change `int* p = malloc(1024);` to `volatile int* p = malloc(1024);`

asm:

  foo:                                    # @foo
        push    rbx
        mov     ebx, edi
        mov     edi, 1024
        call    malloc@PLT
        movsxd  rcx, ebx
        mov     ebx, dword ptr [rax + 4\*rcx]
        mov     rdi, rax
        call    free@PLT
        mov     eax, ebx
        pop     rbx
        ret

https://godbolt.org/z/E6Teqns8b