fix inline caching deoptimization

[Uzlopak]

According to deoptigate, there are two inline caching issues.

This one fixes one of them.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[kibertoad]

@Uzlopak After #17 is merged, can you post benchmark results before and after this change?

[kibertoad]

@Uzlopak Can you pull latest master into this branch before running benchmark?

[Uzlopak]

Actually this benchmark is not representative. Will open an Issue.

[Uzlopak]

This PR does not have an effect on the performance currently. The hot path is still searchstream.

Probably if we optimize searchstream further more it could have an effect. :/

[kibertoad]

@Uzlopak Actually, I'm not sure we need all of this change, the way I read the report, it is unhappy due to ev being initialized as undefined and then changed into a string, and then being used as a key. Can you replace it just with a new const variable and see if that also addresses the cache deoptimization?

[kibertoad]

However, your approach still should be more efficient, as it replaces monomorphic variable with just a constant, which should be more predictable. Let's go with your implementation.

[kibertoad]

Can we drop ev from line 142 now? I think it should not be used anymore

[Uzlopak]

I removed the ev instantiation :)