[llvm-dev] Build a Interference Graph

[Natanael Ramos via llvm-dev]

Ok. Thank you for your help.
Em 18/11/2015 10:50 PM, "Matthias Braun" <mbraun at apple.com> escreveu:

> See MCRegisterInfo.h has a description on what register units are, they
> are an abstraction over physical registers to speedup complicate
> subregister structures.
>
> > On Nov 18, 2015, at 4:41 PM, Natanael Ramos <naelr8 at gmail.com> wrote:
> >
> > Ok, just to clarify, RegUnits, as far I understand, are Physical
> registers or alias to Physical registers. They exist because some
> instructions  use physical registers directly rather than virtual register.
> It's right?
> >
> > And why this RegUnits should be present in the Interference Graph? I
> thought were only the Live Intervals would be the nodes of the graph.
> >
> > Sorry about the trouble to understand my question, my English doesn't
> help that much, I'm from Brazil.
> >
> > Em 18/11/2015 10:19 PM, "Matthias Braun" <mbraun at apple.com> escreveu:
> > I'm not sure I completely understand what you want here. But I think
> this is how you would build a traditional register allocation interference
> graph:
> >
> > Register Units are the things the allocator assigns, I would think it
> would look something like:
> > - Add a node for each register unit and pre-color it!
> > - Add a node for each vreg.
> > - Then pair up: Each vreg against other vregs with overlapping register
> classes, each vreg against each register unit contained in the vregs
> register class.
> >     If there is a liverange overlaps add an edge.
> >
> > - Matthias
> >
> > > On Nov 18, 2015, at 4:09 PM, Natanael Ramos via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> > >
> > > Good Night.
> > >
> > > I'm implementing a Interference Graph in the Register Allocation pass.
> I'm building this graph BEFORE any assignment of a virtual register to
> physical register.  But I have a doubt about how to check the interference
> between two Live Intervals (i.e. They live at same point), should I use:
> > >
> > > L1->overlaps(L2)
> > >
> > > Where L1 and L2 are two different Live Intervals. Or should I use:
> > >
> > > L1->overlaps(RG1)
> > >
> > > Where L1 is a Live Interval and RG1 is a RegUnit for an arbitrary
> physical register.
> > >
> > > I saw this second method in the PBQP allocator code, I think that
> maybe will be related to avoid allocation to reserved physical registers or
> for a on-the-fly check for interference, but the LiveRegMatrix already do
> that.
> > >
> > > So my question is: Considering that I will build this interference
> graph before any assignment (with information only about the Liveness
> Analisys) and I freeze all reserved physical registers before perform
> register allocation, should I use the first or the second method? If the
> second is the right one, why is that?
> > >
> > > I'm using LLVM version 3.6.2.
> > >
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > llvm-dev at lists.llvm.org
> > > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
>
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