From bb23a9b9f2c32a1557378fd2234273e705789eb9 Mon Sep 17 00:00:00 2001
From: Matt Clarkson <mattyclarkson@gmail.com>
Date: Thu, 30 Apr 2015 14:10:52 +0100
Subject: [PATCH] Compile with link time optimisation

Can provide speed improvements
---
 CMakeLists.txt | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 65d807d0..6a9a4493 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2,6 +2,7 @@ cmake_minimum_required (VERSION 2.8.11)
 project (benchmark)
 
 option(BENCHMARK_ENABLE_TESTING "Enable testing of the benchmark library." ON)
+option(BENCHMARK_ENABLE_LTO "Enable link time optimisation of the benchmark library." OFF)
 # Make sure we can import out CMake functions
 list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 
@@ -41,9 +42,25 @@ add_cxx_compiler_flag(-pedantic-errors)
 add_cxx_compiler_flag(-Wshorten-64-to-32)
 add_cxx_compiler_flag(-Wfloat-equal)
 add_cxx_compiler_flag(-Wzero-as-null-pointer-constant)
+
 # Release flags
 add_cxx_compiler_flag(-fno-strict-aliasing RELEASE)
 
+# Link time optimisation
+if (BENCHMARK_ENABLE_LTO)
+  add_cxx_compiler_flag(-flto)
+  if ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU")
+    find_program(GCC_AR gcc-ar)
+    if (GCC_AR)
+      set(CMAKE_AR ${GCC_AR})
+    endif()
+    find_program(GCC_RANLIB gcc-ranlib)
+    if (GCC_RANLIB)
+      set(CMAKE_RANLIB ${GCC_RANLIB})
+    endif()
+  endif()
+endif()
+
 add_cxx_compiler_flag(-Wthread-safety)
 if (HAVE_WTHREAD_SAFETY)
   add_definitions(-DHAVE_WTHREAD_SAFETY)