I thought on sparc64 GCC was configured with -mcpu=ultrasparc by default, so
adding this flag on the command like would not make much difference. If you use
'gcc -v' when compiling files, you'll see what -mcpu options are passed to it
by default.

If you want to test the code generated by GCC of v8 vs v9 instruction sets, you
should probably compile with:

gcc -mcpu=v8
gcc -mcpu=ultrasparc