Material about the new code generator

This page summarises work that Norman Ramsey, Simon M, and Simon PJ are doing on re-architecting GHC's back end.

The new Cmm data type

There is a new Cmm data type:

• ZipCfg contains a generic zipper-based control-flow graph data type. It is generic in the sense that it's polymorphic in the type of middle nodes and last nodes of a block. (Middle nodes don't do control transfers; last nodes only do control transfers.) There are extensive notes at the start of the module.
  
  The key types it defines are:
  • Block identifiers: BlockId, BlockEnv, BlockSet
  • Control-flow blocks: Block
  • Control-flow graphs: Graph
    
    
• ZipCfgCmm instantiates ZipCfg for Cmm, by defining types Middle and Last and using these to instantiate the polymorphic fields of ZipCfg. It also defines a bunch of smart constructor (mkJump, mkAssign, mkCmmIfThenElse` etc) which make it easy to build Cmm.

Todo list:

• Get rid of CmmFormals on LastJump and LastCall in ZipCfgCmm

The pipeline

• Code generator converts STG to Cmm.

• Simple control flow optimisation (implemented in CmmContFlowOpt)