T Compiler Meeting Agenda 2026 03 05

T-compiler Meeting Agenda 2026-03-05

Announcements

  • Today release of Rust 1.94.0, see blog post draft
  • 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

Backport nominations

T-compiler beta / T-compiler stable

  • No beta nominations for T-compiler this time.
  • No stable nominations for T-compiler this time.

T-types beta / T-types stable

  • No beta nominations for T-types this time.
  • No stable nominations for T-types this time.

PRs S-waiting-on-t-compiler

T-compiler

Issues of Note

Short Summary

P-critical

T-compiler

  • No P-critical issues for T-compiler this time.

T-types

  • No P-critical issues for T-types this time.

P-high regressions

P-high beta regressions

  • No P-high beta regressions this time.

Unassigned P-high nightly regressions

  • No unassigned P-high nightly regressions this time.

Performance logs

2026-03-02 Triage Log

A positive week with a few nice improvements coming from query system cleanups.

Triage done by @panstromek. Revision range: eeb94be7..ddd36bd5

Summary:

(instructions:u)meanrangecount
Regressions (primary)0.3%[0.3%, 0.3%]1
Regressions (secondary)0.2%[0.0%, 0.3%]3
Improvements (primary)-0.8%[-2.1%, -0.1%]141
Improvements (secondary)-1.1%[-6.6%, -0.1%]90
All (primary)-0.8%[-2.1%, 0.3%]142

2 Regressions, 5 Improvements, 5 Mixed; 4 of them in rollups 30 artifact comparisons made in total

Regressions

Remove const FLAGS. #152791 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.2%[0.1%, 0.5%]17
Regressions (secondary)0.3%[0.1%, 0.6%]37
Improvements (primary)--0
Improvements (secondary)--0
All (primary)0.2%[0.1%, 0.5%]17

Triaged by @nnethercote: “Perf regressions were minor and deemed worthwhile above for the simplicity improvements.”

Rollup of 12 pull requests #153074 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)1.9%[0.2%, 4.9%]44
Regressions (secondary)0.9%[0.2%, 3.3%]25
Improvements (primary)--0
Improvements (secondary)-0.4%[-0.4%, -0.4%]1
All (primary)1.9%[0.2%, 4.9%]44

Already triaged by @JonathanBrouwer. Caused by https://github.com/rust-lang/rust/pull/152679, reverted in https://github.com/rust-lang/rust/pull/153095.

Improvements

Improve how QueryCache/QueryState/QueryEngine are stored #152835 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.2%[-0.3%, -0.1%]5
Improvements (secondary)-0.2%[-0.3%, -0.1%]16
All (primary)-0.2%[-0.3%, -0.1%]5

Rollup of 7 pull requests #153124 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.2%[-0.4%, -0.1%]17
Improvements (secondary)-0.4%[-0.9%, -0.1%]20
All (primary)-0.2%[-0.4%, -0.1%]17

Rollup of 2 pull requests #153139 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-2.0%[-4.8%, -0.2%]42
Improvements (secondary)-0.9%[-3.2%, -0.2%]25
All (primary)-2.0%[-4.8%, -0.2%]42

Revert “Simplify internals of {Rc,Arc}::default” #153108 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.4%[-0.7%, -0.3%]6
Improvements (secondary)-0.6%[-0.6%, -0.6%]1
All (primary)-0.4%[-0.7%, -0.3%]6

Improve the forcing/promotion functions in DepKindVTable #153122 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)1.9%[1.9%, 1.9%]1
Improvements (primary)-0.8%[-1.7%, -0.3%]102
Improvements (secondary)-1.2%[-6.5%, -0.2%]68
All (primary)-0.8%[-1.7%, -0.3%]102

Mixed

Rollup of 13 pull requests #153116 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.5%[0.3%, 1.0%]4
Regressions (secondary)2.6%[0.3%, 5.9%]5
Improvements (primary)-0.5%[-0.5%, -0.5%]1
Improvements (secondary)-0.3%[-0.3%, -0.3%]1
All (primary)0.3%[-0.5%, 1.0%]5

Already triaged by @JonathanBrouwer, caused by https://github.com/rust-lang/rust/pull/149978, will be addressed by https://github.com/rust-lang/rust/pull/153157.

Prepare NonNull for pattern types #152702 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.5%[0.4%, 0.6%]3
Regressions (secondary)0.5%[0.5%, 0.5%]1
Improvements (primary)-0.3%[-0.5%, -0.2%]3
Improvements (secondary)-1.1%[-1.1%, -1.1%]1
All (primary)0.1%[-0.5%, 0.6%]6

Slightly worse than pre-merge results, but looks somewhat expected - some tiny regressions in LLVM, a bit of codegen unit shuffling.

refactor(mgca): Change DefKind::Const and DefKind::AssocConst to have a is_type_const flag #153050 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)0.0%[0.0%, 0.0%]1
Improvements (primary)-0.5%[-0.8%, -0.2%]17
Improvements (secondary)-0.7%[-1.7%, -0.0%]10
All (primary)-0.5%[-0.8%, -0.2%]17

Tiny regression in include-blob stress test, overall positive.

Optimize dependency file search #153131 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.1%[0.1%, 0.1%]1
Regressions (secondary)--0
Improvements (primary)--0
Improvements (secondary)-0.4%[-0.6%, -0.2%]7
All (primary)0.1%[0.1%, 0.1%]1

Triaged by @Kobzol (author): “The regression seems like noise. Tiny wins on large-workspace, matching pre-merge run.”

Re-add #[inline] to Eq::assert_fields_are_eq #153157 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)0.2%[0.2%, 0.3%]3
Improvements (primary)-0.5%[-0.8%, -0.3%]4
Improvements (secondary)-3.0%[-5.6%, -0.4%]4
All (primary)-0.5%[-0.8%, -0.3%]4

Net positive, addresses previous regression from https://github.com/rust-lang/rust/pull/153116. Small regression in derive stress tests.

Nominated Issues

T-compiler

  • No I-compiler-nominated issues this time.

RFC

  • No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

T-compiler

  • “Add support for xray in aarch64 unknown none target” rust#148666 (last review activity: 3 months ago)
    • cc: @Wesley Wiser
  • “Implement -Z allow-partial-mitigations (RFC 3855)” rust#149357 (last review activity: 2 months ago)
    • cc @Ramon de C Valle
  • “Support using const pointers in asm const operand” rust#138618 (last review activity: 2 months ago)
    • cc: @Sparrow Li was auto-assigned, maybe reroll? Any taker? Needs a rebase btw
  • “Stabilize -Zdebuginfo-compression as -Cdebuginfo-compression” rust#150625 (last review activity: 2 months ago)
    • cc: @Sparrow Li (do you want to pass it on to someone else?)
  • “Try mark no_hash queries as green after execution” rust#150156 (last review activity: about 49 days ago)
    • cc @cjgillot
  • “naked functions: respect function-sections” rust#147811 (last review activity: about 48 days ago)
    • cc @Amanieu d’Antras
  • “Fix incorrect trailing comma suggested in no_accessible_fields” rust#151280 (last review activity: about 46 days ago)
    • rerolled reviewer (but up for grab, I think)
  • “mir-opt: Remove the workaround in UnreachableEnumBranching” rust#146544 (last review activity: about 41 days ago)
    • cc @Wesley Wiser
  • “Cleanup query macros” rust#152424 (last review activity: about 23 days ago)
    • cc: @Zalathar (probably also related PR #152459)

Next meetings’ agenda draft: hackmd link