PR middle-end/27132
PR middle-end/23295
* builtins.c (fold_binary): Remove checks for flag_wrapv
and flag_trapv where negate_expr_p covers these cases.
PR middle-end/29548
* fold-const.c (fold_plusminus_mult_expr): Check exact power
of two on the absolute value.
(fold_binary): Fold x * -C to -x * C if x is easily negatable
and negating -C does not overflow.