[LLVMdev] PBQP & register pairing

[Lang Hames]

Hi Arnaud,

That sounds great. I look forward to seeing a patch.

You may also look forward to big performance improvements in the PBQP
allocator: I'm working on updates which will improve compile speeds and
massively reduce memory use.

Regards,
Lang.

On Tue, Jun 7, 2011 at 7:02 PM, Arnaud Allard de Grandmaison <
Arnaud.AllardDeGrandMaison at dibcom.com> wrote:

>
> I also considered this approach, but did not want to dive in the constraint
> handling for now.
>
> The PBQP path seemed easier at first sight --- and was easy to setup. And I
> always wanted to give a try to the pbqp :)
>
> I will add the hook to the pbqp and propose a patch if this looks clean
> enough.
>
> Thanks,
> --
> Arnaud de Grandmaison
>
> -----Original Message-----
> From: Jakob Stoklund Olesen [mailto:stoklund at 2pi.dk]
> Sent: Monday, June 06, 2011 9:28 PM
> To: Peter Lawrence
> Cc: Arnaud Allard de Grandmaison; llvmdev at cs.uiuc.edu
> Subject: Re: [LLVMdev] PBQP & register pairing
>
>
> On Jun 6, 2011, at 12:14 PM, Peter Lawrence wrote:
>
> > Arnaud,
> >                another way to look at it, if the description of your
> register sets includes "pairs",
> > is that your assembly language syntax for MPQD is redundant, operand-2 is
> the second
> > half of the register-pair in operand-0,  so an alternative is to let llvm
> think this is a two
> > operand instruction (one of them being a pair) rather than a three
> operand instruction.
> >
> > even if you are not currently defining pairs in your register
> definitions, it might be less work
> > to do that than to write and add an extra new pass.  Many many target
> machines have some
> > notion of register pairs, so it should not be too hard to find examples
> of how to do this.
>
> ARM's QQ and QQQQ register classes are examples.
>
> It is currently a bit tedious to specify these constraints; cleaning that
> up is on my todo list.
>
> /jakob
>
>
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