T-compiler Meeting Agenda 2022-11-17

Announcements

Compiler Team Planning meeting at time:2022-11-18T10:00:00-05:00
Reminder: if you see a PR/issue that seems like there might be legal implications due to copyright/IP/etc, please let the Core team know (or at least message @pnkfelix or @Wesley Wiser so we can pass it along).

Other WG meetings

MCPs/FCPs

New MCPs (take a look, see if you like them!)
- “New tier-3 targets for OpenHarmony” compiler-team#568
Old MCPs (not seconded, take a look)
- “Arbitrary annotations in compiletest” compiler-team#513 (last review activity: 6 months ago)
- “Add #[alias] attribute to allow symbol aliasing” compiler-team#526 (last review activity: 3 months ago)
- “Use RangeInclusive in SpanData instead of lo/hi” compiler-team#534 (last review activity: 2 months ago)
- " Promote i586-unknown-linux-gnu to Tier 2 with Host Tools " compiler-team#543 (last review activity: 2 months ago)
- “Lower baseline expectations for i686 unix-like targets” compiler-team#548 (last review activity: 2 months ago)
- “MCP: Flag to disable extended error info.” compiler-team#550 (last review activity: about 50 days ago)
- “configurable rustc timeout for compiletest tests” compiler-team#554 (last review activity: 2 months ago)
- “Rustc Contributor Program Major Change Proposal” compiler-team#557 (last review activity: about 23 days ago)
- “Introduce a #[rustc::*] tool attribute namespace and provide a stable #[rustc::on_unimplemented] attribute” compiler-team#560 (last review activity: about 29 days ago)
- “-Z instrument-xray option” compiler-team#561 (last review activity: about 29 days ago)
- “Redefine dropck in terms of bound-like constructs” compiler-team#563 (last review activity: about 13 days ago)
Pending FCP requests (check your boxes!)
- “Change bindings_with_variant_name to deny-by-default” rust#104154
- “Stabilize native library modifier verbatim” rust#104360
Things in FCP (make sure you’re good with it)
- “Reboot Parallel Rustc WG Proposal” compiler-team#567
- “Raw pointer alignment checks in debug” compiler-team#570
- “Unreserve braced enum variants in value namespace” rust#103578
Accepted MCPs
- “Raise minimum supported macOS and iOS versions” compiler-team#556
- “Custom THIR -> MIR parser for testing purposes” compiler-team#564
- “Support enum as type of static variable with #[linkage]” compiler-team#565
- “Change the global default for download-ci-llvm to if-available” compiler-team#566
Finalized FCPs (disposition merge)
- “Make PROC_MACRO_DERIVE_RESOLUTION_FALLBACK a hard error” rust#84022
- “Make Sized coinductive, again” rust#100386
- “Handle projections as uncovered types during coherence check” rust#100555
- “Elaborate supertrait obligations when deducing closure signatures” rust#101834
- “make const_err a hard error” rust#102091
- “make unaligned_reference a hard error” rust#102513
- “make order_dependent_trait_objects show up in future-breakage reports” rust#102635
- “Stabilize raw-dylib for non-x86” rust#102793
- “Use token::Lit in ast::ExprKind::Lit.” rust#102944

WG checkins

@_WG-polymorphization by @davidtwco (previous checkin):
There’s no update from wg-polymorphization again this cycle, we think it’ll benefit from the trait system refactor work being spearheaded by lcnr.
@_WG-rls2.0 by @Lukas Wirth (previous checkin):
GAT support in r-a landed just a few days before stabilization of the feature. Some improvements were done for making the linkedProjects config of r-a work better for the rust-lang/rust repo. An RFC#3344 has been written that would allow us to get rid of the RUSTC_WRAPPER hack in rust-analyzer. Finally we looked a bit more into whether turning library into a separate workspace would be feasible such that r-a can resolve third party crates used by std as that is still blocking a type inference PR from landing in r-a, unfortunately that seems to introduce too much churn zulip thread.

Backport nominations

T-compiler stable / T-compiler beta

:beta: “Revert “Normalize opaques with escaping bound vars”” rust#103509
- Nominated by @Michael Goulet (compiler-errors)
- approved, just some tests failing
- Fixes P-high perf. regression #103423
:beta: “Use 64 bits for incremental cache in-file positions” rust#104164
- Nominated by @Michael Goulet (compiler-errors)
- Fixes incr-comp issue #79786
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.

:back: / :shrug: / :hand:

PRs S-waiting-on-team

T-compiler

“Stabilize native library modifier verbatim” rust#104360
- Stabilization report
- RFC is open (comment)
“Raise minimum supported Apple OS versions” rust#104385
- RFC is open (comment)
- Mark Rousskov added some thoughts (comment)
(other hidden issues in progress or waiting on other teams, details here)

Oldest PRs waiting for review

T-compiler

“Fix implied outlives bounds logic for projections” rust#101680 (last review activity: 2 months ago)
- cc @Esteban Küber for comment but otherwise waiting on @nikomatsakis?
“support higher-ranked regions in opaque type inference” rust#100503 (last review activity: about 52 days ago)
- assigned now to @nikomatsakis
“Add powerpc64-ibm-aix as Tier-3 target” rust#102293 (last review activity: about 51 days ago)
- was waiting on mcp https://github.com/rust-lang/compiler-team/issues/553, now approved (cc @davidtwco )
“Make missing_copy_implementations more cautious” rust#102406 (last review activity: about 49 days ago)
- @Wesley Wiser is this still waiting for review (comment)?

Issues of Note

Short Summary

P-critical

T-compiler

“ld64.lld: error: too many personalities (4) for compact unwind to encode” rust#102754
- discussed last week (maybe a downgrade to P-high)

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

“Possible codegen regression when matching against nested enums” rust#104519
- issue was filed yesterday. seems a miscompilation in nightly 2022-11-16

Performance logs

triage logs for 2022-11-14

A light week for triage. The biggest of the three regressions has a (hopeful) fix up already. The second biggest is a regression we are accepting for sake of correctness of incremental-compilation. The third regression is small and may well be removed as the type system internals are improved. max-rss seems stable.

Triage done by @pnkfelix. Revision range: 57d3c58e..96ddd32c

Summary:

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.2%, 1.4%]	87
Regressions (secondary)	0.7%	[0.2%, 2.3%]	36
Improvements (primary)	-0.5%	[-1.2%, -0.3%]	12
Improvements (secondary)	-0.9%	[-2.0%, -0.2%]	9
All (primary)	0.5%	[-1.2%, 1.4%]	99

3 Regressions, 4 Improvements, 3 Mixed; 2 of them in rollups 30 Untriaged Pull Requests 40 artifact comparisons made in total

Regressions

Better error for HRTB error from generator interior #103171 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	1.6%	[1.3%, 2.1%]	6
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	-	-	0

Already triaged (by two different people).
Also, according to comment thread, this change is slated to be removed once binders support implied bounds, so even if there is a minor regression attached to this PR, the PR should nonetheless go away eventually.

Recover wrong-cased keywords that start items #99918 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.6%	[0.2%, 1.2%]	80
Regressions (secondary)	0.8%	[0.3%, 1.4%]	11
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.6%	[0.2%, 1.2%]	80

Believed to be fixed by https://github.com/rust-lang/rust/pull/104410

Hash spans when interning types #104282 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.5%	[0.2%, 0.9%]	44
Regressions (secondary)	0.6%	[0.2%, 0.9%]	19
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.5%	[0.2%, 0.9%]	44

already triaged; its a regression we are accepting for sake of correctness

Improvements

Remove allow(rustc::potential_query_instability) in rustc_trait_selection #103723 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.5%	[-0.5%, -0.5%]	1
Improvements (secondary)	-0.8%	[-1.0%, -0.5%]	7
All (primary)	-0.5%	[-0.5%, -0.5%]	1

Rollup of 9 pull requests #104236 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.3%	[-0.4%, -0.2%]	21
Improvements (secondary)	-0.3%	[-0.6%, -0.2%]	12
All (primary)	-0.3%	[-0.4%, -0.2%]	21

Rollup of 9 pull requests #104246 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.7%	[-0.8%, -0.6%]	3
Improvements (secondary)	-0.5%	[-0.6%, -0.3%]	4
All (primary)	-0.7%	[-0.8%, -0.6%]	3

Retry failed macro matching for diagnostics #103898 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.8%	[-1.3%, -0.3%]	11
Improvements (secondary)	-	-	0
All (primary)	-0.8%	[-1.3%, -0.3%]	11

Mixed

resolve: More detailed effective visibility tracking for imports #103965 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.3%	[0.2%, 0.4%]	4
Regressions (secondary)	0.3%	[0.2%, 0.4%]	5
Improvements (primary)	-0.2%	[-0.2%, -0.2%]	3
Improvements (secondary)	-0.5%	[-1.1%, -0.4%]	9
All (primary)	0.1%	[-0.2%, 0.4%]	7

This is an internal refactoring that we need to get more precise tracking of imports in presence of globs.
treating the regressions as acceptable; marked it as triaged.

rustc_codegen_ssa: Better code generation for niche discriminants. #102872 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.5%	[0.5%, 0.6%]	2
Regressions (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements (primary)	-	-	0
Improvements (secondary)	-1.3%	[-2.2%, -0.3%]	4
All (primary)	0.5%	[0.5%, 0.6%]	2

already triaged

Merge crossbeam-channel into std::sync::mpsc #93563 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.8%	[0.4%, 1.1%]	5
Regressions (secondary)	0.5%	[0.5%, 0.5%]	1
Improvements (primary)	-0.7%	[-1.1%, -0.3%]	3
Improvements (secondary)	-	-	0
All (primary)	0.2%	[-1.1%, 1.1%]	8

already triaged

Nominated Issues

T-compiler

“Panic on invalid usages of MaybeUninit::uninit().assume_init()” rust#100423
- @RalfJ provides great summary in this comment
“const eval interpreter step limit being hit on nightly for long-running while loop” rust#103814
- #[const_eval_limit] is now on nightly, people are tripping over it (comments in #93481)
- @pnkfelix says: the lang team did discuss #103877 yesterday, and I think we managed to convince niko that shifting from a hard error to a lint is reasonable
- Felix mentions for context also #67217

RFC

No nominated RFCs for T-compiler this time.

Next week’s WG checkins

@_WG-self-profile @mw and @Wesley Wiser