Anthony Eid 35fd2dd9fc Speed up StreamingDiff::push_new part two (#57849)
Follow-up to #57772.

While comparing the `edit_file_tool_streaming/medium_insertions`
benchmark in Criterion and xctrace, I noticed the DP scoring loop was
spending most of its time on inlined `Matrix::get`/`Matrix::set` access
in `StreamingDiff::push_new`.

This changes the loop to split the previous and current score columns
once per DP column and then index those column slices directly. This
keeps the scoring algorithm the same, but hoists the column offset
calculation out of the inner loop and gives the compiler clearer
aliasing information between the immutable previous column and mutable
current column.

In xctrace, the hottest DP scoring line dropped from 10,407 samples
before to 9,409 samples after on
`edit_file_tool_streaming/medium_insertions`, and total
`StreamingDiff::push_new` leaf samples dropped from 10,800 to 9,822.

This is consistently faster in the end-to-end `edit_file_tool`
benchmark, and gives a small speed-up for the targeted workload without
changing the scoring algorithm.

### Results

Benchmarked with `release-fast` against a clean baseline using
Criterion’s `before_slice` baseline.

#### `streaming_diff_push_new`

| Fixture | Before median | After median | Change |
| --- | ---: | ---: | ---: |
| `tiny_function_rewrite` | `7.6317 ms` | `6.4951 ms` | 10.8% faster |
| `small_function_rewrite` | `45.961 ms` | `44.839 ms` | No significant
change |
| `medium_many_small_changes` | `99.694 ms` | `104.83 ms` | 5.2% slower
|
| `medium_insertions` | `95.909 ms` | `83.093 ms` | 13.5% faster |

#### `edit_file_tool_streaming`

| Fixture | Before median | After median | Change |
| --- | ---: | ---: | ---: |
| `tiny_function_rewrite` | `1.1110 ms` | `1.0617 ms` | 7.1% faster |
| `small_function_rewrite` | `2.4554 ms` | `2.2751 ms` | 7.1% faster |
| `medium_many_small_changes` | `87.272 ms` | `77.065 ms` | 11.5% faster
|
| `medium_insertions` | `92.469 ms` | `87.478 ms` | 5.9% faster |

The lower-level `streaming_diff_push_new` benchmark is mixed, but the
end-to-end `edit_file_tool_streaming` workload improves across all
fixtures.

Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [x] Tests cover the new/changed behavior
- [x] Performance impact has been considered and is acceptable

Release Notes:

- N/A or Added/Fixed/Improved ...
2026-05-27 19:33:04 +00:00
2026-04-30 11:10:14 +00:00
2026-05-27 18:17:59 +00:00
2026-05-27 18:17:59 +00:00
2026-01-22 23:57:26 +05:30
2026-05-27 18:17:59 +00:00
WIP
2023-12-14 09:25:14 -07:00
2026-04-29 10:27:47 +00:00
2026-02-03 20:31:02 -07:00
2025-02-04 09:02:59 -05:00
2025-02-04 09:02:59 -05:00
2026-01-06 12:49:51 -08:00
2025-10-27 13:27:59 -04:00
2025-10-17 18:58:14 +00:00
2026-03-17 16:34:35 +00:00
2026-04-29 10:27:47 +00:00
2026-05-27 16:27:18 +00:00

Zed

Zed CI

Welcome to Zed, a high-performance, multiplayer code editor from the creators of Atom and Tree-sitter.


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