Add interface for querying physical hardware concurrency

Summary:
This will be used by ThinLTO to set the amount of backend
parallelism, which performs better when restricted to the number
of physical cores (on X86 at least, where getHostNumPhysicalCores is
currently defined). If not available this falls back to
thread::hardware_concurrency.

Note I didn't add to the thread class since that is a typedef to
std::thread where available.

Reviewers: mehdi_amini

Subscribers: beanz, llvm-commits, mgorny

Differential Revision: https://reviews.llvm.org/D25585

llvm-svn: 284180

diff --git a/llvm/include/llvm/Support/Threading.h b/llvm/include/llvm/Support/Threading.h
index 09b96df..7e4a289 100644 (file)
--- a/llvm/include/llvm/Support/Threading.h
+++ b/llvm/include/llvm/Support/Threading.h
@@ -115,6 +115,10 @@ namespace llvm {
     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

diff --git a/llvm/lib/Support/Threading.cpp b/llvm/lib/Support/Threading.cpp
index e8f5622..415c63f 100644 (file)
--- a/llvm/lib/Support/Threading.cpp
+++ b/llvm/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 @@ void llvm::llvm_execute_on_thread(void (*Fn)(void*), void *UserData,
 }
 
 #endif
+
+unsigned llvm::hardware_physical_concurrency() {
+  int NumPhysical = sys::getHostNumPhysicalCores();
+  if (NumPhysical == -1)
+    return thread::hardware_concurrency();
+  return NumPhysical;
+}

diff --git a/llvm/unittests/Support/CMakeLists.txt b/llvm/unittests/Support/CMakeLists.txt
index 9aef721..6ae2aed 100644 (file)
--- a/llvm/unittests/Support/CMakeLists.txt
+++ b/llvm/unittests/Support/CMakeLists.txt
@@ -40,6 +40,7 @@ add_llvm_unittest(SupportTests
   StringPool.cpp
   SwapByteOrderTest.cpp
   TargetParserTest.cpp
+  Threading.cpp
   ThreadLocalTest.cpp
   ThreadPool.cpp
   TimerTest.cpp

diff --git a/llvm/unittests/Support/Threading.cpp b/llvm/unittests/Support/Threading.cpp
new file mode 100644 (file)
index 0000000..30a3c74
--- /dev/null
+++ b/llvm/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