RFR: 8227505: SuperWordLoopUnrollAnalysis may lead to over loop unrolling

[Jie Fu]

Hi Vivek,

Thanks for your review and comments.

On 2019/8/22 上午3:37, Deshpande, Vivek R wrote:
> The 2nd compilation(recompilation) of doit2 generates the code which does not use full vector width
I don't understand why we must compile with vector-512 since you didn't 
share the performance of vector-256 and vector-512 respectively.
As for my reproducer[1], when vector-128 is used, performance becomes 
much slower than vector-64.
Does vector-512 runs much faster than vector-256 on your manchine?

Could you please share the detailed performance data?


> and also does not unroll after vectorization.
Sorry. I can't reproduce this issue on my computer.
Here is the compilation log[2] of my testing.
Probably this issue can be only triggered on an AVX-512 machine.
I will investigate it once my AVX-512 machine is ready.

If I missed anything please let me know.

Thanks a lot.
Best regards,
Jie

[1] 
http://cr.openjdk.java.net/~jiefu/8227505/TestSuperWordOverunrolling.java
[2] http://cr.openjdk.java.net/~jiefu/8227505/log/SmallByteAdd.log256