sfl-examples/slide-examples/assembly/ex23.asm

; code optimizations
bits 64

    SECTION .data
var_a:     dq  0

    SECTION .text
global _start
_start:
    %include "header.asm.inc"
    
    mov     rbx, 3
    mov     rcx, 2
    jmp     unswitched

    ; conditional moves (non-optimized)
    cmp     rbx, rcx
    jae     ge2
    mov     rax, 0
    jmp     end2
ge2:
    mov     rax, 1
end2:
    ; conditional moves (optimized)
    mov     rax, 0
    mov     rdx, 1
    cmp     rbx, rcx
    cmovae  rax, rdx
    
    ; tertiary operator (exercise)
    ; rax = (rbx >= rcx) ? 37 : 13;
    xor     rax, rax
    cmp     rbx, rcx
    sbb     rax, rax
    and     rax, -24
    add     rax, 37

    ; tertiary operator (non-optimized)
    ; rax = (rbx >= rcx) ? 1 : 0;
    cmp     rbx, rcx
    jae     ge1
    mov     rax, 0
    jmp end
ge1:
    mov     rax, 1
end:
    ; tertiary operator (optimized)
    cmp     rbx, rcx
    sbb     rax, rax
    inc     rax

    ; constant folding (non-optimized)
    mov     rax, 4
    add     rax, 1
    ; constant folding (optimized)
    mov     rax, 5
   
    ; common subexpression elimination (non-optimized)
    xor     rcx, rcx
    mov     rbx, 8
    ; first multiplication    
    mov     rax, 4
    mul     rbx
    add     rcx, rax
    ; second multiplication    
    mov     rax, 4
    mul     rbx
    add     rcx, rax
    ; third multiplication    
    mov     rax, 4
    mul     rbx
    add     rcx, rax
    ; common subexpression elimination (optimized)
    xor     rcx, rcx
    mov     rbx, 8
    mov     rax, 4
    mul     rbx
    add     rcx, rax
    add     rcx, rax
    add     rcx, rax
    
    ; register uses (non-optimized)
    mov     rax, 0
    mov     [var_a], rax
    mov     rax, 1
    mov     [var_a], rax
    mov     rax, 2
    cmp     [var_a], rax
    je      set_a_1
    jmp     dont_set_a_1
set_a_1:
    mov     rax, 1
    mov     [var_a], rax
dont_set_a_1:
    ; register uses (optimized)
    mov     rax, 0
    mov     rax, 1
    cmp     rax, 2
    je      set_a_2
    jmp     dont_set_a_2
set_a_2:
    mov     rax, 1
dont_set_a_2:

    ; faster assembly equivalents (non-optimized)
    mov     rax, 0
    mov     rbx, 8
    mul     rbx
    mov     rbx, 3
    mul     rbx
    ; faster assembly equivalents (optimized)
    xor     rax, rax    ; = 0
    shl     rax, 3      ; *= 8
    add     rax, rax    ; += a
    add     rax, rax    ; += a (a *= 3)

    ; loop inversion (non-optimized)
    xor     rax, rax
repeat1:
    cmp     rax, 1000
    jae     endloop1
    ; do something
    inc     rax
    jmp     repeat1
endloop1:
    ; loop inversion (optimized)
    xor     rax, rax
    cmp     rax, 1000
    jae     endloop2
repeat2:
    inc     rax
    ; do something
    cmp     rax, 1000
    jb      repeat2
endloop2:

    ; loop unswitching
unswitch:
    xor     rax, rax
    xor     rdx, rdx
    mov     rcx, 3
    mov     rbx, 1
iter3:
    cmp     rax, rcx
    jae     endl3
    test    rbx, rbx    ; if
    jnz     do_else
    add     rdx, 1      ; b==0
    inc     rax
    jmp     finif       
do_else:
    add     rdx, 2      ; b!=1
    inc     rax
finif:
    jmp     iter3
endl3:

    nop
    nop
    nop
    nop

    ; unswitched loop
unswitched:
    xor     rax, rax
    xor     rdx, rdx
    mov     rcx, 3
    mov     rbx, 0
    test    rbx, rbx
    jnz     iterB
iterA:
    cmp     rax, rcx
    jae     finuns
    add     rdx, 1
    inc     rax
    jmp     iterA
iterB:
    cmp     rax, rcx
    jae     finuns
    add     rdx, 2
    inc     rax
    jmp     iterB
finuns:

    %include "sysexit.asm.inc"