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

[Tamir Duberstein]

On Wed, Mar 19, 2025 at 12:43 PM Miguel Ojeda
<miguel.ojeda.sandonis@xxxxxxxxx> wrote:
>
> 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).

Yeah, this elision is what I was trying to allude to in the original
wording. I still think the suggested code is simpler, but gave my RB
either way.