> Here is an operating system containing many nontrivial applications, all written in 100% Asm:

Here's a small snippet I found from draw.asm:

    add   r9  , [copyxe]
    add   r9  , [copyxe]
    add   r9  , [copyxe]
    sub   r9  , [copyx]
    sub   r9  , [copyx]
    sub   r9  , [copyx]
    add   r10 , [sizex]
    add   r10 , [sizex]
    add   r10 , [sizex]
    add   r14 , 1

72 bytes.

Here's what GCC generates with -Os for the same code:

    imul rax,qword ptr [copyxe],3
    inc r14
    add r9,rax
    imul rax,qword ptr [sizex],3
    add r10,rax
    imul rax,qword ptr [copyx],-3
    add r9,rax

36 bytes.

As a bonus, GCC with -O2:

    mov rax,[copyxe]
    add r14,1
    lea rax,[rax+rax*2]
    add r9,rax
    mov rax,[sizex]
    lea rax,[rax+rax*2]
    add r10,rax
    mov rax,[copyx]
    mov rcx,rax
    neg rcx
    lea rax,[rax+rcx*4]   ; clever!
    add r9,rax

52 bytes.

So, not only does GCC hugely beat this snippet of handwritten Menuet assembly in code size, it can even do so handily while folding all the repeated additions into LEA and eliminating most of the loads.

This is an excellent example of why you shouldn't write in assembler.