[Bug tree-optimization/70130] [6 Regression] h264ref fails with verification error starting with r231674

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70130

--- Comment #10 from Richard Biener <rguenth at gcc dot gnu.org> ---
Btw, which loop is it in this function?  There are multiple ones.  I assume
the last loop nest:

  for (j=0;j< MB_BLOCK_SIZE;j++)
  {
    for (i=0;i< MB_BLOCK_SIZE;i++)
    {
     
img->mprr_2[PLANE_16][j][i]=max(0,min((int)img->max_imgpel_value,(iaa+(i-7)*ib
+(j-7)*ic + 16)/32));// store plane prediction
    }
  }

> With images not 16-byte aligned, img->mprr_2 *is* 16-byte aligned, and we take > the vectorized code path.

I'd say it _happens_ to be 16-byte aligned (by luck).  I assume nothing alignes
*img to sth bigger than 8 bytes and thus whether mprr_2 is aligned to 16 bytes
or not depends on random things (like the linker version).