re PR tree-optimization/85726 (div C1 to div C2 match.pd suboptimization)

re PR tree-optimization/85726 (div C1 to div C2 match.pd suboptimization)

	PR tree-optimization/85726
	* generic-match-head.c (optimize_successive_divisions_p): New function.
	* gimple-match-head.c (optimize_successive_divisions_p): Likewise.
	* match.pd: Don't combine successive divisions if they aren't exact
	and optimize_successive_divisions_p is false.

	* gcc.dg/tree-ssa/pr85726-1.c: New test.
	* gcc.dg/tree-ssa/pr85726-2.c: New test.
	* gcc.dg/tree-ssa/pr85726-3.c: New test.
	* gcc.dg/tree-ssa/pr85726-4.c: New test.

From-SVN: r266848