GCC 10 released today

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GCC 10 was released today. Here’s what’s new:

https://gcc.gnu.org/gcc-10/changes.html

For gfortran, to me most notable update is the support of derived types in co_broadcast. Of F2018 features, I use collectives the most.

The page also mentions OpenACC 2.6 support for C, C++, and Fortran. I wasn’t aware of OpenACC development in GCC. Has anybody tried it?

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Yes, and a 10.1.1 version landed in Fedora 32 some days ago.

I have been interested by OpenACC since GCC6, but never succeeded. I think it’s time to try once again !

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I have compiled the following code, inspired by the first example in https://docs.computecanada.ca/wiki/OpenACC_Tutorial_-_Adding_directives

program example_acc

implicit none
integer :: i, N
real(8), dimension(1:200000000) :: x
real(8), dimension(1:200000000) :: y
real(8) :: a

a = 3.14159265d0
N = 200000000

!$acc kernels
do i = 1, N
    x(i) = 1.0d0
    y(i) = 2.0d0
end do

y(:) = a*x(:) + y(:)
!$acc end kernels

end program example_acc

I am using gfortran 9.3.0 under Ubuntu 20.04:

$ gfortran example_acc.f90 && time ./a.out

real    0m2,237s
user    0m1,477s
sys     0m0,760s

When trying to compile with -fopenacc, I had the following error:

lto-wrapper: fatal error: could not find accel/nvptx-none/mkoffload in /usr/lib/gcc/x86_64-linux-gnu/9/:/usr/lib/gcc/x86_64-linux-gnu/9/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/9/:/usr/lib/gcc/x86_64-linux-gnu/ (consider using ‘-B’)

compilation terminated.
/usr/bin/ld : erreur : lto-wrapper failed
collect2: error: ld returned 1 exit status

I have installed the gcc-offload-nvptx packages: “This package contains libgomp plugin for offloading to NVidia PTX. The plugin needs libcuda.so.1 shared library that has to be installed separately.”

$ gfortran -fopenacc example_acc.f90 && time ./a.out

real    0m2,557s
user    0m1,667s
sys     0m0,891s

So, it seems you need a NVidia accelerator, but I have an ATI Radeon on my HP ZBook…

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4

This is the example that I played before (or at least tried) with PGI compiler. I also don’t have an Nvidia card. Maybe I’ll try one day on one of the GPU cloud instances.

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https://gcc.gnu.org/wiki/OpenACC
Compared to GCC 9, the upcoming GCC 10 release series contains the following OpenACC changes:
[…]
- Support for AMD Radeon (GCN) GPUs (Fiji, VEGA)

After installing the Ubuntu package gcc-10-offload-amdgc, I tried:

$ gfortran-10 -fopenacc -foffload=amdgcn-amdhsa="-march=gfx601" example_acc.f90 && time ./a.out
x86_64-linux-gnu-accel-amdgcn-amdhsa-gcc-10: error: unrecognized argument in option ‘-march=gfx601’
x86_64-linux-gnu-accel-amdgcn-amdhsa-gcc-10: note: valid arguments to ‘-march=’ are: fiji gfx900 gfx906; did you mean ‘gfx900’?

Does anyone has that kind of AMD video card (fiji, gfx900 or gfx906) ? Have you succeeded using OpenACC ?