[Bug tree-optimization/112325] Missed vectorization of reduction after unrolling

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112325

--- Comment #4 from liuhongt at gcc dot gnu.org ---
(In reply to liuhongt from comment #3)
> BB vectorizer relies on the backend support of .REDUC_PLUS for reduction,
> but loop vectorizer can manually do reduction. That's why it's not
> vectorized after cunrolli.
> 
> After adding reduc_plus_scal_v4si, it's vectorized.
> Looks like we need to support
> reduc_plus_scal_{v4si,v8si,v16si,v8hi,v16hi,v32hi}
> Similar for reduc_{and,ior,xor}_scal_m.

This one can be vectorized after support reduc_plus_scal_v4si, but the original
loop is still not vectorized, should be other issues.

int
foo (int* a)
{
  int sum = 0;
  sum += a[0];
  sum += a[1];
  sum += a[2];
  sum += a[3];
  return sum;
}