Firefox - log ionmonkey compilation and bailouts

Question

I can start Google Chrome with --js-flags="--trace-opt --trace-deopt" to get a log of what the V8 optimizer is compiling and what is falling out of the optimized execution, but is there anything comparable for Firefox IonMonkey?

Answer 1

SpiderMonkey has IONFLAGS environment variable (but not in the regular build, you have to build with ac_add_options --enable-jitspew to enable it, then run with IONFLAGS=help to see the available flags). It will probably take some time to learn how to use it though, since there is not much documentation.

For web developers work is underway on JIT support in the Performance tool, dubbed "JIT Coach", and I could only find

• the JIT opimizations panel (switch to Performance tab of the DevTools, enable "Show JIT Optimizations" in the cog-menu, switch to the Call Stack view, and find a frame with JIT info denoted with an (i) icon)
• and an accompanying document: JIT Optimization Strategies.

You can follow the dependencies of bug 1143804 to see the progress.