volatile int typecast return value. Could this make problem?

Hello experts, I'm a beginner of embedded system development.

I have question.about difference of two code.

at first, suppose there is function like

   int SomeFunction(void) {

      ......

       return (some integer);

}

And using this function return value like these

• int retval;

       retval = SomeFunction();

       if (retval == {some Variable})  {

         . . .

       }

• if ( {some Variable} == (volatile int) SomeFunction()) {

          ....

        }

former one doesn't make any problem, but when i used like latter one.. some times, retval is not correct and some strange value remains on r0 register...;

I don't know what is problem on latter one exactly...;

Could explain what is the problem of these?

Thank you very much for reading this..... though it is written by pool english...