Enum Spot 

pub enum Spot {
    Always(Held),
    Over(Vec<Span>),
}

Where a local is over the addresses of the function it is in.

Which of the two a local gets is decided by what lowering did with it rather than by the optimization level. A local with a frame slot is in that slot from the first instruction of the function to the last, because the frame layout hands the slot out once and nothing moves it afterwards, and one expression says so. A scalar whose address is never taken is put in an SSA value instead, at every optimization level including -O0, and where the register allocator put that value changes from one program counter to the next.

Variants

Always(Held)

In one place at every address in the function.

Over(Vec<Span>)

In a place that depends on where the program counter is, said stretch by stretch.

The stretches do not have to cover the function, and an address none of them covers is an address the local is nowhere. That is the honest answer rather than a gap: a value that has not been computed yet, or whose last reader is already behind, is somewhere for part of a function and nowhere for the rest, and a debugger stopped in the rest should say the variable is not available rather than print whatever is in the register now.

Trait Implementations

impl Clone for Spot

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Spot

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

Formats the value using the given formatter.

impl Eq for Spot

impl PartialEq for Spot

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Spot