TODO

Limitations and missing features (identified so far):

- use compatible calling convention on x86-64 for C structures
- create better debug info for subprogram return
- debug info for non C compatible types
- support for some -fxxx and -m (e.g -mtune) code generation switches
- track alignment of GL_Values
- properly set and track TBAA tags
- set tbaa.struct metadata
- set range metadata