loop splitting

loop splitting

(approved at https://gcc.gnu.org/ml/gcc-patches/2015-12/msg00648.html )

	* common.opt (-fsplit-loops): New flag.
	* passes.def (pass_loop_split): Add.
	* opts.c (default_options_table): Add OPT_fsplit_loops entry at -O3.
	(enable_fdo_optimizations): Add loop splitting.
	* timevar.def (TV_LOOP_SPLIT): Add.
	* tree-pass.h (make_pass_loop_split): Declare.
	* tree-ssa-loop-manip.h (rewrite_into_loop_closed_ssa_1): Declare.
	* tree-ssa-loop-unswitch.c: Include tree-ssa-loop-manip.h,
	* tree-ssa-loop-split.c: New file.
	* Makefile.in (OBJS): Add tree-ssa-loop-split.o.
	* doc/invoke.texi (fsplit-loops): Document.
	* doc/passes.texi (Loop optimization): Add paragraph about loop
	splitting.

testsuite/
	* gcc.dg/loop-split.c: New test.
	* gcc.dg/tree-ssa/ifc-9.c: Update.
	* gcc.dg/tree-ssa/ifc-10.c: Update.

From-SVN: r241374