Yes, I do have a deep understanding of the code generator.

First read this:

ftp://ftp.freepascal.org/pub/fpc/docs-pdf/comparch.pdf

It is outdated, but still a good read. If someone wants to start a MIPS port, contact me and I'll help you step by step.

A estimate a MIPS port will be between 150 and 200kb of code, assuming an external assembler and linker is available.