[Bug tree-optimization/40168] finding common subexpressions

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=40168

--- Comment #22 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
With the trunk on the second testcase, SLP works but we get stuff like:
  _2 = (*b_420(D))[80];
  _4 = (*b_420(D))[79];
  _538 = {_2, _4};
  _980 = _538 * vect__1.182_559;

Shouldn't that just be loading a vector from (*b_420(D))[79] and then doing an
VEC_PERM?
In a reduced C testcase we get the correct thing:
typedef double array[1000];

void f(array  *a, array *b, array *c)
{
    double t = (*a)[1] * (*b)[0];
    double t1 = (*a)[0] * (*b)[0];
    double t2 = (*a)[3] * (*b)[1];
    double t3 = (*a)[2] * (*b)[1];
    (*c)[0] = t;
    (*c)[1] = t1;
    (*c)[2] = t2;
    (*c)[3] = t3;
}