[experiments] Faster debug impls by panstromek · Pull Request #165179 · rust-lang/rust

panstromek · 2026-10-30T07:47:52Z

They have the same signature now, so we can unify them. The implementation for tuple is selected based on whether the concatenated string contains field names.

panstromek · 2026-10-30T07:48:12Z

@bors try @rust-timer queue priority=-5

[experiments] Faster debug impls

rust-bors · 2026-10-30T08:48:56Z

☀️ Try build successful (CI)
Build commit: bd88fc1 (bd88fc1bc68edcaef4f47570360b140c08c323e8)
Base parent: 92b5b8c (92b5b8c87c61b20adc9001b41baf587634a74734)

rust-timer · 2026-10-30T11:07:11Z

Finished benchmarking commit (bd88fc1): comparison URL.

Overall result: ✅ 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.

@bors rollup=iffy 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)	-0.5%	[-0.5%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.5%	[-0.5%, -0.4%]	4

Max RSS (memory usage)

Results (primary 4.1%, secondary 4.7%)

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

	mean	range	count
Regressions ❌ (primary)	4.1%	[4.1%, 4.1%]	1
Regressions ❌ (secondary)	4.7%	[4.7%, 4.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.1%	[4.1%, 4.1%]	1

Cycles

Results (secondary 3.0%)

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)	3.0%	[3.0%, 3.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

Results (primary -0.4%, 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)	-	-	0
Regressions ❌ (secondary)	0.4%	[0.4%, 0.4%]	1
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.4%	[-0.4%, -0.4%]	4

Bootstrap: 484.843s -> 485.918s (0.22%)
Artifact size: 406.61 MiB -> 406.73 MiB (0.03%)

panstromek · 2026-10-30T11:33:19Z

cool, let's try without unsafe

@bors try @rust-timer queue priority=-5

[experiments] Faster debug impls

rust-bors · 2026-10-30T12:33:19Z

☀️ Try build successful (CI)
Build commit: d144b18 (d144b189ca327131a3f6d567b633bb9c8bfc65ef)
Base parent: 92b5b8c (92b5b8c87c61b20adc9001b41baf587634a74734)

rust-timer · 2026-10-30T13:22:11Z

Finished benchmarking commit (d144b18): comparison URL.

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

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

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=iffy 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)	0.3%	[0.2%, 0.5%]	6
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.1%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-0.5%, -0.1%]	9

Max RSS (memory usage)

Results (primary -2.2%, secondary 5.1%)

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)	5.1%	[5.1%, 5.1%]	1
Improvements ✅ (primary)	-2.2%	[-3.0%, -1.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.2%	[-3.0%, -1.3%]	2

Cycles

Results (primary 1.1%, secondary 2.0%)

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

	mean	range	count
Regressions ❌ (primary)	1.1%	[1.1%, 1.1%]	1
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[1.1%, 1.1%]	1

Binary size

Results (primary 0.1%, secondary 0.5%)

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%]	4
Regressions ❌ (secondary)	0.5%	[0.5%, 0.7%]	35
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-0.4%, 0.5%]	8

Bootstrap: 484.843s -> 486.505s (0.34%)
Artifact size: 406.61 MiB -> 406.72 MiB (0.03%)

panstromek · 2026-10-30T13:36:30Z

let's use existing split_ascii_whitespace method

@bors try @rust-timer queue priority=-5

[experiments] Faster debug impls

rust-bors · 2026-10-30T14:35:08Z

☀️ Try build successful (CI)
Build commit: 9b149e5 (9b149e563aebd85b165bafa74d0d849d857c71b4)
Base parent: 92b5b8c (92b5b8c87c61b20adc9001b41baf587634a74734)

rust-timer · 2026-10-30T15:24:41Z

Finished benchmarking commit (9b149e5): comparison URL.

Overall result: ✅ 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.

@bors rollup=iffy 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)	-0.5%	[-0.5%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.5%	[-0.5%, -0.4%]	4

Max RSS (memory usage)

Results (primary 2.1%, secondary 2.2%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	3.0%	[1.9%, 4.9%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-2.3%, -2.3%]	1
All ❌✅ (primary)	2.1%	[2.1%, 2.1%]	1

Cycles

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

Binary size

Results (primary -0.4%, 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)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.4%	[-0.4%, -0.4%]	4

Bootstrap: 484.843s -> 494.86s (2.07%)
Artifact size: 406.61 MiB -> 406.70 MiB (0.02%)

rust-bors · 2026-11-02T09:43:02Z

☔ The latest upstream changes (presumably #165320) made this pull request unmergeable. Please resolve the merge conflicts by rebasing.

panstromek · 2026-11-02T10:15:38Z

incorporated into #165140

panstromek added 4 commits October 29, 2026 15:33

ref: implement debug_struct helpers in terms of each other

5b88658

ref: replace debug_tuple helpers with debug struct ones

ff7c30e

They have the same signature now, so we can unify them. The implementation for tuple is selected based on whether the concatenated string contains field names.

doc: improve comments for debug_struct_fields_finish

ae82815

test improve debug perf

15ee45a