Because emitting efficient target machine code is a non-trivial problem? ... but also because the LLVM framework is very generic. This is both a blessing and a

Because emitting efficient target machine code is a non-trivial problem? ... but also because the LLVM framework is very generic. This is both a blessing and a challenge. You can implement a new target by writing much less code (due to those TableGen files), but this code will be trickier since you have to grok several generic metaprogramming mechanisms.