llvm dev - Apr 2019 - Interprocedural DSE for -ftrivial-auto-var-init

On Mon, Apr 15, 2019 at 11:02 PM Amara Emerson via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
>
> > On Apr 15, 2019, at 1:51 PM, Vitaly Buka via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> >
> > Hi JF,
> >
> >    I've heard that you are interested DSE improvements and maybe
we need to be in sync.
> >    So far I experimented with following DSE improvements:
> >
> > * Cross-block DSE, it eliminates additional 7% stores comparing to
existing DSE. But it's not visible on benchmarks.
> I take it you couldn’t see any runtime impact? If there’s code size
improvements that could also be useful, CTMark in the llvm test suite is a
useful subset of benchmarks to check this on (as a baseline use -Os to compare
code size).
>
> Thanks,
> Amara
> >
> > * Cross-block + Interprocedural analysis to annotate each function
argument with:
> >   - can read before write
> >   - will always write
> > This annotations gets me 20% stores deleted additional to the current
DSE.
I believe we can only benefit from removing extra stores.
Hot functions in existing benchmarks are probably optimized good
enough already, but speeding up the long tail is also important.
Also, at least the repro in
https://bugs.llvm.org/show_bug.cgi?id=40527 has been extracted from a
real kernel benchmark (hackbench), where this extra store costed us
0.45%
> > This is on LLVM codebase with -ftrivial-auto-var-init=patter.
> >
> > As-is it's less than I expected, so I would like to find good
benchmark to decide if we should work to make production code from my
experiment.
> >
> > So now I am also planing to try to extend that to whole program
analysis.
> > I will cleanup my code and upload this during this weak, if anyone
wants to try.
> >
> > Vitaly.
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev


-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg

I tried -Os and effect of new approach significantly increases.
I run regular DSE and immediately myDSE. With -Os myDSE removes more than
50% of DSE number.
Which is expected as -Os inlines less and regular DSE can't remove over
function call.

On Tue, Apr 16, 2019 at 7:11 AM Alexander Potapenko <glider at google.com>
wrote:
> On Mon, Apr 15, 2019 at 11:02 PM Amara Emerson via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> >
> >
> > > On Apr 15, 2019, at 1:51 PM, Vitaly Buka via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
> > >
> > > Hi JF,
> > >
> > >    I've heard that you are interested DSE improvements and
maybe we
> need to be in sync.
> > >    So far I experimented with following DSE improvements:
> > >
> > > * Cross-block DSE, it eliminates additional 7% stores comparing
to
> existing DSE. But it's not visible on benchmarks.
> > I take it you couldn’t see any runtime impact? If there’s code size
> improvements that could also be useful, CTMark in the llvm test suite is a
> useful subset of benchmarks to check this on (as a baseline use -Os to
> compare code size).
> >
> > Thanks,
> > Amara
> > >
> > > * Cross-block + Interprocedural analysis to annotate each
function
> argument with:
> > >   - can read before write
> > >   - will always write
> > > This annotations gets me 20% stores deleted additional to the
current
> DSE.
> I believe we can only benefit from removing extra stores.
> Hot functions in existing benchmarks are probably optimized good
> enough already, but speeding up the long tail is also important.
> Also, at least the repro in
> https://bugs.llvm.org/show_bug.cgi?id=40527 has been extracted from a
> real kernel benchmark (hackbench), where this extra store costed us
> 0.45%
>
> > > This is on LLVM codebase with -ftrivial-auto-var-init=patter.
> > >
> > > As-is it's less than I expected, so I would like to find good
> benchmark to decide if we should work to make production code from my
> experiment.
> > >
> > > So now I am also planing to try to extend that to whole program
> analysis.
> > > I will cleanup my code and upload this during this weak, if
anyone
> wants to try.
> > >
> > > Vitaly.
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > llvm-dev at lists.llvm.org
> > > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> --
> Alexander Potapenko
> Software Engineer
>
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
>
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
>
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Can you post numbers for how many stores get eliminated from CTMark?
> On Apr 16, 2019, at 11:45 AM, Vitaly Buka <vitalybuka at google.com>
wrote:
> 
> I tried -Os and effect of new approach significantly increases.
> I run regular DSE and immediately myDSE. With -Os myDSE removes more than
50% of DSE number.
> Which is expected as -Os inlines less and regular DSE can't remove over
function call.
> 
> On Tue, Apr 16, 2019 at 7:11 AM Alexander Potapenko <glider at
google.com <mailto:glider at google.com>> wrote:
> On Mon, Apr 15, 2019 at 11:02 PM Amara Emerson via llvm-dev
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
> >
> >
> > > On Apr 15, 2019, at 1:51 PM, Vitaly Buka via llvm-dev
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
> > >
> > > Hi JF,
> > >
> > >    I've heard that you are interested DSE improvements and
maybe we need to be in sync.
> > >    So far I experimented with following DSE improvements:
> > >
> > > * Cross-block DSE, it eliminates additional 7% stores comparing
to existing DSE. But it's not visible on benchmarks.
> > I take it you couldn’t see any runtime impact? If there’s code size
improvements that could also be useful, CTMark in the llvm test suite is a
useful subset of benchmarks to check this on (as a baseline use -Os to compare
code size).
> >
> > Thanks,
> > Amara
> > >
> > > * Cross-block + Interprocedural analysis to annotate each
function argument with:
> > >   - can read before write
> > >   - will always write
> > > This annotations gets me 20% stores deleted additional to the
current DSE.
> I believe we can only benefit from removing extra stores.
> Hot functions in existing benchmarks are probably optimized good
> enough already, but speeding up the long tail is also important.
> Also, at least the repro in
> https://bugs.llvm.org/show_bug.cgi?id=40527
<https://bugs.llvm.org/show_bug.cgi?id=40527> has been extracted from a
> real kernel benchmark (hackbench), where this extra store costed us
> 0.45%
> 
> > > This is on LLVM codebase with -ftrivial-auto-var-init=patter.
> > >
> > > As-is it's less than I expected, so I would like to find good
benchmark to decide if we should work to make production code from my
experiment.
> > >
> > > So now I am also planing to try to extend that to whole program
analysis.
> > > I will cleanup my code and upload this during this weak, if
anyone wants to try.
> > >
> > > Vitaly.
> > > _______________________________________________
> > > LLVM Developers mailing list
> > > llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
> > > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
> 
> 
> 
> -- 
> Alexander Potapenko
> Software Engineer
> 
> Google Germany GmbH
> Erika-Mann-Straße, 33
> 80636 München
> 
> Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
> Registergericht und -nummer: Hamburg, HRB 86891
> Sitz der Gesellschaft: Hamburg
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