How to override the Optimization level for the Release and Debug build.

[AndreaCatania]

I would like to be able to turn the optimization level to Od, for release builds, because of what mentioned here:

Unreal Engine has two type of compilation targets DebugGame and Development. When compiling in DebugGame, despite the name, the produced binary is not a target Debug but it's still target Release but without optimizations.

I've read it's not really possible to control the optimization level using the configuration flags.
I also tried by specifying it on the flags using the following code, but didn't work:

			cmakeOptions += " -DCMAKE_C_FLAGS_RELEASE=\"/GS /Od /Ob0 /RTC1\" ";
			cmakeOptions += " -DCMAKE_CXX_FLAGS_RELEASE=\"/GS /Od /Ob0 /RTC1\" ";
			cmakeOptions += " -DCMAKE_C_FLAGS=\"/GS /Od /Ob0 /RTC1\" ";
			cmakeOptions += " -DCMAKE_CXX_FLAGS=\"/GS /Od /Ob0 /RTC1\" ";

I wonder what's the be way to add this feature in Jolt. Do you think an IF condition here is ok?

Something like this:

if (DEBUG_RELEASE)
    set(CMAKE_CXX_FLAGS_RELEASE "/GS /Od /Ob0 /RTC1")
else()
    set(CMAKE_CXX_FLAGS_RELEASE "/GS- /Gy /O2 /Oi /Ot")
endif()

[jrouwe]

If Unreal uses a config called DebugGame then I'd expect you to need to override CMAKE_CXX_FLAGS_DEBUGGAME instead of CMAKE_CXX_FLAGS_RELEASE.

[AndreaCatania]

Unreal doesn't use CMake to build the engine and the game. It uses the Unreal Build Tool, written in C#. Jolt is build by unreal, using CMake and then the produced binary is linked.

The cmakeOptions, you see above, is used to configure the Jolt build.

The idea I have in mind is to add an additional config flag to jolt's CMakeList, to control the optimization level, so the produced binary can be debugged. (I've already tried changing the opt level manually by modifying the CMakList, and it works. Changing optimization level allows me to debug the jolt code from unreal. I'm just not sure what implementation you prefer, to allow me configuring it from the Unreal Build Tool).

[jrouwe]

In that case you can use OVERRIDE_CXX_FLAGS to skip setting the cxx flags from Jolt's CMakeLists.txt so that you can set it yourself (note this used to work for clang only, I just submitted a fix that makes this work for MSVC too).

[AndreaCatania]

That's perfect, I'll try it tomorrow. Thanks!!

[AndreaCatania]

@jrouwe This works perfectly, thanks!

Here the code I've used to enable it:

cmakeOptions += " -DOVERRIDE_CXX_FLAGS=OFF ";
cmakeOptions += " -DCMAKE_CXX_FLAGS_RELEASE=\"/GS /Od /Ob0 /RTC1\" ";

I would have expected to ENABLE the override using OVERRIDE_CXX_FLAGS=ON and not to disable it, since from the game project prospective I'm overriding what Jolt is providing. Other than that it works really well!

[jrouwe]

I would have expected to ENABLE the override using OVERRIDE_CXX_FLAGS=ON

That's unfortunately a breaking change, which is something I try to avoid as much as possible.

[AndreaCatania]

Yeah, that's fine. No need to change it, it works really well already.