Speed up compilation of type-system-chess

[nnethercote]

type-system-chess is an unusual program that implements a compile-time chess position solver in the trait system(!) This PR is about making it compile faster.

r? @ghost

[nnethercote]

These lines are the cause. They perform deduplication on obligation vectors. The vectors get enormous, the biggest are over 250,000 elements. The deduplication of these huge vectors is effective, typically removing more than half of the elements.

[nnethercote]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 3c59e126ee8f731fb518af16ecafcb0746ae9431 with merge 78d71d60405cf6176f462492f3acea7134e818eb...

[bors]

☀️ Try build successful - checks-actions
Build commit: 78d71d60405cf6176f462492f3acea7134e818eb (78d71d60405cf6176f462492f3acea7134e818eb)

[rust-timer]

Finished benchmarking commit (78d71d60405cf6176f462492f3acea7134e818eb): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

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

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	0.5%	[0.5%, 0.5%]	1
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-2.3%	[-4.5%, -0.9%]	26
All ❌✅ (primary)	-0.5%	[-1.3%, 0.4%]	2

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.6%	[2.6%, 2.6%]	1
Regressions ❌ (secondary)	2.7%	[1.6%, 3.4%]	3
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[-1.3%, 2.6%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-3.2%, -1.9%]	7
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 631.452s -> 631.003s (-0.07%)

[nnethercote]

Perf results look good, various small improvements in secondary benchmarks. The real driver was the type-system-chess program I mentioned above, where the walltime and max-rss changes were both about -85% when I measured them locally.

r? @compiler-errors

[compiler-errors]

@bors r+

[bors]

📌 Commit 698f0e3 has been approved by compiler-errors

It is now in the queue for this repository.

[bors]

⌛ Testing commit 698f0e3 with merge a1e1dba...

[bors]

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing a1e1dba to master...

[rust-timer]

Finished benchmarking commit (a1e1dba): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-1.7%, -1.7%]	1
Improvements ✅ (secondary)	-2.2%	[-4.2%, -0.7%]	28
All ❌✅ (primary)	-1.7%	[-1.7%, -1.7%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.2%	[1.2%, 1.2%]	1
Regressions ❌ (secondary)	2.4%	[2.4%, 2.4%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.3%	[-3.5%, -1.2%]	2
All ❌✅ (primary)	1.2%	[1.2%, 1.2%]	1

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

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

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 633.189s -> 633.173s (-0.00%)
Artifact size: 347.08 MiB -> 347.02 MiB (-0.02%)

[zesterer]

Is this likely to have a meaningful impact on other crates that produce a lot of trait obligations such as chumsky?

[nnethercote]

type-system-chess is an extreme outlier. I doubt this will have any effect on "real world" crates beyond perhaps a couple of percent. But you'd have to measure to be sure (nightly vs release should suffice).