Reduce compiled tdlib size

[salvogiangri]

I've noticed that the libtdjni.so lib compiled in my Android Studio project is slightly bigger than the prebuilt/TGX one (4MB less). Is there any way to optimize even more my build? Here's the CMake flags I'm currently using (took from Issue #77):

string(APPEND CMAKE_CXX_FLAGS "-std=c++14 -fno-omit-frame-pointer -ffunction-sections -fdata-sections -fno-exceptions -fno-rtti")
string(APPEND CMAKE_SHARED_LINKER_FLAGS "-Wl,--gc-sections -Wl,--exclude-libs,ALL")
# ...
add_custom_command(TARGET tdjni POST_BUILD
  COMMAND ${CMAKE_STRIP} --strip-debug --strip-unneeded $<TARGET_FILE:tdjni>)

build.gradle:

externalNativeBuild {
    cmake {
        version '3.18.1'
        targets "tdjni"
        arguments '-DCMAKE_BUILD_TYPE=MinSizeRel'
    }
}

[levlam]

You need to use also
string(APPEND CMAKE_CXX_FLAGS_MINSIZEREL " -flto=thin -Oz")

[levlam]

Also, the prebuilt version links libc++ dynamically, so it still be slighly less even after the change, but the total size of libtdjni and libc++ should be bigger after that.

[salvogiangri]

These flags had no effect unfortunately, I've also just noticed this warning during the build

> Task :app:stripDebugDebugSymbols
Unable to strip the following libraries, packaging them as they are: libtdjni.so.

CMakeOutput.log
CMakeError.log

The warning won't appear with no CMAKE flags+custom strip command set in the CMakeLists file

[salvogiangri]

So I managed to fix the app:stripDebugDebugSymbols error, for some strange reason I also had to add ndkVersion in my app module. unfortunately the two new flags you suggested still have no effect.

[levlam]

Could you recheck that the flags are appended to CMAKE_CXX_FLAGS_MINSIZEREL? I don't see them in CMake logs.

[salvogiangri]

I can see those flags in these files:
build.ninja
compile_commands.json

I noticed that the flags that actually shrink the lib are the SHARED_LINKER ones, CMAKE_CXX_FLAGS have no effect on the lib size. By adding ndkVersion in the app module I could remove the strip custom_command in CMake since it is now done at compile time via gradle with app:stripDebugDebugSymbols

[levlam]

No, the output confirms that there were no flags added. You need to add the line string(APPEND CMAKE_CXX_FLAGS_RELWITHDEBINFO " -flto=thin -Oz") before add_subdirectory(td).

[salvogiangri]

You meant CMAKE_CXX_FLAGS_MINSIZEREL right? I've moved the MinSizeRel flags before the add_subdirectory(td) and now the lib size has finally been reduced. Thank you again for your help, hoping I won't be bothering you again like I already did😅