Replace Hashmaps with FxHashmaps or another data structure

[Ethan-000]

Problem

In some programs hashmaps is taking a lot of time

below is the flamegraph of the tally circuit

Happy Case

FxHashmaps is what the rust compiler uses internally, which should speed it up

Alternatives Considered

or another datastructure

Additional Context

No response

Would you like to submit a PR for this Issue?

Maybe

Support Needs

No response

[Ethan-000]

its not improving as much as id think

hashmap

fxhash

[jfecher]

It's a bit of an improvement still I suppose, and probably not hard to implement. Did you replace the HashMaps of that one function or all through SSA / the compiler?

(edit: there's a PR now)

[kevaundray]

We don't have a tracking issue for benchmarks so putting it here: I wonder how much time we are spending in the arena, here:

noir/crates/arena/src/lib.rs

Line 7 in df9f09e

pub use generational_arena::{Arena, Index};

If its a lot, we could replace that with something simpler like la-arena which should be faster as we are not using the generational component of generational-arena

[jfecher]

We can just replace the arenas with Vecs honestly. We never delete elements anyway