Re: Visual C++ aliasing issue

Hello,

Here is an example, where Visual Studio 2008 produces a code, that
does not work right when compiled with the default Release
configuration. The code works correctly in Debug.
Looks like SP1 has the same problem.

The code was working in VS2003.

The program copies an array of BGR elements into an array of BGRA
elements in place backwards (starting from the last element).

The variable tmp in the loop is introduced specially to prevent the
aliasing issue. The compiler optimizes the variable out however.

 {
   Pixel3 tmp = *(Pixel3*)pBufSrc; //copy to temp variable
   *(Pixel3*)pBufDst = tmp;
   ((Pixel4*)pBufDst)->a = 255;
 }