Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size)
currently GHC's internals and code gen don't provide a strong distinction between Ints as data, and Ints for pointer / address arithmetic. This also comes up as being problematical in a number of ways.
- We wind up having many portability issues around Int and pointer / address sizes.
- adds some inessential complexity / problems to adding new architectures to ghc. eg x32 ABI which has 32bit pointers and 64bit ints somewhat breaks current assumptions in the GHC primops (because arrays are indexed by a byte offset, and the valid range for those is determined by the ABI pointer size!)
- this Ints and Ptrs confusion we currently have, also means we can't leverage the Integer support in SIMD registers that is in most modern CPUs! If we could have those two separated better, theres a lot of low leve optimizations we could do for Int/Word data that we currently cant do!