borrowck nested items in dead code

[lcnr]

fixes #140583

r? @compiler-errors

[lcnr]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 8659c5f with merge 44541a5...

[bors]

☀️ Try build successful - checks-actions
Build commit: 44541a5 (44541a5256c7929fb92abebc7ef12b7851700767)

[rust-timer]

Finished benchmarking commit (44541a5): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.2%, 3.0%]	14
Regressions ❌ (secondary)	0.4%	[0.0%, 1.1%]	21
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.2%, 3.0%]	14

Max RSS (memory usage)

Results (primary 0.7%, secondary 2.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.4%, 7.3%]	37
Regressions ❌ (secondary)	4.2%	[0.9%, 7.4%]	7
Improvements ✅ (primary)	-0.8%	[-2.6%, -0.4%]	10
Improvements ✅ (secondary)	-2.9%	[-3.3%, -2.4%]	2
All ❌✅ (primary)	0.7%	[-2.6%, 7.3%]	47

Cycles

Results (primary 0.7%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.8%	[0.4%, 3.1%]	31
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[-0.4%, 3.1%]	32

Binary size

Results (primary 1.1%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[1.1%, 1.1%]	1

Bootstrap: 766.288s -> 769.539s (0.42%)
Artifact size: 365.55 MiB -> 365.43 MiB (-0.03%)

[lcnr]

Okay, so clap_derive seems bimodal to me. It now spends more time in llvm. The other 0.5% regression seem to be caused by evaluating the nested_bodies_within query.

#138499 was a 1.4% improvement in issue-88862. We don't fully lose that perf gain again. This benchmark has one closure in dead code, so this is expected https://github.com/rust-lang/rustc-perf/blob/18437e0d5ff596de62047b0697b6ce9f2be1b4f5/collector/compile-benchmarks/issue-88862/src/main.rs#L38-L39.

The remaining regressions are ~0.5% in bitmaps and libc. I would expect that both these crates have a lot of small functions, so calling one more query per function body is actually noticeable? 🤔

Making it less expensive seems difficult. We could separately collect all closures by walking the MIR body right after MIR build, similar to required_consts 🤔

[lcnr]

I've talked with @compiler-errors about this in person, and the small perf hit of computing nested_bodies_within will be necessary to stabilize the new solver regardless, as TypingMode::typeck_for_body will also need to rely on this query.

[compiler-errors]

Yeah, I think this is necessary and worth the perf hit. The nested_bodies_within query could be optimized if we had some efficient way of getting a DefId -> [DefId] parent to child mapping, but AFAICT we don't have that.

@bors r+ rollup=never

[bors]

📌 Commit ffa7d1e has been approved by compiler-errors

It is now in the queue for this repository.