Method finalize_stack_layout

src/internal/spill_allocator.rs:278–332

Assigns final stack offsets to all active spill slots.

(
        &mut self,
        move_resolver: &MoveResolver,
        allocations: &Allocations,
        stats: &mut Stats,
    )

    /// Assigns final stack offsets to all active spill slots.
    pub fn finalize_stack_layout(
        &mut self,
        move_resolver: &MoveResolver,
        allocations: &Allocations,
        stats: &mut Stats,
    ) -> Result<(), RegAllocError> {
        self.stack_layout.spillslot_area_size = 0;

        // Collect the set of spillslots that are used in the function. Some
        // spillslots may end up unused due to move optimization.
        self.collect_used_spillslots(move_resolver, allocations);

        // Process spill slots from largest to smallest.
        self.final_slots.clear();
        self.final_slots.extend(
            self.stack_layout
                .slots
                .iter_mut()
                .filter_map(|(slot, layout)| {
                    // Remove any unused spillslots from the layout.
                    if self.used_spillslots.contains(slot) {
                        Some((slot, layout.unwrap().1))
                    } else {
                        *layout = None;
                        None
                    }
                }),
        );
        self.final_slots
            .sort_unstable_by_key(|&(_slot, size)| Reverse(size));

        for &(slot, size) in &self.final_slots {
            // This is guaranteed to be properly aligned because we start
            // allocating from larger sizes first, and all sizes are
            // powers of 2.
            debug_assert_eq!(self.stack_layout.spillslot_area_size % size.bytes(), 0);

            let offset = self.stack_layout.spillslot_area_size;
            self.stack_layout.spillslot_area_size = self
                .stack_layout
                .spillslot_area_size
                .checked_add(size.bytes())
                .ok_or(RegAllocError::FunctionTooBig)?;
            self.stack_layout.slots[slot] = Some((offset, size));
        }

        stat!(stats, final_spillslots, self.final_slots.len());
        stat!(
            stats,
            spill_area_size,
            self.stack_layout.spillslot_area_size as usize
        );

        Ok(())
    }
}