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Push array_gets through array_sets if they act on different constant indices. #5767

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TomAFrench opened this issue Aug 20, 2024 · 0 comments · Fixed by #5772
Closed

Push array_gets through array_sets if they act on different constant indices. #5767

TomAFrench opened this issue Aug 20, 2024 · 0 comments · Fixed by #5772
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enhancement New feature or request optimization

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@TomAFrench
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Looking at the conditional_1 program failure on #5762 I noticed that we're generating SSA with snippets of the form.

 v11060 = array_set mut [v8829, v8910, v8988, v9062, v9142, v9220, v9300, v9376, v9456, v9530, v9610, v9686, v9766, v9842, v9920, v10000, v10076, v10158, v10236, v10310, v10390, v10466, v10544, v10622, v10700, v10778, v10860, v10934, v11014, v11009, v11006, v11003], index u32 2⁵, value v11000
v11061 = array_get v11060, index u32 0
v11063 = array_get v11060, index u32 1
v11065 = array_get v11060, index u32 2
v11067 = array_get v11060, index u32 3
v11093 = array_get v11060, index u32 2⁵
v11099 = array_get v11060, index u32 29
v11104 = array_get v11060, index u32 30
v11109 = array_get v11060, index u32 31

It's clear that v11061 == v8829, etc. as the array_set only affects the index 32. We could then optimize out all of these array_gets using this knowledge.
@TomAFrench TomAFrench changed the title Push array_gets through array_sets if they act one different constant indices. Push array_gets through array_sets if they act on different constant indices. Aug 20, 2024
@TomAFrench TomAFrench added enhancement New feature or request optimization labels Aug 20, 2024
@jfecher jfecher mentioned this issue Aug 20, 2024
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github-merge-queue bot pushed a commit that referenced this issue Aug 20, 2024
@jfecher @TomAFrench
feat(optimization): Follow past array_sets when optimizing `array_g…
090501d 
…et`s (#5772)

# Description

## Problem\*

Resolves #5767

## Summary\*

Instead of checking if an array_get is from a constant array, we can
follow array_sets to find a previous constant array. If the index was
ever unknown we fail to optimize. If the index is known but changed by
an array set we fail as well instead of optimizing to the set value.
This is in case the side effect variables are different for the get &
set.

## Additional Context

I set an arbitrary maximum of 5 array_sets to check before giving up and
failing to find a constant array.

## Documentation\*

Check one:
- [x] No documentation needed.
- [ ] Documentation included in this PR.
- [ ] **[For Experimental Features]** Documentation to be submitted in a
separate PR.

# PR Checklist\*

- [x] I have tested the changes locally.
- [x] I have formatted the changes with [Prettier](https://prettier.io/)
and/or `cargo fmt` on default settings.

---------

Co-authored-by: Tom French <[email protected]>
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enhancement New feature or request optimization
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feat(optimization): Follow past array_sets when optimizing array_gets noir-lang/noir
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