annotate .arcconfig @ 51425:7c6d0b9dde37

rust-index: improve phase computation speed

While less memory efficient, using an array is *much* faster than using a
HashMap, especially with the default hasher. It even makes the code simpler,
so I'm not really sure what I was thinking in the first place, maybe it's more
obvious now.

This fix a significant performance regression when using the rust version of the
code. (however, the C code still outperform rust on this operation)

hg perf::phases on mozilla-try-2023-03-22
- 6.6.3:  0.451239 seconds
- before: 0.982495 seconds
- after:  0.265347 seconds
- C code: 0.183241 second

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