* cfgloopmanip.c (create_preheader): Do not use loop_preheader_edge.
	(create_preheaders): Check that loops are available.
	(fix_loop_structure): Clean up, improve comments.
	* tree-ssa-loop-manip.c (rewrite_into_loop_closed_ssa):
	Check that loops are available.  Set LOOP_CLOSED_SSA to the loops
	state flags.
	* tree-scalar-evolution.c (scev_finalize): Clear scalar_evolution_info.
	* predict.c (tree_estimate_probability): Do not call
	calculate_dominance_info.  Call create_preheaders.
	* tree-cfgcleanup.c (cleanup_tree_cfg_loop): Only call
	rewrite_into_loop_closed_ssa if LOOP_CLOSED_SSA is set in loops state
	flags.
	* cfgloop.c (loop_preheader_edge): Assert that loops have preheaders.
	* cfgloop.h (LOOP_CLOSED_SSA): New constant.
	* tree-cfg.c (tree_split_edge): Make an assert more precise.
	* tree-ssa-threadedge.c (thread_across_edge): Comment the function
	arguments.

From-SVN: r123670