[llvm-dev] [help] How to speed up compilation?

[Bruce Hoult via llvm-dev]

cmake should be a lot faster, especially using ninja instead of makefiles,
because it can run the maximum number of jobs to keep all the cores busy
more of the time.

The problem looks like with eight cores (and therefore 8 parallel jobs) and
only 8 GB of RAM, you don't have enough RAM for the number of cores, so
you'll be using swap a lot. That's mostly true for linking. c++ build steps
don't use all that much RAM.

On Tue, Oct 18, 2016 at 8:25 PM, Sunghyun Park via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm adding feature to detect customized pragma and mark those region in
> LLVM IR using Metadata. I want to let programmer give additional directives
> to compiler.
> So I put some functions, variables, and 'cout' on clang.
>
> So, based on my understanding on your comment, it may be natural to have
> long compilation time.
> My machine has Intel Xeon(R) CPU E31230 @ 3.20GHz * 8 with 8GM RAM, which
> is far behind the recommended build environment ( Intel Core i7-4770K CPU @
> 3.50Hz, 16 GM RAM, and a 1TB 7200RPM HDD or SSD, ref :
> https://blogs.s-osg.org/an-introduction-to-accelerating-
> your-build-with-clang/ )
> Do you think it would be great help if I upgrade my machine?
> I've wanted to upgrade it at some point, but I haven't find right excuse
> to tell my boss. haha
>
> Thank you so much!
>
> On Tue, Oct 18, 2016 at 1:08 PM, Renato Golin <renato.golin at linaro.org>
> wrote:
>
>> On 18 October 2016 at 17:56, Sunghyun Park <sunggg at umich.edu> wrote:
>> > Personally, it feels like compilation become much slower than previous
>> > versions after adopting 'cmake'.
>> > Is this natural when we adopt cmake or are there other big changes on
>> build
>> > structure?
>>
>> So, I decided not to respond to that specific part of your original
>> post because I don't have enough information on what you changed, but
>> we have deprecated autoconf for a while now, so everyone uses CMake.
>>
>> If you're comparing LLVM a long time ago with autoconf versus LLVM
>> today with CMake, then the changes are most likely because LLVM has
>> grown a lot.
>>
>> If you're building LLVM trunk today with autoconf, then it's possible
>> that you're missing a lot of source files from your build (and I'm
>> surprised it worked).
>>
>> But overall, CMake should make absolutely no difference in building
>> speeds, since the number of compilation jobs should (hopefully) be the
>> same and in the same way. But I may be missing something... :)
>>
>> cheers,
>> --renato
>>
>
>
>
> --
> Best, Sung
>
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