tree-optimization/100756 - niter analysis and folding

tree-optimization/100756 - niter analysis and folding

niter analysis, specifically the part trying to simplify the computed
maybe_zero condition against the loop header copying condition, is
confused by us now simplifying

  _15 = n_8(D) * 4;
  if (_15 > 0)

to

  _15 = n_8(D) * 4;
  if (n_8(D) > 0)

which is perfectly sound at the point we do this transform.  One
solution might be to involve ranger in this simplification, another
is to be more aggressive when expanding expressions - the condition
we try to simplify is _15 > 0, so all we need is expanding that
to n_8(D) * 4 > 0.

The following does just that.

	PR tree-optimization/100756
	* tree-ssa-loop-niter.cc (expand_simple_operations): Also
	expand multiplications by invariants.

	* gcc.dg/vect/pr100756.c: New testcase.