[llvm-dev] Status of PBQP register allocator?

[Quentin Colombet via llvm-dev]

+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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