[llvm-commits] Avoid O(#registers*#basicblocks) memory use in LiveVariables

[Chris Lattner]

On May 25, 2009, at 10:59 PM, Evan Cheng wrote:

>>
>> I don't have any specific comment on this patch, but I will raise  
>> the bigger issue: having a bitmap like this is insanity :).  Evan/ 
>> Owen, what do you think the long term solution is for this? Can we  
>> eliminate this bitmap entirely from livevariables by using  
>> dominance based techniques, or build live intervals directly  
>> instead of building live variables?  What is the client of this info?
>
> Actually "UsedBlocks" can be eliminated today. It's not used any  
> more as far as I can tell.

Cool, thanks for doing this.

> As far "AliveBlocks", it's used by liveintervalanalysis and phi  
> elimination.  I believe LiveVariables can be eliminated by moving to  
> dominance based technique. Certainly strongphielim does not make use  
> of LiveVariables at all.

Ok.  It will be nice to see it go away someday.

-Chris