Re: VC++ 7.1 (.net 2003) compiler code optimization bug ?

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From: Tim Brown (TimBrown_at_discussions.microsoft.com)
Date: 06/23/04 

Date: Wed, 23 Jun 2004 07:14:01 -0700

"Victor Bazarov" wrote:

>
> Are you sure the problem is due to the compiler bug and not to the fact
> that your code doesn't have any destructor or copy-constructor that could
> affect the behaviour of the program?
>
> It is rather strange that the compiler inlines a call to a function when
> asked to minimize the _size_ of the resulting code. I should rather think
> that it would _not_ inline.
>
> In any case, the way to work around this is to place the constructor in
> a separate translation unit. The compiler will have no way of knowing
> where to get the body, so inlining would be impossible.
>
> V
>

Hi Victor,
Thanks for the reply, in fact my example is a very cut down version of
the bug which I was trying to explain and I think I got the description
wrong, or rather I've finally spotted what is going wrong. So perhaps
I can have another go :-)

If I add another CTypeInfo variable then the code generated looks like this.

CTypeInfo a(10, 20);
00404B48 mov dword ptr [CTypeInfo::s_pList (4072E0h)],offset a (407040h)
00404B52 ret
CTypeInfo b(104, 220);
00404B53 mov eax,dword ptr [CTypeInfo::s_pList (4072E0h)]
00404B58 mov dword ptr [b (40704Ch)],eax
00404B5D mov dword ptr [CTypeInfo::s_pList (4072E0h)],offset b (40704Ch)
00404B67 ret

But the code for the "construction" of variable a is only correct if s_pList
is zero which is it in the source file. However if you add another file which
also defines a CTypeInfo variable (say c) and if it is created first (which
in my case it was) then s_pList will not be zero.
So when the variable a is created its m_pList element will be left as 0
instead of containing the real value of s_pList (ie the address of variable c).

I hope this makes sense and sorry for any confusion.

Tim.
(I've had problems trying to post this reply sorry if it arrives lots of times)

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