[Bug target/82147] Autovectorization for extraction is slower than done manually

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82147

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
It is even worse for float*4->float*2,float*2.
Take (ignore the obvious aliasing issues):
void f(float *restrict a, float * restrict b, float * restrict c, int s)
{
  for(int i = 0; i< s;i++)
    {
      a[i*2] = c[i*4];
      a[i*2+1] = c[i*4+1];
      b[i*2] = c[i*4 + 2];
      b[i*2+1] = c[i*4 + 3];
    }
}

#define vector16 __attribute__((vector_size(16)))

void f1(float *restrict a, float * restrict b, float * restrict c, int s)
{
  for(int i = 0; i< s;i++)
    {
      vector16 double d = *(vector16 double*)&c[i*2];
      *(double*)&a[i*2] = d[0];
      *(double*)&b[i*2] = d[1];
    }
}