[llvm-dev] Status of PBQP register allocator?

[Lang Hames via llvm-dev]

Hi Nate,

PBQP hasn't received a lot of attention recently, but that's due to the odd
combination of (a) it being fairly robust and isolated (and so not much of
a maintenance burden) and (b) it having few users.

I think you should feel free to use it -- I don't think it's going away any
time soon. Plus, the more users it has the more interested people may be in
improving it further.

If you do encounter any bugs in it please file a bug on bugs.llvm.org and
CC me. In my experience the algorithm is simple enough that fixes are
usually fairly straightforward.

Cheers,
Lang.

On Thu, Oct 5, 2017 at 9:19 PM, Quentin Colombet via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> +Lang
>
> Hi Nate,
>
> > On Oct 5, 2017, at 2:41 PM, Nate Voorhies via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> >
> > Hi all,
> >
> > I was wondering about whether the PBQP register allocator is likely to
> be maintained in the future.  It's proving to be a nice way to encode some
> instruction encoding constraints for an out-of-tree backend we have, but
> there's concern about it being abandoned or bitrotting in the future.
>
> The PBQP allocator is not going away and in particular Lang actively
> maintains it when need be.
>
> >
> > Also, if PBQP is likely to lapse out of regular maintenance in the
> future, is there a simple way to express constraints on allocated registers
> (such as sharing an encoding, despite being in different register classes)
> chosen for a particular instruction in the Greedy allocator?
>
> You can use the hint mechanism to express your encoding constraints based
> on what is already allocated. See TargetRegisterInfo::
> getRegAllocationHints.
>
> Cheers,
> -Quentin
>
> >
> > Thanks!
> > _______________________________________________
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> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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