Вот что написано в статье презентующей freepascal 2
Free Pascal 2 does three passes, constant evalution, collection of information and highlevel optimization, and code generation.<span style='color:red'> The code generator has been split in a front-end and back-end</span>. Tree, constant pass, information collection and highlevel code generation are built into an object oriented class structure. The CPU-dependent back-end is also implemented as class that needs to be overridden for each CPU. A CPU-dependent parameter manager helps the code generator to pass parameters to procedures without knowing anything about the CPU and calling convention that is being used.
The advantage of this architecture is that few CPU-dependent code has to be written to port the compiler, one can suffice by implementing the code generator back-end, the parameter manager and supplying the right information to the other parts of the compiler.
from <a href='http://www.osnews.com/story.php?news_id=10607&page=2' target='_blank'>http://www.osnews.com/story.php?news_id=10607&page=2</a>
Вот меня и интересует какая структура у когда генерируемого frontend для backend
