ZJIT: Optimize opt_aref

[k0kubun]

opt_aref shows up as the top "not optimized instructions" on lobsters, which means we often use dynamic dispatch for #[] method calls.

We should:

1. Check which classes are used by opt_aref but not specialized by try_rewrite_aref
   • I bet most of them are Hash on Rails benchmarks, and some Integer on optcarrot, but it's the kind of thing to be confirmed here.
2. Optimize the un-optimized classes that appear most frequently

[tekknolagi]

@aidenfoxivey is looking into Array#[] with fixnum which showed up in liquid-render, I think

[aidenfoxivey]

@aidenfoxivey is looking into Array#[] with fixnum which showed up in liquid-render, I think

Thanks @tekknolagi - would a separate sub issue here be advisable?

[tekknolagi]

yes

[k0kubun]

I thought Array was already covered, but it seems like I overlooked that it's limited to if array_obj.is_frozen(). So, yes, it'd be nice to optimize Array#[].

[k0kubun]

It looks like people want more fine-grained issues than this with regard to opt_aref, so I broke up the remaining tasks into:

• ZJIT: Specialize #[] into ArrayArefFixnum if a profiled type is Array #792
• ZJIT: Specialize #[] into an rb_hash_aref call if a profiled type is Hash #793

Closing.