---  { *Box {int !x; } int -> int #0}---------------------------
                 arg   rsi
                 box   rdi
                   r15   // r15
                   r14   // r14
                   r13   // r13
                   r12   // r12
                   rbp   // rbp
                   rbx   // rbx
0000             mov   rax = rsi                      // def/empty1 #0
0000             test  rax                           
0000             j<    L4                             // L12
L12:
0000 ??          JMP   L3
L4:
0001             neg   rax                           
L3:
                       rax = phi( N20,N33 )
0001             add8  [rdi] += rax                  
0001             ret   rax  [stk#33]  rbx  rbp  r12  r13  r14  r15  
--- ---------------------------