Scala.js also uses GCC, of course. However, though it's definitely great at shaving off code size, we found that it can have a (sometimes significant) negative

Scala.js also uses GCC, of course. However, though it's definitely great at shaving off code size, we found that it can have a (sometimes significant) negative impact on runtime performance. Also, we seem to run into correctness bugs more often that we would like. I guess we are really stressing it.