_mm_maskmoveu_si128 requires mutable in-bounds memory even when it does nothing

[RalfJung]

That's what @programmerjake said, anyway. The Intel docs don't mention this...

I have no idea if other intrinsics have similar requirements.

[rustbot]

r? @folkertdev

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[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[RalfJung]

@folkertdev @Amanieu friendly review reminder. :)