Add interface to compute number of physical cores on host system

Summary:
For now I have only added support for x86_64 Linux, but other systems
can be added incrementally.

This is to be used for setting the default parallelism for ThinLTO
backends (instead of thread::hardware_concurrency which includes
hyperthreading and is too aggressive). I'll send this as a follow-on
patch, and it will fall back to hardware_concurrency when the new
getHostNumPhysicalCores returns -1 (when not supported for a given
host system).

I also added an interface to MemoryBuffer to force reading a file
as a stream - this is required for /proc/cpuinfo which is a special
file that looks like a normal file but appears to have 0 size.
The existing readers of this file in Host.cpp are reading the first
1024 or so bytes from it, because the necessary info is near the top.
But for the new functionality we need to be able to read the entire
file. I can go back and change the other readers to use the new
getFileAsStream as a follow-on patch since it seems much more robust.

Added a unittest.

Reviewers: mehdi_amini

Subscribers: beanz, mgorny, llvm-commits, modocache

Differential Revision: https://reviews.llvm.org/D25564

llvm-svn: 284138

2 files changed, 48 insertions, 0 deletions

diff --git a/llvm/unittests/Support/CMakeLists.txt b/llvm/unittests/Support/CMakeLists.txt
index 25c5dec80c1..9aef7210b1f 100644
--- a/llvm/unittests/Support/CMakeLists.txt
+++ b/llvm/unittests/Support/CMakeLists.txt
@@ -19,6 +19,7 @@ add_llvm_unittest(SupportTests
   ErrorTest.cpp
   ErrorOrTest.cpp
   FileOutputBufferTest.cpp
+  Host.cpp
   LEB128Test.cpp
   LineIteratorTest.cpp
   LockFileManagerTest.cpp
diff --git a/llvm/unittests/Support/Host.cpp b/llvm/unittests/Support/Host.cpp
new file mode 100644
index 00000000000..1fb0bc73314
--- /dev/null
+++ b/llvm/unittests/Support/Host.cpp
@@ -0,0 +1,47 @@
+//========- unittests/Support/Host.cpp - Host.cpp 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/Host.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Triple.h"
+
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+class HostTest : public testing::Test {
+  Triple Host;
+  SmallVector<std::pair<Triple::ArchType, Triple::OSType>, 4> SupportedArchAndOSs;
+
+protected:
+  bool isSupportedArchAndOS() {
+    if (is_contained(SupportedArchAndOSs, std::make_pair(Host.getArch(), Host.getOS())))
+      return true;
+
+    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.
+    SupportedArchAndOSs.push_back(std::make_pair(Triple::x86_64, Triple::Linux));
+  }
+};
+
+TEST_F(HostTest, NumPhysicalCores) {
+  int Num = sys::getHostNumPhysicalCores();
+
+  if (isSupportedArchAndOS())
+    ASSERT_GT(Num, 0);
+  else
+    ASSERT_EQ(Num, -1);
+}