Posts Tagged ‘DevTools’

[JS-internals] Jit DevTools 0.0.1

June 18th, 2015 No comments


Nicolas B. Pierron via

Hello everybody,

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 [1] 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 [5].

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 [2] this early version from , or build it your-self by using the sources [3] with jpm tool [4].

Have fun, and enjoy.