[Bug optimization/13653] [3.3 regression] -O2 -funroll-loop miscompiles POOMA testcase

["rguenth at tat dot physik dot uni-tuebingen dot de" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From rguenth at tat dot physik dot uni-tuebingen dot de  2004-01-29 22:45 -------
Subject: Re:  [3.3 regression] -O2 -funroll-loop
 miscompiles POOMA testcase

On Thu, 29 Jan 2004, Richard Guenther wrote:

> On Thu, 29 Jan 2004, dberlin at gcc dot gnu dot org wrote:
>
> > I'll attach my even *more* reduced testcase, but that only passes at -O2 and
> > fails at -O2 -funroll-loops (IE it doesn't pass at -O0 or -O1)
>
> That does hint to maybe a stack corruption or somehow.  That would be
> consistent with my observation that the original testcase fails only, if I
> enable assertions in the code, if I disable them and they get #ifdef'ed
> away, the failure does not occour.
>
> So it may be interesting to look at the generated assembly of the main
> function and looking for corrupt stack after calls?

Additionally to the noreturn attribute, I can reduce the main function to

int main(int argc, char *argv[]) {
        Interval<1> D(6);
        Interval<3> I3(D,D,D);
        Loc<3> blocks(2,2,2);
        UniformGridPartition<3> partition(blocks);
        UniformGridLayout<3> layout(I3, partition,ReplicatedTag());
        Array<3, double, MultiPatch<UniformTag,Brick> > u(layout);
        for (int i2 = 0; i2 < 4 /* 3 doesnt segfault */; i2++)
                for (int i1 = 0; i1 < 1; i1++)
                        for (int i0 = 0; i0 < 1; i0++)
                                u(i0,i1,i2) = 0;
        return 0;
}

and still get the segfault, but it is fixed with either running the first
loop only to i2 < 3, or removing any of the loops.

In fact, looking at the assembler, there are two calls to
_ZNK21UniformGridLayoutDataILi3EE8globalIDEiii inside the loop, and the
loop itself doesnt change with the noreturn attribute on toss_cookies, but
the called function does, as it calls toss_cookies several times.

Richard.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13653