[llvm-dev] multiprecision add/sub

[Nemanja Ivanovic via llvm-dev]

I believe that providing additional intrinsics that would directly produce
the ISD::ADDC/ISD::SUBC nodes would provide the additional advantage of
being able to directly produce these nodes for code that doesn't have
anything to do with multiprecision addition/subtraction. I am not aware of
any way currently available to produce IR that will generate these nodes
directly.

On Fri, Feb 17, 2017 at 8:52 PM, Bagel via llvm-dev <llvm-dev at lists.llvm.org
> wrote:

> On 02/16/2017 12:08 PM, Stephen Canon wrote:
> >> On Feb 16, 2017, at 9:12 AM, Bagel <bagel99 at gmail.com
> >> <mailto:bagel99 at gmail.com>> wrote:
> >>
> >> I figured that the optimization of this would bedifficult (else it would
> >> have already been done :-))
> >
> > Don’t make this assumption. There’s lots of opportunities for
> optimization
> > scattered around. Some of them are left because they’re genuinely
> difficult,
> > but most either simply haven’t been noticed by anyone, or are known but
> simply
> > haven’t been done because no one has pushed for them (I’m fairly sure
> that this
> > particular optimization falls into that category—folks have known the
> codegen
> > wasn't great since these intrinsics were added, but no one has really
> > complained about it, so people have worked on higher-impact stuff).
>
> But I am still curious as to whether the optimization is architecture
> independent or must be done again for each backend?
>
> bagel
>
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