T Compiler Meeting Agenda 2026 07 09

T-compiler Meeting Agenda 2026-07-09

Announcements

Other WG meetings

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.

PRs S-waiting-on-t-compiler

T-compiler

Issues of Note

Short Summary

P-critical

T-compiler

  • “dist-i686-msvc hang on lint-docs” rust#158378
    • visited last week, we disabled the tests for this compile target in #158379 to unblock the CI
    • target demotion discussed here, seems the agreement is to demote down to tier 2 without host tools
    • opened a poll to contrast opinions better

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

2026-07-06 Triage Log

This week was dominated by wild swings in benchmarks of the new-solver, which is not enabled by default, yet. Apart from that, we got a very few notable changes, only one unexpected speedup from a bugfix in rustdoc.

Triage done by @panstromek. Revision range: 7dc2c162..3659db0d

Summary:

(instructions:u)meanrangecount
Regressions (primary)0.2%[0.2%, 0.2%]3
Regressions (secondary)162.1%[0.2%, 1116.3%]20
Improvements (primary)-1.4%[-8.4%, -0.1%]7
Improvements (secondary)-1.1%[-8.4%, -0.1%]11
All (primary)-0.9%[-8.4%, 0.2%]10

1 Regression, 1 Improvement, 4 Mixed; 3 of them in rollups 17 artifact comparisons made in total

Regressions

resolve: Explicit Set for detecting resolution cycles #158035 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.2%[0.1%, 0.3%]7
Regressions (secondary)0.4%[0.3%, 0.6%]12
Improvements (primary)--0
Improvements (secondary)--0
All (primary)0.2%[0.1%, 0.3%]7

Regression matches pre-merge run, justified by https://github.com/rust-lang/rust/pull/158035#issuecomment-4833952569: “It looks acceptable now, unused-warnings is a stress benchmark with thousands of imports.” (@petrochenkov)

This is also a stepping stone towards future performance improvements (parallel compiler). IIUC the primary regressions were mostly mitigated by https://github.com/rust-lang/rust/pull/158604, mentioned below.

Improvements

Mixed

Rollup of 7 pull requests #158629 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)0.3%[0.3%, 0.3%]1
Improvements (primary)-8.5%[-8.5%, -8.5%]1
Improvements (secondary)-8.5%[-8.5%, -8.5%]1
All (primary)-8.5%[-8.5%, -8.5%]1

include-blob regression is probably bimodal noise again, improvement in serde doc is https://github.com/rust-lang/rust/pull/158569.

Rollup of 6 pull requests #158639 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)30.5%[0.3%, 51.1%]5
Improvements (primary)--0
Improvements (secondary)-0.2%[-0.3%, -0.1%]2
All (primary)--0

Regression caused by https://github.com/rust-lang/rust/pull/157718, already mitigated by https://github.com/rust-lang/rust/pull/158705 (mentioned above).

resolve: no allocation in resolve_ident_in(_local)_module_* #158604 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.3%[0.2%, 0.3%]3
Regressions (secondary)--0
Improvements (primary)-0.2%[-0.4%, -0.2%]26
Improvements (secondary)-0.2%[-0.3%, -0.1%]5
All (primary)-0.2%[-0.4%, 0.3%]29

Improvements outweigh regressions. Looks like this also mitigates the primary regressions from https://github.com/rust-lang/rust/pull/158035. Regressions are only in tiny incr-unchanged scenarios.

Rollup of 21 pull requests #158795 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)441.1%[0.2%, 1116.0%]7
Improvements (primary)-0.3%[-0.3%, -0.2%]2
Improvements (secondary)-0.6%[-1.2%, -0.3%]6
All (primary)-0.3%[-0.3%, -0.2%]2

Regressions caused by https://github.com/rust-lang/rust/pull/158606#issuecomment-4890167477

Regressions are limited to new-solver, which is not enabled by default. I think we can mark this as triaged and let the types team follow up on this as they see fit.

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

Next meetings’ agenda draft: hackmd link