re PR tree-optimization/68529 (scev failed for while(i--))

re PR tree-optimization/68529 (scev failed for while(i--))

	PR tree-optimization/68529
	* tree-ssa-loop-niter.c (number_of_iterations_ne): Add new param.
	Compute no-overflow information for control iv.
	(number_of_iterations_lt, number_of_iterations_le): Add new param.
	(number_of_iterations_cond): Pass new argument to above functions.

	PR tree-optimization/68529
	* gcc.dg/tree-ssa/pr68529-1.c: New test.
	* gcc.dg/tree-ssa/pr68529-2.c: New test.
	* gcc.dg/tree-ssa/pr68529-3.c: New test.

From-SVN: r231097