#94421 (replace RawVec with Boxed slice) plus soundness fixes

[saethlin]

r? @ghost

[bors]

☔ The latest upstream changes (presumably #94775) made this pull request unmergeable. Please resolve the merge conflicts.

[bors]

☔ The latest upstream changes (presumably #96605) made this pull request unmergeable. Please resolve the merge conflicts.

[thomcc]

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit 2efcdf8 with merge 5ea78121020f716d5359adbefb0abbfb2f885e4c...

[bors]

☀️ Try build successful - checks-actions
Build commit: 5ea78121020f716d5359adbefb0abbfb2f885e4c (5ea78121020f716d5359adbefb0abbfb2f885e4c)

[rust-timer]

Queued 5ea78121020f716d5359adbefb0abbfb2f885e4c with parent 4d6d601, future comparison URL.

[rust-timer]

Finished benchmarking commit (5ea78121020f716d5359adbefb0abbfb2f885e4c): comparison url.

Instruction count

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	1.5%	5.9%	77
Regressions 😿 (secondary)	2.0%	14.0%	28
Improvements 🎉 (primary)	-0.5%	-1.3%	26
Improvements 🎉 (secondary)	-0.7%	-5.6%	31
All 😿🎉 (primary)	1.0%	5.9%	103

Max RSS (memory usage)

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	2.4%	6.9%	54
Regressions 😿 (secondary)	3.0%	5.6%	7
Improvements 🎉 (primary)	-5.7%	-7.0%	3
Improvements 🎉 (secondary)	-3.0%	-3.9%	3
All 😿🎉 (primary)	1.9%	-7.0%	57

Cycles

Results

• Primary benchmarks: mixed results
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions 😿 (primary)	3.6%	7.4%	23
Regressions 😿 (secondary)	3.9%	15.8%	19
Improvements 🎉 (primary)	-4.8%	-6.6%	2
Improvements 🎉 (secondary)	-4.2%	-4.2%	1
All 😿🎉 (primary)	2.9%	7.4%	25

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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-review -S-waiting-on-perf +perf-regression

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³

2. number of relevant changes ↩ ↩² ↩³

[saethlin]

I'm closing this, as I've become convinced that this introduces unfixable performance regressions because the Deref impl on Vec can't be free if its layout is changed.