[PATCH] D20030: [AArch64] Add option to disable speculation of triangle whose tail is the only latch block

[Kristof Beyls via llvm-commits]

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In http://reviews.llvm.org/D20030#430851, @bmakam wrote:

> In http://reviews.llvm.org/D20030#430780, @mcrosier wrote:
>
> > In http://reviews.llvm.org/D20030#430743, @rengolin wrote:
> >
> > > Hi Balaram,
> > >
> > > This seems like a good thing to do overall, not just for Kryo, or when the option is chosen.
> >
> >
> > I agree and would advocate enabling this by default after some additional testing.
> >
> > > It would be good to know how it performs in vanilla AArch64 cores (A53, A57) so we could enable them by default.
> >
> >
> > We should be able to get numbers for at least A57, right?
>
>
> Thanks Renato and Chad,
>
> Yes I will test it on A57 and report the results, but I need others help in testing other AArch64 targets as I do not have access to them.
>
> > > cheers,
>
> > 
>
> > > --renato
>
> > 
>


I ran this patch against r270609, on both Cortex-A53 and Cortex-A57, across spec2000, spec2006, test-suite, and a few other benchmark suites.
The only clear performance differences I saw were:

On Cortex-A53:
SingleSource/Benchmarks/Misc/mandel-2 7.7% speedup

On Cortex-A57:
spec.cpu2006.ref.429_mcf 2.9% slowdown
SingleSource/Benchmarks/Misc/mandel-2 2.9% slowdown

Overall, my measurements seem to indicate this gives a significant performance impact only in very few cases.
I'd be happy for this to be enabled by default for all cores, even though the data indicates this only has a minor impact on performance overall.


http://reviews.llvm.org/D20030