gen_relation
b0 = gen_relation(BPF_JEQ,
b0 = gen_relation(BPF_JGT, gen_loadrnd(), gen_loadi(threshold), 1);
struct block *gen_relation(int, struct arth *, struct arth *, int);
| arth relop arth { $$.b = gen_relation($2, $1, $3, 0);
| arth irelop arth { $$.b = gen_relation($2, $1, $3, 1);