RFR(M):8214751: X86: Support for VNNI instruction

Vladimir Kozlov vladimir.kozlov at oracle.com
Thu Dec 6 19:59:29 UTC 2018

Hi Vivek,

What applications benefit this optimizations?

This optimization may prevent some constant folding and others IGVN optimizations and RA since 
MulAddS2INode is generated too early I think. The only benefit we will have only if vectors are 
generated. Can you generate vectors without MulAddS2INode? Or create MulAddS2INode just before 
vectorization and expand it if vectorization failed? I would prefer first solution to have a struct 
in SuperWord code which find such pattern and try to vectorize it.

You need to add test to verify correctness of results.
Add UseAVX == 0 check to predicates which use SSE2 code. Otherwise they may be selected even if 
UseAVX > 0.


On 12/3/18 8:58 PM, Deshpande, Vivek R wrote:
> Hi All
> Could you please review the VNNI VPDPWSSD instruction support with autovectorization.
> It can vectorize this operation in the loop:
> out[i] += ((in1[2*i] * in2[2*i]) + (in1[2*i+1] * in2[2*i+1]));
> More information on VNNI can be found here:
> https://software.intel.com/sites/default/files/managed/c5/15/architecture-instruction-set-extensions-programming-reference.pdf
> The initial performance gains with micro on skylake with AVX3 is 10.8x.
>   and it generates
> vmovdqu xmm3, xmmword ptr [rbp+r8*2+0x10]
> vmovdqu xmm6, xmmword ptr [rdx+r8*2+0x10]
> vpmaddwd xmm3, xmm6, xmm3
> vpaddd xmm3, xmm3, xmmword ptr [r9+rdi*4+0x10]
> vmovdqu xmmword ptr [r9+rdi*4+0x10], xmm3
> It can generate vpdpwssd instruction on cascadelake.
> The webrev is here:
> http://cr.openjdk.java.net/~vdeshpande/8214751/VNNI/webrev.00/ 
> <http://cr.openjdk.java.net/%7Evdeshpande/8214751/VNNI/webrev.00/>
> The jbs entry for the same is here:
> https://bugs.openjdk.java.net/browse/JDK-8214751
> Regards,
> Vivek

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