[LLVMdev] RE : Is there any llvm neon intrinsic that maps to vmla.f32 instruction ?

[Sebastien DELDON-GNB]

Hi Lang & Renato,

I eventually set up a panda board with latest linaro delivery (eabi-hf). I did some experiments using my own compiler and LLVM 3.2 as back-end.
I use same flagset for my compiler (front-end) and just invoke llc with and without vmlx-forwarding attribute. So base arguments to llc are:

llc  -march=arm -mcpu=cortex-a9 -mattr=+neon -float-abi=hard

to which I added -mattr=-vmlx-forwarding to disable vmlx forwarding for cortex-a9.
When I DISABLE vmlx forwarding I'm observing a 7% speed-up on ref dataset for MILC. So I'm observing something similar to what I've observed on STE platform available on SNOWBALL board.

Hope this helps
Best Regards
Seb


From: Lang Hames [mailto:lhames at gmail.com]
Sent: Wednesday, February 13, 2013 8:31 AM
To: Renato Golin
Cc: Sebastien DELDON-GNB; llvmdev at cs.uiuc.edu
Subject: Re: [LLVMdev] RE : Is there any llvm neon intrinsic that maps to vmla.f32 instruction ?

Hi Sebastien,

How many extra vmlas did you see in 433.milc due to disabling -vmlx-forwarding?
As I mentioned earlier, I saw only two additional integer vmlx instructions when I tested.

Could you send me your 433.milc compile setup? (os, flags, compiler version, etc.). I'd like to try to reproduce your results.

Cheers,
Lang.

On Tue, Feb 12, 2013 at 9:05 AM, Renato Golin <renato.golin at linaro.org<mailto:renato.golin at linaro.org>> wrote:
On 12 February 2013 16:56, Sebastien DELDON-GNB <sebastien.deldon at st.com<mailto:sebastien.deldon at st.com>> wrote:
If this helps taking your decision, there are at least two benchmarks for which disabling vmlx-forwarding makes a significant difference.

I think Evan's worry was to base this decision on visible and comprehensible benchmarks, such as the test-suite.


If I get lucky I may be able to run on a panda board by next week and have more info to share

That'd be great, thanks!

--renato

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