[pklausler]

I have worked on compilers (mostly) for high-performance computing for over 40 years, writing every part of a production compiler twice or more. Optimization and code generation and register allocation/scheduling are definitely the most fun -- but the hardest work is in parsing and semantics, where "hardest" means it takes the most work to get things right for the language and to deal with user errors in the most graceful and informative manner. This is especially true for badly specified legacy languages like Fortran.