tree-loop-distribution.c: Adjust the general comment.

tree-loop-distribution.c: Adjust the general comment.

	* tree-loop-distribution.c: Adjust the general comment.
	(NUM_PARTITION_THRESHOLD): New macro.
	(ssa_name_has_uses_outside_loop_p): Support loop nest distribution.
	(classify_partition): Skip builtin pattern of loop nest's inner loop.
	(merge_dep_scc_partitions): New parameter ignore_alias_p and use it
	in call to build_partition_graph.
	(finalize_partitions): New parameter.  Make loop distribution more
	conservative by fusing more partitions.
	(distribute_loop): Don't do runtime alias check in case of loop nest
	distribution.
	(find_seed_stmts_for_distribution): New function.
	(prepare_perfect_loop_nest): New function.
	(pass_loop_distribution::execute): Refactor code finding seed stmts
	and loop nest into above functions.  Support loop nest distribution.
	Adjust dump information accordingly.

	gcc/testsuite
	* gcc.dg/tree-ssa/ldist-7.c: Adjust test string.
	* gcc.dg/tree-ssa/ldist-16.c: Ditto.
	* gcc.dg/tree-ssa/ldist-25.c: Ditto.
	* gcc.dg/tree-ssa/ldist-33.c: New test.

From-SVN: r253679