gfortran/OpenMP/declare target link issue

Ioannis E. Venetis venetis@ceid.upatras.gr
Thu Sep 3 18:36:46 GMT 2020


Hello everyone,

I have a larger program that I am trying to convert so that the 
computationally intensive part will run on an NVidia GPU using OpenMP. 
However, I am running into trouble when compiling the program. The part 
of the program to run on the GPU contains calls to subroutines, where 
variables declared in a separate module are used. This seems to be 
creating issues. I have reduced the problem to the attached files.

I compile as follows:

gfortran test_link.f90 common_vars.f90 parameters.f90 -O0 -fopenmp -Wall 
-Wextra -o test_link

With the file test_link.f90 as attached, the program compiles and runs 
without a problem.

If I remove the comments for the subroutine TEST() and comment out line 
31 in test_link.f90 (the line "I = NR") the compilation gives the 
following error:

ptxas /tmp/ccw3FqJD.o, line 52; error   : Illegal operand type to 
instruction 'ld'
ptxas /tmp/ccw3FqJD.o, line 52; error   : Unknown symbol 
'__common_vars_MOD_nr$linkptr'
ptxas fatal   : Ptx assembly aborted due to errors
nvptx-as: ptxas returned 255 exit status
mkoffload: fatal error: 
/home/myself/apps/gcc-10.2.0/bin/x86_64-pc-linux-gnu-accel-nvptx-none-gcc 
returned 1 exit status
compilation terminated.
lto-wrapper: fatal error: 
/home/myself/apps/gcc-10.2.0/libexec/gcc/x86_64-pc-linux-gnu/10.2.0//accel/nvptx-none/mkoffload 
returned 1 exit status
compilation terminated.
/usr/bin/ld: error: lto-wrapper failed
collect2: error: ld returned 1 exit status

Is this a bug in gfortran or have I misunderstood how DECLARE TARGET 
LINK works in combination with using subroutines?

And a last point: If I use -O3 during compilation the program compiles 
and runs fine in both cases. I assume that TEST() is inlined in this 
case and the error disappears?

Any help to overcome this issue is more than welcome.

Best regards,

Ioannis E. Venetis

PS1: The problem happens with gcc 10.2 that I compiled myself:

$ ~/apps/gcc-10.2.0/bin/gfortran -v
Using built-in specs.
COLLECT_GCC=/home/myself/apps/gcc-10.2.0/bin/gfortran
COLLECT_LTO_WRAPPER=/home/myself/apps/gcc-10.2.0/libexec/gcc/x86_64-pc-linux-gnu/10.2.0/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-10.2.0/configure 
--enable-offload-targets=nvptx-none 
--with-cuda-driver-include=/usr/local/cuda/include 
--with-cuda-driver-lib=/usr/local/cuda/lib64 --disable-bootstrap 
--disable-multilib --enable-languages=c,c++,fortran,lto 
--prefix=/home/myself/apps/gcc-10.2.0
Thread model: posix
Supported LTO compression algorithms: zlib
gcc version 10.2.0 (GCC)


PS2: Same problem also happens with gcc 9.3 as installed on Ubuntu 16.04 
from apt:

$ gfortran -v
Using built-in specs.
COLLECT_GCC=gfortran
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 
9.3.0-10ubuntu2~16.04' 
--with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs 
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 
--prefix=/usr --with-gcc-major-version-only --program-suffix=-9 
--program-prefix=x86_64-linux-gnu- --enable-shared 
--enable-linker-build-id --libexecdir=/usr/lib 
--without-included-gettext --enable-threads=posix --libdir=/usr/lib 
--enable-nls --enable-clocale=gnu --enable-libstdcxx-debug 
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new 
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin 
--with-system-zlib --with-target-system-zlib=auto --enable-objc-gc=auto 
--enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 
--with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic 
--enable-offload-targets=nvptx-none,hsa --without-cuda-driver 
--enable-checking=release --build=x86_64-linux-gnu 
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.3.0 (Ubuntu 9.3.0-10ubuntu2~16.04)

-------------- next part --------------
MODULE COMMON_VARS

  USE PARAMETERS

  IMPLICIT NONE

!$OMP DECLARE TARGET LINK(NR)
  INTEGER :: NR

END MODULE COMMON_VARS

-------------- next part --------------
MODULE PARAMETERS

      IMPLICIT NONE

      INTEGER, PARAMETER :: MAX_SOURCE_POSITIONS = 100
 
END MODULE PARAMETERS

-------------- next part --------------
      PROGRAM TEST_LINK

      USE COMMON_VARS
      USE PARAMETERS

      IMPLICIT NONE

      REAL    :: XMO(MAX_SOURCE_POSITIONS), DCP(MAX_SOURCE_POSITIONS)
      INTEGER :: IS1(MAX_SOURCE_POSITIONS), IS2(MAX_SOURCE_POSITIONS)

      INTEGER :: X, Y, Z, MAX_X, MAX_Y, MAX_Z, ISOUR, I

      MAX_X = 3
      MAX_Y = 4
      MAX_Z = 5
      NR    = 6

!$OMP TARGET MAP(TOFROM:IS1,IS2,DCP,XMO) MAP(TO:NR)
!$OMP TEAMS DISTRIBUTE PARALLEL DO COLLAPSE(3)
      DO X = 1, MAX_X
         DO Y = 1, MAX_Y
            DO Z = 1, MAX_Z

               ISOUR = (X - 1)*MAX_Y*MAX_Z + (Y - 1)*MAX_Z + Z

               XMO(ISOUR) = 1.0 * NR
               DCP(ISOUR) = 2.0 * NR
               IS1(ISOUR) = 3   * NR
               IS2(ISOUR) = 4   * NR

               I = NR

!               CALL TEST()
 
            ENDDO  ! End of z loop
         ENDDO     ! End of y loop
      ENDDO        ! End of x loop
!$OMP END TEAMS DISTRIBUTE PARALLEL DO
!$OMP END TARGET

      DO X = 1, MAX_X
         DO Y = 1, MAX_Y
            DO Z = 1, MAX_Z

               ISOUR = (X - 1)*MAX_Y*MAX_Z + (Y - 1)*MAX_Z + Z

               WRITE(*, *) 'ISOUR = ', ISOUR, 'XMO = ', XMO(ISOUR), 'DCP = ', DCP(ISOUR), 'IS1 = ', IS1(ISOUR), 'IS2 = ', IS2(ISOUR)
 
            ENDDO  ! End of z loop
         ENDDO     ! End of y loop
      ENDDO        ! End of x loop

      END PROGRAM TEST_LINK

!      SUBROUTINE TEST()
!      !$OMP DECLARE TARGET
!        USE COMMON_VARS
!        IMPLICIT NONE
!        INTEGER I
!        I = NR
!      END SUBROUTINE TEST



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