re PR tree-optimization/82604 (SPEC CPU2006 410.bwaves ~50% performance regression...

re PR tree-optimization/82604 (SPEC CPU2006 410.bwaves ~50% performance regression with trunk@253679 when ftree-parallelize-loops is used)

	PR tree-optimization/82604
	* tree-loop-distribution.c (enum partition_kind): New enum item
	PKIND_PARTIAL_MEMSET.
	(partition_builtin_p): Support above new enum item.
	(generate_code_for_partition): Ditto.
	(compute_access_range): Differentiate cases that equality can be
	proven at all loops, the innermost loops or no loops.
	(classify_builtin_st, classify_builtin_ldst): Adjust call to above
	function.  Set PKIND_PARTIAL_MEMSET for partition appropriately.
	(finalize_partitions, distribute_loop): Don't fuse partition of
	PKIND_PARTIAL_MEMSET kind when distributing 3-level loop nest.
	(prepare_perfect_loop_nest): Distribute 3-level loop nest only if
	parloop is enabled.

From-SVN: r256990