[aarch64-port-dev ] RFR(S): 8241475: AArch64: Add missing support for PopCountVI node

[Andrew Haley]

On 4/3/20 10:13 AM, Andrew Dinn wrote:
> On 03/04/2020 03:41, Ningsheng Jian wrote:
>> Hi Pengfei,
>>
>> On 3/31/20 5:32 PM, Pengfei Li wrote:
>>> Hi,
>>>
>>> Please help review this another missing node support for AArch64.
>>>
>>> JBS: https://bugs.openjdk.java.net/browse/JDK-8241475
>>> Webrev: http://cr.openjdk.java.net/~pli/rfr/8241475/webrev.01/
>>>
>>
>> Just took a close look before pushing your code, and I think this line
>> can be removed?
>>
>> +  effect(TEMP_DEF dst);
> Strictly, I think this is correct but I don't think it matters.
> 
> I believe this usage is meant to identify a case where a generated
> multi-instruction sequence uses the output register (i.e. dst = target
> of Set) both as an output in the final instruction and as an
> intermediate scratch register in intervening instructions. That is the
> case for both these rules.

More simply, it prevents the situation where the same register is used as both
an output and an input. Withe these patterns that doesn't matter.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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