This is the mail archive of the
gcc-bugs@gcc.gnu.org
mailing list for the GCC project.
[Bug tree-optimization/58143] [4.8/4.9 regression] wrong code at -O3
- From: "bernd.edlinger at hotmail dot de" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 15 Oct 2013 13:21:00 +0000
- Subject: [Bug tree-optimization/58143] [4.8/4.9 regression] wrong code at -O3
- Auto-submitted: auto-generated
- References: <bug-58143-4 at http dot gcc dot gnu dot org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58143
--- Comment #24 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
Wall,
the logic behind the loop niter is really strange
and the results are simply insane.
When you consider this example:
int a, b, c, d, e;
int
main ()
{
for (b = 4; b > -30; b--)
{
e = 2147483647 - b;
for (; c;)
for (;;)
{
if (d)
break;
}
}
return 0;
}
then the reasoning is that an "undefined" value will
be written to e in loop iteration #4.
And therefore it does not matter what happens afterwards.
But for the result of main() which will ultimately be 0
the undefined value of e does not matter.
Why should a undefined value that is not used for anything
create such a problem?