T-compiler Meeting Agenda 2026-02-26

--- tags: weekly, rustc type: docs note_id: PlVsh_eMSluYBCXJ-MDhiQ --- # T-compiler Meeting Agenda 2026-02-26 ## Announcements - Heads-up: release of 1.94.0 is next week - New! Backports can now be accepted/declined directly from Zulip, example: ``` @triagebot backport stable accept 123456 @triagebot backport beta decline 123456 ``` - Reminder: if you see a PR/issue that seems like there might be legal implications due to copyright/IP/etc, please let us know (or at least message @_**davidtwco** or @_**Wesley Wiser** so we can pass it along). ## MCPs/FCPs (sorry the list could not be fully generated) - New MCPs (take a look, see if you like them!) - [Remove soft_unstable](https://github.com/rust-lang/compiler-team/issues/972) - [Remove -Csoft-float](https://github.com/rust-lang/compiler-team/issues/971) ## Backport nominations [T-compiler beta](https://github.com/rust-lang/rust/issues?q=is%3Apr+label%3Abeta-nominated+-label%3Abeta-accepted+label%3AT-compiler) / [T-compiler stable](https://github.com/rust-lang/rust/issues?q=is%3Apr+label%3Astable-nominated+-label%3Astable-accepted+label%3AT-compiler) - None [T-types beta](https://github.com/rust-lang/rust/issues?q=is%3Apr+label%3Abeta-nominated+-label%3Abeta-accepted+label%3AT-types) / [T-types stable](https://github.com/rust-lang/rust/issues?q=is%3Apr+label%3Astable-nominated+-label%3Astable-accepted+label%3AT-types) - None ## PRs S-waiting-on-t-compiler [T-compiler](https://github.com/rust-lang/rust/pulls?q=is%3Aopen+label%3AS-waiting-on-t-compiler) - [Issues in progress or waiting on other teams](https://hackmd.io/XYr1BrOWSiqCrl8RCWXRaQ) ## Issues of Note ### Short Summary - [0 T-compiler P-critical issues](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AT-compiler+label%3AP-critical) - None - [60 P-high issues](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AT-compiler+label%3AP-high) - [42 of those are unassigned](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AT-compiler+label%3AP-high+no%3Aassignee) - [0 P-critical, 3 P-high, 3 P-medium, 0 P-low regression-from-stable-to-beta](https://github.com/rust-lang/rust/labels/regression-from-stable-to-beta) - [0 P-critical, 2 P-high, 1 P-medium, 0 P-low regression-from-stable-to-nightly](https://github.com/rust-lang/rust/labels/regression-from-stable-to-nightly) - [0 P-critical, 35 P-high, 121 P-medium, 29 P-low regression-from-stable-to-stable](https://github.com/rust-lang/rust/labels/regression-from-stable-to-stable) ### Stable regression - "`#[no_link]` attribute does not prevent crate linking" [rust#152854](https://github.com/rust-lang/rust/issues/152854) - doesn't seem super urgent, @_**bjorn3** opened #152856 to investigate removing the attribute. Possibly it should go through a T-lang FCP first ([comment](https://github.com/rust-lang/rust/pull/152856#issuecomment-3945510463)) - (FIY in case anyone has opinions) ### P-critical [T-compiler](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AP-critical+label%3AT-compiler) - None [T-types](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AP-critical+label%3AT-types) - None ### P-high regressions [P-high beta regressions](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3Aregression-from-stable-to-beta+label%3AP-high+-label%3AT-infra+-label%3AT-libs+-label%3AT-libs-api+-label%3AT-release+-label%3AT-rustdoc) - "Regression: "rust-lld: error: undefined symbol: Rlog1p" · [rust#150663](https://github.com/rust-lang/rust/issues/150663) - Failed a crater run a while ago. Seems a flaky build or something. We tried to reproduce to no avail. Unsure what we can do here. - "Chromium hitting SIGILL crashes on aarch64 after #144938 enabled outlined atomics by default" [rust#151486](https://github.com/rust-lang/rust/issues/151486) - Should be fixed by #151896 - "regression: undefined symbol: __gxx_personality_v0" [rust#152353](https://github.com/rust-lang/rust/issues/152353) - Another crate that failed a crate run a while ago, still unclear but possibly a flaky build [Unassigned P-high nightly regressions](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3Aregression-from-stable-to-nightly+label%3AP-high+no%3Aassignee+-label%3AT-infra+-label%3AT-libs+-label%3AT-libs-api+-label%3AT-release+-label%3AT-rustdoc) - None ## Performance logs > [Triage logs for 2026-02-17](https://github.com/rust-lang/rustc-perf/blob/master/triage/2026/2026-02-17.md) Several pull requests introduced (usually very small) regressions across the board this week. On the other hand, [#151380](https://github.com/rust-lang/rust/pull/151380) provided a nice performance win in the inference engine. I would also like to bring attention to [#152375](https://github.com/rust-lang/rust/pull/152375), which improved the parallel frontend. It is not shown in this report, because we don't yet have many benchmarks for the parallel frontend, but this PR seemingly improved the `check` (wall-time) performance with multiple frontend threads on several real-world crates by 5-10%! Triage done by **@kobzol**. Revision range: [39219ceb..3c9faa0d](https://perf.rust-lang.org/?start=39219ceb97d1b37dda72517daa9ebe8364ffe186&end=3c9faa0d037b9eecda4a440cc482ff7f960fb8a5&absolute=false&stat=instructions%3Au) **Summary**: | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.7% | [0.2%, 3.1%] | 96 | | Regressions (secondary) | 1.1% | [0.0%, 5.7%] | 62 | | Improvements (primary) | -0.4% | [-0.9%, -0.2%] | 8 | | Improvements (secondary) | -2.6% | [-7.0%, -0.0%] | 45 | | All (primary) | 0.6% | [-0.9%, 3.1%] | 104 | 2 Regressions, 0 Improvements, 9 Mixed; 4 of them in rollups 36 artifact comparisons made in total #### Regressions Rollup of 17 pull requests [#152562](https://github.com/rust-lang/rust/pull/152562) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=47611e16044c68ef27bac31c35fda2ba1dc20b73&end=d7daac06d87e1252d10eaa44960164faac46beff&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:----:|:------------:|:-----:| | Regressions (primary) | - | - | 0 | | Regressions (secondary) | 0.3% | [0.2%, 0.5%] | 11 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | - | - | 0 | | All (primary) | - | - | 0 | - Noise that got reverted in a follow-up PR. - Already marked as triaged. replace box_new with lower-level intrinsics [#148190](https://github.com/rust-lang/rust/pull/148190) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=71e00273c0921e1bc850ae8cc4161fbb44cfa848&end=3c9faa0d037b9eecda4a440cc482ff7f960fb8a5&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.8% | [0.5%, 1.9%] | 8 | | Regressions (secondary) | 1.8% | [0.4%, 5.5%] | 24 | | Improvements (primary) | -0.8% | [-0.8%, -0.8%] | 1 | | Improvements (secondary) | -0.3% | [-0.3%, -0.3%] | 1 | | All (primary) | 0.6% | [-0.8%, 1.9%] | 9 | - Small performance hit across the board caused by refactoring how Box works internally. - Was deemed acceptable pre-merge. - Marked as triaged. #### Mixed Rollup of 12 pull requests [#152399](https://github.com/rust-lang/rust/pull/152399) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=71dc761bfe791895c5997dda654dca1dad817413&end=18d13b5332916ffca8eadb9106d54b5b434e9978&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.2% | [0.2%, 0.2%] | 3 | | Regressions (secondary) | 0.8% | [0.1%, 1.4%] | 26 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.2% | [-0.3%, -0.1%] | 8 | | All (primary) | 0.2% | [0.2%, 0.2%] | 3 | - The largest regressions seem to be caused by [#152327](https://github.com/rust-lang/rust/pull/152327). - That PR fixed some compiler bugs, so the regression on a secondary benchmarks seems justifiable. - Marked as triaged. Update mgca to use `type const` syntax instead of the `#[type_const]` attribute. [#152324](https://github.com/rust-lang/rust/pull/152324) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=18d13b5332916ffca8eadb9106d54b5b434e9978&end=381e9ef09effbed5f1378a24dc6e461fea35a0e1&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.4% | [0.1%, 0.7%] | 18 | | Regressions (secondary) | 0.5% | [0.0%, 1.7%] | 13 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.2% | [-0.3%, -0.0%] | 4 | | All (primary) | 0.4% | [0.1%, 0.7%] | 18 | - It is unclear whether the regressions were expected or not. - Asked the reviewer to follow up. - Not marking as triaged yet. Update to LLVM 22.1.0-rc3 [#152428](https://github.com/rust-lang/rust/pull/152428) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=7dc2e92b83be02dc07f87be7e94266d6e48e5ca5&end=7057231bd78d6c7893f905ea1832365d4c5efe17&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.2% | [0.2%, 0.2%] | 1 | | Regressions (secondary) | 0.1% | [0.0%, 0.2%] | 4 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.3% | [-0.5%, -0.1%] | 10 | | All (primary) | 0.2% | [0.2%, 0.2%] | 1 | - A few tiny changes that got over the noise threshold, but overall a wash. - Marked as triaged. Rollup of 7 pull requests [#152506](https://github.com/rust-lang/rust/pull/152506) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=5fdff787e6ef7cd4458f81e69cbb4d2a39439a98&end=605f49b27444a738ea4032cb77e3bdc4eb811bab&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.2% | [0.2%, 0.2%] | 1 | | Regressions (secondary) | 0.2% | [0.1%, 0.2%] | 3 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.1% | [-0.2%, -0.1%] | 2 | | All (primary) | 0.2% | [0.2%, 0.2%] | 1 | - Very small regressions across the board, but I don't think it's worth it to dig deeper. - Marked as triaged. Start using pattern types in libcore (NonZero and friends) [#148537](https://github.com/rust-lang/rust/pull/148537) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=7ad4e69ad585d8ff214f7b42d01f1959eda08f40&end=bb8b30a5fce59f5d3d17a8f010601c59f0f19d79&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 1.9% | [0.1%, 3.8%] | 12 | | Regressions (secondary) | 2.2% | [0.1%, 3.6%] | 4 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.1% | [-0.1%, -0.1%] | 2 | | All (primary) | 1.9% | [0.1%, 3.8%] | 12 | - The regression was deemed [acceptable](https://github.com/rust-lang/rust/pull/148537#issuecomment-3883425825) pre-merge, and the post-merge results correspond to the previous perf. runs. - Marked as triaged. Make operational semantics of pattern matching independent of crate and module [#150681](https://github.com/rust-lang/rust/pull/150681) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=5d04477ea8118ba54d9ce402848dda19a41d61eb&end=f8463896a9b36a04899c013bd8825a7fd29dd7a4&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.6% | [0.1%, 1.1%] | 7 | | Regressions (secondary) | 0.2% | [0.1%, 0.2%] | 12 | | Improvements (primary) | -2.6% | [-2.6%, -2.6%] | 1 | | Improvements (secondary) | -2.3% | [-2.3%, -2.3%] | 1 | | All (primary) | 0.2% | [-2.6%, 1.1%] | 8 | - A few small regressions across the board, mainly in `doc` builds, the rest of the profiles are a wash. Given the change made here, I suppose the perf. regression is expected. - Marked as triaged. Rollup of 7 pull requests [#152632](https://github.com/rust-lang/rust/pull/152632) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=a33907a7a5381473eec8bcfa0c56e05a856a911c&end=7bee525095c0872e87c038c412c781b9bbb3f5dc&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.4% | [0.1%, 0.8%] | 6 | | Regressions (secondary) | 0.4% | [0.1%, 0.8%] | 3 | | Improvements (primary) | -0.5% | [-1.0%, -0.2%] | 3 | | Improvements (secondary) | -1.0% | [-2.0%, -0.5%] | 5 | | All (primary) | 0.1% | [-1.0%, 0.8%] | 9 | - Performance-wise it's a wash. - Marked as triaged. Shallow resolve ty and const vars to their root vars [#151380](https://github.com/rust-lang/rust/pull/151380) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=7bee525095c0872e87c038c412c781b9bbb3f5dc&end=75b9d89c68a4a92758349272aa4e35a8eb7a6708&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | - | - | 0 | | Regressions (secondary) | 0.3% | [0.2%, 0.4%] | 4 | | Improvements (primary) | -0.3% | [-0.4%, -0.1%] | 14 | | Improvements (secondary) | -2.7% | [-7.1%, -0.1%] | 50 | | All (primary) | -0.3% | [-0.4%, -0.1%] | 14 | - Many more wins than losses. - Marked as triaged. Big query system cleanups [#152636](https://github.com/rust-lang/rust/pull/152636) [(Comparison Link)](https://perf.rust-lang.org/compare.html?start=139651428df86cf88443295542c12ea617cbb587&end=fef627b1ebdc7369ddf8a4031a5d25733ac1fb34&stat=instructions:u) | (instructions:u) | mean | range | count | |:------------------------:|:-----:|:--------------:|:-----:| | Regressions (primary) | 0.3% | [0.2%, 0.4%] | 10 | | Regressions (secondary) | 0.2% | [0.1%, 0.3%] | 9 | | Improvements (primary) | - | - | 0 | | Improvements (secondary) | -0.4% | [-0.4%, -0.3%] | 4 | | All (primary) | 0.3% | [0.2%, 0.4%] | 10 | - The small performance regressions were investigated and deemed to be caused mostly by inlining perturbations. - Already marked as triaged. ## Nominated Issues [T-compiler](https://github.com/rust-lang/rust/issues?q=is%3Aopen+label%3AI-compiler-nominated) - None [RFC](https://github.com/rust-lang/rfcs/issues?q=is%3Aopen+label%3AI-compiler-nominated) - None ### Oldest PRs waiting for review - None this week Next meeting's agenda draft: [hackmd link](https://hackmd.io/Bf6Z0BusSmGwaBr04mP53A)

Syntax	Example	Reference
# Header	Header	基本排版
- Unordered List	Unordered List
1. Ordered List	Ordered List
- [ ] Todo List	Todo List
> Blockquote	Blockquote
Bold font	Bold font
Italics font	Italics font
~~Strikethrough~~	~~Strikethrough~~
19^th^	19^th
H~2~O	H₂O
++Inserted text++	Inserted text
==Marked text==	Marked text
[link text](https:// "title")	Link
![image alt](https:// "title")	Image
`Code`	`Code`	在筆記中貼入程式碼
```javascript var i = 0; ```	`var i = 0;`
:smile:		Emoji list
{%youtube youtube_id %}	Externals
$L^aT_eX$	L^aT_eX
:::info This is a alert area. :::	This is a alert area.