[llvm-dev] Flang landing in the monorepo - next Monday!

[McCormick, Pat via llvm-dev]

Thanks to everyone for the feedback — both concerns and support. 

Let me add a perspective as someone who has been responsible for helping to start part of the initial push and finding funding for a portion of the Flang/f18 efforts to date.  From the outset our mindset was to get Flang to a point where it was worthy of becoming a part of the LLVM community.  So making Flang a successful part of the LLVM community has been a major factor in our viewpoint from the outset.  That may not be reflected in the nature of the code base as some might prefer to see it today but I personally view the monorepo landing as the point in time where Flang actually becomes the community’s project.  

For exactly the same reasons Greg mentions, having Flang in the monorepo will help many of us avoid hassles to be able to contribute to the code base.  Something that makes the formation of a supporting subset of the community extremely difficult.  I strongly believe the longer Flang stays separated from the monorepo the harder it will become to transition — simply because the odds that the steps taken to meet target deliverables and features won’t necessarily be addressed as part of the community’s discussions (I think this thread has in part shown that we’re already here today and need to move beyond it sooner rather than later).  The steps of landing Flang into the monorepo should simply be viewed as the very first steps and should in no way be considered to be the final ones.

Thanks, 

—Pat


> On Jan 8, 2020, at 12:15 PM, Gregory Rodgers via llvm-dev <llvm-dev at lists.llvm.org> wrote:
> 
> Hal, Eric, Johannes, David and Peter, 
> 
> I lead the development of OpenMP for AMD GPUs and work with others at AMD who support OpenMP on AMD CPUs. On behalf of our development teams, we greatly appreciate your efforts to move the development of flang into a subproject in the llvm-project repository and to integrate this development effort into the overall LLVM development community.   
> 
> Like most commercial companies, we have certain procedures (some legal) to participate in open source projects.  Since AMD has already engaged in LLVM development, adding flang as an LLVM subproject makes it much easier to participate in the development of flang.    I look forward to my team getting more involved in the development of flang now that it is part of LLVM.
> 
> I would respectfully disagree with "There's nothing llvm about it".  Flang uses the clang offloading architecture used by cuda, hip, and openmp-target.  And the runtime will use both libomp and libomptarget runtimes found in the llvm project openmp.   While flang frontend may not immediately use clang -cc1 parsing and codegen, the upstream clang driver already supports a flang toolchain. See clang/lib/Driver/Types.cpp and  clang/lib/Driver/ToolChains/Flang.cpp.
> 
> I think it is better for flang to join LLVM sooner than later.  This will help flang developers better adopt llvm development practices.  For example, an earlier variant of flang written in c, generated LLVM-IR without using llvm::IRBuilder.  This is because the origin of that source was from a non-LLVM project. This architecture was rejected partly because it was not llvm enough.  This lead to the creation of the f18 C++ project which will use llvm::IRbuilder.  F18 is the flang that I expect and hope to land in monorepo next Monday.  
> 
> I am also AMD's representative to the OpenMP Architecture Review Board.  Adding flang is an important step to completely cover the OpenMP specification for c, C++, and FORTRAN in LLVM.    
> 
> I agree, flang has a long way to go.  But I believe there is enough critical mass with flang to join the LLVM development now. 
> 
> Thank you
>  
> Greg Rodgers
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