Re: [PATCH] micro-opt DEBUG_ADD_PAGE

[Stephen Wille Padnos <stephenwp@adelphia.net>]

"Richard B. Johnson" wrote:
> 
> On Thu, 8 Feb 2001, Stephen Wille Padnos wrote:
> 
> > "Richard B. Johnson" wrote:
> > [snip]
> > > Another problem with 'volatile' has to do with pointers. When
> > > it's possible for some object to be modified by some external
> > > influence, we see:
> > >
> > >         volatile struct whatever *ptr;
> > >
> > > Now, it's unclear if gcc knows that we don't give a damn about
> > > the address contained in 'ptr'. We know that it's not going to
> > > change. What we are concerned with are the items within the
> > > 'struct whatever'. From what I've seen, gcc just reloads the
> > > pointer.
> > >
[snip]

> Yes. My point is that a lot of authors have declared just about everything
> 'volatile' `grep volatile /usr/src/linux/drivers/net/*.c`, just to
> be "safe". It's likely that there are many hundreds of thousands of
> unneeded register-reloads because of this.
> 
> It might be useful for somebody who has a lot of time on his/her
> hands to go through some of these drivers.

I would be willing to do this (on the slow boat - I don't have THAT much
spare time :), but only if we can be sure that the gcc optimizer will
correctly handle a normal pointer to volatile data.  Your experiences
would seem to indicate that the optimizer needs fixing before much
effort should be spent on this.

-- 
Stephen Wille Padnos
Programmer, Engineer, Problem Solver
swpadnos@adelphia.net
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