[PING**6] [PATCH, ARM] Further improve stack usage on sha512 (PR 77308)

[Bernd Edlinger <bernd.edlinger@hotmail.de>]

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The latest version of this patch was here:
https://gcc.gnu.org/ml/gcc-patches/2017-04/msg01567.html

Thanks
Bernd.

On 06/14/17 14:34, Bernd Edlinger wrote:
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> On 06/01/17 18:01, Bernd Edlinger wrote:
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>> On 05/12/17 18:49, Bernd Edlinger wrote:
>>> Ping...
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>>> On 04/29/17 19:45, Bernd Edlinger wrote:
>>>> Ping...
>>>>
>>>> I attached a rebased version since there was a merge conflict in
>>>> the xordi3 pattern, otherwise the patch is still identical.
>>>> It splits adddi3, subdi3, anddi3, iordi3, xordi3 and one_cmpldi2
>>>> early when the target has no neon or iwmmxt.
>>>>
>>>>
>>>> Thanks
>>>> Bernd.
>>>>
>>>>
>>>>
>>>> On 11/28/16 20:42, Bernd Edlinger wrote:
>>>>> On 11/25/16 12:30, Ramana Radhakrishnan wrote:
>>>>>> On Sun, Nov 6, 2016 at 2:18 PM, Bernd Edlinger
>>>>>> <bernd.edlinger@hotmail.de> wrote:
>>>>>>> Hi!
>>>>>>>
>>>>>>> This improves the stack usage on the sha512 test case for the case
>>>>>>> without hardware fpu and without iwmmxt by splitting all di-mode
>>>>>>> patterns right while expanding which is similar to what the
>>>>>>> shift-pattern
>>>>>>> does.  It does nothing in the case iwmmxt and fpu=neon or vfp as
>>>>>>> well as
>>>>>>> thumb1.
>>>>>>>
>>>>>>
>>>>>> I would go further and do this in the absence of Neon, the VFP unit
>>>>>> being there doesn't help with DImode operations i.e. we do not 
>>>>>> have 64
>>>>>> bit integer arithmetic instructions without Neon. The main reason why
>>>>>> we have the DImode patterns split so late is to give a chance for
>>>>>> folks who want to do 64 bit arithmetic in Neon a chance to make this
>>>>>> work as well as support some of the 64 bit Neon intrinsics which IIRC
>>>>>> map down to these instructions. Doing this just for soft-float 
>>>>>> doesn't
>>>>>> improve the default case only. I don't usually test iwmmxt and I'm 
>>>>>> not
>>>>>> sure who has the ability to do so, thus keeping this restriction for
>>>>>> iwMMX is fine.
>>>>>>
>>>>>>
>>>>>
>>>>> Yes I understand, thanks for pointing that out.
>>>>>
>>>>> I was not aware what iwmmxt exists at all, but I noticed that most
>>>>> 64bit expansions work completely different, and would break if we 
>>>>> split
>>>>> the pattern early.
>>>>>
>>>>> I can however only look at the assembler outout for iwmmxt, and make
>>>>> sure that the stack usage does not get worse.
>>>>>
>>>>> Thus the new version of the patch keeps only thumb1, neon and 
>>>>> iwmmxt as
>>>>> it is: around 1570 (thumb1), 2300 (neon) and 2200 (wimmxt) bytes stack
>>>>> for the test cases, and vfp and soft-float at around 270 bytes stack
>>>>> usage.
>>>>>
>>>>>>> It reduces the stack usage from 2300 to near optimal 272 bytes (!).
>>>>>>>
>>>>>>> Note this also splits many ldrd/strd instructions and therefore I 
>>>>>>> will
>>>>>>> post a followup-patch that mitigates this effect by enabling the
>>>>>>> ldrd/strd
>>>>>>> peephole optimization after the necessary reg-testing.
>>>>>>>
>>>>>>>
>>>>>>> Bootstrapped and reg-tested on arm-linux-gnueabihf.
>>>>>>
>>>>>> What do you mean by arm-linux-gnueabihf - when folks say that I
>>>>>> interpret it as --with-arch=armv7-a --with-float=hard
>>>>>> --with-fpu=vfpv3-d16 or (--with-fpu=neon).
>>>>>>
>>>>>> If you've really bootstrapped and regtested it on armhf, doesn't this
>>>>>> patch as it stand have no effect there i.e. no change ?
>>>>>> arm-linux-gnueabihf usually means to me someone has configured with
>>>>>> --with-float=hard, so there are no regressions in the hard float ABI
>>>>>> case,
>>>>>>
>>>>>
>>>>> I know it proves little.  When I say arm-linux-gnueabihf
>>>>> I do in fact mean --enable-languages=all,ada,go,obj-c++
>>>>> --with-arch=armv7-a --with-tune=cortex-a9 --with-fpu=vfpv3-d16
>>>>> --with-float=hard.
>>>>>
>>>>> My main interest in the stack usage is of course not because of linux,
>>>>> but because of eCos where we have very small task stacks and in fact
>>>>> no fpu support by the O/S at all, so that patch is exactly what we 
>>>>> need.
>>>>>
>>>>>
>>>>> Bootstrapped and reg-tested on arm-linux-gnueabihf
>>>>> Is it OK for trunk?
>>>>>
>>>>>
>>>>> Thanks
>>>>> Bernd.