[llvm-dev] Enable vectorizer-maximize-bandwidth by default?

[Agabaria, Mohammed via llvm-dev]

We’re seeing nice improvements but also significant degradations on IA, which we would like to investigate before the patch is committed.

Major degradations we see:

networking
   ip_pktcheckb1m          -6.80 %
   ip_pktcheckb2m          -6.74 %
   ip_pktcheckb4m          -7.57 %
   ip_pktcheckb512k       -6.58 %
Telecom
   autcor00data_1          -78.02 %
   autcor00data_2          -76.80 %
   autcor00data_3          -77.00 %
(on Atom)

We still working on creating reproducers.
In general we support this patch, just want to have a chance to investigate the issues. We need a few days for that.



From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of Chandler Carruth via llvm-dev
Sent: Tuesday, May 30, 2017 11:27
To: Flamedoge <code.kchoi at gmail.com<mailto:code.kchoi at gmail.com>>; Dehao Chen <dehao at google.com<mailto:dehao at google.com>>
Cc: llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>
Subject: Re: [llvm-dev] Enable vectorizer-maximize-bandwidth by default?

If you care about such hardware, please run benchmarks with the flag?

Dehao has made this flag available. It is important that those who care about particular hardware provid ebenchmark results. Not everyone in the community will have access to particular hardware variants.

On Tue, May 30, 2017 at 1:14 AM Flamedoge <code.kchoi at gmail.com<mailto:code.kchoi at gmail.com>> wrote:
Thank you for running these.

May I suggest testing on AVX2 capable hardware? That would be Intel Haswell, AMD Carrizo and up.
I'm not sure what "vectorizer-maximize-bandwidth" implies, but doubling the vector lanes may help light up parallel regions.

Kevin

On Tue, May 30, 2017 at 12:58 AM, Chandler Carruth via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
On Fri, May 19, 2017 at 4:01 PM Adam Nemet via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
I will run it on Cyclone/AArch64 next week.

FYI, we're still waiting on these Adam...

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