NODE_TAGGED
assert(thrash_state[last_index] != NODE_TAGGED);
assert(thrash_state[last_index] == NODE_TAGGED);
assert(thrash_state[index] == NODE_TAGGED);
assert(thrash_state[index] != NODE_TAGGED);
thrash_state[index] = NODE_TAGGED;
if (thrash_state[index] != NODE_TAGGED)
case NODE_TAGGED: