* tree-ssa-loop-niter.c (refine_value_range_using_guard): New.
	(determine_value_range): Call refine_value_range_using_guard for
	each loop initial condition to improve value range.

	gcc/testsuite/ChangeLog
	* gcc.dg/tree-ssa/loop-bound-1.c: New test.
	* gcc.dg/tree-ssa/loop-bound-3.c: New test.
	* gcc.dg/tree-ssa/loop-bound-5.c: New test.

From-SVN: r226966