ret: O_RET(expr) # 1 # move(bnode->reg, "rax"); ret();
expr: O_ID # 1 # if(bnode->param_index > -1) move(param_reg(bnode->param_index), bnode->reg);
+expr: O_SUB(expr,expr) # 1 # printf("\tsubq %%%s, %%%s\n", bnode->kids[0]->reg, bnode->kids[1]->reg);
%%