* var-tracking.c (struct shared_hash_def, shared_hash): New types.
	(dataflow_set): Change vars type from htab_t to shared_hash.
	(shared_hash_pool, empty_shared_hash): New variables.
	(vars_clear): Removed.
	(shared_hash_shared, shared_hash_htab, shared_hash_copy,
	shared_hash_find_slot_unshare, shared_hash_find_slot,
	shared_hash_find_slot_noinsert, shared_hash_find): New
	static inlines.
	(shared_hash_unshare, shared_hash_destroy): New functions.
	(unshare_variable): Unshare set->vars if shared, use
	shared_hash_htab.
	(vars_copy): Use htab_traverse_noresize instead of htab_traverse.
	(get_init_value, find_src_set_src, dump_dataflow_set,
	clobber_variable_part, emit_notes_for_differences): Use
	shared_hash_htab.
	(dataflow_set_init): Remove second argument, set vars to
	empty_shared_hash instead of creating a new htab.
	(dataflow_set_clear): Call shared_hash_destroy and set vars
	to empty_shared_hash instead of calling vars_clear.
	(dataflow_set_copy): Don't call vars_copy, instead just share
	the src htab with dst.
	(variable_union): Use shared_hash_*, use initially NO_INSERT
	lookup if set->vars is shared.  Don't keep slot cleared before
	calling unshare_variable.  Unshare set->vars if needed.
	Even ->refcount == 1 vars must be unshared if set->vars is shared
	and var needs to be modified.
	(variable_canonicalize): New function.
	(dataflow_set_union): If dst->vars is empty, just share src->vars
	with dst->vars and traverse with variable_canonicalize to canonicalize
	and unshare what is needed.
	(dataflow_set_different): If old_set and new_set use the same shared
	htab, they aren't different.  If number of htab elements is different,
	htabs are different.  Use shared_hash_*.
	(dataflow_set_destroy): Call shared_hash_destroy instead of
	htab_delete.
	(compute_bb_dataflow, emit_notes_in_bb, vt_emit_notes): Don't pass
	second argument to dataflow_set_init.
	(vt_initialize): Likewise.  Initialize shared_hash_pool and
	empty_shared_hash, move bb in/out initialization afterwards.
	Use variable_htab_free instead of NULL as changed_variables del hook.
	(variable_was_changed): Change type of second argument to pointer to
	dataflow_set.  When inserting var into changed_variables, bump
	refcount.  Unshare set->vars if set is shared htab and slot needs to
	be cleared.
	(set_variable_part): Use shared_hash_*, use initially NO_INSERT
	lookup if set->vars is shared.  Unshare set->vars if needed.
	Even ->refcount == 1 vars must be unshared if set->vars is shared
	and var needs to be modified.  Adjust variable_was_changed caller.
	(delete_variable_part): Use shared_hash_*.  Even ->refcount == 1
	vars must be unshared if set->vars is shared and var needs to be
	modified.  Adjust variable_was_changed caller.
	(emit_note_insn_var_location): Don't pool_free var.
	(emit_notes_for_differences_1): Initialize empty_var->refcount to 0
	instead of 1.
	(vt_finalize): Call htab_delete on empty_shared_hash->htab and
	free_alloc_pool on shared_hash_pool.

From-SVN: r148760