SIMD auto-vectorization in hotspot

[Vitaly Davidovich]

Thanks Kris, I'll take a look.  I should've been clearer in my question
though -- I'm mostly interested in packed math (integer and floating point).

Cheers

On Tue, Jan 17, 2012 at 1:36 AM, Krystal Mok <rednaxelafx at gmail.com> wrote:

> Hi,
>
> Apparently, the source code to read is opto/superword.[hpp|cpp] [1][2].
> The flag to trace it is -XX:+TraceSuperWord.
> There's a paper mentioned in [1], which is the origin of the algorithm
> used.
>
> An example to see superword in action is a simple array copy loop:
>
> // byte[] src = ...
> // byte[] dest = ...
> // assert(src.length == dest.length)
> for (int i = 0; i < src.length; i++) {
>   dest[i] = src[i];
> }
>
> This loop will be vectorized by superword and then unrolled a bit, turning
> the actual copy into something like: (on 32-bit x86)
>
> movq   0xc(%ecx,%edi,4),%xmm0
> movq   %xmm0,0xc(%edx,%edi,4)
>
> HTH,
> - Kris
>
> [1]:
> http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/file/tip/src/share/vm/opto/superword.hpp
> [2]:
> http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/file/tip/src/share/vm/opto/superword.cpp<http://hg.openjdk.java.net/hsx/hotspot-main/hotspot/file/tip/src/share/vm/opto/superword.hpp>
>
>
>
> On Tue, Jan 17, 2012 at 1:45 PM, Vitaly Davidovich <vitalyd at gmail.com>wrote:
>
>> Hi guys,
>>
>> Does the -XX:+UseSuperWord (I see it's set to true on 6u23) optimization
>> enable auto-vectorization of certain loops? If so, are there any switches
>> that can be turned on (in product VM) to see if vectorization is being
>> applied or not? In general, would someone be able to describe the current
>> state of loop vectorization (i.e. implementation limits, restrictions,
>> etc)? Which ISAs are supported (i.e. SSE, AVX)? Any other info on this
>> subject would be greatly appreciated ...
>>
>> Thanks very much,
>>
>> Vitaly
>>
>>
>


-- 
Vitaly
617-548-7007 (mobile)
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