# 2025-06-30 Triage Log

Lots of changes this week with results dominated by the 1-5% improvements from
[#142941](https://github.com/rust-lang/rust/pull/142941) across lots of primary
benchmarks in the suite.

Triage done by **@simulacrum**.
Revision range: [42245d34..ad3b7257](https://perf.rust-lang.org/?start=42245d34d22ade32b3f276dcf74deb826841594c&end=ad3b7257615c28aaf8212a189ec032b8af75de51&absolute=false&stat=instructions%3Au)

**Summary**:

| (instructions:u)                   | mean  | range           | count |
|:----------------------------------:|:-----:|:---------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 2.9%  | [0.2%, 21.6%]   | 16    |
| Regressions ❌ <br /> (secondary)  | 1.5%  | [0.1%, 13.5%]   | 38    |
| Improvements ✅ <br /> (primary)   | -0.9% | [-4.5%, -0.1%]  | 99    |
| Improvements ✅ <br /> (secondary) | -6.2% | [-67.9%, -0.1%] | 100   |
| All ❌✅ (primary)                 | -0.4% | [-4.5%, 21.6%]  | 115   |

3 Regressions, 6 Improvements, 5 Mixed; 4 of them in rollups
39 artifact comparisons made in total

#### Regressions

Rollup of 10 pull requests [#143091](https://github.com/rust-lang/rust/pull/143091) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=13c46fd0b089360922a557d8e18a63a2c41dfbeb&end=fe5f3dedf7b4d6bea2cadb17343f747d70b4c66b&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
| Regressions ❌ <br /> (secondary)  | 2.1%  | [0.1%, 2.7%]   | 7     |
| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
| Improvements ✅ <br /> (secondary) | -0.1% | [-0.1%, -0.1%] | 1     |
| All ❌✅ (primary)                 | -     | -              | 0     |

Regressions in ctfe and match stress tests, trying to find the PR that
introduced them in case there's obvious tweaks, but not particularly
noteworthy given the limited impact.

Rollup of 9 pull requests [#143116](https://github.com/rust-lang/rust/pull/143116) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=bdaba05a953eb5abeba0011cdda2560d157aed2e&end=d41e12f1f4e4884c356f319b881921aa37040de5&stat=instructions:u)

| (instructions:u)                   | mean | range        | count |
|:----------------------------------:|:----:|:------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -    | -            | 0     |
| Regressions ❌ <br /> (secondary)  | 1.1% | [0.9%, 1.3%] | 9     |
| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
| All ❌✅ (primary)                 | -    | -            | 0     |

Regressions are in the `coercions` stress test, not clear which of the rolled
up PRs caused it. Started one candidate perf run.

Rollup of 11 pull requests [#143173](https://github.com/rust-lang/rust/pull/143173) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=dddd7ab96229ea5f2ca96afcb5984a9831393a13&end=5ca574e85b67cec0a6fc3fddfe398cbe676c9c69&stat=instructions:u)

| (instructions:u)                   | mean | range        | count |
|:----------------------------------:|:----:|:------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 0.5% | [0.3%, 0.7%] | 2     |
| Regressions ❌ <br /> (secondary)  | -    | -            | 0     |
| Improvements ✅ <br /> (primary)   | -    | -            | 0     |
| Improvements ✅ <br /> (secondary) | -    | -            | 0     |
| All ❌✅ (primary)                 | 0.5% | [0.3%, 0.7%] | 2     |

Likely due to [#142641](https://github.com/rust-lang/rust/pull/142641) which
added extra work to proc-macro crates, which are the benchmarks affected here.

#### Improvements

Encode hir attributes cross-crate properly [#142777](https://github.com/rust-lang/rust/pull/142777) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d14d202262d13df896b0c624b0cec6e4bfde631a&end=0fa4ec6cde46fa17ab07acb5531cfe0dc1349ffa&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
| Improvements ✅ <br /> (primary)   | -0.4% | [-1.4%, -0.1%] | 16    |
| Improvements ✅ <br /> (secondary) | -0.6% | [-1.3%, -0.2%] | 20    |
| All ❌✅ (primary)                 | -0.4% | [-1.4%, -0.1%] | 16    |


Rollup of 8 pull requests [#143057](https://github.com/rust-lang/rust/pull/143057) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=b03b3a7ec92682be2917540b679478d41c95a30c&end=513999b936c37902120380f4171963d1f1d80347&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
| Improvements ✅ <br /> (primary)   | -0.4% | [-0.4%, -0.3%] | 3     |
| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
| All ❌✅ (primary)                 | -0.4% | [-0.4%, -0.3%] | 3     |


Fast path for WF goals in new solver [#142223](https://github.com/rust-lang/rust/pull/142223) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=e61dd437f33b5a640e67dc3628397689c664c17f&end=df32e15c56f582eb2bdde07711af6271f2ae660b&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
| Improvements ✅ <br /> (primary)   | -0.2% | [-0.4%, -0.1%] | 8     |
| Improvements ✅ <br /> (secondary) | -1.5% | [-3.5%, -0.3%] | 13    |
| All ❌✅ (primary)                 | -0.2% | [-0.4%, -0.1%] | 8     |


Collapse Analysis|Borrowck|PostBorrowckAnalysis when there are no opaques [#142802](https://github.com/rust-lang/rust/pull/142802) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=ed2d759783dc9de134bbb3f01085b1e6dbf539f3&end=35f6036521777bdc0dcea1f980be4c192962a168&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -              | 0     |
| Regressions ❌ <br /> (secondary)  | 0.2%  | [0.1%, 0.2%]   | 2     |
| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
| Improvements ✅ <br /> (secondary) | -2.4% | [-7.5%, -0.5%] | 14    |
| All ❌✅ (primary)                 | -     | -              | 0     |


Shallowly bail from `coerce_unsized` more [#142941](https://github.com/rust-lang/rust/pull/142941) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=35f6036521777bdc0dcea1f980be4c192962a168&end=f19142044f270760ce0ebc03b2c3a44217d8703d&stat=instructions:u)

| (instructions:u)                   | mean  | range           | count |
|:----------------------------------:|:-----:|:---------------:|:-----:|
| Regressions ❌ <br /> (primary)    | -     | -               | 0     |
| Regressions ❌ <br /> (secondary)  | 0.8%  | [0.8%, 0.8%]    | 1     |
| Improvements ✅ <br /> (primary)   | -0.8% | [-4.6%, -0.2%]  | 84    |
| Improvements ✅ <br /> (secondary) | -5.6% | [-21.6%, -0.1%] | 71    |
| All ❌✅ (primary)                 | -0.8% | [-4.6%, -0.2%]  | 84    |


#### Mixed

update to literal-escaper 0.0.4 for better API without `unreachable` and faster string parsing [#140999](https://github.com/rust-lang/rust/pull/140999) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=3de5b08ef6b260277dd4c77f7472fe6904bd6002&end=2c2bb995af398383e3b93b859302bdc447ca7a7c&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 0.2%  | [0.2%, 0.3%]   | 3     |
| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.3%, 0.3%]   | 1     |
| Improvements ✅ <br /> (primary)   | -     | -              | 0     |
| Improvements ✅ <br /> (secondary) | -0.7% | [-1.2%, -0.4%] | 16    |
| All ❌✅ (primary)                 | 0.2%  | [0.2%, 0.3%]   | 3     |

Regressions limited to stm32f4, some mild improvements, doesn't seem worth
further investigation.

Stop collecting unmentioned constants [#142893](https://github.com/rust-lang/rust/pull/142893) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=d51b6f97122671c5de27cfc08cded235357e0d97&end=13c46fd0b089360922a557d8e18a63a2c41dfbeb&stat=instructions:u)

| (instructions:u)                   | mean   | range            | count |
|:----------------------------------:|:------:|:----------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 19.2%  | [17.2%, 21.2%]   | 2     |
| Regressions ❌ <br /> (secondary)  | 9.1%   | [6.0%, 13.4%]    | 5     |
| Improvements ✅ <br /> (primary)   | -1.6%  | [-2.3%, -0.8%]   | 8     |
| Improvements ✅ <br /> (secondary) | -67.8% | [-67.9%, -67.8%] | 2     |
| All ❌✅ (primary)                 | 2.6%   | [-2.3%, 21.2%]   | 10    |

Regressed benchmarks are incremental scenarios which have changed codegen units
-- overall, this is an improvement in the typical case.

Don't fold in Instantiate when there's nothing to fold [#142317](https://github.com/rust-lang/rust/pull/142317) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=b63223c152212832ce37a109e26cc5f84c577532&end=7ba34c704529e7fcab80130c3fe40efe415d61b5&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 0.2%  | [0.1%, 0.3%]   | 9     |
| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
| Improvements ✅ <br /> (primary)   | -0.2% | [-0.3%, -0.1%] | 3     |
| Improvements ✅ <br /> (secondary) | -2.6% | [-2.9%, -2.4%] | 6     |
| All ❌✅ (primary)                 | 0.1%  | [-0.3%, 0.3%]  | 12    |

Some mixed results from this but improvements were deemed as outweighing the
regressions ([comment](https://github.com/rust-lang/rust/pull/142317#issuecomment-2964689882)).

Only compute recursive callees once. [#142625](https://github.com/rust-lang/rust/pull/142625) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=7ba34c704529e7fcab80130c3fe40efe415d61b5&end=11ad40bb839ca16f74784b4ab72596ad85587298&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 0.4%  | [0.3%, 0.6%]   | 3     |
| Regressions ❌ <br /> (secondary)  | 0.3%  | [0.3%, 0.3%]   | 2     |
| Improvements ✅ <br /> (primary)   | -1.3% | [-2.5%, -0.2%] | 2     |
| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
| All ❌✅ (primary)                 | -0.3% | [-2.5%, 0.6%]  | 5     |

Per the PR description makes some intentional tradeoffs between two variants of
implementation and is overall an improvement or neutral.

Stop backends from needing to support nullary intrinsics [#142839](https://github.com/rust-lang/rust/pull/142839) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=f19142044f270760ce0ebc03b2c3a44217d8703d&end=ad3b7257615c28aaf8212a189ec032b8af75de51&stat=instructions:u)

| (instructions:u)                   | mean  | range          | count |
|:----------------------------------:|:-----:|:--------------:|:-----:|
| Regressions ❌ <br /> (primary)    | 2.7%  | [2.7%, 2.7%]   | 1     |
| Regressions ❌ <br /> (secondary)  | -     | -              | 0     |
| Improvements ✅ <br /> (primary)   | -0.3% | [-0.4%, -0.3%] | 5     |
| Improvements ✅ <br /> (secondary) | -     | -              | 0     |
| All ❌✅ (primary)                 | 0.2%  | [-0.4%, 2.7%]  | 6     |

Some slight changes, no particularly significant changes.
