int g(int);
int h(int);
int f(int, int);
int F(int x, int y){return f(g(x),h(y));}    

F(int, int):
        stp     x29, x30, [sp, -32]!
        add     x29, sp, 0
        stp     x19, x20, [sp, 16]
        mov     w20, w1
        bl      g(int)
        mov     w19, w0
        mov     w0, w20
        bl      h(int)
        mov     w1, w0
        mov     w0, w19
        ldp     x19, x20, [sp, 16]
        ldp     x29, x30, [sp], 32
        b       f(int, int)    

F(int, int):
        push    rbp
        push    rbx
        mov     ebp, edi
        mov     edi, esi
        sub     rsp, 8
        call    h(int)
        mov     edi, ebp
        mov     ebx, eax
        call    g(int)
        mov     esi, ebx
        mov     edi, eax
        pop     rax
        pop     rbx
        pop     rbp
        jmp     f(int, int)    

int F(int x, int y)
{
  int _g = g(x);
  return f(_g, h(y));
}    

The more I learn about C the more I realise it has many subtle and devastating traps for the unwary programmer. You can't just write the code, you have to write the code and then examine and maintain it for the next infinity years to make sure that the latest update to the compiler doesn't break it.

Why does C even have undefined behaviour? Should it not refuse to compile because of bad or contradictory input?