Tell LLVM Vec::len is invariant across growth

[Mark-Simulacrum]

This allows LLVM to avoid re-loading it from memory.

[rustbot]

r? @jhpratt

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[Mark-Simulacrum]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 066490a with merge e80b3f5...

[bors]

☀️ Try build successful - checks-actions
Build commit: e80b3f5 (e80b3f5562d82301c69775100a4320701d168368)

[rust-timer]

Finished benchmarking commit (e80b3f5): 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)	0.2%	[0.2%, 0.4%]	18
Regressions ❌ (secondary)	0.3%	[0.2%, 0.4%]	13
Improvements ✅ (primary)	-0.5%	[-1.0%, -0.3%]	9
Improvements ✅ (secondary)	-0.2%	[-0.3%, -0.2%]	4
All ❌✅ (primary)	0.0%	[-1.0%, 0.4%]	27

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)	5.2%	[5.2%, 5.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.1%	[-2.6%, -1.6%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[-2.6%, 5.2%]	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)	2.0%	[0.8%, 3.3%]	4
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Binary size

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)	0.0%	[0.0%, 0.1%]	27
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	4
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	11
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	34
All ❌✅ (primary)	-0.0%	[-0.4%, 0.1%]	38

Bootstrap: 677.239s -> 676.592s (-0.10%)
Artifact size: 315.99 MiB -> 315.99 MiB (-0.00%)

[Mark-Simulacrum]

Hard to say whether this is an improvement based on perf results, which seems pretty much as expected. A single, definitely-in-cache load is unlikely to be worth much to remove. I don't have a strong opinion on landing this vs. not, I'd probably bias slightly towards doing so since the load does mean more work for various parts of the pipeline even if it is cheap.

[jhpratt]

What could be causing the regressions here?

[Mark-Simulacrum]

I looked at the regression in hyper-0.14.18 Opt IncrPatched, and it seems to be a little more time spent in LLVM optimizations. My guess is that LLVM is able to potentially benefit from this information and so spends a bit more time processing.

[jhpratt]

So the possibility for slightly better optimization. Given that this is trivially reverted if wanted, I'm going to go ahead and merge.

@bors r+ rollup=never

[bors]

📌 Commit 61ebcf4 has been approved by jhpratt

It is now in the queue for this repository.

[bors]

⌛ Testing commit 61ebcf4 with merge 73e117d...

[klensy]

This needs some test to prevent accidental regression?

[bors]

💥 Test timed out

[RalfJung]

@bors r-
(bors sync fixup)

[Mark-Simulacrum]

@bors r=jhpratt

[bors]

📌 Commit a79d3cc has been approved by jhpratt

It is now in the queue for this repository.

[bors]

⌛ Testing commit a79d3cc with merge 41fa2a0...

[bors]

💔 Test failed - checks-actions

[Mark-Simulacrum]

@bors r=jhpratt

[bors]

📌 Commit f1ae531 has been approved by jhpratt

It is now in the queue for this repository.

[bors]

⌛ Testing commit f1ae531 with merge 13eb8c7...

[bors]

☀️ Test successful - checks-actions
Approved by: jhpratt
Pushing 13eb8c7 to master...

[rust-timer]

Finished benchmarking commit (13eb8c7): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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%	[0.1%, 1.6%]	7
Regressions ❌ (secondary)	0.3%	[0.2%, 0.5%]	11
Improvements ✅ (primary)	-0.5%	[-0.9%, -0.4%]	8
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	3
All ❌✅ (primary)	-0.1%	[-0.9%, 1.6%]	15

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)	5.1%	[5.1%, 5.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.5%	[-4.1%, -1.7%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.0%	[-4.1%, 5.1%]	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)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	2.7%	[2.2%, 3.3%]	4
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[-0.8%, 1.5%]	2

Binary size

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)	0.0%	[0.0%, 0.1%]	31
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	4
Improvements ✅ (primary)	-0.1%	[-0.3%, -0.0%]	9
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	34
All ❌✅ (primary)	0.0%	[-0.3%, 0.1%]	40

Bootstrap: 673.693s -> 672.201s (-0.22%)
Artifact size: 315.30 MiB -> 315.29 MiB (-0.00%)

[rylev]

@Mark-Simulacrum noted the regressions here as coming in LLVM, and it was deemed worth it given the possibility for LLVM to perform more optimization.

@rustbot label: +perf-regression-triaged