The jit-tests are pretty quick, and should give you an idea if you've gotten something wrong. Assuming nothing goes wrong, try the ref-tests:
tests/jstests.py build_DBG.OBJ/dist/bin/js --args="-m -n"
==== Benchmark your changes ====
cd SunSpider
./sunspider --args="-m -n" --shell=../build_DBG.OBJ/dist/bin/js --run=30 --suite=sunspider-0.9.1
cd ..