llvm dev - Aug 2015 - Benchmark GlobalsModRef in non-LTO pass pipeline

Greetings folks!

I would like to enable globalsmodref-aa in the non-LTO pass pipeline so
that it gets tested more and there are fewer differences between the two.
For all of my benchmarks, this is performance neutral, but I'd appreciate
others benchmarking this combination to see if they see any benefits or
regressions.

You can demo this mode easily: -mllvm -enable-non-lto-gmr

Please let me know!
-Chandler
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Hi Chandler,

Sorry it took so long for me to get to this. I'm very keen to get GMR
enabled in the non-LTO pipeline. I see nontrivial perf improvements in a
bunch of workloads I care about with it enabled, but with a patch applied
to run GMR again after the LoopPasses but before the FunctionPasses.

I've found this is critical - LICM needs GMR available, and the passmanager
kills it by the time the early LICM is run.

I'd be really keen to get this enabled by default, with that extra run
added. I assume the need for this extra run will evaporate with the new
pass manager?

Cheers,

James

On Thu, 6 Aug 2015 at 03:45 Chandler Carruth <chandlerc at gmail.com>
wrote:
> Greetings folks!
>
> I would like to enable globalsmodref-aa in the non-LTO pass pipeline so
> that it gets tested more and there are fewer differences between the two.
> For all of my benchmarks, this is performance neutral, but I'd
appreciate
> others benchmarking this combination to see if they see any benefits or
> regressions.
>
> You can demo this mode easily: -mllvm -enable-non-lto-gmr
>
> Please let me know!
> -Chandler
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org         http://llvm.cs.uiuc.edu
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Hi,

To amend what I said earlier, after a lot more investigation it turns out
the problem is that a bunch of optimization passes don't preserve
AliasAnalysis. If I add AU.setPreserved<AliasAnalysis> to a bunch of them,
passes such as LICM end up seeing GMR in its alias analysis chain. That's
when I start to see improvements.

James

On Mon, 10 Aug 2015 at 10:06 James Molloy <james at jamesmolloy.co.uk>
wrote:
> Hi Chandler,
>
> Sorry it took so long for me to get to this. I'm very keen to get GMR
> enabled in the non-LTO pipeline. I see nontrivial perf improvements in a
> bunch of workloads I care about with it enabled, but with a patch applied
> to run GMR again after the LoopPasses but before the FunctionPasses.
>
> I've found this is critical - LICM needs GMR available, and the
> passmanager kills it by the time the early LICM is run.
>
> I'd be really keen to get this enabled by default, with that extra run
> added. I assume the need for this extra run will evaporate with the new
> pass manager?
>
> Cheers,
>
> James
>
> On Thu, 6 Aug 2015 at 03:45 Chandler Carruth <chandlerc at gmail.com>
wrote:
>
>> Greetings folks!
>>
>> I would like to enable globalsmodref-aa in the non-LTO pass pipeline so
>> that it gets tested more and there are fewer differences between the
two.
>> For all of my benchmarks, this is performance neutral, but I'd
appreciate
>> others benchmarking this combination to see if they see any benefits or
>> regressions.
>>
>> You can demo this mode easily: -mllvm -enable-non-lto-gmr
>>
>> Please let me know!
>> -Chandler
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org         http://llvm.cs.uiuc.edu
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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