Re: changing "configure" to default to "gcc -g -O2 -fwrapv ..."

[Vincent Lefevre]

On 2006-12-31 10:08:32 -0500, Richard Kenner wrote:
> > Well, that's not equivalent. For instance, MPFR has many conditions
> > that evaluate to TRUE or FALSE on some/many implementations (mainly
> > because the type sizes depend on the implementation), even without
> > the assumption that an overflow cannot occur.
> 
> Can you give an example of such a condition and show how an
> optimization that assumed overflows were undefined could break that
> code?

This won't break the code. But I'm saying that if the compiler assumes
wrapping, even in some particular cases (e.g. code that *looks like*
"overflow check"), it could miss some potential optimizations. That
is, it is not possible to avoid breaking overflow checks *and*
optimizing everything else.

-- 
Vincent Lefèvre <address@hidden> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)