alloc: remove unsound IsZero for raw pointers

[joboet]

Fixes #135338

[rustbot]

r? @Mark-Simulacrum

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[Noratrieb]

a bit unfortunate to lose this optimization, but it's fine.
@bors r+

[bors]

📌 Commit 4426e9a has been approved by Noratrieb

It is now in the queue for this repository.

[workingjubilee]

@bors rollup=never p=1

[scottmcm]

a bit unfortunate to lose this optimization

More proof that Option<NonNull<_>> is better than raw pointers :D

[bors]

⌛ Testing commit 4426e9a with merge 760b6f8...

[bors]

☀️ Test successful - checks-actions
Approved by: Noratrieb
Pushing 760b6f8 to master...

[rust-timer]

Finished benchmarking commit (760b6f8): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.3%]	2
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -3.9%, 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
Regressions ❌ (secondary)	1.0%	[1.0%, 1.0%]	1
Improvements ✅ (primary)	-3.9%	[-3.9%, -3.9%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.9%	[-3.9%, -3.9%]	1

Cycles

Results (primary -2.3%, 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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-2.2%	[-2.2%, -2.2%]	1
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

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

Bootstrap: 764.797s -> 764.732s (-0.01%)
Artifact size: 325.90 MiB -> 325.97 MiB (0.02%)

[workingjubilee]

...yeah, this was why I wanted to make sure the removal of this optimization landed first.