[aarch64-port-dev ] RFR(L): 8231441: AArch64: Initial SVE backend support

Ningsheng Jian ningsheng.jian at arm.com
Mon Aug 17 10:19:04 UTC 2020

Hi Andrew,

>> As Joshua clarified, we are also working on predicate scalable reg,
>> which is not in this patch. Thanks for the suggestion, I will try to
>> refactor this a bit.
> Ok, I'll wait for an updated patch. Are you planning to include the
> scalable predicate reg code as part of this patch? I think that would be
> better as it would help to clarify the need to distinguish vector regs
> as a subset of scalable regs.

My original plan was not to include scalable predicate reg related code, 
as they are not used and tested without proper mid-end/back-end code. Do 
you think just adding some comments is OK for now, e.g. saying that a 
scalable reg could also be a predicate reg in future?

>> $ java -XX:MaxVectorSize=48 -version
>> OpenJDK 64-Bit Server VM warning: Current system only supports max SVE
>> vector length 32. Set MaxVectorSize to 32
>> (Fallbacks to 32 and issue a warning, as the prctl() call returns 32
>> instead of unsupported 48:
>> https://www.kernel.org/doc/Documentation/arm64/sve.txt)
>> Do you think we need to exit vm instead of warning and fallbacking to 32
>> here?
> Yes, I think a vm exit would probably be a better choice.

OK, will do that. Thanks!


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