At this point, the Higgs JIT is still quite simple and primitive compared to commercial JavaScript VMs, but nevertheless provides marked speedups relative to the interpreter on every benchmark I tested it on. I'm interested in finding the source code for the latest version of the Mozilla TraceMonkey shell (as well as instructions on how to build it) so that I can compare the performance of Higgs to another JavaScript tracing JIT. Previously, Higgs initialized every stack slot as soon as a function was called to make sure that stack frames were always in a consistent state when the garbage collector (GC) was called.