[cfe-dev] [LLVMdev] libiomp, not libgomp as default library linked with -fopenmp

[Michael Wong]

Don't want to derail this train of discussion. But IBM and OpenMP  fully support this move as we have actively worked on this with many other companies. We might be able to get a maintainer as well.  

OpenMP CEO

Sent from my iPhone

> On May 1, 2015, at 1:46 PM, Jack Howarth <howarth.mailing.lists at gmail.com> wrote:
> 
> 
> 
>> On Thu, Apr 30, 2015 at 5:51 PM, Chandler Carruth <chandlerc at google.com> wrote:
>>> On Thu, Apr 30, 2015 at 6:52 AM Andrey Bokhanko <andreybokhanko at gmail.com> wrote:
>>> All,
>>> 
>>> I'd like to resurrect the discussion on replacing libgomp with libiomp as the default OpenMP runtime library linked with -fopenmp.
>> 
>> Just for the record, I'm really excited to see this. =]
>>  
>>> We are very close to getting *full* OpenMP 3.1 specification supported in clang (only one (!) clause is not implemented yet, and the patch is already sent for review today: http://reviews.llvm.org/D9370). This implementation generates Intel API library calls; thus, it can't be used with libgomp and it is simply logical to link a compatible runtime (libiomp) instead.
>> 
>> Is there no way to support libgomp here as well? I don't say this to hold up changing the defaults in any way, just curious. =]
>> 
>> Also, for the record, I'm really excited to see the progress here as well.
>>  
>>> Chandler?
>> 
>> Hi! ;]
>> 
>> I totally agree, I think things are way better now. I generally support the direction. I think there are a few things I'd suggest we do as part of the process, but I think these are really small and just about "how" we switch.
>> 
>> 1) I completely agree with the comments some others have made about us needing to make it clear that this isn't some Intel-only thing, its the LLVM OpenMP runtime. Some suggestions that I think would make sense to help here:
>> - I agree with finding some non-Intel folks to add as explicit code owners. I don't know who has been sufficiently involved, but if Hal makes sense, awesome.
>> - Clearly updating the readme and such would be appropriate.
>> - I suspect we should change the name of the installed library. 'libiomp' is pretty clearly the Intel library. We could continue in the grand tradition of LLVM naming conventions and use 'libllomp'? Of course, we should install symlinks under the name 'libiomp' if needed for existing users to not be broken.
>> - Any other changes?
> 
> Is this naming issue so serious that it will be blocker for the current patches to enabled the openmp build from within llvm/projects? Can't we just proceed with the current library name until the top-level openmp build infrastructure added and the switch of the default for -fopenmp to libiomp5 is made. It seems more sensible to stabilize the openmp support first and then revisit the naming issue in a couple of weeks.
> 
>> 2) I think we need to update the instructions for checking out LLVM and all the tools to include checking out the openmp project. I'm planning to try it out in a bit.
>> 
>> 3) It would be nice to get at least one boring benchmark into the test-suite that uses OpenMP just so there's more coverage that the basic stuff all works. In particular, if we could get the benchmark that Phoronix and others keep pointing at, that'd be nice.
>> 
>> 
>> Speaking of which, have you checked the performance of some of the basic benchmarks using OpenMP with the two runtimes? Or looked at Clang vs GCC there? I'd be interested to see the numbers.
>>  
>>> 
>>> Yours,
>>> Andrey Bokhanko
>>> ==============
>>> Software Engineer
>>> Intel Compiler Team
>>> Intel
>>> 
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