Fix duplicate arcinner_layout_for_value_layout calls when using the uninit Arc constructors

[marc0246]

What this fixes is the duplicate calls to arcinner_layout_for_value_layout seen here: https://godbolt.org/z/jr5Gxozhj

The issue was discovered alongside #111603 but is otherwise unrelated to the duplicate allocas, which remain unsolved. Everything I tried to solve said main issue has failed.

As for the duplicate layout calculations, I also tried slapping #[inline] and #[inline(always)] on everything in sight but the only thing that worked in the end is to dedup the calls by hand.

[rustbot]

r? @thomcc

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[thomcc]

This basically looks fine to me. There could be a perf impact, but I doubt we use this much in the compiler, so I don't feel compelled to do a perf run first.

@bors r+ rollup=never

[bors]

📌 Commit 2a46646 has been approved by thomcc

It is now in the queue for this repository.

[bors]

⌛ Testing commit 2a46646 with merge 2fe47b9...

[bors]

☀️ Test successful - checks-actions
Approved by: thomcc
Pushing 2fe47b9 to master...

[bors]

☀️ Test successful - checks-actions
Approved by: thomcc
Pushing 2fe47b9 to master...

[rust-timer]

Finished benchmarking commit (2fe47b9): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

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)	-	-	0
Regressions ❌ (secondary)	3.1%	[3.1%, 3.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

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

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)	-0.0%	[-0.0%, -0.0%]	10
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-0.0%, -0.0%]	10

Bootstrap: 643.403s -> 643.016s (-0.06%)