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

[Ajit Agarwal <aagarwa1@linux.ibm.com>]

Hello Kewen:

On 07/12/23 4:31 pm, Ajit Agarwal wrote:
> Hello Kewen:
> 
> On 06/12/23 7:52 am, Kewen.Lin wrote:
>> 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).
>>
> 
> Yes with UNSPEC_MMA_EXTRACT it generates lxvp with register pair instead of random
> register by ira and reload pass. But there is an extra moves that gets generated.
> 

With UNSPEC_MMA_EXTRACT I could generate the register pair but functionally here is the
below code which is incorrect.

 l	lxvp %vs0,0(%r4)
        xxlor %vs32,%vs0,%vs0
        xvf32ger 0,%vs34,%vs32
        xvf32gerpp 0,%vs34,%vs33
        xxmfacc 0
        stxvp %vs2,0(%r3)
        stxvp %vs0,32(%r3)
        blr


Here is the RTL Code:

(insn 19 4 20 2 (set (reg:OO 124 [ *ptr_4(D) ])
        (mem:OO (reg/v/f:DI 122 [ ptr ]) [0 *ptr_4(D)+0 S16 A128])) -1
     (nil))
(insn 20 19 9 2 (set (reg:V16QI 129 [orig:124 *ptr_4(D) ] [124])
        (subreg:V16QI (reg:OO 124 [ *ptr_4(D) ]) 0)) -1
     (nil))
(insn 9 20 11 2 (set (reg:XO 119 [ _7 ])
        (unspec:XO [
                (reg/v:V16QI 123 [ src ])
                (reg:V16QI 129 [orig:124 *ptr_4(D) ] [124])
            ] UNSPEC_MMA_XVF32GER)) 2195 {mma_xvf32ger}
     (expr_list:REG_DEAD (reg:OO 124 [ *ptr_4(D) ])
        (nil)))
(insn 11 9 12 2 (set (reg:XO 120 [ _9 ])
        (unspec:XO [
                (reg:XO 119 [ _7 ])
                (reg/v:V16QI 123 [ src ])
                (reg:V16QI 125 [ MEM[(__vector unsigned char *)ptr_4(D) + 16B] ])
            ] UNSPEC_MMA_XVF32GERPP)) 2209 {mma_xvf32gerpp}
     (expr_list:REG_DEAD (reg:V16QI 125 [ MEM[(__vector unsigned char *)ptr_4(D) + 16B] ])
        (expr_list:REG_DEAD (reg/v:V16QI 123 [ src ])
            (expr_list:REG_DEAD (reg:XO 119 [ _7 ])
                (nil)))))
(insn 12 11 18 2 (set (mem:XO (reg:DI 126) [1 *dst_10(D)+0 S64 A128])
        (reg:XO 120 [ _9 ])) "../gcc/testsuite/g++.target/powerpc/vecload.C":13:8 2182 {*movxo}
     (expr_list:REG_DEAD (reg:DI 126)
        (expr_list:REG_DEAD (reg:XO 120 [ _9 ])
            (nil))))
(note 18 12 0 NOTE_INSN_DELETED)

r124 and r129 conflicts live range amd ira generates different registers which will not
serve our purpose.

Making r124 and r129 as same will not allocate register by ira as r124 could have both OOmode
and V16QImode.

Doing this pass before ira_pass has such above issues and we could solve them after making
after reload pass.

Please suggest.

Thanks & Regards
Ajit

> I am working further on this and send the new version of the patch with all the
> comments incorporated.
> 
> Thanks & Regards
> Ajit
>> 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
>>