cprop.c: Clean up hash table building.

cprop.c: Clean up hash table building.

	* cprop.c: Clean up hash table building.
	(reg_avail_info): Remove.
	(oprs_available_p): Remove.
	(record_last_reg_set_info): Remove.
	(record_last_set_info): Remove.
	(reg_available_p): New function.
	(gcse_constant_p): Do not treat unfolded conditions as constants.
	(make_set_regs_unavailable): New function.
	(hash_scan_set): Simplify with new reg_available_p.
	(compute_hash_table_work): Traverse insns stream only once.
	Do not compute reg_avail_info. Traverse insns in reverse order.
	Record implicit sets after recording explicit sets from the block.

From-SVN: r171794