How do I enable link time optimization (LTO) with CMake?

Question

I have the most recent cmake build and trying all build configurations (Debug, MinSizeRel, RelWithDebugInfo, Release, General) I see nowhere (text search) in generated makefiles

Answer 1

Yep, according to source code there are no support for LTO for gcc/clang compilers. They have some support for Intel compiler only.

I have some grep output for cmake 3.4.3:

grep -HiR 'INTERPROCEDURAL_OPTIMIZATION' *
Help/manual/cmake-properties.7.rst:  
/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst:  
/prop_dir/INTERPROCEDURAL_OPTIMIZATION
Help/manual/cmake-properties.7.rst:  
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION_CONFIG
Help/manual/cmake-properties.7.rst:  
/prop_tgt/INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION.rst:INTERPROCEDURAL_OPTIMIZATION
Help/prop_dir/INTERPROCEDURAL_OPTIMIZATION_CONFIG.rst:INTERPROCEDURAL_OPTIMIZATION_GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION"))
Source/cmGeneratorTarget.cxx:          
"INTERPROCEDURAL_OPTIMIZATION", config))
Source/cmMakefileLibraryTargetGenerator.cxx: 
if(this->GetFeatureAsBool("INTERPROCEDURAL_OPTIMIZATION") &&
Tests/IPO/CMakeLists.txt:set_property(DIRECTORY PROPERTY
INTERPROCEDURAL_OPTIMIZATION 1)

As you can see we have only Intel platform module.

So I have created feature request for this extremely useful feature: https://cmake.org/Bug/view.php?id=15939