Article ID: 234511
Article Last Modified on 8/7/2007
APPLIES TO
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition
This article was previously published under Q234511
SYMPTOMS
The Visual C++ 6.0 compiler does not remove certain unneeded temporary instructions, which can slow down code execution.
RESOLUTION
A supported fix for Visual C++ 6.0 that corrects this problem is now available from Microsoft, but it has not been fully regression tested and should be applied only to systems experiencing this specific problem.
To resolve this problem immediately, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, visit the following Web site:
The English version of this fix should have the following file attributes or later.
| Name | Size | Date | Time | Version# | Platform |
|---|---|---|---|---|---|
| c1xx.dll | 1,169KB | 6/4/99 | 11:01 PM | 12.00.8520.0 | x86 |
STATUS
Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section. This bug was corrected in the next service pack for Visual Studio 6.0.
For more information about Visual Studio service packs, click the following article numbers to view the articles in the Microsoft Knowledge Base:
194022 INFO: Visual Studio 6.0 Service packs, What, Where, Why
194295 HOWTO: Tell That a Visual Studio service Pack Is Installed
To download the latest Visual Studio service pack, visit the following Microsoft Web site:
MORE INFORMATION
Steps to reproduce the behavior
Compile the following code with /O2 in Visual C++ 6.0:
#include <time.h>
#include <stdio.h>
class boo
{
int a;
int b;
int c;
int d;
public:
boo():
a(0), b(0), c(0), d(0) {}
boo(int x):
a(x), b(x), c(x), d(x) {}
};
boo fun(int x)
{
if (x)
return boo(x);
else
return boo();
}
void main()
{
time_t start, finish;
double elapsed_time;
int i;
time( &start );
for (i=0; i<200000000; i++)
{
fun(0);
}
for (i=0; i<200000000; i++)
{
fun(10);
}
time( &finish );
elapsed_time = difftime( finish, start );
printf( "\nProgram takes %6.0f seconds.\n", elapsed_time );
}
And compare the following snippet of the generated code:
; 21 : if (x)
mov ecx, DWORD PTR _x$[esp-4]
test ecx, ecx
je SHORT $L622
; 22 : return boo(x);
mov eax, DWORD PTR ___$ReturnUdt$[esp-4]
mov edx, eax
mov DWORD PTR [edx], ecx
mov DWORD PTR [edx+4], ecx
mov DWORD PTR [edx+8], ecx
mov DWORD PTR [edx+12], ecx
; 25 : }
ret 0
$L622:
; 23 : else
; 24 : return boo();
mov eax, DWORD PTR ___$ReturnUdt$[esp-4]
push ebx
mov ebx, eax
xor ecx, ecx
xor edx, edx
push esi
mov DWORD PTR [ebx], ecx
xor esi, esi
push edi
xor edi, edi
mov DWORD PTR [ebx+4], edx
mov DWORD PTR [ebx+8], esi
mov DWORD PTR [ebx+12], edi
pop edi
pop esi
pop ebx
; 25 : }
ret 0
With that generated by Visual C++ 5.0 when compiled with /O2:
; 21 : if (x)
mov ecx, DWORD PTR _x$[esp-4]
; 22 : return boo(x);
mov eax, DWORD PTR ___$ReturnUdt$[esp-4]
xor edx, edx
cmp ecx, edx
je SHORT $L547
mov DWORD PTR [eax], ecx
mov DWORD PTR [eax+4], ecx
mov DWORD PTR [eax+8], ecx
mov DWORD PTR [eax+12], ecx
; 25 : }
ret 0
$L547:
; 23 : else
; 24 : return boo();
mov DWORD PTR [eax], edx
mov DWORD PTR [eax+4], edx
mov DWORD PTR [eax+8], edx
mov DWORD PTR [eax+12], edx
; 25 : }
ret 0
The Visual C++ 6.0 version of the code contains more instructions, which can slow down program execution. The executable built with Visual C++ 6.0 runs slower than the one built with Visual C++ 5.0 on a comparable system.
Additional query words: sp4 code generation performance slow codegen
Keywords: kbhotfixserver kbqfe kbqfe kbbug kbcompiler kbfix kbvs600sp4fix kbvs600sp5fix KB234511
