Re: [PATCH v2] rs6000: Add new pass for replacement of contiguous addresses vector load lxv with lxvp

["Kewen.Lin" <linkw@linux.ibm.com>]

on 2023/12/6 02:01, Ajit Agarwal wrote:
> Hello Kewen:
> 
> 
> On 05/12/23 7:13 pm, Ajit Agarwal wrote:
>> Hello Kewen:
>>
>> On 04/12/23 7:31 am, Kewen.Lin wrote:
>>> Hi Ajit,
>>>
>>> on 2023/12/1 17:10, Ajit Agarwal wrote:
>>>> Hello Kewen:
>>>>
>>>> On 24/11/23 3:01 pm, Kewen.Lin wrote:
>>>>> Hi Ajit,
>>>>>
>>>>> Don't forget to CC David (CC-ed) :), some comments are inlined below.
>>>>>
>>>>> on 2023/10/8 03:04, Ajit Agarwal wrote:
>>>>>> Hello All:
>>>>>>
>>>>>> This patch add new pass to replace contiguous addresses vector load lxv with mma instruction
>>>>>> lxvp.
>>>>>
>>>>> IMHO the current binding lxvp (and lxvpx, stxvp{x,}) to MMA looks wrong, it's only
>>>>> Power10 and VSX required, these instructions should perform well without MMA support.
>>>>> So one patch to separate their support from MMA seems to go first.
>>>>>
>>>>
>>>> I will make the changes for Power10 and VSX.
>>>>
>>>>>> This patch addresses one regressions failure in ARM architecture.
>>>>>
>>>>> Could you explain this?  I don't see any test case for this.
>>>>
>>>> I have submitted v1 of the patch and there were regressions failure for Linaro.
>>>> I have fixed in version V2.
>>>
>>> OK, thanks for clarifying.  So some unexpected changes on generic code in v1
>>> caused the failure exposed on arm.
>>>
>>>>
>>>>  
>>>>> Besides, it seems a bad idea to put this pass after reload? as register allocation
>>>>> finishes, this pairing has to be restricted by the reg No. (I didn't see any
>>>>> checking on the reg No. relationship for paring btw.)
>>>>>
>>>>
>>>> Adding before reload pass deletes one of the lxv and replaced with lxvp. This
>>>> fails in reload pass while freeing reg_eqivs as ira populates them and then
>>>
>>> I can't find reg_eqivs, I guessed you meant reg_equivs and moved this pass right before
>>> pass_reload (between pass_ira and pass_reload)?  IMHO it's unexpected as those two passes
>>> are closely correlated.  I was expecting to put it somewhere before ira.
>>
>> Yes they are tied together and moving before reload will not work.
>>
>>>
>>>> vecload pass deletes some of insns and while freeing in reload pass as insn
>>>> is already deleted in vecload pass reload pass segfaults.
>>>>
>>>> Moving vecload pass before ira will not make register pairs with lxvp and
>>>> in ira and that will be a problem.
>>>
>>> Could you elaborate the obstacle for moving such pass before pass_ira?
>>>
>>> Basing on the status quo, the lxvp is bundled with OOmode, then I'd expect
>>> we can generate OOmode move (load) and use the components with unspec (or
>>> subreg with Peter's patch) to replace all the previous use places, it looks
>>> doable to me.
>>
>> Moving before ira passes, we delete the offset lxv and generate lxvp and replace all
>> the uses, that I am doing. But the offset lxvp register generated by ira are not
>> register pair and generate random register and hence we cannot generate lxvp.
>>
>> For example one lxv is generated with register 32 and other pair is generated
>> with register 45 by ira if we move it before ira passes.
> 
> It generates the following.
> 	lxvp %vs32,0(%r4)
>         xvf32ger 0,%vs34,%vs32
>         xvf32gerpp 0,%vs34,%vs45

What do the RTL insns for these insns look like?

I'd expect you use UNSPEC_MMA_EXTRACT to extract V16QI from the result of lxvp,
the current define_insn_and_split "*vsx_disassemble_pair" should be able to take
care of it further (eg: reg and regoff).

BR,
Kewen

>         xxmfacc 0
>         stxvp %vs2,0(%r3)
>         stxvp %vs0,32(%r3)
>         blr
> 
> 
> Instead of vs33 ira generates vs45 if we move before pass_ira.
> 
> Thanks & Regards
> Ajit
> 
>  
>> Thanks & Regards
>> Ajit
>>>
>>
>>>>
>>>> Making after reload pass is the only solution I see as ira and reload pass
>>>> makes register pairs and vecload pass will be easier with generation of
>>>> lxvp.
>>>>
>>>> Please suggest.
>>>>  
>>>>> Looking forward to the comments from Segher/David/Peter/Mike etc.
>>>
>>> Still looking forward. :)
>>>
>>> BR,
>>> Kewen