Re: [WIP 0/3] Memory model and atomic API in Rust

Philipp Stanner
2024-04-05T17:14:18Z

On Wed, 2024-03-27 at 12:07 -0700, Linus Torvalds wrote:
> On Wed, 27 Mar 2024 at 11:51, Kent Overstreet
> <kent.overstreet@linux.dev> wrote:
> >
> > On Wed, Mar 27, 2024 at 09:16:09AM -0700, comex wrote:
> > > Meanwhile, Rust intentionally lacks strict aliasing.
> >
> > I wasn't aware of this. Given that unrestricted pointers are a real
> > impediment to compiler optimization, I thought that with Rust we
> > were
> > finally starting to nail down a concrete enough memory model to
> > tackle
> > this safely. But I guess not?
>
> Strict aliasing is a *horrible* mistake.
>
> It's not even *remotely* "tackle this safely". It's the exact
> opposite. It's completely broken.
>
> Anybody who thinks strict aliasing is a good idea either
>
>  (a) doesn't understand what it means
>
>  (b) has been brainwashed by incompetent compiler people.
>
> it's a horrendous crock that was introduced by people who thought it
> was too complicated to write out "restrict" keywords, and that
> thought
> that "let's break old working programs and make it harder to write
> new
> programs" was a good idea.
>
> Nobody should ever do it. The fact that Rust doesn't do the C strict
> aliasing is a good thing. Really.

Btw, for the interested, that's a nice article on strict aliasing:
https://blog.regehr.org/archives/1307

Dennis Ritchie, the Man Himself, back in the 1980s pushed back quite
strongly on (different?) aliasing experiments:
https://www.yodaiken.com/2021/03/19/dennis-ritchie-on-alias-analysis-in-the-c-programming-language-1988/

No idea why they can't just leave C alone... It's not without reason
that new languages like Zig and Hare want to freeze the language
(standard) once they are released.

P.

>
> I suspect you have been fooled by the name. Because "strict aliasing"
> sounds like a good thing. It sounds like "I know these strictly can't
> alias". But despite that name, it's the complete opposite of that,
> and
> means "I will ignore actual real aliasing even if it exists, because
> I
> will make aliasing decisions on entirely made-up grounds".
>
> Just say no to strict aliasing. Thankfully, there's an actual
> compiler
> flag for that: -fno-strict-aliasing. It should absolutely have been
> the default.
>
>                  Linus