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Sep 30, 2020
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Perf triage this week #1539

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22 changes: 10 additions & 12 deletions draft/2020-09-30-this-week-in-rust.md
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Expand Up @@ -89,21 +89,19 @@ If you are a Rust project owner and are looking for contributors, please submit

## Rust Compiler Performance Triage

* [2020-09-21](https://github.com/rust-lang/rustc-perf/blob/master/triage/2020-09-21.md):
2 Regressions, 5 Improvements, 4 Mixed
* [2020-09-28](https://github.com/rust-lang/rustc-perf/blob/master/triage/2020-09-28.md):
0 Regressions, 1 Improvements, 3 Mixed

This was the first week of semi-automated perf triage, and thank goodness:
There was a lot going on. Most regressions are either quite small or already
have a fix published.

[#72412](https://github.com/rust-lang/rust/issues/72412) is probably the most
interesting case. It fixes a pathological problem involving nested closures by
adding cycle detection to what seems to be a relatively hot part of the code.
As a result, most users will see a slight [compile-time
regression](https://perf.rust-lang.org/compare.html?start=2c69266c0697b0c0b34abea62cba1a1d3c59c90c&end=fdc3405c20122fd0f077f5a77addabc873f20e4c&stat=task-clock)
for their crates.
Most significant changes this week came in response to regressions discussed in
last week's triage report. Curious readers may be interested in
[#77058](https://github.com/rust-lang/rust/issues/77058), in which the removal
of a single field from a struct caused a 25% decrease in wall-times for one
seemingly unrelated benchmark, or
[#76986](https://github.com/rust-lang/rust/issues/76986), an ABI change that
should be a pretty clear win but seems to have mixed results.

See the [full report](https://github.com/rust-lang/rustc-perf/blob/master/triage/2020-09-21.md) for more.
See the [full report](https://github.com/rust-lang/rustc-perf/blob/master/triage/2020-09-28.md) for more.

## Approved RFCs

Expand Down