llvm dev - May 2017 - [GlobalISel][AArch64] Toward flipping the switch for O0: Please give it a try!

Hi Kristof,
> On May 25, 2017, at 2:09 AM, Kristof Beyls <kristof.beyls at arm.com>
wrote:
> 
>> 
>> On 24 May 2017, at 22:01, Quentin Colombet <qcolombet at apple.com
<mailto:qcolombet at apple.com>> wrote:
>> 
>> Hi Kristof,
>> 
>> Thanks for going back so fast!
>> 
>>> On May 24, 2017, at 12:57 PM, Kristof Beyls <kristof.beyls at
arm.com <mailto:kristof.beyls at arm.com>> wrote:
>>> 
>>>> 
>>>> On 24 May 2017, at 19:31, Quentin Colombet <qcolombet at
apple.com <mailto:qcolombet at apple.com>> wrote:
>>>> 
>>>> Hi Kristof,
>>>> 
>>>> Thanks for the measurements.
>>>> 
>>>>> On May 24, 2017, at 6:00 AM, Kristof Beyls
<kristof.beyls at arm.com <mailto:kristof.beyls at arm.com>> wrote:
>>>>> 
>>>>>> 
>>>>>>> - Comparing against -O0 without globalisel but with
the above regalloc options: 5.6% performance drop, 1% code size drop.
>>>>>>> 
>>>>>>> In summary, the measurements indicate some good
improvements.
>>>>>>> I also haven't measure the impact on compile
time.
>>>>>> 
>>>>>> Do you have a mean to make this measurement?
>>>>>> Ahmed did a bunch of compile time measurements on our
side and I wanted to see if I need to put him on the hook again :).
>>>>> 
>>>>> I did a quick setup with CTMark (part of the test-suite). I
ran each of
>>>>> * '-O0 -g',
>>>>> * '-O0 -g -mllvm -global-isel=true -mllvm
-global-isel-abort=0', and
>>>>> * '-O0 -g -mllvm -global-isel=true -mllvm
-global-isel-abort=0 -mllvm -optimize-regalloc -mllvm -regalloc=greedy'
>>>>> 5 times, cross-compiling from X86 to AArch64, and took the
median measured compile times.
>>>>> In summary, I see GlobalISel having a compile time
that's 3.5% higher than the current -O0 default.
>>>>> With enabling the greedy register allocator, this increases
to 28%.
>>>>> 28% is probably too high?
>>>> 
>>>> I think it is yes.
>>>> I have attached a quick hack to the greedy allocator to feature
a fast mode.
>>>> Could you give it a try?
>>>> 
>>>> To enable the fast mode, please use (-mllvm)
-regalloc-greedy-fast=true (default is false).
>>> 
>>> I'm afraid it doesn't seem to save much compile time. On
geomean, I see about 26% compile time increase against the current -O0 default
(compared to 28% increase for regalloc greedy without your patch).
>> 
>> Interesting, I guess a lot of time is spent in the coalescer. Could you
give a try with -join-liveintervals=false?
> 
> With adding -join-liveintervals=false, I see the compile time increase
going up to 28% again.
Heh, I am mildly surprised we hand much more live-ranges to the allocator when
we do that.
> 
>> 
>> Do you know where the time is spent (-time-passes)?
> 
> I'm afraid I won't have time to have a closer look in the next
couple of days - I don't know where the time is spent at the moment.
Fair enough, will investigate later.
> 
>> 
>> Anyhow, fixing all of those, although this is I think the right
approach, will take time, so we can go with the localizer.
> 
> Right, I don't understand the register allocator well enough to know if
that compile time overhead can be fixed, while still getting the necessary
codegen benefits the greedy allocator gives.
> Is there any specific help you're looking for with getting the
localizer work well enough for production use?
I’ll clean-up the WIP patch for the localizer, then you guys can fix the bug
that you found.

I’ll do that tomorrow.

Cheers,
-Quentin
> 
> Thanks,
> 
> Kristof
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Hi Kristof,

I’ve pushed the localizer in r304051 and added it in the AArch64 O0 pipeline in
r304052.

I let Diana investigate the seg fault she was seeing.

@Diana, let me know if you need help.

Cheers,
-Quentin
> On May 25, 2017, at 1:53 PM, Quentin Colombet via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hi Kristof,
> 
>> On May 25, 2017, at 2:09 AM, Kristof Beyls <kristof.beyls at arm.com
<mailto:kristof.beyls at arm.com>> wrote:
>> 
>>> 
>>> On 24 May 2017, at 22:01, Quentin Colombet <qcolombet at
apple.com <mailto:qcolombet at apple.com>> wrote:
>>> 
>>> Hi Kristof,
>>> 
>>> Thanks for going back so fast!
>>> 
>>>> On May 24, 2017, at 12:57 PM, Kristof Beyls <kristof.beyls
at arm.com <mailto:kristof.beyls at arm.com>> wrote:
>>>> 
>>>>> 
>>>>> On 24 May 2017, at 19:31, Quentin Colombet <qcolombet at
apple.com <mailto:qcolombet at apple.com>> wrote:
>>>>> 
>>>>> Hi Kristof,
>>>>> 
>>>>> Thanks for the measurements.
>>>>> 
>>>>>> On May 24, 2017, at 6:00 AM, Kristof Beyls
<kristof.beyls at arm.com <mailto:kristof.beyls at arm.com>> wrote:
>>>>>> 
>>>>>>> 
>>>>>>>> - Comparing against -O0 without globalisel but
with the above regalloc options: 5.6% performance drop, 1% code size drop.
>>>>>>>> 
>>>>>>>> In summary, the measurements indicate some good
improvements.
>>>>>>>> I also haven't measure the impact on
compile time.
>>>>>>> 
>>>>>>> Do you have a mean to make this measurement?
>>>>>>> Ahmed did a bunch of compile time measurements on
our side and I wanted to see if I need to put him on the hook again :).
>>>>>> 
>>>>>> I did a quick setup with CTMark (part of the
test-suite). I ran each of
>>>>>> * '-O0 -g',
>>>>>> * '-O0 -g -mllvm -global-isel=true -mllvm
-global-isel-abort=0', and
>>>>>> * '-O0 -g -mllvm -global-isel=true -mllvm
-global-isel-abort=0 -mllvm -optimize-regalloc -mllvm -regalloc=greedy'
>>>>>> 5 times, cross-compiling from X86 to AArch64, and took
the median measured compile times.
>>>>>> In summary, I see GlobalISel having a compile time
that's 3.5% higher than the current -O0 default.
>>>>>> With enabling the greedy register allocator, this
increases to 28%.
>>>>>> 28% is probably too high?
>>>>> 
>>>>> I think it is yes.
>>>>> I have attached a quick hack to the greedy allocator to
feature a fast mode.
>>>>> Could you give it a try?
>>>>> 
>>>>> To enable the fast mode, please use (-mllvm)
-regalloc-greedy-fast=true (default is false).
>>>> 
>>>> I'm afraid it doesn't seem to save much compile time.
On geomean, I see about 26% compile time increase against the current -O0
default (compared to 28% increase for regalloc greedy without your patch).
>>> 
>>> Interesting, I guess a lot of time is spent in the coalescer. Could
you give a try with -join-liveintervals=false?
>> 
>> With adding -join-liveintervals=false, I see the compile time increase
going up to 28% again.
> 
> Heh, I am mildly surprised we hand much more live-ranges to the allocator
when we do that.
> 
>> 
>>> 
>>> Do you know where the time is spent (-time-passes)?
>> 
>> I'm afraid I won't have time to have a closer look in the next
couple of days - I don't know where the time is spent at the moment.
> 
> Fair enough, will investigate later.
> 
>> 
>>> 
>>> Anyhow, fixing all of those, although this is I think the right
approach, will take time, so we can go with the localizer.
>> 
>> Right, I don't understand the register allocator well enough to
know if that compile time overhead can be fixed, while still getting the
necessary codegen benefits the greedy allocator gives.
>> Is there any specific help you're looking for with getting the
localizer work well enough for production use?
> 
> I’ll clean-up the WIP patch for the localizer, then you guys can fix the
bug that you found.
> 
> I’ll do that tomorrow.
> 
> Cheers,
> -Quentin
> 
>> 
>> Thanks,
>> 
>> Kristof
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Thanks Quentin, it's in progress now, I'll let you know how it goes.

Cheers,
Diana

On 27 May 2017 at 03:36, Quentin Colombet <qcolombet at apple.com>
wrote:
> Hi Kristof,
>
> I’ve pushed the localizer in r304051 and added it in the AArch64 O0
pipeline
> in r304052.
>
> I let Diana investigate the seg fault she was seeing.
>
> @Diana, let me know if you need help.
>
> Cheers,
> -Quentin
>
> On May 25, 2017, at 1:53 PM, Quentin Colombet via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>
> Hi Kristof,
>
> On May 25, 2017, at 2:09 AM, Kristof Beyls <kristof.beyls at arm.com>
wrote:
>
>
> On 24 May 2017, at 22:01, Quentin Colombet <qcolombet at apple.com>
wrote:
>
> Hi Kristof,
>
> Thanks for going back so fast!
>
> On May 24, 2017, at 12:57 PM, Kristof Beyls <kristof.beyls at
arm.com> wrote:
>
>
> On 24 May 2017, at 19:31, Quentin Colombet <qcolombet at apple.com>
wrote:
>
> Hi Kristof,
>
> Thanks for the measurements.
>
> On May 24, 2017, at 6:00 AM, Kristof Beyls <kristof.beyls at arm.com>
wrote:
>
>
> - Comparing against -O0 without globalisel but with the above regalloc
> options: 5.6% performance drop, 1% code size drop.
>
> In summary, the measurements indicate some good improvements.
> I also haven't measure the impact on compile time.
>
>
> Do you have a mean to make this measurement?
> Ahmed did a bunch of compile time measurements on our side and I wanted to
> see if I need to put him on the hook again :).
>
>
> I did a quick setup with CTMark (part of the test-suite). I ran each of
> * '-O0 -g',
> * '-O0 -g -mllvm -global-isel=true -mllvm -global-isel-abort=0',
and
> * '-O0 -g -mllvm -global-isel=true -mllvm -global-isel-abort=0 -mllvm
> -optimize-regalloc -mllvm -regalloc=greedy'
> 5 times, cross-compiling from X86 to AArch64, and took the median measured
> compile times.
> In summary, I see GlobalISel having a compile time that's 3.5% higher
than
> the current -O0 default.
> With enabling the greedy register allocator, this increases to 28%.
> 28% is probably too high?
>
>
> I think it is yes.
> I have attached a quick hack to the greedy allocator to feature a fast
mode.
> Could you give it a try?
>
> To enable the fast mode, please use (-mllvm) -regalloc-greedy-fast=true
> (default is false).
>
>
> I'm afraid it doesn't seem to save much compile time. On geomean, I
see
> about 26% compile time increase against the current -O0 default (compared
to
> 28% increase for regalloc greedy without your patch).
>
>
> Interesting, I guess a lot of time is spent in the coalescer. Could you
give
> a try with -join-liveintervals=false?
>
>
> With adding -join-liveintervals=false, I see the compile time increase
going
> up to 28% again.
>
>
> Heh, I am mildly surprised we hand much more live-ranges to the allocator
> when we do that.
>
>
>
> Do you know where the time is spent (-time-passes)?
>
>
> I'm afraid I won't have time to have a closer look in the next
couple of
> days - I don't know where the time is spent at the moment.
>
>
> Fair enough, will investigate later.
>
>
>
> Anyhow, fixing all of those, although this is I think the right approach,
> will take time, so we can go with the localizer.
>
>
> Right, I don't understand the register allocator well enough to know if
that
> compile time overhead can be fixed, while still getting the necessary
> codegen benefits the greedy allocator gives.
> Is there any specific help you're looking for with getting the
localizer
> work well enough for production use?
>
>
> I’ll clean-up the WIP patch for the localizer, then you guys can fix the
bug
> that you found.
>
> I’ll do that tomorrow.
>
> Cheers,
> -Quentin
>
>
> Thanks,
>
> Kristof
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>