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cmake
Jakub Klinkovský
Jakub Klinkovský

Reputation: 1362

How to exclude compile options for one target?

I have this in my top-level CMakeLists.txt:

set( CMAKE_CXX_FLAGS_RELEASE "-O3 -march=native -mtune=native -DNDEBUG" )

Now, I realized that there is one target for which -march=native -mtune=native should be excluded. What is the easiest way to do that? Obviously, I can set these options using target_compile_options() for all targets except for the one, but surely there is a less verbose way?

Upvotes: 3

Views: 2413

Answers (1)

Kevin
Kevin

Reputation: 18386

In modern CMake, manually manipulating the CMAKE_<LANG>_FLAGS_<CONFIG> variables is often discouraged. It is better to set these using add_compile_options() and add_compile_definitions(), and you can use generator expressions to control which options apply to the Debug or Release configurations.

Note: With this add_compile_options() syntax, separate the flags/options with a semicolon ; since you are using GCC; if you are using Visual Studio's VC++ compiler, spaces should work fine.

add_compile_definitions("$<$<CONFIG:RELEASE>:NDEBUG>")    
add_compile_options("$<$<CONFIG:RELEASE>:-O3;-march=native;-mtune=native>")

If you have some different Debug options also, you can add those:

add_compile_options(
    "$<$<CONFIG:RELEASE>:-O3;-march=native;-mtune=native>"
    "$<$<CONFIG:DEBUG>:-O2;-march=something-else>"
)

Then, your compilation flags will be accessible via the target property COMPILE_OPTIONS, and you can remove the unwanted flags for a specific target using string(REPLACE ...):

get_target_property(MyLib_COMPILE_OPTIONS MyLib COMPILE_OPTIONS)
if(MyLib_COMPILE_OPTIONS)
  string(REPLACE "-march=native" "" MyLib_COMPILE_OPTIONS "${MyLib_COMPILE_OPTIONS}")
  string(REPLACE "-mtune=native" "" MyLib_COMPILE_OPTIONS "${MyLib_COMPILE_OPTIONS}")
  set_target_properties(MyLib PROPERTIES COMPILE_OPTIONS "${MyLib_COMPILE_OPTIONS}")
endif()

Upvotes: 3

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