PR tree-optimization/36550
	* tree-ssa-threadupdate.c (count_stmts_and_phis_in_block): New.
	(mark_threaded_blocks): Rewrite code to avoid block copying when
	optimizing for size.  Don't pessimize blocks which will be
	copied, but all the statements will be dead.

	PR tree-optimization/36550
	* gcc.dg/tree-ssa/pr36550.c: New test.

From-SVN: r255731