I would have to defer to someone with more expertise regarding compilers to answer your questions. Moreover, it may well require expertise specific to your particular compiler to address your questions. As for myself, I always prefer to work as close to the leadframe as possible, which is to say that I tend to write out my code in assembler, or directly in machine specific instructions. Then I don't have to worry about how a compiler handles things. Of course, your task may be too complex for such an approach to be feasible.
Does anyone else have any suggestions?