PR optimization/12322
	* gcse.c (struct ls_expr): Change type of hash_index from int to
	unsigned int.
	(hash_expr): Document hash_table_size parameter and wrap long line.
	(ldst_entry): Calculate expression's hash_index and record in ptr.
	(trim_ld_motion_mems): Use hash_index to search a single bucket
	instead of scanning the entire hash_table.  Remove the "del" local
	variable and use the equivalent "expr == 0" instead.  Change last
	to be a pointer to the pointer to the current element, to simplify
	and speed-up deleting from a linked list.

From-SVN: r74144