The splashscreen lib is currently built with LOW optimization.
This might be fine because it is not very performance critical.
But building it with SIZE optimization makes it 10-20 % smaller on some platforms which helps to reduce image size.
Results are from gcc 11.3 on Linux x86_64 / ppc64le / aarch64 . macOS uses XCode 15.4 .

current settings (LOW optimization) :
---------------------------------------------------
2.5M /aix_ppc64/jdk-opt/images/jdk/lib/libsplashscreen.so

468K /macosaarch64/jdk-opt/images/jdk/lib/libsplashscreen.dylib
1.6M /macosaarch64/jdk-opt/images/jdk/lib/libsplashscreen.dylib.dSYM
388K /macosintel64/jdk-opt/images/jdk/lib/libsplashscreen.dylib
1.5M /macosintel64/jdk-opt/images/jdk/lib/libsplashscreen.dylib.dSYM

368K /linux_aarch64/jdk-opt/images/jdk/lib/libsplashscreen.so
1.7M /linux_aarch64/jdk-opt/images/jdk/lib/libsplashscreen.debuginfo
376K /linux_alpine_x86_64/jdk-opt/images/jdk/lib/libsplashscreen.so
1.8M /linux_alpine_x86_64/jdk-opt/images/jdk/lib/libsplashscreen.debuginfo
500K /linux_ppc64le/jdk-opt/images/jdk/lib/libsplashscreen.so
1.7M /linux_ppc64le/jdk-opt/images/jdk/lib/libsplashscreen.debuginfo
364K /linux_x86_64/jdk-opt/images/jdk/lib/libsplashscreen.so
1.7M /linux_x86_64/jdk-opt/images/jdk/lib/libsplashscreen.debuginfo


new settings (SIZE optimization) :
--------------------------------------------------
2.1M /aix_ppc64/jdk-dev-opt/images/jdk/lib/libsplashscreen.so

404K /macosaarch64/jdk-dev-opt/images/jdk/lib/libsplashscreen.dylib
1.5M /macosaarch64/jdk-dev-opt/images/jdk/lib/libsplashscreen.dylib.dSYM
316K /macosintel64/jdk-dev-opt/images/jdk/lib/libsplashscreen.dylib
1.4M /macosintel64/jdk-dev-opt/images/jdk/lib/libsplashscreen.dylib.dSYM

372K /linux_aarch64/jdk-dev-opt/images/jdk/lib/libsplashscreen.so
1.5M /linux_aarch64/jdk-dev-opt/images/jdk/lib/libsplashscreen.debuginfo
304K /linux_alpine_x86_64/jdk-dev-opt/images/jdk/lib/libsplashscreen.so
1.5M /linux_alpine_x86_64/jdk-dev-opt/images/jdk/lib/libsplashscreen.debuginfo
376K /linux_ppc64le/jdk-dev-opt/images/jdk/lib/libsplashscreen.so
1.4M /linux_ppc64le/jdk-dev-opt/images/jdk/lib/libsplashscreen.debuginfo
304K /linux_x86_64/jdk-dev-opt/images/jdk/lib/libsplashscreen.so
1.4M /linux_x86_64/jdk-dev-opt/images/jdk/lib/libsplashscreen.debuginfo

On Linux aarch64 only the debuginfo shrinks but the lib stays about the same in size. Maybe -Os does not work as well on this platform.
Other UNIX platforms have a reduction by ~ 10-20 % .
For Windows, LOW and SIZE optimization have currently the same O - flags so no reduction.