[Bug tree-optimization/113552] [11/12/13/14 Regression] vectorizer generates calls to vector math routines with 1 simd lane.

["tnfchris at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113552

Tamar Christina <tnfchris at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |NEW

--- Comment #5 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
__attribute__ ((__simd__ ("notinbranch"), const))
double cos (double);

void foo (float *a, double *b)
{
    for (int i = 0; i < 12; i+=3)
      {
        b[i] = cos (5.0 * a[i]);
        b[i+1] = cos (5.0 * a[i+1]);
        b[i+2] = cos (5.0 * a[i+2]);
      }
}

Simple C example that shows the problem.

This seems to happen when SLP succeeds and the group size is a non power of
two.
The vectorizer then unrolls to make it a power of two and during vectorization
it seems to destroy the vector, make the call and reconstruct it.

So this seems like an SLP vectorization bug.  I can't seem to trigger it
however on GCC < 14 since SLP consistently fails for all my examples because it
tries a mode that's larger than the vector size.

So It may be a GCC 14 only regression, but I think it's latent in the
vectorizer.