getParamBody

pub fn getParamBody(zir: Zir, fn_inst: Inst.Index) []const Zir.Inst.Index {
    const tags = zir.instructions.items(.tag);
    const datas = zir.instructions.items(.data);
    const inst_data = datas[@backingInt(fn_inst)].pl_node;

    const param_block_index = switch (tags[@backingInt(fn_inst)]) {
        .func, .func_inferred => blk: {
            const extra = zir.extraData(Inst.Func, inst_data.payload_index);
            break :blk extra.data.param_block;
        },
        .func_fancy => blk: {
            const extra = zir.extraData(Inst.FuncFancy, inst_data.payload_index);
            break :blk extra.data.param_block;
        },
        else => unreachable,
    };

    switch (tags[@backingInt(param_block_index)]) {
        .block, .block_comptime, .block_inline => {
            const param_block = zir.extraData(Inst.Block, datas[@backingInt(param_block_index)].pl_node.payload_index);
            return zir.bodySlice(param_block.end, param_block.data.body_len);
        },
        .declaration => {
            return zir.getDeclaration(param_block_index).value_body.?;
        },
        else => unreachable,
    }
}