[LLVMdev] [LLVMDev] Reg Alloc: Spiller::Spill question

[Jeff Kunkel]

Thanks, I think I have figured it out. However, I moved on to SplitEditor
class. It was quite well done; I must say. Although the SpillAnalysis is a
bit heavy-weight for the stuff I would like to do.

- Jeff

On Fri, Jan 21, 2011 at 6:11 PM, David A. Greene <greened at obbligato.org>wrote:

> Jeff Kunkel <jdkunk3 at gmail.com> writes:
>
> > Spiller::Spill( LiveInterval *li,
> >                           SmallVectorImpl<LiveInterval*> &newIntervals,
> >                           const SmallVectorImpl<LiveInterval*> &spillIs
> );
> >
> > has two reference vectors which contain a small list of Live
> > Intervals. What is the register allocator's job to do with these
> > intervals other than analysis. What more needed other than to know
> > they exist?
>
> It's been a while since I looked at this, so Evan can correct any
> mistakes I make.  :)
>
> spillIs is passed into the spiller and indicates the intervals that
> alias the interval being spilled.  In other words, they indicate
> registers that are sub-/super-registers of the one being spilled.  These
> intervals must be spilled along with the "primary" one.
>
> I think this comes into play in linear scan when it has to force a
> reallocation of a physical register and must backtrack.  The details of
> this are very fuzzy to me.
>
> The newIntervals vector gets filled in by LiveIntervalAnalysis with the
> new intervals created when spilling in done.  Spilling is essentially a
> splitting of a live interval into multiple sub-intervals.  Those
> sub-intervals will need to be allocated to registers.  The newIntervals
> output tells the register allocator the new intervals it must add to its
> work queue.
>
>                             -Dave
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20110121/3b9ad9d5/attachment.html>