading's functions.

The big change here is that now if you have threading disabled,
`llvm::get_physical_cores()` will return -1, as if it had not been able
to work out the right info. This is due to how Threading.cpp includes
OS-specific code/headers. This seems ok, as if threading is disabled,
LLVM should not need to know the number of physical cores.

Differential Revision: https://reviews.llvm.org/D137836

1 files changed, 6 insertions, 3 deletions

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index bd954fd..910437c 100644
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/lib/Support/Threading.cpp
@@ -14,7 +14,7 @@
 #include "llvm/Support/Threading.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/Config/config.h"
-#include "llvm/Support/Host.h"
+#include "llvm/Config/llvm-config.h"
 
 #include <cassert>
 #include <errno.h>
@@ -45,13 +45,16 @@ unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
   return 1;
 }
 
+// Unknown if threading turned off
+int llvm::get_physical_cores() { return -1; }
+
 #else
 
 static int computeHostNumHardwareThreads();
 
 unsigned llvm::ThreadPoolStrategy::compute_thread_count() const {
-  int MaxThreadCount = UseHyperThreads ? computeHostNumHardwareThreads()
-                                       : sys::getHostNumPhysicalCores();
+  int MaxThreadCount =
+      UseHyperThreads ? computeHostNumHardwareThreads() : get_physical_cores();
   if (MaxThreadCount <= 0)
     MaxThreadCount = 1;
   if (ThreadsRequested == 0)