T Compiler Meeting Agenda 2026 03 12

T-compiler Meeting Agenda 2026-03-12

Announcements

  • Discussion about a possible 1.94.1 (but nothing from T-compiler)
  • 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).

Other WG meetings

MCPs/FCPs

Backport nominations

T-compiler beta / T-compiler stable

  • :beta: “Don’t look for non-type-level assoc consts when checking trait object types” rust#153738
    • Authored by fmease
    • Voting Zulip topic
    • both issue and PR just opened, we can review next week
  • :beta: “Don’t add empty target features for target-cpu=native on macOS” rust#153763
    • Authored by nikic
    • Fixes #153397 (P-critical, in beta), miscompile on mac M5/M4 (and with different flags on M1 as well)
    • Voting Zulip topic, PR just opened but seems to be a good backport candidate
  • 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

  • “[ICE]: LLVM ERROR “Broken module” with -C target-cpu=native on aarch64-apple-darwin (Apple M5, LLVM 22.1.0)” rust#153397
    • Fixed by #153763 (see backports)

T-types

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

P-high regressions

P-high beta regressions

  • “1.95 beta regression affecting old versions of bitvec: “… is not dyn compatible”” rust#153731
    • Just opened, waiting for feedback

Unassigned P-high nightly regressions

  • No unassigned P-high nightly regressions this time.

Performance logs

2026-03-10 Triage Log

Almost no regressions this week, while there was a handful of performance improvements caused by the ongoing refactoring of the compiler query system. The largest one was from #153521.

Triage done by @kobzol. Revision range: ddd36bd5..3945997a

Summary:

(instructions:u)meanrangecount
Regressions (primary)0.4%[0.4%, 0.5%]3
Regressions (secondary)0.6%[0.1%, 1.2%]8
Improvements (primary)-0.9%[-2.5%, -0.1%]110
Improvements (secondary)-0.8%[-2.7%, -0.1%]77
All (primary)-0.9%[-2.5%, 0.5%]113

0 Regressions, 6 Improvements, 3 Mixed; 5 of them in rollups 31 artifact comparisons made in total

Improvements

Remove tls::with_related_context. #153316 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.2%[-0.2%, -0.1%]5
Improvements (secondary)-0.2%[-0.2%, -0.0%]21
All (primary)-0.2%[-0.2%, -0.1%]5

Get rid of QueryVTable::call_query_method_fn #153387 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.3%[-0.3%, -0.2%]15
Improvements (secondary)-0.2%[-0.2%, -0.2%]5
All (primary)-0.3%[-0.3%, -0.2%]15

Rollup of 2 pull requests #153541 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)--0
Improvements (secondary)-0.2%[-0.3%, -0.1%]9
All (primary)--0

Don’t use incremental disk-cache for query predicates_of #153521 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.8%[-2.0%, -0.1%]92
Improvements (secondary)-1.0%[-2.6%, -0.2%]40
All (primary)-0.8%[-2.0%, -0.1%]92

Rollup of 6 pull requests #153579 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.2%[-0.4%, -0.1%]3
Improvements (secondary)-0.2%[-0.2%, -0.2%]1
All (primary)-0.2%[-0.4%, -0.1%]3

core: respect precision in ByteStr Display #153025 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)--0
Improvements (primary)-0.4%[-0.8%, -0.2%]4
Improvements (secondary)-0.8%[-0.8%, -0.8%]1
All (primary)-0.4%[-0.8%, -0.2%]4

Mixed

Rollup of 10 pull requests #153304 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.4%[0.1%, 0.6%]5
Regressions (secondary)0.3%[0.0%, 0.5%]3
Improvements (primary)-0.7%[-1.0%, -0.4%]2
Improvements (secondary)-0.1%[-0.1%, -0.1%]1
All (primary)0.1%[-1.0%, 0.6%]7
  • Only tiny perf. changes and it was overall a wash.
  • Marked as triaged.

Rollup of 8 pull requests #153377 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)0.1%[0.1%, 0.1%]1
Regressions (secondary)0.2%[0.1%, 0.3%]6
Improvements (primary)--0
Improvements (secondary)-0.8%[-0.8%, -0.7%]2
All (primary)0.1%[0.1%, 0.1%]1

Rollup of 4 pull requests #153552 (Comparison Link)

(instructions:u)meanrangecount
Regressions (primary)--0
Regressions (secondary)0.3%[0.3%, 0.3%]1
Improvements (primary)-2.3%[-2.5%, -2.2%]4
Improvements (secondary)-0.8%[-0.8%, -0.8%]1
All (primary)-2.3%[-2.5%, -2.2%]4
  • The coercions tiny loss swung back in the next PR.
  • Marked as triaged.

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

  • “Convert -Ctarget-cpu into a target-modifier for AVR, AMDGCN and NVPTX " rust#150732 (last review activity: about 59 days ago)
    • Unsure who should review next (@RalfJ and @Alice Ryhl already gave a first pass)
  • “Fix Hexagon ABI calling convention for small aggregates” rust#151572 (last review activity: about 47 days ago)
    • cc @Jack Huey bot assigned so feel free to reroll. PR has been bouncing for a while - any taker?
  • “Fix wrong suggestion for returning async closure” rust#151194 (last review activity: about 40 days ago)
    • This is reviewed by someone else - maybe just merge?

Next meetings’ agenda draft: hackmd link