Difference between Inline function and Ordinary function

A

Amal P

Hi,

This is the program that i made to test the usage of inline
function. I am using vc 6.0 compiler. Please see the below program.

int NonInline( int a, int b )
{
return ( a > b )? a: b;
}

inline int InLineFun( int a, int b )
{
return ( a > b )? a: b;
}

int main(int argc, char* argv[])
{
int a=10,b=20;
NonInline( a,b );
InLineFun( a,b );
return 0;
}

When i compile this source code with vc6.0 compiler i can get the
following code,

; Listing generated by Microsoft (R) Optimizing Compiler Version
12.00.9044.0

TITLE D:\Personal Data\VC Studies\AssembleAnalyze\AssembleAnalyze.cpp
.386P
include listing.inc
if @Version gt 510
..model FLAT
else
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
_DATA SEGMENT DWORD USE32 PUBLIC 'DATA'
_DATA ENDS
CONST SEGMENT DWORD USE32 PUBLIC 'CONST'
CONST ENDS
_BSS SEGMENT DWORD USE32 PUBLIC 'BSS'
_BSS ENDS
$$SYMBOLS SEGMENT BYTE USE32 'DEBSYM'
$$SYMBOLS ENDS
$$TYPES SEGMENT BYTE USE32 'DEBTYP'
$$TYPES ENDS
_TLS SEGMENT DWORD USE32 PUBLIC 'TLS'
_TLS ENDS
; COMDAT ?NonInline@@YAHHH@Z
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
; COMDAT ?InLineFun@@YAHHH@Z
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
; COMDAT _main
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
FLAT GROUP _DATA, CONST, _BSS
ASSUME CS: FLAT, DS: FLAT, SS: FLAT
endif

INCLUDELIB LIBCD
INCLUDELIB OLDNAMES

PUBLIC ?NonInline@@YAHHH@Z ; NonInline
; Function compile flags: /Odt /GZ /ZI
; File D:\Personal Data\VC Studies\AssembleAnalyze\AssembleAnalyze.cpp
; COMDAT ?NonInline@@YAHHH@Z
_TEXT SEGMENT
_a$ = 8
_b$ = 12
?NonInline@@YAHHH@Z PROC NEAR ; NonInline, COMDAT

; 7 : {

push ebp
mov ebp, esp
sub esp, 68 ; 00000044H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-68]
mov ecx, 17 ; 00000011H
mov eax, -858993460 ; ccccccccH
rep stosd

; 8 : return ( a > b )? a: b;

mov eax, DWORD PTR _a$[ebp]
cmp eax, DWORD PTR _b$[ebp]
jle SHORT $L546
mov ecx, DWORD PTR _a$[ebp]
mov DWORD PTR -68+[ebp], ecx
jmp SHORT $L547
$L546:
mov edx, DWORD PTR _b$[ebp]
mov DWORD PTR -68+[ebp], edx
$L547:
mov eax, DWORD PTR -68+[ebp]

; 9 : }

pop edi
pop esi
pop ebx
mov esp, ebp
pop ebp
ret 0
?NonInline@@YAHHH@Z ENDP ; NonInline
_TEXT ENDS
PUBLIC ?InLineFun@@YAHHH@Z ; InLineFun
PUBLIC _main
EXTRN __chkesp:NEAR
; Function compile flags: /Odt /GZ /ZI
; COMDAT _main
_TEXT SEGMENT
_a$ = -4
_b$ = -8
_main PROC NEAR ; COMDAT

; 17 : {

push ebp
mov ebp, esp
sub esp, 72 ; 00000048H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-72]
mov ecx, 18 ; 00000012H
mov eax, -858993460 ; ccccccccH
rep stosd

; 18 : int a=10,b=20;

mov DWORD PTR _a$[ebp], 10 ; 0000000aH
mov DWORD PTR _b$[ebp], 20 ; 00000014H

; 19 : NonInline( a,b );

mov eax, DWORD PTR _b$[ebp]
push eax
mov ecx, DWORD PTR _a$[ebp]
push ecx
call ?NonInline@@YAHHH@Z ; NonInline
add esp, 8

; 20 : InLineFun( a,b );

mov eax, DWORD PTR _b$[ebp]
push eax
mov ecx, DWORD PTR _a$[ebp]
push ecx
call ?InLineFun@@YAHHH@Z ; InLineFun
add esp, 8

; 21 : return 0;

xor eax, eax

; 22 : }

pop edi
pop esi
pop ebx
add esp, 72 ; 00000048H
cmp ebp, esp
call __chkesp
mov esp, ebp
pop ebp
ret 0
_main ENDP
; Function compile flags: /Odt /GZ /ZI
_TEXT ENDS
; COMDAT ?InLineFun@@YAHHH@Z
_TEXT SEGMENT
_a$ = 8
_b$ = 12
?InLineFun@@YAHHH@Z PROC NEAR ; InLineFun, COMDAT

; 12 : {

push ebp
mov ebp, esp
sub esp, 68 ; 00000044H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-68]
mov ecx, 17 ; 00000011H
mov eax, -858993460 ; ccccccccH
rep stosd

; 13 : return ( a > b )? a: b;

mov eax, DWORD PTR _a$[ebp]
cmp eax, DWORD PTR _b$[ebp]
jle SHORT $L553
mov ecx, DWORD PTR _a$[ebp]
mov DWORD PTR -68+[ebp], ecx
jmp SHORT $L554
$L553:
mov edx, DWORD PTR _b$[ebp]
mov DWORD PTR -68+[ebp], edx
$L554:
mov eax, DWORD PTR -68+[ebp]

; 14 : }

pop edi
pop esi
pop ebx
mov esp, ebp
pop ebp
ret 0
?InLineFun@@YAHHH@Z ENDP ; InLineFun
_TEXT ENDS
END

And my doubt is there is no difference in the calling of the inline
function and the non inline function. Why is it so? Wont inline
function's code get replaced inside the calling function?

Thanks,
Amal P.
 
A

Amal P

I am sorry. I found my mistake. The problem was there is compiler
option to set. Or else you have make release build in vc6.0




Amal said:
Hi,

This is the program that i made to test the usage of inline
function. I am using vc 6.0 compiler. Please see the below program.

int NonInline( int a, int b )
{
return ( a > b )? a: b;
}

inline int InLineFun( int a, int b )
{
return ( a > b )? a: b;
}

int main(int argc, char* argv[])
{
int a=10,b=20;
NonInline( a,b );
InLineFun( a,b );
return 0;
}

When i compile this source code with vc6.0 compiler i can get the
following code,

; Listing generated by Microsoft (R) Optimizing Compiler Version
12.00.9044.0

TITLE D:\Personal Data\VC Studies\AssembleAnalyze\AssembleAnalyze.cpp
.386P
include listing.inc
if @Version gt 510
.model FLAT
else
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
_DATA SEGMENT DWORD USE32 PUBLIC 'DATA'
_DATA ENDS
CONST SEGMENT DWORD USE32 PUBLIC 'CONST'
CONST ENDS
_BSS SEGMENT DWORD USE32 PUBLIC 'BSS'
_BSS ENDS
$$SYMBOLS SEGMENT BYTE USE32 'DEBSYM'
$$SYMBOLS ENDS
$$TYPES SEGMENT BYTE USE32 'DEBTYP'
$$TYPES ENDS
_TLS SEGMENT DWORD USE32 PUBLIC 'TLS'
_TLS ENDS
; COMDAT ?NonInline@@YAHHH@Z
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
; COMDAT ?InLineFun@@YAHHH@Z
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
; COMDAT _main
_TEXT SEGMENT PARA USE32 PUBLIC 'CODE'
_TEXT ENDS
FLAT GROUP _DATA, CONST, _BSS
ASSUME CS: FLAT, DS: FLAT, SS: FLAT
endif

INCLUDELIB LIBCD
INCLUDELIB OLDNAMES

PUBLIC ?NonInline@@YAHHH@Z ; NonInline
; Function compile flags: /Odt /GZ /ZI
; File D:\Personal Data\VC Studies\AssembleAnalyze\AssembleAnalyze.cpp
; COMDAT ?NonInline@@YAHHH@Z
_TEXT SEGMENT
_a$ = 8
_b$ = 12
?NonInline@@YAHHH@Z PROC NEAR ; NonInline, COMDAT

; 7 : {

push ebp
mov ebp, esp
sub esp, 68 ; 00000044H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-68]
mov ecx, 17 ; 00000011H
mov eax, -858993460 ; ccccccccH
rep stosd

; 8 : return ( a > b )? a: b;

mov eax, DWORD PTR _a$[ebp]
cmp eax, DWORD PTR _b$[ebp]
jle SHORT $L546
mov ecx, DWORD PTR _a$[ebp]
mov DWORD PTR -68+[ebp], ecx
jmp SHORT $L547
$L546:
mov edx, DWORD PTR _b$[ebp]
mov DWORD PTR -68+[ebp], edx
$L547:
mov eax, DWORD PTR -68+[ebp]

; 9 : }

pop edi
pop esi
pop ebx
mov esp, ebp
pop ebp
ret 0
?NonInline@@YAHHH@Z ENDP ; NonInline
_TEXT ENDS
PUBLIC ?InLineFun@@YAHHH@Z ; InLineFun
PUBLIC _main
EXTRN __chkesp:NEAR
; Function compile flags: /Odt /GZ /ZI
; COMDAT _main
_TEXT SEGMENT
_a$ = -4
_b$ = -8
_main PROC NEAR ; COMDAT

; 17 : {

push ebp
mov ebp, esp
sub esp, 72 ; 00000048H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-72]
mov ecx, 18 ; 00000012H
mov eax, -858993460 ; ccccccccH
rep stosd

; 18 : int a=10,b=20;

mov DWORD PTR _a$[ebp], 10 ; 0000000aH
mov DWORD PTR _b$[ebp], 20 ; 00000014H

; 19 : NonInline( a,b );

mov eax, DWORD PTR _b$[ebp]
push eax
mov ecx, DWORD PTR _a$[ebp]
push ecx
call ?NonInline@@YAHHH@Z ; NonInline
add esp, 8

; 20 : InLineFun( a,b );

mov eax, DWORD PTR _b$[ebp]
push eax
mov ecx, DWORD PTR _a$[ebp]
push ecx
call ?InLineFun@@YAHHH@Z ; InLineFun
add esp, 8

; 21 : return 0;

xor eax, eax

; 22 : }

pop edi
pop esi
pop ebx
add esp, 72 ; 00000048H
cmp ebp, esp
call __chkesp
mov esp, ebp
pop ebp
ret 0
_main ENDP
; Function compile flags: /Odt /GZ /ZI
_TEXT ENDS
; COMDAT ?InLineFun@@YAHHH@Z
_TEXT SEGMENT
_a$ = 8
_b$ = 12
?InLineFun@@YAHHH@Z PROC NEAR ; InLineFun, COMDAT

; 12 : {

push ebp
mov ebp, esp
sub esp, 68 ; 00000044H
push ebx
push esi
push edi
lea edi, DWORD PTR [ebp-68]
mov ecx, 17 ; 00000011H
mov eax, -858993460 ; ccccccccH
rep stosd

; 13 : return ( a > b )? a: b;

mov eax, DWORD PTR _a$[ebp]
cmp eax, DWORD PTR _b$[ebp]
jle SHORT $L553
mov ecx, DWORD PTR _a$[ebp]
mov DWORD PTR -68+[ebp], ecx
jmp SHORT $L554
$L553:
mov edx, DWORD PTR _b$[ebp]
mov DWORD PTR -68+[ebp], edx
$L554:
mov eax, DWORD PTR -68+[ebp]

; 14 : }

pop edi
pop esi
pop ebx
mov esp, ebp
pop ebp
ret 0
?InLineFun@@YAHHH@Z ENDP ; InLineFun
_TEXT ENDS
END

And my doubt is there is no difference in the calling of the inline
function and the non inline function. Why is it so? Wont inline
function's code get replaced inside the calling function?

Thanks,
Amal P.
Click to expand...
 
M

Michiel.Salters

Amal said:
Hi,

This is the program that i made to test the usage of inline
function. I am using vc 6.0 compiler. Please see the below program.

int NonInline( int a, int b )
{
return ( a > b )? a: b;
}

inline int InLineFun( int a, int b )
{
return ( a > b )? a: b;
}
Click to expand...

No real difference there. Since these are the only two definitions, it
doesn't
matter, but you could define InLineFun again in another Translation
Unit.
Now, "inline" is also a suggestion to the compiler that the function
call
overhead may exceed the work done in the function, but a good compiler
can figure that out anyway. All functions are visible tot he compiler.

Usually, the inline keyword is (should be) used only after profiling
shows
that the compiler misjudged the call overhead versus work done ratio.

HTH,
Michiel Salters
 

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