Re: wrong-code bug in gcc-4.5.x?

[Wouter Vermaelen <wouter dot vermaelen at scarlet dot be>]

On 04/25/2011 08:00 PM, Ian Lance Taylor wrote:
> Wouter Vermaelen<wouter.vermaelen@scarlet.be>  writes:
>
> > I believe I found a wrong-code bug. The problem triggers when using
> > gcc-4.5.1, 4.5.2 or 4.5.3, but not when using 4.4.5 or 4.7.0 (snapshot
> > 20110419). It also only triggers with certain optimization levels/flags.
> > I wonder if this is a known problem and already fixed in 4.7.0, or that
> > the problem still exists but for some reason doesn't trigger in 4.7.0
> > (I couldn't easily find something in bugzilla).
> >
> > Below is a reduced test-case that shows the problem. I tried, but I
> > couldn't get it smaller than these 4 files (combined about 60 lines).
> >
> > While reducing this problem I realized that it *might* not be a compiler
> > bug, but undefined behaviour with the usage of __restrict in
> > Buffer::read(). What I wanted to express there is that the memory write
> > done by memcpy() can never overwrite the member variable 'p'. At the
> > moment I still believe it's a compiler bug, but I'm not 100% sure
> > anymore.
> >
> > So is this a compiler bug or undefined behaviour in my program? In case
> > of the latter I would appreciate if someone could explain what the
> > problem is and maybe suggest a way to fix it.
>
> I don't see anything wrong with your use of __restrict here.  If this
> programs works without __restrict and fails with __restrict then I think
> this is a compiler bug.

Ok, thanks. I've reported it as bug 48764:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48764