Fix wrong par_slice implementation

[zetanumbers]

#152375 (comment)

[rustbot]

r? @JonathanBrouwer

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[jieyouxu]

@bors try @rust-timer queue

[JonathanBrouwer]

cc @Zoxc @jieyouxu @lqd
Change looks good to me, r=me
I think we should redo the perf numbers

[JonathanBrouwer]

I think last time rust-timer didn't show any perf impact, how were the statistics in that PR generated?

[lqd]

I think last time rust-timer didn't show any perf impact, how were the statistics in that PR generated?

Zoxc ran rcb and posted that; rustc-perf did show wall time improvements for the multithreaded benchmark we have.

[rust-bors]

☀️ Try build successful (CI)
Build commit: 532510f (532510fc9b4953f08a24a2fd52f36860df85a645, parent: 71e00273c0921e1bc850ae8cc4161fbb44cfa848)

[rust-timer]

Finished benchmarking commit (532510f): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible 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 (secondary -5.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.1%	[-5.1%, -5.1%]	1
All ❌✅ (primary)	-	-	0

Cycles

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

Binary size

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

Bootstrap: 485.967s -> 483.907s (-0.42%)
Artifact size: 397.80 MiB -> 397.81 MiB (0.00%)