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

[Ningsheng Jian]

On 4/3/20 5:22 PM, Andrew Haley wrote:
> 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.
> 

Yeah, in this code block dst and src are not necessary to be different regs.

Thanks,
Ningsheng