Tell LLVM that the negation in <*const T>::sub cannot overflow

[scottmcm]

Today it's just sub https://rust.godbolt.org/z/8EzEPnMr5; with this PR it's sub nsw.

[rustbot]

r? @joshtriplett

(rustbot has picked a reviewer for you, use r? to override)

[scottmcm]

I don't think sub is as common as add, but just in case...

@bors try @rust-timer queue

[bors]

⌛ Trying commit ab6e2bc with merge b4b635338cfd4b18dc878054b630903d604090f1...

[bors]

☀️ Try build successful - checks-actions
Build commit: b4b635338cfd4b18dc878054b630903d604090f1 (b4b635338cfd4b18dc878054b630903d604090f1)

[rust-timer]

Finished benchmarking commit (b4b635338cfd4b18dc878054b630903d604090f1): 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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.3%]	3
Improvements ✅ (secondary)	-0.5%	[-0.7%, -0.2%]	6
All ❌✅ (primary)	-0.3%	[-0.7%, 0.3%]	4

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)	6.0%	[2.5%, 8.1%]	3
Regressions ❌ (secondary)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-5.2%	[-5.5%, -4.9%]	2
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	1.5%	[-5.5%, 8.1%]	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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.6%	[-3.6%, -3.6%]	1
All ❌✅ (primary)	-	-	0

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)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.6%, -0.0%]	44
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.6%, 0.1%]	45

Bootstrap: 632.934s -> 631.913s (-0.16%)

[scottmcm]

One small regression that seems easily outweighed by the larger number of improvements.

@rustbot label: +perf-regression-triaged

[workingjubilee]

neat!

[workingjubilee]

...huh, I for some reason didn't expect that to be true.

[workingjubilee]

Agreed.

@bors r+ rollup

[bors]

📌 Commit ab6e2bc has been approved by workingjubilee

It is now in the queue for this repository.

[workingjubilee]

wait I'm silly.
@bors rollup=never

[workingjubilee]

r? @workingjubilee

[bors]

⌛ Testing commit ab6e2bc with merge b08dd92...

[bors]

☀️ Test successful - checks-actions
Approved by: workingjubilee
Pushing b08dd92 to master...

[rust-timer]

Finished benchmarking commit (b08dd92): 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)	-0.3%	[-0.3%, -0.2%]	9
Improvements ✅ (secondary)	-0.4%	[-0.5%, -0.3%]	4
All ❌✅ (primary)	-0.3%	[-0.3%, -0.2%]	9

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%	[2.5%, 8.1%]	5
Regressions ❌ (secondary)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-2.5%	[-4.9%, -0.1%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.0%	[-4.9%, 8.1%]	7

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)	2.8%	[2.8%, 2.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

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)	0.1%	[0.1%, 0.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.7%, -0.0%]	44
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.7%, 0.1%]	45

Bootstrap: 631.476s -> 632.009s (0.08%)

[workingjubilee]

and the one regression was just noise lol.