re PR target/47440 (Use LCM for vzeroupper insertion)

	PR target/47440
	* config/i386/i386.c (gate_insert_vzeroupper): New function.
	(rest_of_handle_insert_vzeroupper): Ditto.
	(struct rtl_opt_pass pass_insert_vzeroupper): New.
	(ix86_option_override): Register vzeroupper insertion pass here.
	(ix86_check_avx256_register): Handle SUBREGs properly.
	(ix86_init_machine_status): Remove optimize_mode_switching[AVX_U128]
	initialization.

From-SVN: r193503