Cache block seeking results for initialized_at_terminator and _exit by jackh726 · Pull Request #162450 · rust-lang/rust

jackh726 · 2026-09-08T01:37:46Z

Caching the block values post-seek results in significant performance wins (especially on pathological benchmarks). These wins extend to NLL, too.

Possibly, this caching could be done further up the stack (more generically), but figured this is a "safer" approach - rather than dealing with other potential fallout.

r? lqd

LLM-generated perf summary table

jackh726 · 2026-09-08T01:38:06Z

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

jackh726 · 2026-09-08T01:38:17Z

@bors try @rust-timer queue

Cache block seeking results for initialized_at_terminator and _exit

jackh726 · 2026-09-08T01:40:42Z

+            if self.cx.initialized_at_terminator(location.block, mpi) {
+                let inserted = self.drop_live_at.insert(drop_point);
+                // Right now, we should visit a drop_point twice.
+                // If we do, this trigger a debug assert so we need we can optimize.
+                debug_assert!(inserted, "drop point should not have been visited yet");


This is technically completely unrelated - but sticking it in as a drive-by pass. I had a though that we might be visiting drop points twice (and thus could switch these conditions for a perf benefit) - but the iteration here is unique.

View changes since the review

rust-bors · 2026-09-08T02:37:15Z

☀️ Try build successful (CI)
Build commit: 2bf7717 (2bf77177e903bc66ebe183042d1ad525545e866a)
Base parent: 2e6e39f (2e6e39f684e1c6b0bbfe16593a23d901e61219ca)

rust-timer · 2026-09-08T03:22:24Z

Finished benchmarking commit (2bf7717): 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)	-3.1%	[-5.7%, -0.2%]	9
Improvements ✅ (secondary)	-4.1%	[-5.7%, -0.2%]	10
All ❌✅ (primary)	-3.1%	[-5.7%, -0.2%]	9

Max RSS (memory usage)

Results (primary -0.4%)

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

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-1.4%, -0.4%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.4%	[-1.4%, 0.5%]	4

Cycles

Results (primary -1.4%, secondary -0.3%)

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

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	3.7%	[3.7%, 3.7%]	1
Improvements ✅ (primary)	-1.8%	[-2.6%, -0.7%]	4
Improvements ✅ (secondary)	-2.2%	[-2.4%, -2.1%]	2
All ❌✅ (primary)	-1.4%	[-2.6%, 0.4%]	5

Binary size

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

Bootstrap: 482.327s -> 479.101s (-0.67%)
Artifact size: 403.54 MiB -> 403.54 MiB (0.00%)

lqd · 2026-09-16T16:17:35Z

Beautiful.

@bors r+ rollup=never

rust-bors · 2026-09-16T16:17:39Z

📌 Commit bbfef75 has been approved by lqd

It is now in the queue for this repository.

JonathanBrouwer · 2026-09-16T18:09:36Z

@bors rollup=iffy
Making a rollup of perf-sensitive PRs

…uwer Rollup of 4 perf-sensitive pull requests Successful merges: - #162450 (Cache block seeking results for initialized_at_terminator and _exit) - #162543 ([rustc_resolve] Correctly keep all reexports in `ModChild::reexport_chain`) - #162712 (perf: Keep the first macro syntax-context mapping inline) - #162747 (Lowering cleanups)

rust-bors · 2026-09-17T00:15:20Z

⌛ Testing commit bbfef75 with merge 40e5555...

Workflow: https://github.com/rust-lang/rust/actions/runs/35165799977

Cache block seeking results for initialized_at_terminator and _exit Caching the block values post-seek results in significant performance wins (especially on pathological benchmarks). These wins extend to NLL, too. Possibly, this caching could be done further up the stack (more generically), but figured this is a "safer" approach - rather than dealing with other potential fallout. r? lqd

Zalathar · 2026-09-17T00:38:20Z

@bors yield (to enclosing perf-sensitive rollup)

rust-bors · 2026-09-17T00:38:24Z

Auto build was cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/35165799977

The next pull request likely to be tested is #162859.

…uwer Rollup of 4 perf-sensitive pull requests Successful merges: - #162450 (Cache block seeking results for initialized_at_terminator and _exit) - #162543 ([rustc_resolve] Correctly keep all reexports in `ModChild::reexport_chain`) - #162712 (perf: Keep the first macro syntax-context mapping inline) - #162747 (Lowering cleanups)

Rollup merge of #162450 - jackh726:polonius-cleanups-4, r=lqd Cache block seeking results for initialized_at_terminator and _exit Caching the block values post-seek results in significant performance wins (especially on pathological benchmarks). These wins extend to NLL, too. Possibly, this caching could be done further up the stack (more generically), but figured this is a "safer" approach - rather than dealing with other potential fallout. r? lqd

rust-timer · 2026-09-17T07:41:42Z

Note

This PR was benchmarked as part of triage of its containing rollup: triage URL.

Finished benchmarking commit (89b0093): 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)	-4.5%	[-5.8%, -3.6%]	12
Improvements ✅ (secondary)	-4.6%	[-5.3%, -4.0%]	3
All ❌✅ (primary)	-4.5%	[-5.8%, -3.6%]	12

Max RSS (memory usage)

Results (primary -3.1%, secondary 3.2%)

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)	3.2%	[2.3%, 4.0%]	2
Improvements ✅ (primary)	-3.1%	[-4.2%, -2.3%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.1%	[-4.2%, -2.3%]	3

Cycles

Results (primary 0.5%)

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

	mean	range	count
Regressions ❌ (primary)	2.0%	[1.7%, 2.4%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-2.5%, -2.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-2.5%, 2.4%]	3

Binary size

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

Bootstrap: missing data
Artifact size: 406.75 MiB -> 406.83 MiB (0.02%)

rustbot assigned lqd Sep 8, 2026

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 8, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 8, 2026

Auto merge of #162450 - jackh726:polonius-cleanups-4, r=<try>

2bf7717

Cache block seeking results for initialized_at_terminator and _exit

jackh726 commented Sep 8, 2026

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 8, 2026

jackh726 commented Sep 16, 2026

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Comment thread compiler/rustc_borrowck/src/type_check/liveness/trace.rs Outdated

rust-cloud-vms Bot force-pushed the polonius-cleanups-4 branch 4 times, most recently from 9664d1b to a18e438 Compare September 16, 2026 16:12

Cache block seeking results for initialized_at_terminator and _exit

bbfef75

rust-cloud-vms Bot force-pushed the polonius-cleanups-4 branch from a18e438 to bbfef75 Compare September 16, 2026 16:13

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Sep 16, 2026

JonathanBrouwer mentioned this pull request Sep 16, 2026

Rollup of 4 perf-sensitive pull requests #162859

Merged

rust-bors Bot merged commit 99aea09 into rust-lang:main Sep 17, 2026
13 of 14 checks passed

rustbot added this to the 1.100.0 milestone Sep 17, 2026

jackh726 deleted the polonius-cleanups-4 branch September 17, 2026 12:15

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Overall result: ✅ improvements - no action needed

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Overall result: ✅ improvements - no action needed

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