PR middle-end/43866
	* tree-ssa-loop-unswitch.c (tree_may_unswitch_on): If stmt is always
	true or always false, return NULL_TREE.
	(tree_unswitch_single_loop): Optimize conditions even when reaching
	max-unswitch-level parameter.  If num > 0, optimize first all conditions
	using entry checks, then do still reachable block discovery and consider
	only conditions in still reachable basic blocks in the loop.

	* gfortran.dg/pr43866.f90: New test.

From-SVN: r161375