Improve hard reg preference propapagation.

Improve hard reg preference propapagation.

2020-05-08  Vladimir Makarov  <vmakarov@redhat.com>

	* ira-color.c (update_costs_from_allocno): Remove
	conflict_cost_update_p argument.  Propagate costs only along
	threads. Always do conflict cost update.  Add printing debugging
	info.
	(update_costs_from_copies): Add printing debugging info.
	(restore_costs_from_copies): Ditto.
	(assign_hard_reg): Improve debug info.
	(push_only_colorable): Ditto. Call update_costs_from_prefs.
	(color_allocnos): Remove update_costs_from_prefs.

2020-05-08  Vladimir Makarov  <vmakarov@redhat.com>

	* gcc.target/i386/pr92807-1.c: Improve the regex.