re PR tree-optimization/30562 (remove unused variable is removing a referenced variable (in STORED_SYMS or LOADED_SYMS))


	PR 30562
	* tree-flow.h (struct var_ann_d): Remove field 'is_used'.
	Update all users.
	* tree-ssa-alias.c (compute_is_aliased): Remove.  Update all
	users.
	(init_alias_info):
	* tree-ssa-live.c (remove_unused_locals): Do not remove
	TREE_ADDRESSABLE variables.
	* tree-ssa-structalias.c (compute_points_to_sets): Tidy.
	* tree-ssa-operands.c (add_virtual_operand): Remove argument
	FOR_CLOBBER.  Update all users.
	If VAR has an associated alias set, add a virtual operand for
	it if no alias is found to conflict with the memory reference.

From-SVN: r121715