Function label_exception_targets

crates/codegen/src/ir.rs:2917–3049

Label exception targets: walk CFG with except stack, set per-instruction handler info and block preserve_lasti flag. Converts POP_BLOCK to NOP. flowgraph.c label_exception_targets + push_except_block

(blocks: &mut [Block])

/// handler info and block preserve_lasti flag. Converts POP_BLOCK to NOP.
/// flowgraph.c label_exception_targets + push_except_block
pub(crate) fn label_exception_targets(blocks: &mut [Block]) {
    #[derive(Clone)]
    struct ExceptEntry {
        handler_block: BlockIdx,
        preserve_lasti: bool,
    }

    let num_blocks = blocks.len();
    if num_blocks == 0 {
        return;
    }

    let mut visited = vec![false; num_blocks];
    let mut block_stacks: Vec<Option<Vec<ExceptEntry>>> = vec![None; num_blocks];

    // Entry block
    visited[0] = true;
    block_stacks[0] = Some(Vec::new());

    let mut todo = vec![BlockIdx(0)];

    while let Some(block_idx) = todo.pop() {
        let bi = block_idx.idx();
        let mut stack = block_stacks[bi].take().unwrap_or_default();
        let mut last_yield_except_depth: i32 = -1;

        let instr_count = blocks[bi].instructions.len();
        for i in 0..instr_count {
            // Read all needed fields (each temporary borrow ends immediately)
            let target = blocks[bi].instructions[i].target;
            let arg = blocks[bi].instructions[i].arg;
            let is_push = blocks[bi].instructions[i].instr.is_block_push();
            let is_pop = blocks[bi].instructions[i].instr.is_pop_block();

            if is_push {
                // Determine preserve_lasti from instruction type (push_except_block)
                let preserve_lasti = matches!(
                    blocks[bi].instructions[i].instr.pseudo(),
                    Some(
                        PseudoInstruction::SetupWith { .. }
                            | PseudoInstruction::SetupCleanup { .. }
                    )
                );

                // Set preserve_lasti on handler block
                if preserve_lasti && target != BlockIdx::NULL {
                    blocks[target.idx()].preserve_lasti = true;
                }

                // Propagate except stack to handler block if not visited
                if target != BlockIdx::NULL && !visited[target.idx()] {
                    visited[target.idx()] = true;
                    block_stacks[target.idx()] = Some(stack.clone());
                    todo.push(target);
                }

                // Push handler onto except stack
                stack.push(ExceptEntry {