read_volatile __rust_no_alloc_shim_is_unstable in alloc_zeroed

[saethlin]

It was pointed out in #128854 (comment) that the magic volatile read was probably missing from alloc_zeroed. I can't find any mention of alloc_zeroed on #86844, so it looks like this was just missed initially.

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 4676144 with merge e72f848...

[bors]

☀️ Try build successful - checks-actions
Build commit: e72f848 (e72f8484040362cd7db7b6ee18d387e94e1b8d38)

[rust-timer]

Finished benchmarking commit (e72f848): 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%, -0.4%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.7%, 0.3%]	3

Max RSS (memory usage)

Results (primary 2.4%, secondary 1.8%)

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)	3.4%	[1.4%, 4.7%]	5
Regressions ❌ (secondary)	3.7%	[3.3%, 4.0%]	2
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-1.8%	[-1.8%, -1.8%]	1
All ❌✅ (primary)	2.4%	[-2.3%, 4.7%]	6

Cycles

Results (primary -0.9%, secondary 2.1%)

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)	2.1%	[2.0%, 2.1%]	2
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.9%	[-0.9%, -0.9%]	1

Binary size

Results (primary -0.0%, secondary 0.1%)

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%	[0.0%, 0.2%]	14
Regressions ❌ (secondary)	0.1%	[0.0%, 0.3%]	14
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.1%]	7
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	-0.0%	[-0.2%, 0.2%]	21

Bootstrap: 767.556s -> 767.346s (-0.03%)
Artifact size: 341.28 MiB -> 341.23 MiB (-0.02%)

[saethlin]

r? @bjorn3

[bjorn3]

@bors r+

[bors]

📌 Commit 4676144 has been approved by bjorn3

It is now in the queue for this repository.

[bors]

⌛ Testing commit 4676144 with merge 7fc70f8...

[bors]

☀️ Test successful - checks-actions
Approved by: bjorn3
Pushing 7fc70f8 to master...

[rust-timer]

Finished benchmarking commit (7fc70f8): 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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-0.7%, 0.5%]	3

Max RSS (memory usage)

Results (primary 2.7%, secondary -0.2%)

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)	3.5%	[1.4%, 5.0%]	6
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	1
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	2.7%	[-2.2%, 5.0%]	7

Cycles

Results (primary -0.8%, secondary -3.4%)

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%	[2.0%, 2.0%]	2
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-5.6%	[-8.3%, -2.5%]	5
All ❌✅ (primary)	-0.8%	[-0.8%, -0.8%]	1

Binary size

Results (primary 0.0%, secondary 0.1%)

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%	[0.0%, 0.2%]	12
Regressions ❌ (secondary)	0.1%	[0.0%, 0.3%]	14
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.1%]	7
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	0.0%	[-0.2%, 0.2%]	19

Bootstrap: 765.7s -> 768.056s (0.31%)
Artifact size: 341.29 MiB -> 341.27 MiB (-0.01%)

[pnkfelix]

• cranelift-codegen opt-full-llvm regressed by -0.48%.
• marking as triaged; this is bringing the two allocator paths into consistency with eachother (the question of whether we want these volatile reads at all, and how to otherwise achieve their effect on the end-to-end developer ex
  perience, is an entirely separate question).

@rustbot label: +perf-regression-triaged