Question about Compile process?

[Keivan]

When I use compiler flags (even -O2), using gcc or icc, to compile IV, there is a significant difference in the size of "libUnidrawhines.so.3.0.3" and " libIVhines.so.3.0.3", compared to the version that compiled without flags.
without flags --> libIVhines.so.3.0.3=7.9mb and libUnidrawhines.so.3.0.3=5.7mb
with flag -O2 --> libIVhines.so.3.0.3=2.6mb and libUnidrawhines.so.3.0.3=1.6mb
If I do not use flag, program automatically uses "-O2 -g" glags -->but why, when they use the same flag, they differ in size?
Is this OK?

[hines]

-g adds debugging information