Upgrading projects from VC2005 / VC2003 to VC2008 may not properly port /O2 switch

Source: Microsoft Support

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Use the Conversion Wizard to upgrade a C++ project from Visual Studio 2005 / 2003 (with default settings) to Visual Studio 2008.  Typically, this is started by using VS 2008 to open a solution or project from an earlier version.

The porting completes successfully and the Project Properties->Configuration Properties->C/C++->Optimization for release mode configuration will show Maximize Speed (/O2).

But when you build the application, the /O2 switch may not be not passed to the compiler. This could be observed in the build log or by checking Project Properties->Configuration Properties->C/C++-> Command Line.

As a result the VC2008-SP1-built application could perform more slowly.

This is a known issue in the project conversion modules.

In VS2008, change the Optimization setting to anything besides "Maximize Speed (/O2)", click Apply, then change it back to /O2, and Apply again.

This happens only for projects being converted from earlier versions to VS2008.

Projects created in (rather than upgraded to) VS2008 will not have this issue.

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