[CMake] overriding -03 -DNDEBUG Release flags

[Mark Ferry]

Have just worked through this and I think in short there is no *good*
way.

The method I decided to live with is caching the CFLAGS in the
toolchain file.

If you don't have a custom toolchain file for that project, create one.
Assuming you're using a GNU-derived toolchain try this:

    set(CMAKE_C_FLAGS_RELEASE "-O2" CACHE STRING "Some description")
    include(Compiler/GNU)

Pass the toolchain file to cmake:

cmake -DCMAKE_TOOLCHAIN_FILE=/path/to/my/toolchain-file.cmake ...

The downside is you can no longer change the C_FLAGS from a cmake UI
(like ccmake) though you *can* change them from the command line.
 ( cmake -DCMAKE_C_FLAGS_RELEASE=... )

What doesn't work and why:

 * Setting CMAKE_CFLAGS_RELEASE in a CMakeLists.txt
   -> Obviously. It's too late, we're past toolchain
   determination and try_compile

 * Setting CMAKE_CFLAGS_RELEASE_INIT in a toolchain file
   -> GNU compiler determination appends -O3 and -NDEBUG

ciao
  Mark

On Mon, 10 Sep 2018 14:34:26 +0200, Stéphane Ancelot wrote:
> Hi,
> 
> In one project I need to compile with -O2 option , how to set it and remove
> -O3 -DNDEBUG flags for this project ?
> 
> Regards,
> 
> Steph
> 
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