Set writable and dead_on_unwind attributes for sret arguments

[nikic]

Set the writable and dead_on_unwind attributes for sret arguments. This allows call slot optimization to remove more memcpy's.

See https://llvm.org/docs/LangRef.html#parameter-attributes for the specification of these attributes. In short, the statement we're making here is that:

• The return slot is writable.
• The return slot will not be read if the function unwinds.

Fixes #90595.

[rustbot]

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[nikic]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 5c66f83 with merge b47488b...

[bors]

☀️ Try build successful - checks-actions
Build commit: b47488b (b47488b90dd6a20d00a1d40779a009b874c67255)

[rust-timer]

Finished benchmarking commit (b47488b): 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)	0.4%	[0.3%, 0.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-4.4%	[-26.5%, -0.3%]	8
Improvements ✅ (secondary)	-1.4%	[-3.8%, -0.3%]	9
All ❌✅ (primary)	-3.4%	[-26.5%, 0.5%]	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)	1.5%	[1.5%, 1.5%]	1
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-0.7%	[-0.7%, -0.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[-0.7%, 1.5%]	2

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)	-5.1%	[-27.8%, -0.9%]	7
Improvements ✅ (secondary)	-3.3%	[-4.6%, -2.4%]	11
All ❌✅ (primary)	-5.1%	[-27.8%, -0.9%]	7

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.2%	[-0.5%, -0.1%]	16
Improvements ✅ (secondary)	-0.2%	[-0.8%, -0.0%]	16
All ❌✅ (primary)	-0.2%	[-0.5%, -0.1%]	16

Bootstrap: 641.758s -> 639.466s (-0.36%)
Artifact size: 308.80 MiB -> 308.59 MiB (-0.07%)

[bors]

☔ The latest upstream changes (presumably #122050) made this pull request unmergeable. Please resolve the merge conflicts.

[nikic]

Rebase & ping

[nikic]

r? @cuviper

[cuviper]

Sound good! And for reference, I also found that you added this to Clang in llvm/llvm-project#77116.

@bors r+

[bors]

📌 Commit e2b946e has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit e2b946e with merge cf9a460...

[nikic]

The problem on AArch64 is that SROA raises the alignment of an alloca when rewriting it: https://llvm.godbolt.org/z/szb1soPYs Because of that, we later no longer know that replacing the alloca with the (lower-aligned) sret parameter is legal.

In this case the rewrite done by SROA is pretty spurious, and I think #122053 is going to avoid the issue by dint of directly using the type it rewrites to.

I do wonder whether SROA really ought to be raising the alignment here...

[nikic]

Let's try this again now that #122053 has landed...

@bors r=cuviper

[bors]

📌 Commit 9cdc44b has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9cdc44b with merge 0702ea6...

[bors]

💔 Test failed - checks-actions

[matthiaskrgr]

@bors r-

[nikic]

Added missing needs-unwind annotation to the codegen test.

@bors r=cuviper

[bors]

📌 Commit 976267b has been approved by cuviper

It is now in the queue for this repository.

[bors]

⌛ Testing commit 976267b with merge 284f94f...

[bors]

☀️ Test successful - checks-actions
Approved by: cuviper
Pushing 284f94f to master...

[rust-timer]

Finished benchmarking commit (284f94f): 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)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.1%	[-26.0%, -0.3%]	12
Improvements ✅ (secondary)	-1.6%	[-4.4%, -0.5%]	11
All ❌✅ (primary)	-2.8%	[-26.0%, 0.5%]	13

Max RSS (memory usage)

This benchmark run did not return any relevant results for this metric.

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)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-7.9%	[-27.3%, -1.0%]	4
Improvements ✅ (secondary)	-4.1%	[-6.3%, -2.5%]	12
All ❌✅ (primary)	-7.9%	[-27.3%, -1.0%]	4

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%	[-0.5%, -0.0%]	16
Improvements ✅ (secondary)	-0.8%	[-0.8%, -0.8%]	5
All ❌✅ (primary)	-0.2%	[-0.5%, 0.1%]	17

Bootstrap: 673.228s -> 670.551s (-0.40%)
Artifact size: 315.45 MiB -> 315.96 MiB (0.16%)