hi
i've rebuild irrlicht 1.8.1 with TDM-GCC 4.7.1 and with some compiler tweaking , i got irrlicht.dll = 2.9mb instead of the usual 6mb
and after upx it i got only 765kb !
ok the trick is : i i choose Win32 -Release -fast math -dll project
add -msse2 -mfpmath=sse -ffast-math -ffunction-sections -fdata-sections -Os to the compiler options (if you remove sse2 switchs you may get less size)
add -gc-sections to the linker options .
thats all