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

[Praveen Velliengiri via llvm-dev]

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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