Previously, we saw a lot of crashes when SpiderMonkey 60 JIT was enabled and we ended up turning it off in SERVER-32683 (BF-7559, BF-7548, BF-7140, BF-6782). Now that we've upgraded to SpiderMonkey 91, this issue might be gone.

As part of this ticket, we want to investigate the possibility of turning JIT on by default.

We have one proof point that SpiderMonkey Baseline JIT was unintentionally enabled on master between SERVER-61008 (master@26bab13) and SERVER-66498 (master@13ec926). However, we didn't see any crashes related to JIT, except for BUILD-14966 (which was expected due to a notarization issue).

In addition, enabling Baseline JIT has shown a noticeable performance improvement for some performance tests (e.g., BF-25338), which justifies enabling it by default.

There are several options for SpiderMonkey JIT (e.g., Baseline JIT, ION JIT, etc.) As part of this ticket, we want to enable the Baseline JIT by default. But, it makes sense to also evaluate the impact of more aggressive JIT engines in SpiderMonkey 91 and check whether they cause crashes or not.