* tree-ssa-reassoc.c (repropagate_negates): Merge negates also
	into MINUS_EXPRs.
	(can_reassociate_p): New function.
	(break_up_subtract_bb, reassociate_bb): Use it.

testsuite/
	* gcc.dg/tree-ssa/negate.c: New testcase.

From-SVN: r158265