RFR: JDK-8216437 : PPC64: Add intrinsic for GHASH algorithm [v31]

[Julian Waters]

On Mon, 6 Jan 2025 13:47:11 GMT, Suchismith Roy <sroy at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/stubGenerator_ppc.cpp line 686:
>> 
>>> 684:   Label L_end, L_aligned;
>>> 685: 
>>> 686:   static const unsigned char perm_pattern[16] __attribute__((aligned(16))) = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15};
>> 
>> This pattern can be produced by `lvsl`. Loading it from memory is not needed.
>
> Hi @TheRealMDoerr  
> 
> I had tried something like 
>  __ lvsl(loadOrder, 0);
>  
>  This generated a pattern as below 
>  {0xf, 0xe, 0xd, 0xc, 0xb, 0xa, 0x9, 0x8, 0x7, 0x6, 0x5, 0x4, 0x3, 
>     0x2, 0x1, 0x0}}
>  This causes the the data to be loaded into vector in wrong order. 
>  
>  The desired pattern is    {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15} 
>  
>  Since the data is stored in bytes and we don't have lxvb16x in power8, the pattern has to be enforced. 
>  
>  Is there a better way  to do this ?

I know this code has been changed already, but I would like to point out that you should use alignas(alignment) for alignment purposes and not __attribute__((aligned(alignment))) like the HotSpot Style Guide recommends for any future changes

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PR Review Comment: https://git.openjdk.org/jdk/pull/20235#discussion_r2063241103