[wip] terminator perf experiments by panstromek · Pull Request #159928 · rust-lang/rust

panstromek · 2026-07-25T21:32:11Z

panstromek · 2026-07-25T21:33:06Z

hoping for no impact here for now

[wip] terminator perf experiments

rust-bors · 2026-07-25T23:41:48Z

☀️ Try build successful (CI)
Build commit: c9696d1 (c9696d172403366b5d28ed4bee1020bea22674ce)
Base parent: 008fa22 (008fa22ce3f8d3c8dfaca2e6486043c2b21851eb)

rust-timer · 2026-07-26T00:22:23Z

Finished benchmarking commit (c9696d1): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@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)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 4.3%, secondary -4.1%)

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

	mean	range	count
Regressions ❌ (primary)	4.3%	[4.3%, 4.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-4.1%	[-6.5%, -1.7%]	2
All ❌✅ (primary)	4.3%	[4.3%, 4.3%]	1

Cycles

Results (secondary -1.0%)

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)	4.1%	[4.1%, 4.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.0%	[-6.0%, -6.0%]	1
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.2%]	41
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	41
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.2%]	41

Bootstrap: 489.346s -> 488.243s (-0.23%)
Artifact size: 387.69 MiB -> 387.82 MiB (0.03%)

panstromek · 2026-07-26T04:50:06Z

Good, but looks like the metadata is slightly bigger. Probably because it encodes enum instead of just values & targets arrays. We could optimize that by encoding it as two arrays in all cases.

panstromek · 2026-07-26T07:23:53Z

@bors try @rust-timer queue

[wip] terminator perf experiments

rust-bors · 2026-07-26T09:29:48Z

☀️ Try build successful (CI)
Build commit: a75e38e (a75e38eed3fb412c5725c75ad8ccb15cbc512bd2)
Base parent: fdbd8ee (fdbd8ee70d9b68d98be873e1095d74cf9441f0c8)

rust-timer · 2026-07-26T10:10:23Z

Finished benchmarking commit (a75e38e): comparison URL.

Overall result: ❌ regressions - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@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)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.6%, secondary 4.4%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[3.0%, 3.0%]	1
Regressions ❌ (secondary)	4.4%	[4.4%, 4.4%]	1
Improvements ✅ (primary)	-1.7%	[-1.7%, -1.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.6%	[-1.7%, 3.0%]	2

Cycles

Results (secondary 3.4%)

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)	3.4%	[3.0%, 3.8%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.2%]	37
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	40
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.2%]	37

Bootstrap: 487.865s -> 487.9s (0.01%)
Artifact size: 387.69 MiB -> 387.68 MiB (-0.00%)

panstromek · 2026-07-26T18:13:12Z

This is the first one that's supposed to have some impact - one byte down from TerminatorKind (and consequently Terminator and BasicBlockData), but achieved with ThinVec for Call args. That is less shrink_to_fit calls and possible reallocs, but also more heap usage for non-empty args.

@bors try @rust-timer queue

[wip] terminator perf experiments

rust-bors · 2026-07-26T20:17:24Z

☀️ Try build successful (CI)
Build commit: 1338b91 (1338b91d2abc3d1e9cca32ce60d67321e973062f)
Base parent: 9451e06 (9451e069c34e1d7db23a155dcf9c25d1bc127055)

rust-timer · 2026-07-26T22:06:23Z

Finished benchmarking commit (1338b91): comparison URL.

Overall result: ❌ regressions - 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
Regressions ❌ (secondary)	0.6%	[0.2%, 2.6%]	19
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.2%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.7%, secondary 0.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.5%, 2.1%]	12
Regressions ❌ (secondary)	1.8%	[1.2%, 2.4%]	2
Improvements ✅ (primary)	-3.1%	[-3.1%, -3.1%]	1
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	0.7%	[-3.1%, 2.1%]	13

Cycles

Results (secondary 3.7%)

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)	3.7%	[2.2%, 5.2%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.2%]	38
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	40
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[0.0%, 0.2%]	38

Bootstrap: 489.176s -> 487.69s (-0.30%)
Artifact size: 387.73 MiB -> 387.69 MiB (-0.01%)

panstromek · 2026-07-27T06:38:20Z

hm. I wonder what's up with the new solver that it stresses this code that much. That doesn't seem super related.

panstromek · 2026-07-31T15:54:00Z

new solver changes were caused by thin-vec update. Those were resolved in other PRs, I also got a better Decodable impl from review on other PR. Let's try to test the impact after all those changes. I also tweaked take_array to avoid reallocating thinvec to box on error (bug!) path (probably negligible, but maybe optimizes better?).

@bors try @rust-timer queue

[wip] terminator perf experiments

rust-bors · 2026-07-31T18:01:11Z

☀️ Try build successful (CI)
Build commit: ec6ec96 (ec6ec96bab4d0725e243de12ac839706103c3552)
Base parent: fc0f51f (fc0f51f5ca44d4586b0e309181382608cd6a8441)

rust-timer · 2026-07-31T18:47:54Z

Finished benchmarking commit (ec6ec96): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@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)	0.7%	[0.7%, 0.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.2%]	2
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.9%, 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)	1.1%	[0.6%, 3.6%]	20
Regressions ❌ (secondary)	1.4%	[0.4%, 2.4%]	2
Improvements ✅ (primary)	-0.5%	[-0.6%, -0.5%]	4
Improvements ✅ (secondary)	-0.6%	[-1.0%, -0.5%]	6
All ❌✅ (primary)	0.9%	[-0.6%, 3.6%]	24

Cycles

Results (primary -0.7%, secondary 0.7%)

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)	1.7%	[0.5%, 4.0%]	8
Improvements ✅ (primary)	-0.9%	[-1.5%, -0.5%]	10
Improvements ✅ (secondary)	-0.7%	[-0.9%, -0.4%]	6
All ❌✅ (primary)	-0.7%	[-1.5%, 0.5%]	11

Binary size

Results (primary 0.1%, 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)	0.1%	[0.0%, 0.2%]	48
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	41
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	9
All ❌✅ (primary)	0.1%	[0.0%, 0.2%]	48

Bootstrap: 491.246s -> 488.936s (-0.47%)
Artifact size: 390.66 MiB -> 390.59 MiB (-0.02%)

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jul 25, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 25, 2026

rust-bors Bot pushed a commit that referenced this pull request Jul 25, 2026

Auto merge of #159928 - panstromek:shrink-terminator-kind, r=<try>

c9696d1

[wip] terminator perf experiments

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 26, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 26, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 26, 2026

Auto merge of #159928 - panstromek:shrink-terminator-kind, r=<try>

a75e38e

[wip] terminator perf experiments

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rustbot added A-attributes Area: Attributes (`#[…]`, `#![…]`) and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jul 26, 2026

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 26, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 26, 2026

Auto merge of #159928 - panstromek:shrink-terminator-kind, r=<try>

1338b91

[wip] terminator perf experiments

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jul 26, 2026

panstromek mentioned this pull request Jul 27, 2026

Use real ThinVec in StmtDebugInfos #159975

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panstromek added 9 commits July 31, 2026 17:34

generalize Decodable impl to all array types

591fa9a

refactor SwitchTargets to use explicit heap/inline and shrink its size

172bc96

use ThinVec for targets in InlineAsm

bace7ab

wip thinvec args

7fc2861

tidy

7d885ce

fixup

7e8ac17

size assert

b15ccf6

take better decodable impl from the other PR

33ccbf4

avoid realloc on error path

4067656

panstromek force-pushed the shrink-terminator-kind branch from 8a6e1dc to 4067656 Compare July 31, 2026 15:51

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rust-bors Bot pushed a commit that referenced this pull request Jul 31, 2026

Auto merge of #159928 - panstromek:shrink-terminator-kind, r=<try>

ec6ec96

[wip] terminator perf experiments

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rustbot removed S-waiting-on-perf Status: Waiting on a perf run to be completed. perf-regression Performance regression. labels Jul 31, 2026

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rust-timer commented Jul 26, 2026

Overall result: ❌ regressions - no action needed

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Overall result: ❌ regressions - no action needed

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rust-timer commented Jul 26, 2026

Overall result: ❌ regressions - please read:

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rust-timer commented Jul 31, 2026

Overall result: ❌✅ regressions and improvements - no action needed

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