T Compiler Meeting Agenda 2024 06 06

T-compiler Meeting Agenda 2024-06-06

Announcements

  • Rust stable release 1.79 in a week!
  • 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

  • New MCPs (take a look, see if you like them!)
    • No new proposals this time.
  • Old MCPs (stale MCP might be closed as per MCP procedure)
    • None at this time
  • Old MCPs (not seconded, take a look)
    • “Target families for executable format” compiler-team#716 (Zulip) (last review activity: 4 months ago)
    • “Promote riscv64gc-unknown-linux-musl to tier 2” compiler-team#728 (Zulip) (last review activity: 3 months ago)
    • “Only emit forward compatible v0 symbol names with graceful degradation” compiler-team#737 (Zulip) (last review activity: 2 months ago)
    • “Partial compilation using MIR-only rlibs” compiler-team#738 (Zulip) (last review activity: about 55 days ago)
    • “Add Hotpatch flag” compiler-team#745 (Zulip) (last review activity: about 20 days ago)
    • “Add a --emit=nameres for IDEs” compiler-team#749 (Zulip) (last review activity: about 13 days ago)
  • Pending FCP requests (check your boxes!)
    • “Stabilize --env-set option” rust#119926
    • “sanitizers: stabilize core sanitizers (i.e., AddressSanitizer, LeakSanitizer, MemorySanitizer, ThreadSanitizer)” rust#123617
    • “allow overwriting the output of rustc --version” rust#124339
    • “Add --print host-triple to print host target triple” rust#125579
    • “Remove the box_pointers lint.” rust#126018
  • Things in FCP (make sure you’re good with it)
  • Accepted MCPs
  • MCPs blocked on unresolved concerns
  • Finalized FCPs (disposition merge)
    • “Do not try to reveal hidden types when trying to prove auto-traits in the defining scope” rust#122192
    • “Show files produced by --emit foo in json artifact notifications” rust#122597
    • “Item bounds can reference self projections and still be object safe” rust#122804
    • “change method resolution to constrain hidden types instead of rejecting method candidates” rust#123962
    • “Make WHERE_CLAUSES_OBJECT_SAFETY a regular object safety violation” rust#125380
  • Other teams finalized FCPs
    • “Tracking Issue for asm_const” rust#93332
    • “Do not try to reveal hidden types when trying to prove auto-traits in the defining scope” rust#122192
    • “Item bounds can reference self projections and still be object safe” rust#122804
    • “Edition 2024: Make ! fall back to !” rust#123508
    • “change method resolution to constrain hidden types instead of rejecting method candidates” rust#123962
    • “Turn remaining non-structural-const-in-pattern lints into hard errors” rust#124661
    • “Use a default lifetime of 'static in associated consts” rust#125190
    • “Make WHERE_CLAUSES_OBJECT_SAFETY a regular object safety violation” rust#125380

WG checkins

None this week

Backport nominations

T-compiler beta / T-compiler stable

  • :beta: “Fix insufficient logic when searching for the underlying allocation” rust#124761
    • Authored by Urgau
    • Fixes #124685, a diagnostic papercut
    • Urgau: regression introduced in rust#118983 when extending the already stable and deny-by-default ìnvalid_refernce_casting lint
  • :beta: “Handle field projections like slice indexing in invalid_reference_casting” rust#124908
    • Authored by saethlin
    • Follow-up to #124761, improves diagnostics
  • :beta: “Handle Deref expressions in invalid_reference_casting” rust#124978
    • Authored by saethlin
    • Again, follow-up to #124761 to fix diagnostics (fixes the last of the known false positive we encountered in the crater run)
  • :beta: “Closures are recursively reachable” rust#125996
    • Authored by tmiasko
    • Fixes #126012, P-medium regression in MIR optimization
  • 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

  • “regression: trait bound not satisfied” rust#125194
    • reverted breaking changes in #125629
  • “regression: ambiguous outer attributes” rust#125199
    • This will soon get into stable. @Wesley Wiser could you get around cooking a revert for this? Need support? (comment)

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
    • Fixed in #125734, probably another fix will be reworked in #125741 (comment)

Unassigned P-high nightly regressions

  • No unassigned P-high nightly regressions this time.

Performance logs

triage logs for 2024-06-03

A quiet week; we did have one quite serious regression (#115105, “enable DestinationPropagation by default”), but it was shortly reverted (#125794). The only other PR identified as potentially problematic was rollup PR #125824, but even that is relatively limited in its effect.

Triage done by @pnkfelix. Revision range: a59072ec..1d52972d

Summary:

(instructions:u) mean range count
Regressions (primary) 0.9% [0.2%, 2.0%] 28
Regressions (secondary) 0.4% [0.2%, 0.6%] 6
Improvements (primary) -0.4% [-1.2%, -0.2%] 30
Improvements (secondary) -0.5% [-0.9%, -0.2%] 24
All (primary) 0.2% [-1.2%, 2.0%] 58

3 Regressions, 5 Improvements, 6 Mixed; 4 of them in rollups 57 artifact comparisons made in total

Regressions

Rollup of 5 pull requests #125649 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.3% [0.5%, 2.1%] 12
Regressions (secondary) 0.3% [0.3%, 0.4%] 3
Improvements (primary) -0.1% [-0.1%, -0.1%] 1
Improvements (secondary) - - 0
All (primary) 1.2% [-0.1%, 2.1%] 13
  • all 12 of the regressing primary benchmarks are diesel-1.4.8 (in a variety of configurations).
  • problem was isolated to PR #125089 (improve diagnostic output of non_local_definitions lint)
  • Urgau notes: “The lint triggers nearly 150 times in the version of diesel used by rustc-perf, so the benchmark has become a bit a linting machinery benchmark”
  • cc rustc-perf#1819
  • marked as triaged.

Rollup of 5 pull requests #125665 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.5% [0.5%, 0.5%] 1
Regressions (secondary) 0.4% [0.2%, 0.5%] 7
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.5% [0.5%, 0.5%] 1
  • helloworld is sole primary regression.
  • marked as triaged (my own opinion is that helloworld is a useful canary when it regresses by a more significant amount than this)
  • (also the 30-day history shows the story for helloworld to be quite a bit more complicated than what is presented by the effects of this single PR, there are lots of spikes mixed in there)

fn_arg_sanity_check: fix panic message #125695 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.8%, 0.9%] 4
Regressions (secondary) 0.5% [0.2%, 1.5%] 19
Improvements (primary) - - 0
Improvements (secondary) - - 0
All (primary) 0.8% [0.8%, 0.9%] 4
  • helloworld is the sole primary regression.
  • (already) marked as triaged

Improvements

Omit non-needs_drop drop_in_place in vtables #122662 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.6% [-1.5%, -0.2%] 9
Improvements (secondary) -0.5% [-1.0%, -0.2%] 18
All (primary) -0.6% [-1.5%, -0.2%] 9
  • improvements are to helloworld-opt and regex-opt.
  • small but seems real given nature of PR (largely a binary size reduction)

Update cargo #125682 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.5% [-0.6%, -0.5%] 3
Improvements (secondary) -0.4% [-0.5%, -0.2%] 12
All (primary) -0.5% [-0.6%, -0.5%] 3
  • improvements are to helloworld-check
  • probably just noise

Stabilize custom_code_classes_in_docs feature #124577 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.8%, -0.2%] 9
Improvements (secondary) -0.7% [-0.9%, -0.5%] 2
All (primary) -0.4% [-0.8%, -0.2%] 9
  • improvements are to various doc-full benchmarks.
  • Probably measurement bias (unless somehow the stability checks are a noticeable expense?)

Increase vtable layout size #123572 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) - - 0
Improvements (secondary) -0.3% [-0.6%, -0.2%] 10
All (primary) - - 0
  • all “improvements” are to secondary benchmarks: unify-linearly, match-stress, and unused-warnings
  • (the improvement from this PR is expected to be realized in runtime performance, especially for code heavy with vtable lookups. Its unsurprising that it wouldn’t have a noticeable effect on the compiler tooolchain.)

Avoid checking the edition as much as possible #125828 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.4%, -0.3%] 6
Improvements (secondary) -0.4% [-0.5%, -0.3%] 4
All (primary) -0.4% [-0.4%, -0.3%] 6
  • this is recovering performance that was lost in PR #123865

Mixed

Create const block DefIds in typeck instead of ast lowering #124650 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.2% [0.2%, 0.2%] 2
Regressions (secondary) 0.2% [0.2%, 0.2%] 3
Improvements (primary) -0.5% [-0.6%, -0.3%] 6
Improvements (secondary) -0.3% [-0.3%, -0.3%] 1
All (primary) -0.3% [-0.6%, 0.2%] 8
  • as previously noted by @lqd : “Tiny changes, and overall more gains than losses, probably not worth investigation effort imho.”
  • marking as triaged

Rollup of 8 pull requests #125691 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.4% [0.4%, 0.4%] 1
Regressions (secondary) 1.2% [1.2%, 1.2%] 1
Improvements (primary) -0.5% [-0.6%, -0.4%] 2
Improvements (secondary) -0.3% [-0.3%, -0.3%] 1
All (primary) -0.2% [-0.6%, 0.4%] 3
  • regression to image-opt-full
  • improvements to webrender-2022-opt-full and regex-opt-incr-patched
  • had a broad (if small) improvement to binary sizes, which was isolated to PR #124251
  • overall wins seem to outweigh losses; marking as triaged.

don’t inhibit random field reordering on repr(packed(1)) #125360 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.9% [0.6%, 1.3%] 13
Regressions (secondary) 0.4% [0.4%, 0.4%] 2
Improvements (primary) -0.7% [-0.8%, -0.7%] 4
Improvements (secondary) -0.4% [-0.7%, -0.3%] 13
All (primary) 0.5% [-0.8%, 1.3%] 17

Enable DestinationPropagation by default. #115105 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.0% [0.3%, 3.4%] 18
Regressions (secondary) 1.3% [0.3%, 3.3%] 22
Improvements (primary) -0.5% [-4.0%, -0.2%] 23
Improvements (secondary) -0.8% [-1.6%, -0.2%] 18
All (primary) 0.2% [-4.0%, 3.4%] 41

Revert “Auto merge of #115105 - cjgillot:dest-prop-default, r=oli-obk” #125794 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.5% [0.2%, 4.2%] 18
Regressions (secondary) 0.8% [0.1%, 1.5%] 20
Improvements (primary) -1.0% [-3.2%, -0.3%] 15
Improvements (secondary) -1.5% [-3.1%, -0.4%] 18
All (primary) -0.2% [-3.2%, 4.2%] 33
  • revert of above PR
  • marking as triaged

Rollup of 7 pull requests #125824 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.7% [0.5%, 1.1%] 3
Regressions (secondary) - - 0
Improvements (primary) -0.4% [-0.4%, -0.4%] 1
Improvements (secondary) - - 0
All (primary) 0.4% [-0.4%, 1.1%] 4
  • instruction-counts regressed webrender-2022-opt-full, cargo-opt-{incr-patched, full}
  • cycle-counts regressed webrender-2022-opt-{full, incr-full}, cranelift-codegen-opt-incr-full, and clap-opt-incr-patched
  • history view for webrender shows that the cycle-count effect seems real though not quite as pronounced as the original measurements indicate.
  • there are many potential candidates for the cause here in this rollup.
  • not marking as triaged; doing some followup perf runs on individual PR’s

Nominated Issues

T-compiler

  • “Reserve guarded string literals (RFC 3593)” rust#123951
    • This guard will be enabled in Edition 2024 (RFC rendered)
    • @nethercote left a review, seems not too positive about the proposal (was reviewed by T-lang)
    • Nominated by @Esteban Küber asking T-compiler an opinion (comment)

RFC

  • No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

  • “tidy watcher” rust#114209 (last review activity: 5 months ago)
    • This PR looks to me dead in the water. It’s lacking a review and the author seems to not respond. Any taker?
  • “Remove unnecessary impl sorting in queries and metadata” rust#120812 (last review activity: 3 months ago)
    • cc @cjgillot
  • “Suggest a borrow when using dbg” rust#120990 (last review activity: 3 months ago)
    • cc @Esteban Küber
  • “Always emit native-static-libs note, even if it is empty” rust#121216 (last review activity: 3 months ago)
    • cc @Wesley Wiser

Next week’s WG checkins

None

Next meetings' agenda draft: hackmd link