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[perf experiment] Enable DeduplicateBlocks#106551

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saethlin wants to merge2 commits intorust-lang:masterfromsaethlin:deduplicate-blocks

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[perf experiment] Enable DeduplicateBlocks#106551

saethlin wants to merge2 commits intorust-lang:masterfromsaethlin:deduplicate-blocks

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saethlin commentedJan 7, 2023

It looks to me like all this really does is delete duplicated emptyunreachable blocks, and the occasionalStorageDead + drop block. Perhaps something unexpected turns up in perf.

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rustbot added S-waiting-on-review

Status: Awaiting review from the assignee but also interested parties.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue. labels

Jan 7, 2023

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rustbot added the S-waiting-on-perfStatus: Waiting on a perf run to be completed. label

Jan 7, 2023

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bors commentedJan 7, 2023

⌛ Trying commit 098af8fbffa06926b3d72b2e136cc2e3c224431f with merge 11d6ba903e6762c93f69ccf2ece4c445cfc575ae...

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bors commentedJan 7, 2023

☀️ Try build successful -checks-actions
Build commit: 11d6ba903e6762c93f69ccf2ece4c445cfc575ae (11d6ba903e6762c93f69ccf2ece4c445cfc575ae)

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rust-timer commentedJan 7, 2023

Finished benchmarking commit (11d6ba903e6762c93f69ccf2ece4c445cfc575ae):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)	0.9%	[0.3%, 2.1%]	7
Regressions ❌ (secondary)	1.4%	[0.2%, 2.6%]	11
Improvements ✅ (primary)	-0.6%	[-1.0%, -0.3%]	15
Improvements ✅ (secondary)	-0.5%	[-0.6%, -0.3%]	4
All ❌✅ (primary)	-0.2%	[-1.0%, 2.1%]	22

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)	2.7%	[1.2%, 4.7%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-3.0%, -0.0%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-3.0%, 4.7%]	6

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)	2.2%	[2.2%, 2.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.2%	[-1.2%, -1.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-1.2%, 2.2%]	2

rustbot added perf-regressionPerformance regression. and removed S-waiting-on-perfStatus: Waiting on a perf run to be completed. labels

Jan 7, 2023

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saethlin commentedJan 7, 2023•
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Cachegrind diffs look like this:

--------------------------------------------------------------------------------Ir          --------------------------------------------------------------------------------173,178,186  PROGRAM TOTALS--------------------------------------------------------------------------------Ir           file:function--------------------------------------------------------------------------------176,073,369  ???:<rustc_data_structures::obligation_forest::ObligationForest<rustc_trait_selection::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection::traits::fulfill::FulfillProcessor>

rust/compiler/rustc_data_structures/src/obligation_forest/mod.rs

Line 413 ina2112fc

pubfnprocess_obligations<P>(&mutself,processor:&mutP) ->P::OUT

Which is interesting. I have never seen a case like this where the whole regression is accounted for by a codegen change in one function.

Enable DeduplicateBlocks

ee29825

saethlin force-pushed thededuplicate-blocks branch from098af8f toee29825Compare

January 8, 2023 01:06

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saethlin commentedJan 8, 2023

Compiling rustc, here is the size of the blocks that get deduplicated:

(  1)     9855 (91.4%, 91.4%): 0(  2)      597 ( 5.5%, 96.9%): 2(  3)      260 ( 2.4%, 99.3%): 1(  4)       55 ( 0.5%, 99.8%): 3(  5)        7 ( 0.1%, 99.9%): 4(  6)        1 ( 0.0%, 99.9%): 5

And with DestinationPropagation enabled, this distribution slants much more towards 0.

The limit of this pass was previously set at 10. Things must have been very different back in the day to justify setting it that high. I'm setting the limit down to 3.

@bors try@rust-timer queue

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rustbot added the S-waiting-on-perfStatus: Waiting on a perf run to be completed. label

Jan 8, 2023

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bors commentedJan 8, 2023

⌛ Trying commitee29825 with merge 303c0a1f5a0e2a8be2e7b8e1eac1978c0a63f3e5...

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bors commentedJan 8, 2023

☀️ Try build successful -checks-actions
Build commit: 303c0a1f5a0e2a8be2e7b8e1eac1978c0a63f3e5 (303c0a1f5a0e2a8be2e7b8e1eac1978c0a63f3e5)

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rust-timer commentedJan 8, 2023

Finished benchmarking commit (303c0a1f5a0e2a8be2e7b8e1eac1978c0a63f3e5):comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

@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)	0.7%	[0.3%, 1.1%]	6
Regressions ❌ (secondary)	1.4%	[0.1%, 2.5%]	10
Improvements ✅ (primary)	-0.6%	[-0.8%, -0.4%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.8%, 1.1%]	10

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)	1.7%	[1.7%, 1.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-4.7%, -0.0%]	2
Improvements ✅ (secondary)	-3.4%	[-3.7%, -3.1%]	2
All ❌✅ (primary)	-1.0%	[-4.7%, 1.7%]	3

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

rustbot removed the S-waiting-on-perfStatus: Waiting on a perf run to be completed. label

Jan 8, 2023

Remove limit

3b77094

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saethlin commentedJan 8, 2023•
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Adding a tighter limit to this seems to have removed our improvements but hardly altered the regressions. I would not have expected that. So if I remove the limit entirely, I should see huge regression due to makingoptimized_mir slow, but what else will show up?

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rustbot added the S-waiting-on-perfStatus: Waiting on a perf run to be completed. label

Jan 8, 2023

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bors commentedJan 8, 2023

⌛ Trying commit3b77094 with merge 8992fea7489ae2ab19a68d91257bc3ea778fcf79...

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bors commentedJan 8, 2023

☀️ Try build successful -checks-actions
Build commit: 8992fea7489ae2ab19a68d91257bc3ea778fcf79 (8992fea7489ae2ab19a68d91257bc3ea778fcf79)

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rust-timer commentedJan 9, 2023

Finished benchmarking commit (8992fea7489ae2ab19a68d91257bc3ea778fcf79):comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

@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)	0.6%	[0.2%, 0.9%]	5
Regressions ❌ (secondary)	1.3%	[0.4%, 2.6%]	17
Improvements ✅ (primary)	-0.5%	[-0.9%, -0.2%]	13
Improvements ✅ (secondary)	-0.5%	[-0.7%, -0.3%]	3
All ❌✅ (primary)	-0.2%	[-0.9%, 0.9%]	18

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)	2.3%	[1.8%, 3.0%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.3%	[-4.5%, -0.0%]	2
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	0.5%	[-4.5%, 3.0%]	5

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)	1.6%	[1.6%, 1.6%]	1
Regressions ❌ (secondary)	2.6%	[2.2%, 3.1%]	4
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[-0.6%, 1.6%]	2

rustbot removed the S-waiting-on-perfStatus: Waiting on a perf run to be completed. label

Jan 9, 2023

cjgillot added the A-mir-optArea: MIR optimizations label

Jan 21, 2023

Noratrieb added S-waiting-on-authorStatus: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-reviewStatus: Awaiting review from the assignee but also interested parties. labels

Feb 24, 2023

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Noratrieb commentedFeb 24, 2023

Marking as waiting on author because it's still a draft.

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saethlin commentedApr 2, 2023

#106428 enabled deduplicating unreachable blocks. The distribution of block sizes now looks like this (it used to be dominated by 0):

(  1)     5006 (63.2%, 63.2%): 1(  2)     1469 (18.5%, 81.7%): 0(  3)     1301 (16.4%, 98.1%): 2(  4)       62 ( 0.8%, 98.9%): 3(  5)       54 ( 0.7%, 99.6%): 4(  6)        9 ( 0.1%, 99.7%): 6(  7)        6 ( 0.1%, 99.8%): 5(  8)        3 ( 0.0%, 99.8%): 7(  9)        2 ( 0.0%, 99.9%): 8( 10)        1 ( 0.0%, 99.9%): 9

It looks like most of the 0-statement blocks aredrop terminators. the 1-statement blocks are split between_0 = +goto andStorageDead +goto.

I suspect that this distribution will be significantly reshaped by jump threading or whatever other passes land, and since this pass isn't deleting enough MIR to produce a benefit, I'm closing this.