Re: [PATCH v2 2/3] rust: alloc: add Vec::resize method

[Miguel Ojeda]

On Wed, Mar 19, 2025 at 5:13 PM Tamir Duberstein <tamird@xxxxxxxxx> wrote:
>
> No, I meant avoiding the check. The existing code already explicitly
> checks `new_len > self.len()` before evaluating `new_len -
> self.len()`. This means the check occurs twice. `checked_sub` reduces
> the number of checks by 1. Perhaps my wording could have been clearer
> ("avoid *an* underflow check").

Ah, you mean in the function you suggested, I see.

I think it they all may compile down to the same thing, whether
overflows checks are enabled or not, and whether the version in the
patch or `checked_sub` is used or not. At least in a quick Compiler
Explorer test it seems so, but I didn't check in an actual kernel
build.

The implicit check is gated behind the other one, so that one can be
removed, even if values are unknown -- we always have optimizations
enabled, even under "debug" builds (assuming "debug" means overflow
checking enabled).

Cheers,
Miguel