Re: [PATCH v2 1/3] app/testpmd: add register keyword

["Varghese, Vipin" <vipin.varghese@amd.com>]

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On 8/21/2024 8:25 PM, Stephen Hemminger wrote:
> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding.
>
>
> On Wed, 21 Aug 2024 20:08:55 +0530
> Vipin Varghese<vipin.varghese@amd.com>  wrote:
>
>> diff --git a/app/test-pmd/macswap_sse.h b/app/test-pmd/macswap_sse.h
>> index 223f87a539..29088843b7 100644
>> --- a/app/test-pmd/macswap_sse.h
>> +++ b/app/test-pmd/macswap_sse.h
>> @@ -16,13 +16,13 @@ do_macswap(struct rte_mbuf *pkts[], uint16_t nb,
>>        uint64_t ol_flags;
>>        int i;
>>        int r;
>> -     __m128i addr0, addr1, addr2, addr3;
>> +     register __m128i addr0, addr1, addr2, addr3;
> Some compilers treat register as a no-op. Are you sure? Did you check with godbolt.

Thank you Stephen, I have tested the code changes on Linux using GCC and 
Clang compiler.

In both cases in Linux environment, we have seen the the values loaded 
onto register `xmm`.

```
registerconst__m128i shfl_msk = _mm_set_epi8(15, 14, 13, 12, 5, 4, 3, 2, 
1, 0, 11, 10, 9, 8, 7, 6);
vmovdqaxmm0, xmmwordptr[rip+ .LCPI0_0]

```

Both cases we have performance improvement.


Can you please help us understand if we have missed out something?

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