FIX: /Og Causes Invalid Double Result Returned from Function

• The C/C++ Compiler (CL.EXE), included with:
  • Microsoft Visual C++, 32-bit Editions, version 5.0

SYMPTOMS

When you are building with /Og and you call a function that returns a double, it apparently returns invalid results. The sample below demonstrates one form of this bug.

CAUSE

The compiler generating code pops the FPU stack without storing the result.

RESOLUTION

Disable /Og around the function that is calling the function returning double by using #pragma optimize("g",off).

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. This bug has been corrected in Visual Studio 97 Service Pack 1.

For additional information about the Visual Studio 97 Service Pack 1, please see the following article in the Microsoft Knowledge Base:

Q170365 INFO: Visual Studio 97 Service Packs - What, Where, and Why

MORE INFORMATION

If you stepping through the following code in a debugger, demonstrates how the return of f1 is not stored in d.

Sample Code

   // Compile options needed: /Og
   double f1()
   {
      return 1.0;
   }
   void f2()
   {
      double d = 0.0;
      d=f1();
   } 

Additional query words: /O2

Keywords : kbcode kbtool kbCompiler kbVS97sp1fix kbVS97sp2fix
Version : 5.0
Platform : NT WINDOWS
Issue type : kbbug