T-compiler Meeting Agenda 2024-07-18

Announcements

• Next week release of next stable Rust 1.80
• Is there interest/capacity to pick a topic from this list and schedule a meeting?
  • by the way, 40 P-high unassigned isues
• 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

• Types Team: ITE (Impl Trait Everywhere) Triage time:2024-07-18T22:00:00+01:00

MCPs/FCPs

• New MCPs (take a look, see if you like them!)
  • No new proposals this time.
• Old MCPs (not seconded, take a look)
  • “Add hygiene attributes to compile expanded source code” compiler-team#692 (Zulip) (last review activity: 6 months ago)
    • concern: added-complexity-to-frontend
  • “Target families for executable format” compiler-team#716 (Zulip) (last review activity: 5 months ago)
  • “Partial compilation using MIR-only rlibs” compiler-team#738 (Zulip) (last review activity: 3 months ago)
  • “Add Hotpatch flag” compiler-team#745 (Zulip) (last review activity: 2 months ago)
• Pending FCP requests (check your boxes!)
  • merge: sanitizers: Stabilize AddressSanitizer and LeakSanitizer for the Tier 1 targets (rust#123617)
    • no pending checkboxes
    • concerns: stabilization-scope (by wesleywiser)
    • Note: @Wesley Wiser you approved the MCP, is your recorded concern still standing?
  • merge: Disallow setting some built-in cfg via set the command-line (rust#126158)
    • @|116083 @|125250 @|119031 @|232957
    • no pending concerns
  • merge: Remove the missing_copy_implementations lint. (rust#126293)
    • @|125250 @|426609 @|123856
    • no pending concerns
• Things in FCP (make sure you’re good with it)
  • “Implement lint against ambiguous negative literals” rust#121364
• Accepted MCPs
  • “Add -Z embed-source (DWARFv5 source code embedding extension)” compiler-team#764 (Zulip)
  • “MCP: Alternate cargo freshness algorithm, unstable flag to annotate depinfo file with checksums and file sizes” compiler-team#765 (Zulip)
• MCPs blocked on unresolved concerns
  • merge: Add --print host-triple to print host target triple (rust#125579)
    • @|125250 @|232957
    • concerns: triple vs tuple (by lcnr)
    • with regard to the naming question (“tuple” or “triple”), there’s a Zulip topic
  • merge: Add a new --build-id flag to rustc (compiler-team#635)
    • @|125250 @|116107 @|125294 @|123856
    • concerns: other-existing-options (by petrochenkov) option-name (by wesleywiser)
  • “Retire the mailing list and make all decisions on zulip” compiler-team#649 (Zulip)
    • concern: automatic-sync
  • merge: Stabilize --env-set option (rust#119926)
    • @|119009 @|124288 @|123586 @|125250 @|119031 @|124287 @_|116118
    • concerns: other-rustc-vars (by petrochenkov)
• Finalized FCPs (disposition merge)
  • No new finished FCP (disposition merge) this time.
• Other teams finalized FCPs
  • “Fix ambiguous cases of multiple & in elided self lifetimes” rust#117967
  • “offset_from: always allow pointers to point to the same address” rust#124921

WG checkins

None

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 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 in progress or waiting on other teams

Issues of Note

Short Summary

• 0 T-compiler P-critical issues
  • 0 of those are unassigned
• 68 T-compiler P-high issues
  • 40 of those are unassigned
• 0 P-critical, 2 P-high, 2 P-medium, 2 P-low regression-from-stable-to-beta
• 0 P-critical, 0 P-high, 6 P-medium, 2 P-low regression-from-stable-to-nightly
• 0 P-critical, 35 P-high, 100 P-medium, 17 P-low regression-from-stable-to-stable

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 new beta regressions (#127339 fixed by #127568 now beta-backport accepted and #127342 fixed downstream)

Unassigned P-high nightly regressions

• No unassigned P-high nightly regressions this time.

Performance logs

triage logs 2024-07-16

Fairly quite week with the only pure regressions being small and coming from correctness fixes. The biggest single change came from turning off the -Zenforce-type-length-limit check which had positive impacts across many different benchmarks since the compiler is doing strictly less work.

Triage done by @rylev. Revision range: a2d58197..5572759b

Summary:

2 Regressions, 3 Improvements, 2 Mixed; 1 of them in rollups 56 artifact comparisons made in total

Regressions

Fix regression in the MIR lowering of or-patterns #127028 (Comparison Link)

• Given this is a correctness fix, and the regressions seem in line with previous historical performance (i.e., it regressed back to a previous baseline), I think it’s safe to call this triaged

Avoid follow-up errors and ICEs after missing lifetime errors on data structures #127311 (Comparison Link)

• Instruction counts go up, cycles do not (deeply nested multi is probably just noise in mono collection). In any case, this is a correctness fix so it seems like a small perf hit would be acceptable in any case.

Improvements

Fix Parser::look_ahead #127636 (Comparison Link)

Gate the type length limit check behind a nightly flag #127670 (Comparison Link)

find_field does not need to be a query. #127718 (Comparison Link)

Mixed

Rollup of 7 pull requests #127580 (Comparison Link)

• Noise

Only track mentioned places for jump threading #127087 (Comparison Link)

• The perf impact was expected given the pre-merge runs and is less severe than it was pre-merge.

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

• “Remove unnecessary impl sorting in queries and metadata” rust#120812 (last review activity: 5 months ago)
  • cc: @cjgillot
• “Stop using LLVM struct types for array/pointer offset GEPs” rust#122325 (last review activity: 4 months ago)
  • cc: @Nikita Popov (author replied to your comment from last March)

Next week’s WG checkins

None

Next meetings' agenda draft: hackmd link