basilisp-lang / basilisp / #574

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coveralls-python

Improve the lookup speed for Keywords by pre-computing hash (#592)

This PR includes a change to pre-compute the hash of a Keyword a new instance is created. Keyword hashes are used as the lookup key for Keywords inside the intern cache. Keywords are also commonly used as map keys and in other collections requiring hashability, so having a pre-computed hash should help improve performance by not requiring repeated computations of the otherwise static hash.

The compiler now also uses the pre-computed Keyword hash to lookup Keywords directly from the intern cache, which should reduce the cost of repeated lookups (particularly if a function makes heavy use of keywords).

This change appears to have improved the lookup speed by around 9%.

Before these changes:

```
basilisp.user=> (import timeit)
<module 'timeit' from '/Users/christopher/.pyenv/versions/3.6.9/lib/python3.6/timeit.py'>

basilisp.user=> (timeit/timeit (fn [] :abc))
0.7336159450060222
```

Afterwards:

```
basilisp.user=> (import timeit)
<module 'timeit' from '/Users/christopher/.pyenv/versions/3.6.9/lib/python3.6/timeit.py'>

basilisp.user=> (timeit/timeit (fn [] :abc))
0.668459995999001
```

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