T-compiler Meeting Agenda 2024-01-04

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!)
- “Start using clippy on rustc” compiler-team#709
- “Promote tier 3 *-pc-windows-gnullvm targets to tier 2” compiler-team#710

WG checkins

No checkins this week

Backport nominations

T-compiler stable / T-compiler beta

[beta] Fix: Properly set vendor in i686-win7-windows-msvc target" rustc#119544
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

“🐛 Symbol multiply defined since nightly-2023-12-02 with custom builtins.” rust#118609

Unassigned P-high nightly regressions

No unassigned P-high nightly regressions this time.

Performance logs

triage logs for 2024-01-02

Overall, this week had very few regressions and a moderate amount of improvements. The two biggest improvements came in how metadata was being encoded including a change to only store StableCrateId once in DefPathTable which yielded a 0.3% average improvement across 79 different benchmarks.

Triage done by @rylev. Revision range: 1ab783112..67b6975

Summary:

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.3%, 1.5%]	8
Regressions (secondary)	0.8%	[0.2%, 1.3%]	23
Improvements (primary)	-0.6%	[-2.6%, -0.2%]	121
Improvements (secondary)	-5.2%	[-62.5%, -0.2%]	53
All (primary)	-0.5%	[-2.6%, 1.5%]	129

2 Regressions, 3 Improvements, 1 Mixed; 0 of them in rollups 46 artifact comparisons made in total

Regressions

Emit better suggestions for &T == T and T == &T #118431 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	24.0%	[18.1%, 29.5%]	3
Regressions (secondary)	-	-	0
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	24.0%	[18.1%, 29.5%]	3

Blip in the perf infrastructure that was reversed in the next run

rustc_lint: Enforce rustc::potential_query_instability lint #119251 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.2%	[0.2%, 0.3%]	2
Regressions (secondary)	0.3%	[0.2%, 0.4%]	8
Improvements (primary)	-	-	0
Improvements (secondary)	-	-	0
All (primary)	0.2%	[0.2%, 0.3%]	2

Small regression that might just be worth it. There is discussion in #119488 on whether to do a partial revert, but so far the argument is being made to just accept the small regression.

Improvements

Suggest = to == in more cases, even in the face of reference mismatch #119328 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-19.2%	[-22.7%, -15.3%]	3
Improvements (secondary)	-	-	0
All (primary)	-19.2%	[-22.7%, -15.3%]	3

Reversal of perf infrastructure blip in previous run

Only store StableCrateId once in DefPathTable. #119259 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.8%	[0.8%, 0.8%]	1
Regressions (secondary)	-	-	0
Improvements (primary)	-0.3%	[-0.6%, -0.2%]	78
Improvements (secondary)	-0.4%	[-0.6%, -0.3%]	16
All (primary)	-0.3%	[-0.6%, 0.8%]	79

Shrink span encoding further #119367 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	-	-	0
Regressions (secondary)	-	-	0
Improvements (primary)	-0.3%	[-0.5%, -0.2%]	27
Improvements (secondary)	-0.5%	[-0.6%, -0.3%]	11
All (primary)	-0.3%	[-0.5%, -0.2%]	27

Mixed

Implement constant propagation on top of MIR SSA analysis #116012 (Comparison Link)

(instructions:u)	mean	range	count
Regressions (primary)	0.7%	[0.2%, 1.9%]	10
Regressions (secondary)	0.6%	[0.2%, 1.1%]	15
Improvements (primary)	-0.6%	[-2.6%, -0.2%]	26
Improvements (secondary)	-31.2%	[-62.1%, -0.2%]	8
All (primary)	-0.2%	[-2.6%, 1.9%]	36

Change has positive impacts on runtime performance and the improvements outweigh the regressions

Nominated Issues

T-compiler

No I-compiler-nominated issues this time.

RFC

No I-compiler-nominated RFCs this time.

Oldest PRs waiting for review

None this week

Next week’s WG checkins

TODO

Next meetings’ agenda draft: hackmd link