re PR debug/43176 (var-tracking fails to notice a value change)

	PR debug/43176
	* Makefile.in (var-tracking.o): Depend on pointer-set.h.
	* cselib.c (struct expand_value_data): Add dummy field.
	(cselib_expand_value_rtx, cselib_expand_value_rtx_cb): Initialize
	dummy to false.
	(cselib_dummy_expand_value_rtx_cb): New function.
	(cselib_expand_value_rtx_1): If evd->dummy is true, don't allocate
	any rtl.
	* cselib.h (cselib_dummy_expand_value_rtx_cb): New prototype.
	* var-tracking.c: Include pointer-set.h.
	(variable): Change n_var_parts to char from int.  Add
	cur_loc_changed and in_changed_variables fields.
	(variable_canonicalize): Remove.
	(shared_var_p): New inline function.
	(unshare_variable): Maintain cur_loc_changed and
	in_changed_variables fields.  If var was in changed_variables,
	replace it there with new_var.  Just copy cur_loc instead of
	resetting it to something else.
	(variable_union): Don't recompute cur_loc.  Use shared_var_p.
	(dataflow_set_union): Don't call variable_canonicalize.
	(loc_cmp): If both x and y are DEBUG_EXPRs, compare uids
	of their DEBUG_EXPR_TREE_DECLs.
	(canonicalize_loc_order_check): Verify that cur_loc is NULL
	and in_changed_variables and cur_loc_changed is false.
	(variable_merge_over_cur): Clear cur_loc, in_changed_variables
	and cur_loc_changed.  Don't update cur_loc here.
	(variable_merge_over_src): Don't call variable_canonicalize.
	(dataflow_set_preserve_mem_locs): Use shared_var_p.  When
	removing loc that is equal to cur_loc, clear cur_loc,
	set cur_loc_changed and ensure variable_was_changed is called.
	(dataflow_set_remove_mem_locs): Use shared_var_p.  Only
	compare pointers in cur_loc check, if it is equal to loc,
	clear cur_loc and set cur_loc_changed.  Don't recompute cur_loc here.
	(variable_different_p): Remove compare_current_location argument,
	don't compare cur_loc.
	(dataflow_set_different_1): Adjust variable_different_p caller.
	(variable_was_changed): If dv had some var in changed_variables
	already, reset in_changed_variables flag for it and propagate
	cur_loc_changed over to the new variable.  On empty var
	always set cur_loc_changed.  Set in_changed_variables on whatever
	var is added to changed_variables.
	(set_slot_part): Clear cur_loc_changed and in_changed_variables.
	Use shared_var_p.  When removing loc that is equal to cur_loc,
	clear cur_loc and set cur_loc_changed.  If cur_loc is NULL at the
	end, don't set it to something else, just call variable_was_changed.
	(delete_slot_part): Use shared_var_p.  When cur_loc equals to
	loc being removed, clear cur_loc and set cur_loc_changed.
	Set cur_loc_changed if all locations have been removed.
	(struct expand_loc_callback_data): New type.
	(vt_expand_loc_callback): Add dummy mode in which no rtxes are
	allocated.  Always create SUBREGs if simplify_subreg failed.
	Prefer to use cur_loc, when that fails and still in
	changed_variables (and seen first time) recompute it.  Set
	cur_loc_changed of variables which had to change cur_loc and
	compute elcd->cur_loc_changed if any of the subexpressions used
	had to change cur_loc.
	(vt_expand_loc): Adjust to pass arguments in
	expand_loc_callback_data structure.
	(vt_expand_loc_dummy): New function.
	(emitted_notes): New variable.
	(emit_note_insn_var_location): For VALUEs and DEBUG_EXPR_DECLs
	that weren't used for any other decl in current
	emit_notes_for_changes call call vt_expand_loc_dummy to update
	cur_loc.  For -fno-var-tracking-assignments, set cur_loc to
	first loc_chain location if NULL before.  Always use just
	cur_loc instead of first loc_chain location.  When cur_loc_changed
	is false, when not --enable-checking=rtl just don't emit any note.
	When rtl checking, compute the note and assert it is the same
	as previous note.  Clear cur_loc_changed and in_changed_variables
	at the end before removing from changed_variables.
	(check_changed_vars_3): New function.
	(emit_notes_for_changes): Traverse changed_vars to call
	check_changed_vars_3 on each changed var.
	(emit_notes_for_differences_1): Clear cur_loc_changed and
	in_changed_variables.  Recompute cur_loc of new_var.
	(emit_notes_for_differences_2): Clear cur_loc if new variable
	appears.
	(vt_emit_notes): Initialize and destroy emitted_notes.

From-SVN: r157264