Add zero-cost loops for xtensa port.

Add zero-cost loops for xtensa port.

2014-10-10  Felix Yang  <felix.yang@huawei.com>

	* config/xtensa/xtensa.h (TARGET_LOOPS): New Macro.
	* config/xtensa/xtensa.c: Include dumpfile.h and hw-doloop.h.
	(xtensa_reorg, xtensa_reorg_loops): New.
	(xtensa_can_use_doloop_p, xtensa_invalid_within_doloop): New.
	(hwloop_optimize, hwloop_fail, hwloop_pattern_reg): New.
	(xtensa_emit_loop_end): Emit the zero-overhead loop end label.
	(xtensa_doloop_hooks): Define.
	* config/xtensa/xtensa.md (doloop_end, loop_end): New
	(zero_cost_loop_start): Rewritten.
	(zero_cost_loop_end): Likewise.

From-SVN: r216945