[llvm-dev] Should we split llvm Support and ADT?

[Mehdi AMINI via llvm-dev]

2017-05-30 13:50 GMT-07:00 Zachary Turner via llvm-dev <
llvm-dev at lists.llvm.org>:

>
>
> On Tue, May 30, 2017 at 12:52 PM Bob Haarman <llvm at inglorion.net> wrote:
>
>> I would like to better understand how you came to conclude that the
>> tablegen re-runs based on changes in Support are what's causing your build
>> to be slow and what part specifically is taking all that time. I can do a
>> clean release + assertions build of LLVM, Clang, compiler-rt and lld in
>> about 5 minutes, plus 40 seconds to run cmake, on what I think is similar
>> hardware to what Zach is using. If I swap Ptr += ret and Size -= Ret in
>> raw_fd_ostream::write_impl so that Support changes, I can do an incremental
>> build in about 10 seconds, including the regeneration of various .inc
>> files. How do we get from there to 10 minutes for an incremental build?
>>
>
> For the sake of comparison, I made the same change and it took  1:58.39.
> A slightly different but more intrusive change to Format.h in
> format_object_base::print() took 5:6.54.  A clean build on the same machine
> takes about 12 minutes.
>
> I tried a few hacks to the CMake to say "don't run tablegen, no matter
> what, and don't make anything depend on tablegen's output", but I couldn't
> come up with the right magic.  If anyone knows, I can test a side-by-side
> comparison without tablegen.
>

I mentioned earlier in the thread that there is already a CMake option for
this: -DLLVM_TABLEGEN=path/to/llvm-tblgen


-- 
Mehdi
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