Enabling -O4 (link-time optimization) only if compiler/linker support it.
- The -O4 option requires the linker to have bitcode support, currently for
clang this means using the gold linker and the LLVM-gold plugin:
http://llvm.org/docs/GoldPlugin.html.
- Otherwise you get (confusing) 'file format not recognised' errors ala:
http://llvm.org/bugs/show_bug.cgi?id=9897.
- Adding explicit check for LTO support as at least some package installs of
clang on linux do not use the gold linker by default.
Change-Id: I2a4c670e470d9b48da2a15b7e91a59fb4ad3e8ad
diff --git a/CMakeLists.txt b/CMakeLists.txt
index e3fcd19..c3b536b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -614,7 +614,17 @@
ENDIF (${BUILD_ANDROID})
ENDIF (CMAKE_COMPILER_IS_GNUCXX)
IF ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
- SET(CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -O4")
+ # Use of -O4 requires use of gold linker & LLVM-gold plugin, which might
+ # well not be present / in use and without which files will compile, but
+ # not link ('file not recognized') so explicitly check for support
+ INCLUDE(CheckCXXCompilerFlag)
+ CHECK_CXX_COMPILER_FLAG("-O4" HAVE_LTO_SUPPORT)
+ IF (HAVE_LTO_SUPPORT)
+ MESSAGE(STATUS "Enabling link-time optimization (-O4)")
+ SET(CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -O4")
+ ELSE()
+ MESSAGE(STATUS "Compiler/linker does not support link-time optimization (-O4), disabling.")
+ ENDIF (HAVE_LTO_SUPPORT)
ENDIF()
ENDIF (CMAKE_BUILD_TYPE STREQUAL "Release")
