2018-05-04  Richard Biener  <rguenther@suse.de>

	PR middle-end/85574
	* fold-const.c (negate_expr_p): Restrict negation of operand
	zero of a division to when we know that can happen without
	overflow.
	(fold_negate_expr_1): Likewise.

	* gcc.dg/torture/pr85574.c: New testcase.
	* gcc.dg/torture/pr57656.c: Use dg-additional-options.

From-SVN: r259922