When does the compiler listen to the inline specifier

This simple program does not expand the inline functions. After the code there is a listing of masm and source code showing its not inlining. Rather it calling the function doin' the whole epilog then function then prolog rather than expanding the code in place. I've tried without the inline specifier which defaults to inline when defined in the class (which it is).

Code:

---


#include "stdafx.h"

class tstring
{

        long m_nTStringLength;

public:

        inline tstring( int nLength = 100 ) : m_nTStringLength( nLength )
        {        }

        inline int GetTString( )
        {
                return m_nTStringLength;
        }
};

int main(int argc, char* argv[])
{

        tstring t1;

        long i = t1.GetTString( );

        return 0;

}

---

Generates:

Code:

---

        TITLE        C:\Practice\tstringTest\tstringTest.cpp
PUBLIC        ??0tstring@@QAE@H@Z                                ; tstring::tstring
PUBLIC        ?GetTString@tstring@@QAEHXZ                        ; tstring::GetTString
PUBLIC        _main
EXTRN        __chkesp:NEAR
;        COMDAT _main
_TEXT        SEGMENT
_t1$ = -4
_i$ = -8
_main        PROC NEAR                                        ; COMDAT

; 26  : {

        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

; 27  :
; 28  :        tstring t1;

        push        100                                        ; 00000064H
        lea        ecx, DWORD PTR _t1$[ebp]
        call        ??0tstring@@QAE@H@Z                        ; tstring::tstring

; 29  :
; 30  :        long i = t1.GetTString( );

        lea        ecx, DWORD PTR _t1$[ebp]
        call        ?GetTString@tstring@@QAEHXZ                ; tstring::GetTString
        mov        DWORD PTR _i$[ebp], eax

; 31  :
; 32  :        return 0;

        xor        eax, eax

; 33  :
; 34  : }

        pop        edi
        pop        esi
        pop        ebx
        add        esp, 72                                        ; 00000048H
        cmp        ebp, esp
        call        __chkesp
        mov        esp, ebp
        pop        ebp
        ret        0
_main        ENDP
_TEXT        ENDS
;        COMDAT ??0tstring@@QAE@H@Z
_TEXT        SEGMENT
_nLength$ = 8
_this$ = -4
??0tstring@@QAE@H@Z PROC NEAR                                ; tstring::tstring, COMDAT

; 17  :        {        }

        push        ebp
        mov        ebp, esp
        sub        esp, 68                                        ; 00000044H
        push        ebx
        push        esi
        push        edi
        push        ecx
        lea        edi, DWORD PTR [ebp-68]
        mov        ecx, 17                                        ; 00000011H
        mov        eax, -858993460                                ; ccccccccH
        rep stosd
        pop        ecx
        mov        DWORD PTR _this$[ebp], ecx
        mov        eax, DWORD PTR _this$[ebp]
        mov        ecx, DWORD PTR _nLength$[ebp]
        mov        DWORD PTR [eax], ecx
        mov        eax, DWORD PTR _this$[ebp]
        pop        edi
        pop        esi
        pop        ebx
        mov        esp, ebp
        pop        ebp
        ret        4
??0tstring@@QAE@H@Z ENDP                                ; tstring::tstring
_TEXT        ENDS
;        COMDAT ?GetTString@tstring@@QAEHXZ
_TEXT        SEGMENT
_this$ = -4
?GetTString@tstring@@QAEHXZ PROC NEAR                        ; tstring::GetTString, COMDAT

; 20  :        {

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

; 21  :                return m_nTStringLength;

        mov        eax, DWORD PTR _this$[ebp]
        mov        eax, DWORD PTR [eax]

; 22  :        }

        pop        edi
        pop        esi
        pop        ebx
        mov        esp, ebp
        pop        ebp
        ret        0
?GetTString@tstring@@QAEHXZ ENDP                        ; tstring::GetTString
_TEXT        ENDS
END

---

thanks

dang

It should be inlining those functions. The only thing I can think of that you might try is to make 'm_nTStringLength' an int so that no type-casting goes on in those functions.

Thanks, but still won't inline. I've even fooled around with the /obx compiler optimization command for inline expansion and no luck.

thanks


dang

if you are using visual c (and i guess you are) then check out __forceinline.

inline, __inline, __forceinline
inline

function_declarator; // C++ Specific

__inline

function_declarator;// Microsoft Specific

__forceinline

function_declarator;// Microsoft Specific

The inline and __inline keywords allow the compiler to insert a copy of the function body into each place the function is called. The insertion occurs only if the compiler's cost/benefit analysis show it to be profitable. The __forceinline keyword overrides the cost/benefit analysis and relies on the judgement of the programmer instead. Exercise caution when using __forceinline. Indiscriminate use of __forceinline can result in larger code with only marginal performance gains or, in some cases, even performance losses (due to increased paging of a larger executable, for example).

You cannot force the compiler to inline a function when conditions other than cost/benefit analysis prevent it. You cannot inline a function if:

The function or its caller is compiled with /Ob0 (the default option for debug builds).


The function and the caller use different types of exception handling (C++ exception handling in one, structured exception handling in the other).


The function has a variable argument list.


The function uses inline assembly and is not compiled with /Og, /Ox, /O1, or /O2).


Function returns an unwindable object by value and is not compiled with /GX, /EHs, or /EHa).


The function receives a copy-constructed object passed by value, when compiled with /GX, /EHs,, or /EHa.


The function is recursive and is not accompanied by #pragma(inline_recursion, on). With the pragma, recursive functions can be inlined to a default depth of eight calls. To change the inlining depth, use #pragma(inline_depth, n).
If the compiler cannot inline a function declared __forceinline, it generates a level 1 warning (4714).

The inline keyword is available only in C++. The __inline and __forceinline keywords are available in both C and C++. For compatibility with previous versions, _inline is a synonym for __inline.

Using inline functions can make your program faster because they eliminate the overhead associated with function calls. Functions expanded inline are subject to code optimizations not available to normal functions.

The /Ob compiler optimization option determines whether inline function expansion actually occurs.

For related information, see auto_inline.

Example 1

inline int max( int a , int b )
{
if( a > b ) return a;
return b;
}
A class's member functions can be declared inline either by using the inline keyword or by placing the function definition within the class definition.

Example 2

class MyClass
{
public:
void print() { cout << i << ''; } // Implicitly inline
private:
int i;
};

Thank Stoned_Coder that did the trick.

Thanks alot!

dang

Are you compiling the debug build? The compiler can't inline functions if the /ZI compiler option is enabled. I compiled your code in release build and by changing the debug option to /Zi (and enabled inling in optimisations) and in both cases even without the inline specifiers in the source code the functions were inlined in the asm output.