llvm dev - Oct 2019 - How to configure cmake to not rebuild .inc (tablegen) files?

Dear all,

I’m developing Clang&LLVM on MacOS Catalina 10.15.
Now every time I "make clang", the building systems rebuilds
all the .inc files generated by cmake, which essentially
rebuilds all the tablegen files in llvm, although I did not
change any of the tablegen files. The building is unnecessary
and slow, especially when it builds the X86GenSubtargetInfo.inc.
Is there a way to prevent cmake generating Makefiles that
rebuilds all the tablegen files?

Here is my command line to run cmake for generating Makefiles:

cmake -G “Unix Makefiles” -DLLVM_TARGETS_TO_BUILD=“X86"
-DCMAKE_BUILD_TYPE=Debug $(LLVM_SRC)

The cmake version is 3.13.4. And I did not experience the same behavior on a
Linux.

Thanks,
- Jie
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Hi Jie,

I’m using a Mac with Xcode and found that specifying DLLVM_OPTIMIZED_TABLEGEN=On
helped. Incremental builds are faster but tablegen files are run every time
anyway, so it’s not actually a fix. I posted this issue before but it seems
solving this is not that easy, at least for Xcode.

In the case of Xcode I found big speed improvements after saving the project
xcuserdata folder in a safe place, deleting the entire “build” folder,
re-creating a fresh “build” with cmake, and moving the xcuserdata folder I saved
before in place. Unfortunately, this stops working as soon as I checkout
branches, or pull commits from origin, so I need to repeat the same procedure to
get fast compiles again.

John, 

> On 21 Oct 2019, at 01:20, Jie Zhou via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Dear all,
> 
> I’m developing Clang&LLVM on MacOS Catalina 10.15.
> Now every time I "make clang", the building systems rebuilds
> all the .inc files generated by cmake, which essentially
> rebuilds all the tablegen files in llvm, although I did not
> change any of the tablegen files. The building is unnecessary
> and slow, especially when it builds the X86GenSubtargetInfo.inc.
> Is there a way to prevent cmake generating Makefiles that
> rebuilds all the tablegen files?
> 
> Here is my command line to run cmake for generating Makefiles:
> 
> cmake -G “Unix Makefiles” -DLLVM_TARGETS_TO_BUILD=“X86"
-DCMAKE_BUILD_TYPE=Debug $(LLVM_SRC)
> 
> The cmake version is 3.13.4. And I did not experience the same behavior on
a Linux.
> 
> Thanks,
> - Jie
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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On Sun, Oct 20, 2019 at 4:21 PM Jie Zhou via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Dear all,
>
> I’m developing Clang&LLVM on MacOS Catalina 10.15.
> Now every time I "make clang", the building systems rebuilds
> all the .inc files generated by cmake,
>
Are you saying that if you re-run `make clang` immediately after the first
invocation complete you see these files rebuilt? You're not changing
anything in the repo or running `git pull` (or equivalent)? This would
really not be expected.

-- 
Mehdi



> which essentially
> rebuilds all the tablegen files in llvm, although I did not
> change any of the tablegen files. The building is unnecessary
> and slow, especially when it builds the X86GenSubtargetInfo.inc.
> Is there a way to prevent cmake generating Makefiles that
> rebuilds all the tablegen files?
>
> Here is my command line to run cmake for generating Makefiles:
>
> cmake -G “Unix Makefiles” -DLLVM_TARGETS_TO_BUILD=“X86"
> -DCMAKE_BUILD_TYPE=Debug $(LLVM_SRC)
>
> The cmake version is 3.13.4. And I did not experience the same behavior on
> a Linux.
>
> Thanks,
> - Jie
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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On Oct 21, 2019, at 14:16, Mehdi AMINI <joker.eph at
gmail.com<mailto:joker.eph at gmail.com>> wrote:



On Sun, Oct 20, 2019 at 4:21 PM Jie Zhou via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Dear all,

I’m developing Clang&LLVM on MacOS Catalina 10.15.
Now every time I "make clang", the building systems rebuilds
all the .inc files generated by cmake,

Are you saying that if you re-run `make clang` immediately after the first
invocation complete you see these files rebuilt? You're not changing
anything in the repo or running `git pull` (or equivalent)? This would really
not be expected.

Yes the tablegen files get recompiled immediately after I run a `make clang`. I
checked on a Ubuntu and did not see the same behavior.
But luckily Joan's suggestion works: the -DLLVM_OPTIMIZED_TABLEGEN for cmake
will do the trick.

- Jie
--
Mehdi



which essentially
rebuilds all the tablegen files in llvm, although I did not
change any of the tablegen files. The building is unnecessary
and slow, especially when it builds the X86GenSubtargetInfo.inc.
Is there a way to prevent cmake generating Makefiles that
rebuilds all the tablegen files?

Here is my command line to run cmake for generating Makefiles:

cmake -G “Unix Makefiles” -DLLVM_TARGETS_TO_BUILD=“X86"
-DCMAKE_BUILD_TYPE=Debug $(LLVM_SRC)

The cmake version is 3.13.4. And I did not experience the same behavior on a
Linux.

Thanks,
- Jie
_______________________________________________
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://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwMFaQ&c=kbmfwr1Yojg42sGEpaQh5ofMHBeTl9EI2eaqQZhHbOU&r=KAtyTEI8n3FritxDpKpR7rv3VjdmUs0luiVKZLb_bNI&m=a6d-_XqSI-3_vhs7WPW2QDFf8_o0tG-HnAow9qGcbys&s=Y5yX8hc8QmLTgMtpKpLop-queU5nUZ7pJXeHoGDxJ7I&e=>

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