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[Bug middle-end/33780] different results between O3 and O0
- From: "jv244 at cam dot ac dot uk" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 15 Oct 2007 15:30:02 -0000
- Subject: [Bug middle-end/33780] different results between O3 and O0
- References: <bug-33780-6642@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #2 from jv244 at cam dot ac dot uk 2007-10-15 15:30 -------
(In reply to comment #1)
> As Fortran allows open-coding of integral powers this is not a bug. But
> I'll leave final closing as INVALID to more fortran-knowing people.
I agree that Fortran-wise this is not a bug. However, gcc tends to do some of
the things that Fortran allows by default (x/y -> x*(1/y) ; x+Y+z -> (x=z)+y ;
..) only at -ffast-math. AFAIK, this seems to be the only optimisation in gcc
that causes numerical results with CP2K to change going from -O0 to -O3.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33780