T Compiler Meeting Agenda 2023 10 05

T-compiler Meeting Agenda 2023-10-05

Announcements

Other WG meetings (calendar link)

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)
    • “Consistently use “region” terminology in later stages of the compiler” compiler-team#634 (last review activity: 4 months ago)
    • “Add a new --build-id flag to rustc” compiler-team#635 (last review activity: 4 months ago)
    • “Simplify and improve explicitness of the check-cfg syntax” compiler-team#636 (last review activity: about 0 days ago)
    • “Add support for visionOS targets” compiler-team#642 (last review activity: about 33 days ago)
    • “Match the behavior of strip and split-debuginfo across platforms” compiler-team#669 (last review activity: about 30 days ago)
  • Pending FCP requests (check your boxes!)
    • “Retire the mailing list and make all decisions on zulip” compiler-team#649
    • " Add type field to distinguish json diagnostic outputs" compiler-team#673
    • “Stabilize --json=unused-externs(-silent)compiler-team#674
    • “Tracking issue for dyn upcasting coercion” rust#65991
    • “Support overriding warnings level for a specific lint via command line” rust#113307
    • “Update Windows platform support” rust#115141
    • “Remove support for compiler plugins.” rust#116412
  • Things in FCP (make sure you’re good with it)
  • Accepted MCPs
  • Finalized FCPs (disposition merge)
    • “stabilize combining +bundle and +whole-archive link modifiers” rust#113301

WG checkins

  • @_WG-rustc-dev-guide by @Santiago Pastorino and @Yuki Okushi|217081 (previous checkin):

    Checkin text

  • Impl Trait initiative by @oli (previous checkin):

    Checkin text

Backport nominations

T-compiler stable / T-compiler beta

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

PRs S-waiting-on-team

T-compiler

Issues of Note

Short Summary

P-critical

T-compiler

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

T-types

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

T-rustdoc

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

P-high regressions

P-high beta regressions

  • No P-high beta regressions this time.

Unassigned P-high nightly regressions

  • “ICE: “no errors encountered even though delay_span_bug issued” on tantivy v0.21 in release mode” rust#116333
    • PR rust#116415 should take care of that (among other similar reported regressions) (comment)
    • PR authored by @Oguz (thanks), review in progress

Performance logs

triage logs for 2023-10-03

A week completely free of pure regressions! The compiler has definitely come out of this week a decent amount faster and less memory hungry than before with the large gain coming from building the compiler with a single CGU on x64 Linux. This not only allows LLVM to do more optimizations across the entire compiler, but should hopefully also result in less non-deterministic performance regressions in the future. This improvement largely comes only at the expense of a few more minutes spent when bootstrapping the compiler.

Triage done by @rylev. Revision range: 27b4eb..9998f4

Summary:

(instructions:u) mean range count
Regressions (primary) 1.0% [0.3%, 6.1%] 41
Regressions (secondary) 2.0% [0.9%, 7.8%] 21
Improvements (primary) -1.3% [-5.1%, -0.2%] 134
Improvements (secondary) -1.8% [-6.9%, -0.2%] 175
All (primary) -0.8% [-5.1%, 6.1%] 175

0 Regressions, 2 Improvements, 4 Mixed; 0 of them in rollups 74 artifact comparisons made in total

Regressions

Improvements

rustdoc: speed up processing of cross-crate fns to fix a perf regression #116195 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.3% [-0.5%, -0.2%] 6
Improvements (secondary) -0.6% [-0.8%, -0.3%] 11
All (primary) -0.3% [-0.5%, -0.2%] 6

Cleanup number handling in match exhaustiveness #116281 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) - - 0
Regressions (secondary) - - 0
Improvements (primary) -0.7% [-1.5%, -0.3%] 3
Improvements (secondary) - - 0
All (primary) -0.7% [-1.5%, -0.3%] 3

Mixed

Don’t use a thread to load the dep graph #116109 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.5%, 1.1%] 2
Regressions (secondary) 0.5% [0.1%, 1.2%] 3
Improvements (primary) -0.2% [-0.3%, -0.2%] 4
Improvements (secondary) - - 0
All (primary) 0.1% [-0.3%, 1.1%] 6
  • A very small regression that basically results in net zero change to performance.

Build rustc with a single CGU on x64 Linux #115554 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.8% [0.3%, 2.6%] 39
Regressions (secondary) 1.6% [0.7%, 2.5%] 23
Improvements (primary) -1.2% [-3.9%, -0.2%] 89
Improvements (secondary) -1.6% [-3.5%, -0.4%] 124
All (primary) -0.6% [-3.9%, 2.6%] 128
  • The change is overwhelmingly positive (especially when taking other measures like max RSS and artifact size) making the small regressions acceptable
  • Take a look at cycles for a nearly completely regression free view of the positive nature of this change.

Rebased: Mark drop calls in landing pads cold instead of noinline #102099 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 1.5% [0.3%, 5.9%] 12
Regressions (secondary) 2.7% [0.4%, 7.7%] 5
Improvements (primary) -0.5% [-4.5%, -0.2%] 78
Improvements (secondary) -0.9% [-6.9%, -0.1%] 65
All (primary) -0.2% [-4.5%, 5.9%] 90
  • Largely positive with a few large regressions caused by more time spent in LLVM. This seems to be expected and acceptable.

Make subtyping explicit in MIR #115025 (Comparison Link)

(instructions:u) mean range count
Regressions (primary) 0.6% [0.4%, 0.8%] 2
Regressions (secondary) 0.5% [0.1%, 1.1%] 17
Improvements (primary) -0.5% [-0.6%, -0.5%] 2
Improvements (secondary) -0.5% [-0.5%, -0.5%] 1
All (primary) 0.0% [-0.6%, 0.8%] 4
  • Small regression that is basically only seen in some secondary benchmarks. Unlikely to be worth deep investigation.

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

  • “Improve print_ttsrust#114571 (last review activity: about 48 days ago)
    • Some review talks with @Vadim Petrochenkov, seems this is waiting on him? (see last comments)
  • “compiler: be more clear about transparent layout violations” rust#114015 (last review activity: about 41 days ago)
    • cc: @pnkfelix
  • “Remove -Zfuel.” rust#115293 (last review activity: about 38 days ago)
    • seems to be ready for a review (though not 100% sure since it receives updates) cc: @Wesley Wiser
  • “Remove -Zfuel.” rust#115293 (last review activity: about 38 days ago)
    • cc: @Wesley Wiser
  • “Suggest adding return if the for semi which can coerce to the fn return type” rust#115196 (last review activity: about 33 days ago)
    • cc @Esteban K├╝ber
  • “Extract suitable code from rustc_query_impl into a new crate rustc_query_misc” rust#115118 (last review activity: about 32 days ago)
    • probably ready for another round review cc: @cjgillot
  • “Parse unnamed fields and anonymous structs or unions” rust#115732 (last review activity: about 24 days ago)
    • cc: @Vadim Petrochenkov

Next week’s WG checkins

  • @_WG-llvm by @nagisa and @Nikita Popov
  • @_WG-mir-opt by @oli

Next meetings' agenda draft: hackmd link