Defer extra liveness calculation for Polonius Alpha

[jackh726]

Based on #161937

Best reviewed by commit.

This moves liveness calculation of NLL-boring/Polonius-relevant locals to be lazy. This allows us to skip unnecessary work.

r? lqd

[jackh726]

@bors try @rust-time queue

[jackh726]

@rust-timer queue

[jackh726]

Disclosure: An LLM was used for experiments here, but all code here is written fresh.

[rust-bors]

💔 Test for 254d008 failed: CI. Failed job:

• try - dist-x86_64-linux-quick (web logs, enhanced plaintext logs)

[jackh726]

@bors try

[rust-bors]

☀️ Try build successful (CI)
Build commit: f904a04 (f904a046d815a8f17021ba39511de661f74c1612)
Base parent: 344f790 (344f7902949345394fa40a5d7dda31f012ccbc0d)

[rust-timer]

Finished benchmarking commit (f904a04): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

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.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	0.4%	[0.3%, 0.5%]	11
Regressions ❌ (secondary)	1.2%	[0.1%, 3.5%]	20
Improvements ✅ (primary)	-3.3%	[-11.9%, -0.2%]	18
Improvements ✅ (secondary)	-4.5%	[-11.6%, -0.1%]	19
All ❌✅ (primary)	-1.9%	[-11.9%, 0.5%]	29

Max RSS (memory usage)

Results (primary -2.0%, secondary 1.2%)

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)	2.9%	[0.8%, 9.2%]	16
Improvements ✅ (primary)	-2.0%	[-2.0%, -2.0%]	1
Improvements ✅ (secondary)	-4.4%	[-5.3%, -3.1%]	5
All ❌✅ (primary)	-2.0%	[-2.0%, -2.0%]	1

Cycles

Results (primary -3.6%, secondary -5.5%)

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)	4.6%	[4.2%, 5.0%]	2
Improvements ✅ (primary)	-3.6%	[-4.4%, -3.0%]	6
Improvements ✅ (secondary)	-6.9%	[-19.1%, -2.3%]	14
All ❌✅ (primary)	-3.6%	[-4.4%, -3.0%]	6

Binary size

Results (secondary -0.0%)

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
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	4
All ❌✅ (primary)	-	-	0

Bootstrap: 475.673s -> 475.822s (0.03%)
Artifact size: 403.60 MiB -> 402.91 MiB (-0.17%)