RFR: 8287697: Limit auto vectorization to 32-byte vector on Cascade Lake [v3]

[Vladimir Kozlov]

On Thu, 2 Jun 2022 05:38:57 GMT, Jatin Bhateja <jbhateja at openjdk.org> wrote:

>> Sandhya Viswanathan has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Change SuperWordMaxVectorSize to develop option
>
> src/hotspot/cpu/x86/vm_version_x86.cpp line 1306:
> 
>> 1304:       // Limit auto vectorization to 256 bit (32 byte) by default on Cascade Lake
>> 1305:       FLAG_SET_DEFAULT(SuperWordMaxVectorSize, 32);
>> 1306:     } else {
> 
> SuperWordMaxVectorSize is set to 32 bytes by default, it should still be capped by MaxVectorSize, in case user sets MaxVectorSize to 16 bytes.

Yes. I submitted testing with `FLAG_SET_DEFAULT(SuperWordMaxVectorSize, MIN2(MaxVectorSize, (intx)32));`
And the flag declared as `DIAGNOSTIC` - product build fail otherwise.

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PR: https://git.openjdk.java.net/jdk/pull/8877