VLIW architectures

[Jason Eckhardt]

>
>
>> 
>> There is little to no support in gcc explicitly for VLIW.  In two
>> years time, there will be more.
>> 
>   
> Well, but do you have any suggestions for describing such an  
>architecture by present means? For instance, do you think I could make use
>of define_function_unit and insn attributes to get parallelism from the
>instruction scheduler ?
>

  One may attempt to use the current define_function_unit, etc. attributes to
  describe a VLIW machine to the instruction scheduler. However, the current
  mechanism is very imprecise with respect to modelling the machine. This
  makes it difficult to schedule non-interlocked VLIWs since one may get
  undefined results/wrong answers/processor hangs if resources (e.g. read/
  write ports, functional units, etc.) are oversubscribed or latencies are
  not honored.
  One could write a target-specific function to pack operations, insert
  NOPs, ensure resource and latency constraints are honored, etc. But
  this isn't the best long-term solution.
  In any case, support for precise scheduling (and hence VLIWs) is probably
  not far off. 
  jason.