Mark Mitchell <[EMAIL PROTECTED]> writes:
> > let's disable the assumption about signed overflow not wrapping for
> > VRP, but leave it in place for loop analysis.
On Mon, Jan 01, 2007 at 06:09:41PM -0800, Paul Eggert wrote:
> As far as I know this will work for all the wrapv-assuming code that
>
On Mon, Jan 01, 2007 at 07:33:06AM -0500, Richard Kenner wrote:
> > the seemingly prevalent attitude "but it is undefined; but it is not
> > C" is the opinion of the majority of middle-end maintainers.
>
> Does anybody DISAGREE with that "attitude"? It isn't valid C to assume that
> signed overfl
On Mon, Jan 01, 2007 at 10:24:36AM -0800, Andrew Pinski wrote:
> Then the question is why does C developers act differently than Fortran
> developers when it comes to undefinedness?
In the case of int overflow wrapping, I think it's because the Bell Labs
folks appeared to assume wrapping semantics
On Sat, Dec 30, 2006 at 08:57:12PM -0500, Richard Kenner wrote:
> > I suppose there is
> >
> > *hv = (HOST_WIDE_INT) -(unsigned HOST_WIDE_INT) h1;
> >
> > to make it safe.
>
> Can't that conversion overflow?
Not on a two's complement machine, and I know of no gcc ports
to a non-two's-comp
On Sat, Dec 30, 2006 at 09:52:24PM -0800, Paul Eggert wrote:
> Wait, though: K&Rv2 is post-C89. If memory serves, it was C89
> that established the rule that signed integer overflow has
> undefined behavior whereas unsigned overflow is well-defined.
I don't have the original K&R book so can't tel
On Fri, Dec 29, 2006 at 10:44:02PM +0100, Florian Weimer wrote:
> Does autoconf enable higher optimization levels for other compilers by
> default?
Yes.
Rather, some other compilers default to optimization on, unless the
user explicitly turns it off with -O0. (Example: icc).
On Sat, Dec 30, 2006 at 04:13:08PM -0800, Paul Eggert wrote:
> I am. I just now looked and found another example.
> gcc-4.3-20061223/gcc/fold-const.c's neg_double function
> contains this line:
>
> *hv = - h1;
>
> This one is a bit less obvious because it doesn't have a
> "Danger Will Robi
On Tue, Dec 19, 2006 at 10:25:41PM +0100, Denis Vlasenko wrote:
> ... It's not about standards. It's about sanity.
So what happens when two different people's concept of "sanity" differs?
That's why we have standards, so both can consult a reference and
wind up with the same concept, even though o
On Tue, Dec 19, 2006 at 12:05:44PM -0800, Ian Lance Taylor wrote:
> Here is a quick list of optimizations that mainline gcc performs which
> rely on the idea that signed overflow is undefined. All the types
> are, of course, signed. I made have made some mistakes. I think this
> gives a good fee
