T-compiler Meeting Agenda 2024-04-25

Announcements

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)

No meetings scheduled for next week

MCPs/FCPs

New MCPs (take a look, see if you like them!)
- “Build LLVM using CI image’s Clang on Win + MacOS, instead of installing a copy” compiler-team#742 (Zulip)
- “Add –print=check-cfg” compiler-team#743 (Zulip)
Old MCPs (not seconded, take a look)
- “Target families for executable format” compiler-team#716 (Zulip) (last review activity: 2 months ago)
- “Promote riscv64gc-unknown-linux-musl to tier 2” compiler-team#728 (Zulip) (last review activity: about 48 days ago)
- “Add -Zemit-thin-lto-index=<path> to enable distributed ThinLTO users” compiler-team#735 (Zulip) (last review activity: about 20 days ago)
- “Only emit forward compatible v0 symbol names with graceful degradation” compiler-team#737 (Zulip) (last review activity: about 20 days ago)
- “Partial compilation using MIR-only rlibs” compiler-team#738 (Zulip) (last review activity: about 13 days ago)
Pending FCP requests (check your boxes!)
- merge: Add a new --build-id flag to rustc (compiler-team#635)
  - @|125250 @|116107 @|125294 @|123856
  - concerns: other-existing-options (by petrochenkov) option-name (by wesleywiser)
- merge: Retire the mailing list and make all decisions on zulip (compiler-team#649)
  - no pending checkboxs
  - concerns: automatic-sync (by compiler-errors) single-point-of-failure-via-stream-archival (by pnkfelix)
- merge: Stabilize --env-set option (rust#119926)
  - @|119009 @|116083 @|124288 @|123586 @|125250 @|119031 @|124287 @|116118
  - concerns: other-rustc-vars (by petrochenkov)
- merge: Show files produced by --emit foo in json artifact notifications (rust#122597)
  - @|119009 @|116083 @|123586 @|116107 @|125294 @|119031 @|248906 @|124287 @|426609 @|116118 @_|232957
  - no pending concerns
- merge: Disable version_check::supports_feature on nightly (rust#124339)
  - @|119009 @|116083 @|123586 @|125250 @|116107 @|119031 @|248906 @|124287 @|426609 @|123856 @|116118 @|216206 @_|232957
  - no pending concerns
Things in FCP (make sure you’re good with it)
- “Skip virtual drop for !needs_drop types” compiler-team#730 (Zulip)
- “Make casts of pointers to trait objects stricter” rust#120248
Accepted MCPs
- “allow all command line flags to be passed multiple times, overwriting previous usages” compiler-team#731 (Zulip)
- “Policy: no discussions on T-compiler tracking issues” compiler-team#739 (Zulip)
MCPs blocked on unresolved concerns
- “Add hygiene attributes to compile expanded source code” compiler-team#692 (Zulip) (last review activity: 3 months ago)
  - concern: added-complexity-to-frontend
Finalized FCPs (disposition merge)
- “Tracking Issue for RFC 3013: Checking conditional compilation at compile time” rust#82450
- “Ignore -C strip on MSVC” rust#115120
- “sess: stabilize -Zrelro-level as -Crelro-level” rust#121694
- “stabilize -Znext-solver=coherence” rust#121848
- “Use fulfillment in method probe, not evaluation” rust#122317
- “Fix trait solver overflow with non_local_definitions lint” rust#123594
- “More DefineOpaqueTypes::Yes” rust#123794
Other teams finalized FCPs
- “Stabilise inline_const” rust#104087
- “restrict promotion of const fn calls” rust#121557
- “stabilize -Znext-solver=coherence” rust#121848
- “Use fulfillment in method probe, not evaluation” rust#122317
- “Fix trait solver overflow with non_local_definitions lint” rust#123594
- “More DefineOpaqueTypes::Yes” rust#123794

WG checkins

None today

Backport nominations

T-compiler beta / T-compiler stable

No beta nominations for T-compiler this time.
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 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 P-high beta regressions this time.

Unassigned P-high nightly regressions

No unassigned P-high nightly regressions this time.

Performance logs

triage logs for 2024-04-23

A week dominated by small mixed changes to perf with improvements slightly outweighing regressions. There were no pure regressions, and many of the mixed perf results were deemed worth it for their potential improvements to runtime performance through further optimization from LLVM.

Triage done by @rylev. Revision range: ccfcd950..a77f76e2

Summary:

(instructions:u)	mean	range	count
Regressions (primary)	0.4%	[0.2%, 1.8%]	57
Regressions (secondary)	0.4%	[0.2%, 1.9%]	26
Improvements (primary)	-0.8%	[-3.4%, -0.2%]	50
Improvements (secondary)	-0.6%	[-1.9%, -0.1%]	32
All (primary)	-0.2%	[-3.4%, 1.8%]	107

0 Regressions, 5 Improvements, 6 Mixed; 2 of them in rollups 62 artifact comparisons made in total

Regressions

None (😎)

Improvements

Simplify shallow resolver to just fold ty/consts #123537 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.3%	[0.3%, 0.3%]	1
Regressions (secondary)	-	-	0
Improvements (primary)	-0.9%	[-1.4%, -0.2%]	8
Improvements (secondary)	-0.3%	[-0.4%, -0.2%]	11
All (primary)	-0.8%	[-1.4%, 0.3%]	9

rustdoc-search: single result for items with multiple paths #119912 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.2%	[-0.3%, -0.2%]	3
Improvements (secondary)	-	-	0
All (primary)	-0.2%	[-0.3%, -0.2%]	3

interpret: use ScalarInt for bin-ops; avoid PartialOrd for ScalarInt #124113 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.3%	[-0.4%, -0.2%]	4
Improvements (secondary)	-	-	0
All (primary)	-0.3%	[-0.4%, -0.2%]	4

PatRangeBoundary::compare_with: als add a fast-path for signed integers #124190 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-	-	0
Improvements (secondary)	-3.3%	[-3.3%, -3.3%]	1
All (primary)	-	-	0

Rollup of 7 pull requests #124271 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	0.5%	[0.5%, 0.5%]	1
Improvements (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements (secondary)	-0.9%	[-2.1%, -0.4%]	9
All (primary)	-0.2%	[-0.2%, -0.2%]	1

Mixed

Implement syntax for impl Trait to specify its captures explicitly (feature(precise_capturing)) #123468 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.2%	[0.2%, 0.2%]	4
Regressions (secondary)	-	-	0
Improvements (primary)	-	-	0
Improvements (secondary)	-0.8%	[-0.8%, -0.8%]	1
All (primary)	0.2%	[0.2%, 0.2%]	4

Very small regression on a stress test

At debuginfo=0, don’t inline debuginfo when inlining #123949 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	1.0%	[0.3%, 1.8%]	5
Regressions (secondary)	1.0%	[0.2%, 3.4%]	4
Improvements (primary)	-0.9%	[-2.4%, -0.1%]	22
Improvements (secondary)	-1.2%	[-1.8%, -0.2%]	10
All (primary)	-0.6%	[-2.4%, 1.8%]	27

Improvements outweighed the regressions and was deemed worth it by the reviewer.

Always display stability version even if it’s the same as the containing item #118441 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.3%	[0.2%, 0.3%]	2
Regressions (secondary)	-	-	0
Improvements (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements (secondary)	-	-	0
All (primary)	0.1%	[-0.2%, 0.3%]	3

Noise that is reversed in the next run.

Tell LLVM Vec::len is invariant across growth #123930 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.4%	[0.1%, 1.6%]	7
Regressions (secondary)	0.3%	[0.2%, 0.5%]	11
Improvements (primary)	-0.5%	[-0.9%, -0.4%]	8
Improvements (secondary)	-0.2%	[-0.2%, -0.1%]	3
All (primary)	-0.1%	[-0.9%, 1.6%]	15

The regressions come from LLVM, and it was deemed worth it given the possibility for LLVM to perform more optimization.

fix normalizing in different ParamEnvs with the same InferCtxt #124203 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	4.1%	[4.1%, 4.1%]	1
Improvements (primary)	-0.7%	[-2.4%, -0.2%]	9
Improvements (secondary)	-0.9%	[-0.9%, -0.9%]	1
All (primary)	-0.7%	[-2.4%, -0.2%]	9

Noise

Rollup of 5 pull requests #124241 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.2%, 1.6%]	7
Regressions (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements (primary)	-0.9%	[-2.8%, -0.3%]	7
Improvements (secondary)	-3.9%	[-3.9%, -3.9%]	1
All (primary)	-0.1%	[-2.8%, 1.6%]	14

More time spent in LLVM previously
Pinged the author and reviewer for their perspective.

Nominated Issues

T-compiler

“Tracking issue: 32bit x86 targets without SSE2 have unsound floating point behavior” rust#114479
- Nominated by @apiraino (github comment, zulip prioritization topic)
- This tracking issue shows that we have targets that intersect tier platforms support in different ways. For example i686 are tier 1 but i686 “non-SSE2” are tier 2 (and suffer from codegen unsoundnesses). All these differences are not apparent in our documentation. Should we add a bit of nuances to our target policy? If yes, how?
- [Ralf] Altogether I think there are enough issues with floating point on x86 without SSE (this one, and also #115567) that IMO we should say that tier 1 hardfloat targets require SSE period. It is already the case that using feature flags to turn a hardfloat target into a softfloat target is unsound (Cc #116344), and we should simply hard-error in those cases (e.g. disabling the x87 feature on any hardfloat x86 target). IMO we should do the same when disabling SSE/SSE2 on an i686 target.

RFC

No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

T-compiler

“Enable DestinationPropagation by default.” rust#115105 (last review activity: 3 months ago)
- cc @mw
“Remove unnecessary impl sorting in queries and metadata” rust#120812 (last review activity: 2 months ago)
- @cjgillot
“Use Box<[T]> for ProcessResult::Changed” rust#121355 (last review activity: 2 months ago)
- cc: @Esteban Küber? Note: @Michael Goulet (compiler-errors) was not in favour of this patch
“Handle .init_array link_section specially on wasm” rust#121533 (last review activity: 2 months ago)
- cc @Esteban Küber
“Allow a MIR analysis to perform the state join directly” rust#114900 (last review activity: about 59 days ago)
- cc: @cjgillot

Next week’s WG checkins

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

Next meetings' agenda draft: hackmd link