[LLVMdev] Regalloc Refactoring

David Greene greened at obbligato.org
Wed Apr 18 09:10:43 PDT 2007

Evan Cheng wrote:

> the given infrastructure? Perhaps. But not without pain. The current  
> data structure is lacking detailed def-use info to properly determine  
> the correct split point. The register allocator even treat  
> "fixed" (i.e. physical register) intervals separately from other  
> active ones.
> The point is, the current code needs a lot of massaging. If you are  
> interested (after your first rounds of refactoring), please consider  
> a replacement for LiveInterval that keeps more accurate info that can  
> be plugged into the same existing allocator. The next step is to do  
> away with the r2rmap and rep().

This gets back to my questions about what LiveIntervals lacks.

- What "data structure" are you referring to above?

- What specific def-use info is needed that we don't have access
   to currently?

- A couple of weeks ago I asked about the comment in
   LiveIntervalAnalysis referring to "conservative" computation.
   What's conservative about it?  What information does it lack that
   a traditional live variable/live range analysis provides?

   The answers I got back said essentially that it's not conservative
   at all and can't be improved upon.  I'm getting a different sense
   from you so I'd like to understand this better.


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