Add empty loop exit block in transform_to_exit_first_loop_alt

Add empty loop exit block in transform_to_exit_first_loop_alt

2015-07-07  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/66642
	* tree-parloops.c (transform_to_exit_first_loop_alt): Update function
	header comment.  Rename split_edge variable to edge_at_split.  Split
	exit edge to create new loop exit bb.  Insert loop exit phis in new loop
	exit bb.

	* testsuite/libgomp.c/parloops-exit-first-loop-alt-3.c (main): Test low
	iteration count case.
	* testsuite/libgomp.c/parloops-exit-first-loop-alt.c (init): New
	function, factor out of ...
	(main): ... here.  Test low iteration count case.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@225521 138bc75d-0d04-0410-961f-82ee72b054a4