Introduce Arena::try_alloc_from_iter.

[cjgillot]

alloc_from_iter already collects the iterator for reentrancy. So adding an early exit for a fallible iterator integrates naturally into the code. This avoids the other solution to allocate and dump the allocation.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[cjgillot]

@bors try @rustc-timer queue

[bors]

⌛ Trying commit d0d3021 with merge b52d335...

[bors]

☀️ Try build successful - checks-actions
Build commit: b52d335 (b52d3352518a7502ce32354b94ec6cf8b5855fee)

[oli-obk]

@rust-timer build b52d335

[rust-timer]

Finished benchmarking commit (b52d335): comparison URL.

Overall result: no relevant changes - 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 benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary 0.7%, secondary 1.0%)

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)	0.8%	[0.4%, 1.9%]	9
Regressions ❌ (secondary)	2.5%	[2.2%, 2.8%]	2
Improvements ✅ (primary)	-0.9%	[-0.9%, -0.9%]	1
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	0.7%	[-0.9%, 1.9%]	10

Cycles

Results (primary -0.3%)

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)	0.5%	[0.5%, 0.5%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-1.0%, -0.4%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.3%	[-1.0%, 0.5%]	7

Binary size

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

Bootstrap: 772.31s -> 773.339s (0.13%)
Artifact size: 365.02 MiB -> 365.05 MiB (0.01%)

[cjgillot]

r? compiler

[BoxyUwU]

@bors r+

[bors]

📌 Commit d0d3021 has been approved by BoxyUwU

It is now in the queue for this repository.

[bors]

⌛ Testing commit d0d3021 with merge 0fbb922...

[bors]

☀️ Test successful - checks-actions
Approved by: BoxyUwU
Pushing 0fbb922 to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing 7450913 (parent) -> 0fbb922 (this PR)

Test differences

No test diffs found

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard 0fbb922e530399599aab8296ea975cb9e7ed67bf --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. dist-arm-linux: 6596.1s -> 4550.9s (-31.0%)
2. x86_64-apple-1: 6751.0s -> 8448.5s (25.1%)
3. dist-powerpc-linux: 6231.7s -> 5210.9s (-16.4%)
4. x86_64-gnu-distcheck: 4955.6s -> 4380.6s (-11.6%)
5. dist-x86_64-apple: 9580.9s -> 8516.1s (-11.1%)
6. x86_64-gnu-llvm-19-1: 5277.1s -> 5657.9s (7.2%)
7. armhf-gnu: 4778.1s -> 4437.6s (-7.1%)
8. x86_64-apple-2: 4729.7s -> 5064.3s (7.1%)
9. dist-aarch64-apple: 5530.6s -> 5159.2s (-6.7%)
10. x86_64-msvc-2: 6740.9s -> 7173.3s (6.4%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (0fbb922): comparison URL.

Overall result: ❌ regressions - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

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

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.4%]	3
Regressions ❌ (secondary)	0.3%	[0.1%, 0.4%]	15
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.4%]	3

Max RSS (memory usage)

Results (primary 0.1%, secondary 1.4%)

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)	0.9%	[0.4%, 2.8%]	7
Regressions ❌ (secondary)	5.9%	[2.3%, 9.5%]	2
Improvements ✅ (primary)	-1.1%	[-2.7%, -0.6%]	5
Improvements ✅ (secondary)	-3.1%	[-3.7%, -2.4%]	2
All ❌✅ (primary)	0.1%	[-2.7%, 2.8%]	12

Cycles

Results (primary 0.6%, secondary -2.2%)

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)	0.6%	[0.4%, 0.8%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	0.6%	[0.4%, 0.8%]	4

Binary size

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

Bootstrap: 766.94s -> 769.061s (0.28%)
Artifact size: 365.61 MiB -> 365.55 MiB (-0.02%)

[Mark-Simulacrum]

Regressions look plausibly real (they've held up for a bit) but given they're small and limited to just doc builds I'm inclined to accept. It seems plausible this is just some slight differences in the ABI of the functions here or similar...