Function check_no_loop_splits

language/move-bytecode-verifier/src/control_flow.rs:187–217

(context: &ControlFlowVerifier, labels: &[Label])

}

fn check_no_loop_splits(context: &ControlFlowVerifier, labels: &[Label]) -> PartialVMResult<()> {
    let is_break = |loop_stack: &Vec<(CodeOffset, CodeOffset)>, jump_target: CodeOffset| -> bool {
        match loop_stack.last() {
            None => false,
            Some((_cur_loop_head, last_continue)) => jump_target > *last_continue,
        }
    };
    let loop_depth = count_loop_depth(labels);
    check_code(context, labels, |loop_stack, i, instr| {
        match instr {
            // Forward jump/"break"
            Bytecode::Branch(j) | Bytecode::BrTrue(j) | Bytecode::BrFalse(j)
                if *j > i && !is_break(loop_stack, *j) =>
            {
                let j = *j;
                let before_depth = loop_depth[i as usize];
                let after_depth = match &labels[j as usize] {
                    Label::Loop { .. } => loop_depth[j as usize] - 1,
                    Label::Code => loop_depth[j as usize],
                };
                if before_depth != after_depth {
                    // Invalid forward jump. Entered the middle of a loop
                    Err(context.error(StatusCode::INVALID_LOOP_SPLIT, i))
                } else {
                    Ok(())
                }
            }
            _ => Ok(()),
        }
    })
}

// Only called after continues are verified, so we can assume that loops are well nested
fn count_loop_depth(labels: &[Label]) -> Vec<usize> {