Re: OpenMP for both clang and GCC, part II

On 6/5/19 7:42 PM, j@bitminer.ca wrote:
> TLDR: Multi-core is a thing. Let's do it the OpenMP way. My diffs to come.
>
> I know some devs have thought about this before. I'm looking for comments
> or advice on how I can help this along.
>
> The clang in base (and flang in ports) currently support OpenMP directives
> with the -fopenmp option. They are missing the runtime. The LLVM OpenMP
> runtime could be supplied as a port.
>
> The GNU C, C++ and Fortran in ports (gcc version 8.3) currently support
> OpenMP directives and with a small patch can add OpenMP support to their
> runtime libraries (gcc-libs). The two OpenMP runtimes (GCC and LLVM)
> can coexist this way.
>
> Example ports, compiler, build system, and status/issues:
>
> devel/boost (base-clang gcc-ports, unique build, uncertain support)
> devel/cmake (base-clang gcc-ports, simple, fails to correctly find OpenMP)
> graphics/lensfun (base-clang gcc-ports, cmake, unswitchable OpenMP)
> graphics/GraphicsMagick (base-clang gcc-ports, gnu configure, OpenMP disabled)
>
> Proposed changes:
> - identify ports with embedded (hidden) OpenMP support and patch to disable it
> (I guess from 10 to 40 such ports aside from the 7 that turn it off now)
> - fix cmake (and other build systems) to detect both OpenMP implementations
> - add a new port devel/libomp containing the LLVM OpenMP runtime for clang/flang
> - patch gcc-libs package to deliver OpenMP runtime support for GNU c/c++/fortran
> - help port maintainers build with OpenMP flavors if they want it
>
> (I have patches for cmake, gcc-libs, and a proposed new devel/libomp package).
>
> Eventually ports maintaners will migrate to OpenMP as they can or want to.
> Users will adopt flavors such as -withopenmp, or -noopenmp, as they become
> available.
>
> Some issues and questions:
>
> - this will work for amd64, but will it work for arm64, sparc? Others?
> - should the flavors be -withopenmp or -noopenmp?
> - how to successfully detect 90% or more of ports with hidden OpenMP support?
> I will do this and am looking for advice on how best to approach it.
> Any pre-existing info would be very welcome.
>
> Does anyone have comments? I'll be submitting diffs as I can.
>
>
>
> --John
>

On LLVM OpenMP: https://marc.info/?l=openbsd-ports&m=155642976702196&w=2

~Brian