1.14. CONDITIONAL JUMPS
jge SHORT $LN2@my_min
; reload A to EAX if otherwise and jump to exit
mov eax, DWORD PTR _a$[ebp]
jmp SHORT $LN3@my_min
jmp SHORT $LN3@my_min ; this is redundant JMP
$LN2@my_min:
; return B
mov eax, DWORD PTR _b$[ebp]
$LN3@my_min:
pop ebp
ret 0
_my_min ENDP
_a$ = 8
_b$ = 12
_my_max PROC
push ebp
mov ebp, esp
mov eax, DWORD PTR _a$[ebp]
; compare A and B:
cmp eax, DWORD PTR _b$[ebp]
; jump if A is less or equal to B:
jle SHORT $LN2@my_max
; reload A to EAX if otherwise and jump to exit
mov eax, DWORD PTR _a$[ebp]
jmp SHORT $LN3@my_max
jmp SHORT $LN3@my_max ; this is redundant JMP
$LN2@my_max:
; return B
mov eax, DWORD PTR _b$[ebp]
$LN3@my_max:
pop ebp
ret 0
_my_max ENDP
These two functions differ only in the conditional jump instruction:JGE(“Jump if Greater or Equal”) is used
in the first one andJLE(“Jump if Less or Equal”) in the second.
There is one unneededJMPinstruction in each function, which MSVC presumably left by mistake.
Branchless
ARM for Thumb mode reminds us of x86 code:
Listing 1.132: Optimizing Keil 6/2013 (Thumb mode)my_max PROC
; R0=A
; R1=B
; compare A and B:
CMP r0,r1
; branch if A is greater then B:
BGT |L0.6|
; otherwise (A<=B) return R1 (B):
MOVS r0,r1
|L0.6|
; return
BX lr
ENDP
my_min PROC
; R0=A
; R1=B
; compare A and B:
CMP r0,r1
; branch if A is less then B:
BLT |L0.14|
; otherwise (A>=B) return R1 (B):
MOVS r0,r1