Nicolas B. Pierron via lists.mozilla.org
I am please to do an early announce a new tool named Jit DevTools.
This new tool is an addon which mostly target Jit developers. It uses the recently added Debugger.onIonCompilation hook to display the latest MIR  and LIR graphs within the dev tools.
To use this tool, go to a web page, and open the Jit DevTools panel, then wait until a function got compiled.
Once a function is compiled, you can select a compiled script, which will display the MIR graph of the compilation. If you need to, you can also have a look at the LIR graph. The output is similar to the one rendered with iongraph .
By selecting any inlined script, the background of the block titles will change color, if the block correspond to the inlined instance. This feature is quite useful to identify how a function plays in a compiled script.
You might find this tool quite handy to use for the following use cases: - Investigating DOM optimization. - Investigating jsperf issues. - Comparing function implementations, and impacts on the generated code.
This addon works on optimized builds, and even with parallel compilation enabled.
You can download  this early version from http://people.mozilla.org/~npierron/jit-dev-tools/ , or build it your-self by using the sources  with jpm tool .
Have fun, and enjoy.
 http://people.mozilla.org/~npierron/jit-dev-tools/jit-dev-tools-0.0.1.png  http://people.mozilla.org/~npierron/jit-dev-tools/jit-dev-tools-0.0.1.xpi  https://github.com/nbp/jit-dev-tools/  https://developer.mozilla.org/en-US/Add-ons/SDK/Tools/jpm  https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Hacking_Tips#Using_IonMonkey_spew_%28JS_shell%29