The trace 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/js --args="-m -j -pn"
==== Benchmark your changes ====
cd SunSpider
./sunspider --args="-m -j -pn" --shell=../build_DBG.OBJ/js --run=30 --suite=sunspider-0.9.1
cd ..