re PR rtl-optimization/50205 (ICE: in code_motion_path_driver, at sel-sched.c:6581 with -fselective-scheduling2 and custom flags)

	PR rtl-optimization/50205
	* sel-sched.c (count_occurrences_1): Simplify on the assumption that
	p->x is a register.  Forbid substitution when the same register is
	found in a different mode.
	(count_occurrences_equiv): Assert that 'what' is a register.

	* gcc.dg/pr50205.c: New.

From-SVN: r180135