[llvm-dev] Tablegen ridiculously slow when compiling for Debug

[Nicolai Hähnle via llvm-dev]

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
>>>
>>>
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>>>         llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>
>>>         https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>
>>
> 
> 
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