Introducing a new, advanced Visual C++ code optimizer
Undefined behavior notice:  > Historically, Visual C++ did not take advantage of the 
  > fact that the C and C++ standards consider the result 
  > of overflowing signed operations undefined. Other 
  > compilers are very aggressive in this regard, which 
  > motivated the decision to implement some patterns which 
  > take advantage of undefined integer overflow behavior. 
  > We implemented the ones we thought were safe and didn’t 
  > impose any unnecessary security risks in generated code.

  > A new undocumented compiler flag has been added to 
  > disable these optimizations, in case an application 
  > that is not standard-conformant fails: 
  > -d2SSAOptimizerUndefinedIntOverflow-. Due to security 
  > concerns, we have seen cases where these patterns 
  > should not be optimized, even though following the C 
  > and C++ standards allows us to [...]

It sounds like they're not doing anything that GCC/Clang aren't already, but if you've only ever compiled with MSVC then be careful not to overlook this.