[llvm-dev] Dataflow analysis regression in 3.7
Johan Engelen via llvm-dev
llvm-dev at lists.llvm.org
Fri Jul 7 23:29:19 PDT 2017
Hi Chad and Davide,
Thanks for working on this.
I don't know enough about LLVM internals (yet?) to contribute here, but
it's nice to "listen-in" on the discussion and watch the progress :)
On Fri, Jul 7, 2017 at 10:59 PM, Davide Italiano <davide at freebsd.org> wrote:
> On Fri, Jul 7, 2017 at 1:47 PM, Chad Rosier <mcrosier at codeaurora.org>
> > David/Johan,
> > I would love to claim victory, but I don't think that D34901 catches this
> > case.
> Hi Chad, thanks for taking another look at this.
> Maybe I didn't bisect correctly. Apologies. Anyway, more fun for us.
> > However, I got interested and threw this together quickly:
> > https://reviews.llvm.org/D35140.
> > This does catch the below case. If people are interested I can add test
> > cases and submit for formal review. FWIW, it does hit about 1/3 of all
> > the SPEC benchmarks. I haven't done any performance analysis to see if
> > matters, however.
> As I stated earlier, I think this calls for a slightly better VRP
> [and/or improvements in VRP] & I'm not entirely sure `InstCombine` is
> the best place for this transform.
> OTOH, the fact this triggers a lot is a good thing, if your WIP patch
> actually results in performance improvements, we should consider a
> more general solution to address this kind of issues.
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