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T-compiler Meeting Agenda 2023-07-06

Announcements

MCPs/FCPs

  • New MCPs (take a look, see if you like them!)
  • Old MCPs (not seconded, take a look)
    • "2024: Decrease debuginfo generated by -Cdebuginfo=1" compiler-team#613 (last review activity: 2 months ago)
    • "Cell Broadband Engine SPU support" compiler-team#614 (last review activity: 2 months ago)
    • "Revise error code documentation standard" compiler-team#615 (last review activity: 2 months ago)
    • "Add support for Zephyr OS" compiler-team#629 (last review activity: about 14 days ago)
    • "Consistently use "region" terminology in later stages of the compiler" compiler-team#634 (last review activity: about 41 days ago)
    • "Add a new --build-id flag to rustc" compiler-team#635 (last review activity: about 41 days ago)
    • "Simplify and improve explicitness of the check-cfg syntax" compiler-team#636 (last review activity: about 22 days ago)
    • "[MCP] proposing a macros working group" compiler-team#637 (last review activity: about 20 days ago)
    • "Add support for visionOS targets" compiler-team#642 (last review activity: about 6 days ago)
    • "Add illumos Tier3 targets" compiler-team#644 (last review activity: about 6 days ago)
    • "Changes to StatementKind::Coverage" compiler-team#645 (last review activity: about 6 days ago)
  • Pending FCP requests (check your boxes!)
    • "Retire the mailing list and make all decisions on zulip" compiler-team#649
    • "Tracking issue for the thiscall calling convention" rust#42202
    • "Add documentation on v0 symbol mangling." rust#97571
    • "Support overriding warnings level for a specific lint via command line" rust#113307
  • Things in FCP (make sure you're good with it)
  • Accepted MCPs
  • Finalized FCPs (disposition merge)
    • "rustdoc: Allow whitespace as path separator like double colon" rust#108537
    • "Add internal_features lint" rust#108955
    • "style-guide: Add chapter about formatting for nightly-only syntax" rust#111119
    • "Don't require associated types with Self: Sized bounds in dyn Trait objects" rust#112319

WG checkins

@_WG-llvm by @nagisa and @Nikita Popov(previous checkin):

  • LLVM 17 branches in about three weeks, which is when we'll start with the update in Rust as well.
  • After much nagging from T-opsem, we've changed getelementptr inbounds semantics to always allow zero offsets.
  • cbeuw has been fuzzing Rust and finding lots of miscompiles on the LLVM side, which I've been working on fixing.

Types team by @nikomatsakis and @Jack Huey (previous checkin):

Progress continues. We've set up a weekly "solver meeting", essentially a deep dive into the new trait solver, a-mir-formality, polonius, etc. Also planning to have an in-person meetup around EuroRust.

Backport nominations

T-compiler stable / T-compiler beta

  • :beta: [1.71? 1.72?] "Fix dropping_copy_types lint from linting in match-arm with side-effects" rust#113231
    • nominated by @Urgau
  • :beta: [1.72.0?] "Revert the lexing of c"…" string literals" rust#113334
    • open for review from @Michael Goulet (compiler-errors)
    • fixes #113235 a P-medium regression
  • No stable nominations for T-compiler this time.

T-rustdoc stable / T-rustdoc beta

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

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PRs S-waiting-on-team

T-compiler

Issues of Note

Short Summary

P-critical

T-compiler

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

T-types

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

T-rustdoc

  • No P-critical issues for T-rustdoc at 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

triage logs for 2023-07-04

A quiet week, with a mixed set of improvements and regressions. Overall
slightly more improvements than regressions.

Triage done by @simulacrum.
Revision range: b5e51db16dfbf5685e32dfe2d9a835a5c695afe4..52d8c490a3aabe65cdd9f2d3aed95034dd5dbad7

Summary:

(instructions:u) mean range count
Regressions (primary) 1.1% [0.3%, 2.8%] 46
Regressions (secondary) 1.5% [0.4%, 6.9%] 71
Improvements (primary) -2.0% [-4.2%, -0.5%] 7
Improvements (secondary) -2.5% [-7.3%, -0.3%] 7
All (primary) 0.7% [-4.2%, 2.8%] 53

2 Regressions, 3 Improvements, 2 Mixed; 0 of them in rollups

51 artifact comparisons made in total

Regressions

Backtrace 0.3.68 #113176 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 2.2% [1.8%, 2.6%] 12
Regressions (secondary) 1.6% [0.3%, 6.8%] 38
Improvements (primary) - - 0
Improvements (secondary) -2.1% [-2.1%, -2.1%] 1
All (primary) 2.2% [1.8%, 2.6%] 12

Appears to be due to increases in binary size, leading to longer link times.

Rewrite UnDerefer #112882 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.7% [0.3%, 1.5%] 26
Regressions (secondary) 1.1% [0.2%, 1.9%] 21
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.7% [0.3%, 1.5%] 26

Another rewrite is pending
which is expected to help resolve the regression.

Improvements

A mish-mash of micro-optimizations #113116 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.8% [-1.7%, -0.3%] 16
Improvements (secondary) -1.4% [-2.3%, -0.8%] 15
All (primary) -0.8% [-1.7%, -0.3%] 16

Make simd_shuffle_indices use valtrees #112718 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.5%, -0.4%] 3
Improvements (secondary) - - 0
All (primary) -0.4% [-0.5%, -0.4%] 3

cargo update #113046 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -1.1% [-2.0%, -0.4%] 119
Improvements (secondary) -0.9% [-1.6%, -0.2%] 48
All (primary) -1.1% [-2.0%, -0.4%] 119

Mixed

Refactor metadata emission to avoid visiting HIR #98867 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.5%, 0.9%] 7
Regressions (secondary) 1.0% [0.2%, 2.3%] 19
Improvements (primary) -2.1% [-3.9%, -0.8%] 6
Improvements (secondary) -4.4% [-7.2%, -1.5%] 2
All (primary) -0.5% [-3.9%, 0.9%] 13

Upgrade to indexmap 2.0.0 #113304 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.4%, 1.2%] 20
Regressions (secondary) 0.7% [0.3%, 1.2%] 16
Improvements (primary) - - 0
Improvements (secondary) -0.6% [-0.6%, -0.5%] 4
All (primary) 0.8% [0.4%, 1.2%] 20

Nominated Issues

T-compiler

  • "Consistently use the highest bit of vector masks when converting to i1 vectors" rust#104693
    • issue nominated by @nils (Nilstrieb) to help find a reviewer for these changes (review assignment has been bounced a few times)
  • "Put needs-triage label on every new issue" rust#113261
    • Proposal advanced by @nils (Nilstrieb), asks opinion from teams

RFC

  • No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

  • "-Z trait-solver=next: Deduplicate region constraints in query responses" rust#111172 (last review activity: about 52 days ago)
    • cc: @lcnr
  • "Only consider places with the same local in each_borrow_involving_path." rust#111753 (last review activity: about 48 days ago)
    • cc: @eholk
  • "Fix #[inline(always)] on closures with target feature 1.1" rust#111836 (last review activity: about 45 days ago)
    • cc: @Jubilee
  • "Simplify duplicate checks for mir validator" rust#111917 (last review activity: about 41 days ago)
    • cc: @oli

Next week's WG checkins

  • @_WG-mir-opt by @oli
  • @_WG-polymorphization by @davidtwco
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