Avoid a cast in `ptr::slice_from_raw_parts(_mut)` #124795

scottmcm · 2024-05-06T08:57:38Z

Casting to *const () or *mut () is no longer needed after #123840 so let's make the MIR smaller (and more inline-able, as seen in the tests).

If ACP#362 goes through we can keep calling ptr::from_raw_parts(_mut) in these also without the cast, but that hasn't had any libs-api attention yet, so I'm not waiting on it.

Casting to `*const ()` or `*mut ()` just bloats the MIR, so let's not. If ACP#362 goes through we can keep calling `ptr::from_raw_parts(_mut)` in these also without the cast, but that hasn't had any libs-api attention yet, so I'm not waiting on it.

rustbot · 2024-05-06T08:57:47Z

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joboet · 2024-05-07T10:11:10Z

Looks fine! Let's see what the performance improvements are...
@bors try @rust-timer queue

…ts, r=<try> Avoid a cast in `ptr::slice_from_raw_parts(_mut)` Casting to `*const ()` or `*mut ()` is no longer needed after rust-lang#123840 so let's make the MIR smaller (and more inline-able, as seen in the tests). If [ACP#362](rust-lang/libs-team#362) goes through we can keep calling `ptr::from_raw_parts(_mut)` in these also without the cast, but that hasn't had any libs-api attention yet, so I'm not waiting on it.

bors · 2024-05-07T10:24:02Z

⌛ Trying commit 61517db with merge 8466125...

bors · 2024-05-07T12:02:26Z

☀️ Try build successful - checks-actions
Build commit: 8466125 (8466125667d2a47a9fb56f64629d03a88eafa09e)

rust-timer · 2024-05-07T13:17:11Z

Finished benchmarking commit (8466125): comparison URL.

Overall result: ✅ improvements - no 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.

@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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-0.5%, -0.2%]	7
Improvements ✅ (secondary)	-0.4%	[-1.3%, -0.2%]	17
All ❌✅ (primary)	-0.3%	[-0.5%, -0.2%]	7

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)	5.7%	[2.8%, 8.0%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.4%	[-4.4%, -0.5%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.0%	[-4.4%, 8.0%]	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)	17.0%	[0.5%, 34.0%]	14
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.3%, -2.2%]	2
All ❌✅ (primary)	17.0%	[0.5%, 34.0%]	14

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)	0.2%	[0.1%, 0.2%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-1.3%, -0.0%]	85
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.1%]	18
All ❌✅ (primary)	-0.4%	[-1.3%, 0.2%]	87

Bootstrap: 675.387s -> 674.274s (-0.16%)
Artifact size: 315.97 MiB -> 315.94 MiB (-0.01%)

joboet · 2024-05-08T12:08:36Z

Lovely!
@bors r+

bors · 2024-05-08T12:08:39Z

📌 Commit 61517db has been approved by joboet

It is now in the queue for this repository.

bors · 2024-05-08T19:38:00Z

⌛ Testing commit 61517db with merge ec1b698...

bors · 2024-05-08T21:46:27Z

☀️ Test successful - checks-actions
Approved by: joboet
Pushing ec1b698 to master...

rust-timer · 2024-05-08T23:21:08Z

Finished benchmarking commit (ec1b698): 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)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.6%, -0.3%]	6
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.2%]	16
All ❌✅ (primary)	-0.3%	[-0.6%, 0.3%]	7

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)	4.8%	[2.8%, 6.6%]	3
Regressions ❌ (secondary)	3.2%	[3.2%, 3.2%]	1
Improvements ✅ (primary)	-2.1%	[-4.0%, -0.5%]	3
Improvements ✅ (secondary)	-3.2%	[-3.2%, -3.2%]	1
All ❌✅ (primary)	1.4%	[-4.0%, 6.6%]	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)	-	-	0
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-3.9%, -2.1%]	3
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)	0.4%	[0.1%, 0.9%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-1.3%, -0.0%]	83
Improvements ✅ (secondary)	-0.3%	[-0.4%, -0.1%]	21
All ❌✅ (primary)	-0.4%	[-1.3%, 0.9%]	86

Bootstrap: 675.214s -> 675.971s (0.11%)
Artifact size: 315.83 MiB -> 315.94 MiB (0.03%)

nnethercote · 2024-05-09T04:22:31Z

Nice binary size reductions here.

scottmcm · 2024-05-09T16:48:22Z

Good to see that the 17.0% average cycle regression from the first perf run was fake.

Kobzol · 2024-05-14T08:37:26Z

The wins far outweigh the single regression.

@rustbot label: +perf-regression-triaged

…=WaffleLapkin [ACP 362] genericize `ptr::from_raw_parts` This implements rust-lang/libs-team#362 As such, it can partially undo rust-lang#124795 , letting `slice_from_raw_parts` just call `from_raw_parts` again without re-introducing the unnecessary cast to MIR. By doing this it also removes a spurious cast from `str::from_raw_parts`. And I think it does a good job of showing the value of the ACP, since the only thing that needed new turbofishing because of this is inside `ptr::null(_mut)`, but only because `ptr::without_provenance(_mut)` doesn't support pointers to extern types, which it absolutely could (without even changing the implementation).

Rollup merge of rust-lang#125701 - scottmcm:generic-from-raw-parts, r=WaffleLapkin [ACP 362] genericize `ptr::from_raw_parts` This implements rust-lang/libs-team#362 As such, it can partially undo rust-lang#124795 , letting `slice_from_raw_parts` just call `from_raw_parts` again without re-introducing the unnecessary cast to MIR. By doing this it also removes a spurious cast from `str::from_raw_parts`. And I think it does a good job of showing the value of the ACP, since the only thing that needed new turbofishing because of this is inside `ptr::null(_mut)`, but only because `ptr::without_provenance(_mut)` doesn't support pointers to extern types, which it absolutely could (without even changing the implementation).

…pkin [ACP 362] genericize `ptr::from_raw_parts` This implements rust-lang/libs-team#362 As such, it can partially undo rust-lang/rust#124795 , letting `slice_from_raw_parts` just call `from_raw_parts` again without re-introducing the unnecessary cast to MIR. By doing this it also removes a spurious cast from `str::from_raw_parts`. And I think it does a good job of showing the value of the ACP, since the only thing that needed new turbofishing because of this is inside `ptr::null(_mut)`, but only because `ptr::without_provenance(_mut)` doesn't support pointers to extern types, which it absolutely could (without even changing the implementation).

rustbot assigned joboet May 6, 2024

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label May 7, 2024

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 8, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label May 8, 2024

bors merged commit ec1b698 into rust-lang:master May 8, 2024
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rustbot added this to the 1.80.0 milestone May 8, 2024

rustbot added the perf-regression Performance regression. label May 8, 2024

scottmcm deleted the simplify-slice-from-raw-parts branch May 9, 2024 16:46

rustbot added the perf-regression-triaged The performance regression has been triaged. label May 14, 2024

scottmcm mentioned this pull request May 29, 2024

[ACP 362] genericize ptr::from_raw_parts #125701

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Avoid a cast in `ptr::slice_from_raw_parts(_mut)` #124795

Avoid a cast in `ptr::slice_from_raw_parts(_mut)` #124795

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Kobzol commented May 14, 2024

Avoid a cast in ptr::slice_from_raw_parts(_mut) #124795

Avoid a cast in ptr::slice_from_raw_parts(_mut) #124795

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scottmcm commented May 6, 2024

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rust-timer commented May 7, 2024

Overall result: ✅ improvements - no action needed

joboet commented May 8, 2024

bors commented May 8, 2024

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bors commented May 8, 2024

rust-timer commented May 8, 2024

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

nnethercote commented May 9, 2024

scottmcm commented May 9, 2024

Kobzol commented May 14, 2024

Avoid a cast in `ptr::slice_from_raw_parts(_mut)` #124795

Avoid a cast in `ptr::slice_from_raw_parts(_mut)` #124795