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

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?.

Thanks.

John Lluch

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

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
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