There. Do I have your attention? With this post my intention is to finally figure out what this pair of instructions actually mean. I mean, they show up everywhere. To do this I'd like to deal with a simple C example.

int main(void)
{
    for (int i = 0; i < 5; ++i);
}

First let's compile it

gcc -g -O0 test.c -c

and then let's disassemble

objdump -S test.o

The output is the assembly interleaved with the source code.

test.o:     file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <main>:
int main(void)
{
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
    for (int i = 0; i < 5; ++i);
   4:   c7 45 fc 00 00 00 00    movl   $0x0,-0x4(%rbp)
   b:   eb 04                   jmp    11 <main+0x11>
   d:   83 45 fc 01             addl   $0x1,-0x4(%rbp)
  11:   83 7d fc 04             cmpl   $0x4,-0x4(%rbp)
  15:   7e f6                   jle    d <main+0xd>
  17:   b8 00 00 00 00          mov    $0x0,%eax
}
  1c:   5d                      pop    %rbp
  1d:   c3                      retq

An interesting thing to note, and what made me write this post was the idea:

a loop is 5 instructions

and indeed it is:

1. assignment
2. unconditional jump to comparison
3. increment
4. comparison
5. conditional jump out of loop

When I was figuring this out in my head it looked slightly different:

1. assignment
2. comparison
3. conditional jump out of loop
4. increment
5. unconditional jump to comparison

but reordering does not change the logic.