tree-optimization/100934 - properly mark irreducible regions for DOM

tree-optimization/100934 - properly mark irreducible regions for DOM

The jump threading code requires marked irreducible regions for the
purpose of validating jump threading paths but DOM fails to provide
that resulting in mised number of iteration upper bounds clearing.

2021-06-14  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/100934
	* tree-ssa-dom.c (pass_dominator::execute): Properly
	mark irreducible regions.

	* gcc.dg/torture/pr100934.c: New testcase.