T Compiler Meeting Agenda 2024 05 30

T-compiler Meeting Agenda 2024-05-30

Announcements

  • Friday [steering meeting]: Project Goals by @_nikomatsakis
  • 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

WG checkins

  • @_WG-async by @nikomatsakis and @tmandry

    Checkin text

  • @_WG-diagnostics by @Esteban Küber and @oli

    Checkin text

Backport nominations

T-compiler beta / T-compiler stable

  • :beta: “Fix ICE in non-operand aggregate_raw_ptr intrinsic codegen” rust#125184
    • Authored by scottmcm
    • Ben nominated:

      I would like this in beta so that the stage0 compiler does not ICE if it gets passed -Zmir-opt-level=0. Yes I can work around this issue without huge difficulty, but the diff here is so small.

  • :beta: “Revert problematic opaque type change” rust#125489
    • Authored by oli-obk
    • Fixes P-critical beta regression
  • :beta: “[BETA] revert leak check changes” rust#125629
    • Authored by lcnr
    • Fixes P-critical beta regression
  • :beta: “ast: Revert a breaking attribute visiting order change #125734”
    • Authored by petrochenkov
    • Fixes P-high beta regression
  • No stable nominations for T-compiler this time.

T-types stable / T-types beta

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

PRs S-waiting-on-team

T-compiler

Issues of Note

Short Summary

P-critical

T-compiler

  • “-C target_cpu=cortex-a72 (and -target-cpu=native on Raspberry Pi) wrongly enables crypto features that are optional on Cortex-A72” rust#125033
    • Discussed extensively last week
  • “regression: trait bound not satisfied” rust#125194
    • Fix was beta nominated
  • “regression: type annotations needed” rust#125196
  • “regression: ambiguous outer attributes” rust#125199

T-types

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

P-high regressions

P-high beta regressions

  • “regression: cannot find macro in scope” rust#125201
    • Fix was beta nominated

Unassigned P-high nightly regressions

  • No unassigned P-high nightly regressions this time.

Performance logs

2024-05-27 Triage Log

A relatively quiet week, with few large changes, the largest driven by further increasing the scope of unsafe precondition checking.

Triage done by @simulacrum. Revision range: 1d0e4afd..a59072ec

Summary:

(instructions:u)meanrangecount
Regressions ❌ (primary)1.6%[0.2%, 6.3%]84
Regressions ❌ (secondary)0.9%[0.1%, 3.8%]66
Improvements ✅ (primary)-0.4%[-2.3%, -0.2%]37
Improvements ✅ (secondary)-1.7%[-3.8%, -0.2%]22
All ❌✅ (primary)1.0%[-2.3%, 6.3%]121

2 Regressions, 3 Improvements, 5 Mixed; 3 of them in rollups 51 artifact comparisons made in total

Regressions

Rewrite native thread-local storage #116123 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)0.4%[0.2%, 1.2%]10
Regressions ❌ (secondary)1.0%[0.7%, 1.6%]9
Improvements ✅ (primary)--0
Improvements ✅ (secondary)--0
All ❌✅ (primary)0.4%[0.2%, 1.2%]10

Regressions deemed worth the overall change’s contents (see https://github.com/rust-lang/rust/pull/116123#issuecomment-2009408868). The TLS state is now stored in a single thread-local object rather than two, which should decrease costs of addressing it in general (modulo LLVM difficulties).

Rollup of 6 pull requests #125463 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)1.4%[1.1%, 2.0%]8
Regressions ❌ (secondary)1.0%[0.4%, 1.8%]23
Improvements ✅ (primary)-0.5%[-0.5%, -0.5%]1
Improvements ✅ (secondary)-0.3%[-0.3%, -0.3%]1
All ❌✅ (primary)1.2%[-0.5%, 2.0%]9

Likely related to fixing an issue around LLD discovery, see https://github.com/rust-lang/rust/pull/125463#issuecomment-2129069901. Bugfix warrants spending a bit more time.

Improvements

Move the checks for Arguments constructors to inline const #125518 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)--0
Regressions ❌ (secondary)--0
Improvements ✅ (primary)-0.5%[-0.7%, -0.3%]5
Improvements ✅ (secondary)-0.5%[-0.9%, -0.4%]7
All ❌✅ (primary)-0.5%[-0.7%, -0.3%]5

Remove DefId from EarlyParamRegion #125468 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)--0
Regressions ❌ (secondary)--0
Improvements ✅ (primary)-0.4%[-0.9%, -0.2%]48
Improvements ✅ (secondary)-0.8%[-2.0%, -0.3%]19
All ❌✅ (primary)-0.4%[-0.9%, -0.2%]48

[perf] Delay the construction of early lint diag structs #125410 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)--0
Regressions ❌ (secondary)--0
Improvements ✅ (primary)-0.5%[-0.7%, -0.3%]12
Improvements ✅ (secondary)-2.0%[-2.8%, -1.2%]13
All ❌✅ (primary)-0.5%[-0.7%, -0.3%]12

Mixed

Follow-up fixes to report_return_mismatched_types #123812 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)1.1%[0.6%, 1.8%]3
Regressions ❌ (secondary)0.2%[0.1%, 0.2%]6
Improvements ✅ (primary)--0
Improvements ✅ (secondary)-1.1%[-1.1%, -1.1%]2
All ❌✅ (primary)1.1%[0.6%, 1.8%]3

Seems to be limited primarily to one scenario in regex, with lots of new metadata decoding. Asked for follow-up by PR author.

Make early lints translatable #124417 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)1.5%[0.2%, 6.3%]66
Regressions ❌ (secondary)0.4%[0.3%, 0.5%]7
Improvements ✅ (primary)--0
Improvements ✅ (secondary)-0.7%[-1.1%, -0.6%]12
All ❌✅ (primary)1.5%[0.2%, 6.3%]66

Regressions are partially mitigated by #125410 (see earlier in the report). Further follow-up is expected to investigate closing remaining gap (https://github.com/rust-lang/rust/pull/124417#issuecomment-2126056523).

Panic directly in Arguments::new* instead of recursing #117804 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)0.3%[0.3%, 0.3%]2
Regressions ❌ (secondary)0.4%[0.1%, 0.9%]9
Improvements ✅ (primary)-0.5%[-0.5%, -0.5%]1
Improvements ✅ (secondary)--0
All ❌✅ (primary)0.0%[-0.5%, 0.3%]3

Regressions are likely to be inliner noise, not meaningful changes.

Rollup of 7 pull requests #125456 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)--0
Regressions ❌ (secondary)0.3%[0.2%, 0.4%]8
Improvements ✅ (primary)-0.3%[-0.4%, -0.3%]2
Improvements ✅ (secondary)-0.5%[-0.9%, -0.4%]7
All ❌✅ (primary)-0.3%[-0.4%, -0.3%]2

Seems plausible that the regression is due to #124389 (since it affected derive macros). But also seems not worth further investigation given it’s a secondary benchmark and minimal impact. Marked as triaged.

Add assert_unsafe_precondition to unchecked_{add,sub,neg,mul,shl,shr} methods #121571 (Comparison Link)

(instructions:u)meanrangecount
Regressions ❌ (primary)1.5%[0.2%, 3.4%]27
Regressions ❌ (secondary)1.8%[0.4%, 3.8%]5
Improvements ✅ (primary)-0.9%[-2.5%, -0.3%]5
Improvements ✅ (secondary)--0
All ❌✅ (primary)1.1%[-2.5%, 3.4%]32

Regressions are likely expected as we’re lowering more code that’s late-removed.

Nominated Issues

T-compiler

  • No I-compiler-nominated issues this time.

RFC

  • No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

None this week

Next meetings’ agenda draft: hackmd link