A couple polonius constraints perf improvements

[jackh726]

These give some nice wins in situations where traversal dominates, independent of the lazy liveness change. (This does conflict but the changes are conceptually independent.)

r? lqd

LLM-generated perf summary table

[jackh726]

@bors try @rust-timer queue

[jackh726]

Disclosure: An LLM was used to identify this perf effect and to check the performance of the solution.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 1d91cb4 (1d91cb490050ad9537ce8f1194876a97f435a15a)
Base parent: 36b04f3 (36b04f3ad12a98b1a3cf9efe5313306ef7d5848d)

[rust-timer]

Finished benchmarking commit (1d91cb4): comparison URL.

Overall result: ✅ improvements - no action needed

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-1.0%, -0.2%]	17
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	9
All ❌✅ (primary)	-0.4%	[-1.0%, -0.2%]	17

Max RSS (memory usage)

Results (primary -2.7%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.7%	[-2.7%, -2.7%]	1

Cycles

Results (primary 33.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	33.1%	[2.2%, 64.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	33.1%	[2.2%, 64.0%]	2

Binary size

Results (primary -0.0%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.0%	[-0.1%, -0.0%]	15
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	5
All ❌✅ (primary)	-0.0%	[-0.1%, -0.0%]	15

Bootstrap: 497.193s -> 495.146s (-0.41%)
Artifact size: 408.84 MiB -> 408.91 MiB (0.02%)

[lqd]

r=me with the comments fixed, and discussing the tiny questions

View changes since this review

[jackh726]

@bors r=lqd

[rust-bors]

📌 Commit c690179 has been approved by lqd

It is now in the queue for this repository.

🌲 The tree is currently closed for pull requests below priority 5. This pull request will be tested once the tree is reopened.

Reason for tree closure: GitHub outage

[rust-bors]

☀️ Test successful - CI
Approved by: lqd
Duration: 3h 11m 29s
Pushing d287eb7 to main...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing bba5310 (parent) -> d287eb7 (this PR)

Test differences

Show 4 test diffs

4 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard d287eb7a292caa8abbe12051dce2ee707fe03200 --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. test-x86_64-gnu-llvm-21-1: 34m 14s -> 57m 40s (+68.5%)
2. test-x86_64-rust-for-linux: 33m 46s -> 55m 48s (+65.3%)
3. test-x86_64-gnu-llvm-21-2: 1h 3m -> 1h 41m (+60.4%)
4. test-x86_64-gnu-gcc: 52m 3s -> 1h 17m (+48.5%)
5. test-i686-gnu-1: 2h 16m -> 1h 18m (-42.7%)
6. dist-x86_64-solaris: 1h 15m -> 1h 46m (+39.9%)
7. test-x86_64-gnu-llvm-21-3: 1h 23m -> 1h 55m (+38.5%)
8. dist-powerpc64-linux-musl: 1h 12m -> 1h 39m (+36.8%)
9. test-x86_64-msvc-ext3: 1h 6m -> 1h 30m (+35.6%)
10. test-x86_64-msvc-ext1: 2h 23m -> 1h 34m (-34.5%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (d287eb7): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-1.1%, -0.2%]	16
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	9
All ❌✅ (primary)	-0.5%	[-1.1%, -0.2%]	16

Max RSS (memory usage)

Results (primary 2.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.2%, 2.4%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.2%, 2.4%]	2

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 496.585s -> 503.997s (1.49%)
Artifact size: 408.87 MiB -> 408.93 MiB (0.01%)