llvm dev - Jun 2019 - Tablegen ridiculously slow when compiling for Debug

Hi Praveen,

Thanks for the tip, but Xcode seems to spend all the time running tablegen
"custom shell scripts", one by one at a time, not linking. Linking is
actually very fast, possibly less than a second. The “scripts” that take longer
are  “AArch64CommonTableGen" and “AMDGPUCommonTableGen”.  As said this is
on LLVM 9.0.

However, on LLVM 7.0.1, the same process takes just 5-6 seconds in total, with
individual “scripts” taking significantly less than 1 second each. There must be
some difference between LLVM 9.0 and LLVM 7.0 that might cause this (?)

John

> On 30 Jun 2019, at 11:17, Praveen Velliengiri <praveenvelliengiri at
gmail.com> wrote:
> 
> 
> cmake BUILD_SHARED_LIBS option, it builds llvm as .so not as .a. It will
use less memory during linking so you can increase the link threads and your
build time will be lesser.
> Check this in : https://llvm.org/docs/CMake.html
<https://llvm.org/docs/CMake.html>
> 
> 
> On Sun, 30 Jun 2019 at 14:42, Joan Lluch <joan.lluch at icloud.com
<mailto:joan.lluch at icloud.com>> wrote:
> Hi Praveen,
> 
> Please, can you elaborate on this?. What do do mean by “building as shared
objects”.
> 
> Thanks,
> 
> John
> 
> 
> 
>> On 30 Jun 2019, at 07:32, Praveen Velliengiri <praveenvelliengiri at
gmail.com <mailto:praveenvelliengiri at gmail.com>> wrote:
>> 
>> Maybe try building llvm as a shared objects.. 
>> 
>> On Jun 30, 2019 1:30 AM, "Joan Lluch via llvm-dev"
<llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>>
wrote:
>> Hi Florian,
>> 
>> Ok, I ran this:
>> 
>> cmake -S LLVM -DCMAKE_INSTALL_PREFIX=INSTALL
-DLLVM_OPTIMIZED_TABLEGEN=On -G Xcode
>> 
>> Compiled it again from clean, and the situation is worse than before.
Incremental builds take an incredible amount of time stuck in running Tablegen
scripts for all targets. Now this happens both in Release and Debug
configurations. Just before this, at least Release compiled fine, but that’s no
longer the case.
>> 
>> Any other suggestions?  What could actually cause this? 
>> 
>> Thanks
>> John
>>  
>> 
>> 
>>> On 29 Jun 2019, at 19:37, Florian Hahn <florian_hahn at
apple.com <mailto:florian_hahn at apple.com>> wrote:
>>> 
>>> Hi,
>>> 
>>>> On Jun 29, 2019, at 18:26, Joan Lluch via llvm-dev <llvm-dev
at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>>>> 
>>>> Hi all,
>>>> 
>>>> On LLVM version 7.0.1, incremental builds are very fast for
both Release and Debug. I’m compiling with Xcode
>>>> 
>>>> I recently downloaded LLVM 9.0 from the LLVM-mirror Github
repository and found that Incremental "Debug” builds take a ridiculously
long time due to Tablegen taking ages (literally more than 10 minutes) to
generate files. This makes it totally unusable for debug purposes. However,
incremental ‘Release’ builds only take a few seconds.
>>>> 
>>>> Why is that?. Any suggestions?.
>>> 
>>> 
>>> 
>>> You could give setting LLVM_OPTIMIZED_TABLEGEN a try
(https://llvm.org/docs/CMake.html <https://llvm.org/docs/CMake.html>).
>>> 
>>> Cheers,
>>> Florian
>> 
>> 
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
<https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev>
>> 
> 
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Hi Joan :)
Oh I don't have any experience in Xcode & previous versions of LLVM
though..

On Sun, 30 Jun 2019 at 14:58, Joan Lluch <joan.lluch at icloud.com> wrote:
> Hi Praveen,
>
> Thanks for the tip, but Xcode seems to spend all the time running tablegen
> "custom shell scripts", one by one at a time, not linking.
Linking is
> actually very fast, possibly less than a second. The “scripts” that take
> longer are  “AArch64CommonTableGen" and “AMDGPUCommonTableGen”.  As
said
> this is on LLVM 9.0.
>
> However, on LLVM 7.0.1, the same process takes just 5-6 seconds in total,
> with individual “scripts” taking significantly less than 1 second each.
> There must be some difference between LLVM 9.0 and LLVM 7.0 that might
> cause this (?)
>
> John
>
>
> On 30 Jun 2019, at 11:17, Praveen Velliengiri <
> praveenvelliengiri at gmail.com> wrote:
>
>
> cmake *BUILD_SHARED_LIBS* option, it builds llvm as .so not as .a. It
> will use less memory during linking so you can increase the link threads
> and your build time will be lesser.
> Check this in : https://llvm.org/docs/CMake.html
>
>
> On Sun, 30 Jun 2019 at 14:42, Joan Lluch <joan.lluch at icloud.com>
wrote:
>
>> Hi Praveen,
>>
>> Please, can you elaborate on this?. What do do mean by “building as
>> shared objects”.
>>
>> Thanks,
>>
>> John
>>
>>
>>
>> On 30 Jun 2019, at 07:32, Praveen Velliengiri <
>> praveenvelliengiri at gmail.com> wrote:
>>
>> Maybe try building llvm as a shared objects..
>>
>> On Jun 30, 2019 1:30 AM, "Joan Lluch via llvm-dev" <
>> llvm-dev at lists.llvm.org> wrote:
>>
>>> Hi Florian,
>>>
>>> Ok, I ran this:
>>>
>>> cmake -S LLVM -DCMAKE_INSTALL_PREFIX=INSTALL
>>> -DLLVM_OPTIMIZED_TABLEGEN=On -G Xcode
>>>
>>> Compiled it again from clean, and the situation is worse than
before.
>>> Incremental builds take an incredible amount of time stuck in
running
>>> Tablegen scripts for all targets. Now this happens both in Release
and
>>> Debug configurations. Just before this, at least Release compiled
fine, but
>>> that’s no longer the case.
>>>
>>> Any other suggestions?  What could actually cause this?
>>>
>>> Thanks
>>> John
>>>
>>>
>>>
>>> On 29 Jun 2019, at 19:37, Florian Hahn <florian_hahn at
apple.com> wrote:
>>>
>>> Hi,
>>>
>>> On Jun 29, 2019, at 18:26, Joan Lluch via llvm-dev <
>>> llvm-dev at lists.llvm.org> wrote:
>>>
>>> Hi all,
>>>
>>> On LLVM version 7.0.1, incremental builds are very fast for both
Release
>>> and Debug. I’m compiling with Xcode
>>>
>>> I recently downloaded LLVM 9.0 from the LLVM-mirror Github
repository
>>> and found that Incremental "Debug” builds take a ridiculously
long time due
>>> to Tablegen taking ages (literally more than 10 minutes) to
generate files.
>>> This makes it totally unusable for debug purposes. However,
incremental
>>> ‘Release’ builds only take a few seconds.
>>>
>>> Why is that?. Any suggestions?.
>>>
>>>
>>>
>>>
>>> You could give setting LLVM_OPTIMIZED_TABLEGEN a try (
>>> https://llvm.org/docs/CMake.html).
>>>
>>> Cheers,
>>> Florian
>>>
>>>
>>>
>>> _______________________________________________
>>> LLVM Developers mailing list
>>> llvm-dev at lists.llvm.org
>>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>>
>>
>
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Are you saying that the TableGen execution isn't parallelized? That 
seems like an obvious Xcode-specific problem...

The TableGen executions are parallelized with cmake/ninja just fine.

Cheers,
Nicolai

On 30.06.19 11:28, Joan Lluch via llvm-dev wrote:
> Hi Praveen,
> 
> Thanks for the tip, but Xcode seems to spend all the time running 
> tablegen "custom shell scripts", one by one at a time, not
linking.
> Linking is actually very fast, possibly less than a second. The 
> “scripts” that take longer are  “AArch64CommonTableGen" and 
> “AMDGPUCommonTableGen”.  As said this is on LLVM 9.0.
> 
> However, on LLVM 7.0.1, the same process takes just 5-6 seconds in 
> total, with individual “scripts” taking significantly less than 1 second 
> each. There must be some difference between LLVM 9.0 and LLVM 7.0 that 
> might cause this (?)
> 
> John
> 
> 
>> On 30 Jun 2019, at 11:17, Praveen Velliengiri 
>> <praveenvelliengiri at gmail.com <mailto:praveenvelliengiri at
gmail.com>>
>> wrote:
>>
>> *
>> *
>> cmake *BUILD_SHARED_LIBS* option, it builds llvm as .so not as .a. It 
>> will use less memory during linking so you can increase the link 
>> threads and your build time will be lesser.
>> Check this in : https://llvm.org/docs/CMake.html
>>
>> **
>> **
>>
>> On Sun, 30 Jun 2019 at 14:42, Joan Lluch <joan.lluch at icloud.com 
>> <mailto:joan.lluch at icloud.com>> wrote:
>>
>>     Hi Praveen,
>>
>>     Please, can you elaborate on this?. What do do mean by “building
>>     as shared objects”.
>>
>>     Thanks,
>>
>>     John
>>
>>
>>
>>>     On 30 Jun 2019, at 07:32, Praveen Velliengiri
>>>     <praveenvelliengiri at gmail.com
>>>     <mailto:praveenvelliengiri at gmail.com>> wrote:
>>>
>>>     Maybe try building llvm as a shared objects..
>>>
>>>     On Jun 30, 2019 1:30 AM, "Joan Lluch via llvm-dev"
>>>     <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
>>>
>>>         Hi Florian,
>>>
>>>         Ok, I ran this:
>>>
>>>         cmake -S LLVM -DCMAKE_INSTALL_PREFIX=INSTALL
>>>         -DLLVM_OPTIMIZED_TABLEGEN=On -G Xcode
>>>
>>>         Compiled it again from clean, and the situation is worse
than
>>>         before. Incremental builds take an incredible amount of
time
>>>         stuck in running Tablegen scripts for all targets. Now this
>>>         happens both in Release and Debug configurations. Just
before
>>>         this, at least Release compiled fine, but that’s no longer
>>>         the case.
>>>
>>>         Any other suggestions?  What could actually cause this?
>>>
>>>         Thanks
>>>         John
>>>
>>>
>>>
>>>>         On 29 Jun 2019, at 19:37, Florian Hahn
>>>>         <florian_hahn at apple.com <mailto:florian_hahn
at apple.com>> wrote:
>>>>
>>>>         Hi,
>>>>
>>>>>         On Jun 29, 2019, at 18:26, Joan Lluch via llvm-dev
>>>>>         <llvm-dev at lists.llvm.org <mailto:llvm-dev
at lists.llvm.org>>
>>>>>         wrote:
>>>>>
>>>>>         Hi all,
>>>>>
>>>>>         On LLVM version 7.0.1, incremental builds are very
fast for
>>>>>         both Release and Debug. I’m compiling with Xcode
>>>>>
>>>>>         I recently downloaded LLVM 9.0 from the LLVM-mirror
Github
>>>>>         repository and found that Incremental "Debug”
builds take a
>>>>>         ridiculously long time due to Tablegen taking ages
>>>>>         (literally more than 10 minutes) to generate files.
This
>>>>>         makes it totally unusable for debug purposes.
However,
>>>>>         incremental ‘Release’ builds only take a few
seconds.
>>>>>
>>>>>         Why is that?. Any suggestions?.
>>>>
>>>>
>>>>
>>>>         You could give setting LLVM_OPTIMIZED_TABLEGEN a try
>>>>         (https://llvm.org/docs/CMake.html).
>>>>
>>>>         Cheers,
>>>>         Florian
>>>
>>>
>>>         _______________________________________________
>>>         LLVM Developers mailing list
>>>         llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
>>>         https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
> 
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> 
-- 
Lerne, wie die Welt wirklich ist,
Aber vergiss niemals, wie sie sein sollte.

This is also the case with the Visual Studio generators. Custom commands in
a single cmake file essentially get written out line by line into a single
batch file that gets processed as a custom build step. In the VS case this
means that it can, for example, run X86 and Aarch64 tablegen steps in
parallel with each other but all of the individual X86 invocations get
processed serially. I can well imagine that the Xcode situation is similar
although I've no experience with it myself to know for sure.

As previously mentioned, the best solution is probably to try to adjust
your workflow to use the Ninja (
https://ninja-build.org
 ) CMake generator if at all possible.  It's a bit of an adjustment but it
does work very nicely with the LLVM build system.

-Greg


On Sun, 30 Jun 2019 at 12:08, Nicolai Hähnle via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Are you saying that the TableGen execution isn't parallelized? That
> seems like an obvious Xcode-specific problem...
>
> The TableGen executions are parallelized with cmake/ninja just fine.
>
> Cheers,
> Nicolai
>
> On 30.06.19 11:28, Joan Lluch via llvm-dev wrote:
> > Hi Praveen,
> >
> > Thanks for the tip, but Xcode seems to spend all the time running
> > tablegen "custom shell scripts", one by one at a time, not
linking.
> > Linking is actually very fast, possibly less than a second. The
> > “scripts” that take longer are  “AArch64CommonTableGen" and
> > “AMDGPUCommonTableGen”.  As said this is on LLVM 9.0.
> >
> > However, on LLVM 7.0.1, the same process takes just 5-6 seconds in
> > total, with individual “scripts” taking significantly less than 1
second
> > each. There must be some difference between LLVM 9.0 and LLVM 7.0 that
> > might cause this (?)
> >
> > John
> >
> >
> >> On 30 Jun 2019, at 11:17, Praveen Velliengiri
> >> <praveenvelliengiri at gmail.com <mailto:praveenvelliengiri
at gmail.com>>
> >> wrote:
> >>
> >> *
> >> *
> >> cmake *BUILD_SHARED_LIBS* option, it builds llvm as .so not as .a.
It
> >> will use less memory during linking so you can increase the link
> >> threads and your build time will be lesser.
> >> Check this in : https://llvm.org/docs/CMake.html
> >>
> >> **
> >> **
> >>
> >> On Sun, 30 Jun 2019 at 14:42, Joan Lluch <joan.lluch at
icloud.com
> >> <mailto:joan.lluch at icloud.com>> wrote:
> >>
> >>     Hi Praveen,
> >>
> >>     Please, can you elaborate on this?. What do do mean by
“building
> >>     as shared objects”.
> >>
> >>     Thanks,
> >>
> >>     John
> >>
> >>
> >>
> >>>     On 30 Jun 2019, at 07:32, Praveen Velliengiri
> >>>     <praveenvelliengiri at gmail.com
> >>>     <mailto:praveenvelliengiri at gmail.com>> wrote:
> >>>
> >>>     Maybe try building llvm as a shared objects..
> >>>
> >>>     On Jun 30, 2019 1:30 AM, "Joan Lluch via
llvm-dev"
> >>>     <llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>> wrote:
> >>>
> >>>         Hi Florian,
> >>>
> >>>         Ok, I ran this:
> >>>
> >>>         cmake -S LLVM -DCMAKE_INSTALL_PREFIX=INSTALL
> >>>         -DLLVM_OPTIMIZED_TABLEGEN=On -G Xcode
> >>>
> >>>         Compiled it again from clean, and the situation is
worse than
> >>>         before. Incremental builds take an incredible amount
of time
> >>>         stuck in running Tablegen scripts for all targets. Now
this
> >>>         happens both in Release and Debug configurations. Just
before
> >>>         this, at least Release compiled fine, but that’s no
longer
> >>>         the case.
> >>>
> >>>         Any other suggestions?  What could actually cause
this?
> >>>
> >>>         Thanks
> >>>         John
> >>>
> >>>
> >>>
> >>>>         On 29 Jun 2019, at 19:37, Florian Hahn
> >>>>         <florian_hahn at apple.com
<mailto:florian_hahn at apple.com>>
> wrote:
> >>>>
> >>>>         Hi,
> >>>>
> >>>>>         On Jun 29, 2019, at 18:26, Joan Lluch via
llvm-dev
> >>>>>         <llvm-dev at lists.llvm.org
<mailto:llvm-dev at lists.llvm.org>>
> >>>>>         wrote:
> >>>>>
> >>>>>         Hi all,
> >>>>>
> >>>>>         On LLVM version 7.0.1, incremental builds are
very fast for
> >>>>>         both Release and Debug. I’m compiling with
Xcode
> >>>>>
> >>>>>         I recently downloaded LLVM 9.0 from the
LLVM-mirror Github
> >>>>>         repository and found that Incremental
"Debug” builds take a
> >>>>>         ridiculously long time due to Tablegen taking
ages
> >>>>>         (literally more than 10 minutes) to generate
files. This
> >>>>>         makes it totally unusable for debug purposes.
However,
> >>>>>         incremental ‘Release’ builds only take a few
seconds.
> >>>>>
> >>>>>         Why is that?. Any suggestions?.
> >>>>
> >>>>
> >>>>
> >>>>         You could give setting LLVM_OPTIMIZED_TABLEGEN a
try
> >>>>         (https://llvm.org/docs/CMake.html).
> >>>>
> >>>>         Cheers,
> >>>>         Florian
> >>>
> >>>
> >>>         _______________________________________________
> >>>         LLVM Developers mailing list
> >>>         llvm-dev at lists.llvm.org <mailto:llvm-dev at
lists.llvm.org>
> >>>        
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >>>
> >>
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
> --
> Lerne, wie die Welt wirklich ist,
> Aber vergiss niemals, wie sie sein sollte.
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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