2017-08-03 Richard Biener  <rguenther@suse.de>

	PR middle-end/81148
	* fold-const.c (split_tree): Add minus_var and minus_con
	arguments, remove unused loc arg.  Never generate NEGATE_EXPRs
	here but always use minus_*.
	(associate_trees): Assert we never associate with MINUS_EXPR
	and NULL first operand.  Do not recurse for PLUS_EXPR operands
	when associating as MINUS_EXPR either.
	(fold_binary_loc): Track minus_var and minus_con.

	* c-c++-common/ubsan/pr81148.c: New testcase.

From-SVN: r250853