compile time

matteo@raver:/tmp/zlib-1.2.8$ CFLAGS=-O0 ./configure >/dev/null ; make -s clean ; time make -s

real    0m3.174s
user    0m2.504s
sys     0m0.284s
matteo@raver:/tmp/zlib-1.2.8$ CFLAGS=-O1 ./configure >/dev/null ; make -s clean ; time make -s

real    0m4.572s
user    0m3.876s
sys     0m0.324s
matteo@raver:/tmp/zlib-1.2.8$ CFLAGS=-O2 ./configure >/dev/null ; make -s clean ; time make -s

real    0m6.177s
user    0m5.412s
sys     0m0.368s
matteo@raver:/tmp/zlib-1.2.8$ CFLAGS=-O3 ./configure >/dev/null ; make -s clean ; time make -s

real    0m7.488s
user    0m6.708s
sys     0m0.392s
matteo@raver:/tmp/zlib-1.2.8$ CFLAGS=-Ofast ./configure >/dev/null ; make -s clean ; time make -s

real    0m7.236s
user    0m6.428s
sys     0m0.392s
matteo@raver:/tmp/zlib-1.2.8$