Struct Wrapping 

pub struct Wrapping {
    pub signed: bool,
    pub pointer: bool,
    pub trap: bool,
}

What overflows rather than being undefined, which is -fwrapv and its relatives.

Every licence the walk grants the optimizer about overflow is one flag on one instruction, and withdrawing a licence is not setting it. So this is read where the flags are chosen and nowhere else, and a unit built with either of these is a unit whose IR carries less rather than a unit the passes are told something extra about. That is also what makes it correct across link time optimization: a body from a unit that wraps and a body from one that does not keep their own answers when they end up in the same module.

-ftrapv is the exception and is the reason this is not simply two flags. It is the other answer to the question -fwrapv answers, and it is the only one of the three that asks for something to be generated rather than for something to be left out.

Fields

signed: bool

Whether signed arithmetic wraps, from -fwrapv. Set, and an add, a subtract, a multiply, a shift and a negation in a signed type stop saying they do not wrap.

pointer: bool

Whether pointer arithmetic wraps, from -fwrapv-pointer. Set, and the multiply that turns an index into a number of bytes stops saying so.

That multiply is the whole of it here, because the addition itself never claimed anything: a ptradd carries no flags in this IR and no pass reads one off it.

trap: bool

Whether a signed overflow stops the program, from -ftrapv. Set, and an add, a subtract, a multiply and a negation in a signed type become calls to the routine in the runtime that does the arithmetic and checks it.

Never set at the same time as Wrapping::signed, because a program cannot both wrap and stop. The driver is what keeps that true.

Trait Implementations

impl Clone for Wrapping

fn clone(&self) -> Wrapping

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for Wrapping

impl Debug for Wrapping

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Wrapping

fn default() -> Wrapping

Returns the “default value” for a type.

impl Eq for Wrapping

impl PartialEq for Wrapping

fn eq(&self, other: &Wrapping) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Wrapping