T-compiler Meeting Agenda 2023-12-28

Announcements

Today release of Rust 1.75.0 (blog post draft)
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 (calendar link)

Stable MIR Weekly Meeting at time:2023-12-29T10:00:00-05:00
Types team meeting at time:2024-01-01T10:00:00-05:00
[Types] Rotating new solver / formality / polonius deep dive at time:2024-01-01T11:00:00-05:00
- @Jack Huey are these T-type meetings happening on New Year’s Eve or it’s just calendar repetition? :-)

MCPs/FCPs

New MCPs (take a look, see if you like them!)
- “Add -Z direct-access-external-data” compiler-team#707 (Zulip)
Old MCPs (not seconded, take a look)
- “Require --known-broken-llvm flag for x.py to skip codegen tests on old LLVM” compiler-team#687 (Zulip) (last review activity: about 15 days ago)
  - concern codegen-tests-are-for-new-optimizations
- “Semantics of -Cinstrument-coverage=all” compiler-team#690 (Zulip) (last review activity: about 15 days ago)
- “Add hygiene attributes to compile expanded source code” compiler-team#692 (Zulip) (last review activity: about 15 days ago)
  - concern: added-complexity-to-frontend
- “New Tier-3 target: wasm32-wasi-preview2” compiler-team#694 (Zulip) (last review activity: about 9 days ago)
- “Smooth the renaming transition of wasm32-wasi” compiler-team#695 (Zulip) (last review activity: about 15 days ago)
- “Introduce perma-unstable wasm-c-abi flag” compiler-team#703 (Zulip) (last review activity: about 13 days ago)
- “Support patchable-function-entry” compiler-team#704 (Zulip) (last review activity: about 13 days ago)
Pending FCP requests (check your boxes!)
- “Add a new --build-id flag to rustc” compiler-team#635 (Zulip)
  - concern option-name
  - concern other-existing-options
- “Retire the mailing list and make all decisions on zulip” compiler-team#649 (Zulip)
  - concern automatic-sync
  - concern single-point-of-failure-via-stream-archival
- “Stabilize --json=unused-externs(-silent)” compiler-team#674 (Zulip)
  - concern lint-interactions
- “Support overriding warnings level for a specific lint via command line” rust#113307
  - concern nesting
- “Update Windows platform support” rust#115141
- “Stabilize Wasm target features that are in phase 4 and 5” rust#117457
- “Undeprecate lint unstable_features and make use of it in the compiler” rust#118639
Things in FCP (make sure you’re good with it)
- “Add a stable flag to enable/disable codegen UB checks” compiler-team#625 (Zulip)
  - concern needs-fcp, can someone from T-compiler start it?
- “Report all lints, even if other errors already occurred.” compiler-team#633 (Zulip)
- “Stabilize --json=unused-externs(-silent)” compiler-team#674 (Zulip)
- “Provide option to shorten symbol names by replacing them with a digest” compiler-team#705 (Zulip)
- “uplift some -Zverbose calls and rename to -Zverbose-internals” compiler-team#706 (Zulip)
Accepted MCPs
- “Add infrastructure to “compute the ABI of a Rust type, described as a C type”” compiler-team#672 (Zulip)
- “Support response files generated by ninja with @ninja:path syntax” compiler-team#684 (Zulip)
- “De-llvm some integer intrinsics that on the Rust side always use u32” compiler-team#693 (Zulip)
- “Consistent Handler naming” compiler-team#699 (Zulip)
- “Promote tier 3 riscv32 bare metal targets to tier 2” compiler-team#701 (Zulip)
- “Use the MSVC provided Address Sanitizer runtime when building for MSVC” compiler-team#702 (Zulip)
Finalized FCPs (disposition merge)
- “make soft_unstable show up in future breakage reports” rust#116274
- “Stabilize THIR unsafeck” rust#117673
- “Support async recursive calls (as long as they have indirection)” rust#117703
- “Properly reject default on free const items” rust#117818
- “Make inductive cycles in coherence ambiguous always” rust#118649

WG checkins

@_WG-mir-opt (any WG members have news to share?) (previous checkin):
Checkin text
@_T-rust-analyzer by @Lukas Wirth (previous checkin):
Checkin text

Backport nominations

T-compiler stable / T-compiler beta

:beta: [1.76.0] “Exhaustiveness: Improve complexity on some wide matches” rust#118796
- (mentioned last week)
- PR is now approved and merged, fixes a (P-high) exhaustiveness check rust#118437 (comment)

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

Other issues in progress or waiting on other teams

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.

P-high regressions

P-high beta regressions

No new beta P-high regressions

Unassigned P-high nightly regressions

No unassigned P-high nightly regressions this time.

Performance logs

triage logs for 2023-12-26

Some of the recent noise swings have been appearing again this week, but luckily less often than before. There were a few actual regressions, but most of them were localized to a single stress test. On the other hand, there were a few very nice wins across the board, especially for check and incremental builds, primarily thanks to #118824 and #119265.

Triage done by @kobzol. Revision range: bf9229a2e366b4c311f059014a4aa08af16de5d8..1ab783112ab4e4807304dbd249b39771246013ef

Summary:

(instructions:u)	mean	range	count
Regressions (primary)	0.6%	[0.6%, 0.6%]	1
Regressions (secondary)	2.5%	[0.3%, 4.2%]	10
Improvements (primary)	-0.8%	[-3.3%, -0.1%]	180
Improvements (secondary)	-1.2%	[-5.5%, -0.2%]	109
All (primary)	-0.8%	[-3.3%, 0.6%]	181

5 Regressions, 7 Improvements, 2 Mixed; 1 of them in rollups 58 artifact comparisons made in total

Regressions

Make exhaustiveness usable outside of rustc #118842 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	0.9%	[0.9%, 1.0%]	6
Improvements (primary)	-	-	0
Improvements (secondary)	-0.4%	[-0.4%, -0.4%]	1
All (primary)	-	-	0

This PR enables the use of exhaustiveness checking e.g. in rust-analyzer, which is part of the “librarification effort”. The small regression in a single stress-test benchmark is worth it.

mark ty::Const::Error when meet unsupport ty for const generic params #117176 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.6%, 0.7%]	4
Regressions (secondary)	0.4%	[0.2%, 0.6%]	19
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.7%	[0.6%, 0.7%]	4

This PR only added a test, so this has to be noise.
Already marked as triaged by @jackh726

Exhaustiveness: Improve complexity on some wide matches #118796 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	2.9%	[2.6%, 3.1%]	6
Improvements (primary)	-	-	0
Improvements (secondary)	-1.3%	[-1.3%, -1.3%]	1
All (primary)	-	-	0

This PR fixed a potential hang in the compiler, the regression of the match checking stress-test is unfortunate, but it’s more important to avoid the pathological case.
Already marked as triaged by @apiraino

Subtree sync for rustc_codegen_cranelift #119278 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.9%	[0.8%, 0.9%]	3
Regressions (secondary)	0.5%	[0.3%, 0.7%]	20
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.9%	[0.8%, 0.9%]	3

Noise

fix ICE when using raw ptr in a pattern #119274 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.7%, 0.7%]	1
Regressions (secondary)	0.4%	[0.3%, 0.5%]	6
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.7%	[0.7%, 0.7%]	1

Noise

Improvements

fast path for declared_generic_bounds_from_env #119084 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-1.9%	[-2.9%, -0.2%]	8
Improvements (secondary)	-	-	0
All (primary)	-1.9%	[-2.9%, -0.2%]	8

Very nice improvement to diesel.

use Vec for region constraints instead of BTreeMap #118824 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.5%	[-1.3%, -0.2%]	39
Improvements (secondary)	-0.7%	[-1.7%, -0.2%]	29
All (primary)	-0.5%	[-1.3%, -0.2%]	39

Nice improvements to check builds across the board.

Rollup of 6 pull requests #119237 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.5%	[-0.8%, -0.3%]	17
Improvements (secondary)	-0.4%	[-0.6%, -0.2%]	10
All (primary)	-0.5%	[-0.8%, -0.3%]	17

Nice win for type checking across several benchmarks. It’s unclear which PR from the rollup has caused the wins though.

Stabilize ip_in_core feature #119276 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.9%	[-0.9%, -0.8%]	4
Improvements (secondary)	-0.5%	[-0.8%, -0.2%]	21
All (primary)	-0.9%	[-0.9%, -0.8%]	4

This is just noise returning back to steady state.

Unify SourceFile::name_hash and StableSourceFileId #119139 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.2%	[-0.2%, -0.1%]	3
Improvements (secondary)	-0.8%	[-0.9%, -0.6%]	3
All (primary)	-0.2%	[-0.2%, -0.1%]	3

A few small wins for incremental benchmarks.

Fix display of warning block if it is first element of the top doc block #119283 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.7%	[-0.7%, -0.7%]	2
Improvements (secondary)	-0.4%	[-0.6%, -0.3%]	5
All (primary)	-0.7%	[-0.7%, -0.7%]	2

This PR only modified the UI and tests of rustdoc, so this is just noise.

Make closures carry their own ClosureKind #119258 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements (secondary)	-	-	0
All (primary)	-1.1%	[-1.1%, -1.1%]	1

This is probably just noise.

Mixed

add more niches to rawvec #106790 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.4%	[0.1%, 0.7%]	20
Regressions (secondary)	0.6%	[0.2%, 1.0%]	2
Improvements (primary)	-0.4%	[-2.0%, -0.1%]	27
Improvements (secondary)	-0.9%	[-5.3%, -0.2%]	16
All (primary)	-0.1%	[-2.0%, 0.7%]	47

This PR enabled more optimization opportunities for LLVM, which could in theory help with program optimization, but it also caused some binary size increases and compile-time regressions.
Not marking as triaged yet.

Remove metadata decoding DefPathHash cache #119265 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.9%	[0.9%, 0.9%]	1
Regressions (secondary)	-	-	0
Improvements (primary)	-0.6%	[-2.1%, -0.2%]	101
Improvements (secondary)	-1.2%	[-3.2%, -0.2%]	65
All (primary)	-0.6%	[-2.1%, 0.9%]	102

Very nice check and incremental wins across the board.
The single regression is probably just noise returning back to steady state.

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

“large_assignments: Lint on specific large args passed to functions” rust#116520 (last review activity: 2 months ago)
- cc: WG-compiler-performance? (comment)
“Add -Zuse-sync-unwind” rust#117744 (last review activity: about 41 days ago)
- Do these changes need an MCP?
revert for benchmark rust#118436
- cc: @vadim petrochenkov @pnkfelix seems PR author is waiting on a feedback about perf. results (comment)

Next week’s WG checkins

@_WG-async-foundations by @nikomatsakis and @tmandry
@WG-diagnostics by @Esteban Küber and @oli

Next meetings’ agenda draft: hackmd link