Re: Linux 2.6.7-rc2

[Albert Cahalan <albert@users.sf.net>]

On Mon, 2004-05-31 at 12:53, Linus Torvalds wrote:
> On Mon, 31 May 2004, Albert Cahalan wrote:
> > 
> > This would be required because of the -Wno-strict-aliasing
> > option. For the 2.7.xx kernels, how about we start off by
> > replacing -Wno-strict-aliasing with -std=gnu99 ? It's been
> > 5 years since 1999. The "restrict" keyword is useful too.
> 
> No can do.
> 
> Aliasing in gcc is so broken (_purely_ type-based and no way to avoid it
> sanely in older versions) that it's not going to happen.
> 
> When we can depend on everybody having gcc-3.3+ something, and that one
> properly supports the "may_alias" attribute, we may change that.

By the time Linux 2.8.0 is out, gcc-3.3+ should be
a perfectly reasonable requirement.

In the mean time, adding may_alias as needed would be
a good idea.

If all this were behind CONFIG_BROKEN, it sure wouldn't
hurt even today. People might as well get started.
The compiler will keep being pessimistic and dumb until
the -Wno-strict-aliasing option is dropped.

> "restrict" is pretty much useless. It just weakens the already too-weak
> alias rules of standard gcc.

It's easiest to use on function parameters. This helps
the optimizer without being a mind-warping excercise.