Options to disable specific optimizations in Ion?

[Terrence Lim]

I am curious whether there are any options for the 'js' to disable specific Ion
optimizations, e.g.,typing etc, for all the optimization options or not. I know there are options for some optimizations, but I am wondering whether we have full control of "all" the optimizations without actually modifying the Ion compiler source code.

[tri...@mozilla.com]

On Thursday, August 25, 2022 at 10:21:20 PM UTC-4, heuich...@gmail.com wrote:
> I am curious whether there are any options for the 'js' to disable specific Ion
> optimizations, e.g.,typing etc, for all the optimization options or not. I know there are options for some optimizations, but I am wondering whether we have full control of "all" the optimizations without actually modifying the Ion compiler source code.

It would be better to ask this in #spidermonkey on Element. (I am not a spidermonkey engineer)

We have a number of options here: https://searchfox.org/mozilla-central/source/js/src/jit/JitOptions.h#40 that exist for fuzzing only AFAICT, in the sense that they can only be toggled via the JS shell. (At least for the two I spot-checked.) However it probably wouldn't be too much effort to create a local patch that wires these flags up to a preference, so the local modifications are relatively small.

-tom