Method use_label_at_offset

cranelift/codegen/src/machinst/buffer.rs:789–811

Emit a reference to the given label with the given reference type (i.e., branch-instruction format) at the current offset. This is like a relocation, but handled internally. This can be called before the branch is actually emitted; fixups will not happen until an island is emitted or the buffer is finished.

(&mut self, offset: CodeOffset, label: MachLabel, kind: I::LabelUse)

    /// This can be called before the branch is actually emitted; fixups will
    /// not happen until an island is emitted or the buffer is finished.
    pub fn use_label_at_offset(&mut self, offset: CodeOffset, label: MachLabel, kind: I::LabelUse) {
        trace!(
            "MachBuffer: use_label_at_offset: offset {} label {:?} kind {:?}",
            offset, label, kind
        );

        // Add the fixup, and update the worst-case island size based on a
        // veneer for this label use.
        let fixup = MachLabelFixup {
            label,
            offset,
            kind,
        };
        self.pending_fixup_deadline = self
            .pending_fixup_deadline
            // Subtract one alignment here to the deadline to account for
            // extra space taken by aligning an island.
            .min(fixup.deadline() - I::LabelUse::ALIGN);
        trace!("pending_fixup_deadline = {}", self.pending_fixup_deadline);
        self.pending_fixup_records.push(fixup);

        // Post-invariant: no mutations to branches/labels data structures.
    }

    /// Inform the buffer of an unconditional branch at the given offset,
    /// targeting the given label. May be used to optimize branches.