bind(c) variables optimized away

Accelerated Computing HPC Compilers Legacy PGI Compilers
1

There appears to be a bug that the pgfortran compiler is optimizing away unused variables even when they are bind(c):

> pgfortran -c test.f90
> pgcc main.c
/usr/bin/ld: /tmp/andy/pgccFUIeD6ja2FdJ.o: in function `main':
/home/andy/pgi/a/main.c:4: undefined reference to `global_var'




> gfortran -c test.f90
> gcc main.c test.o
> ./a.out
9




> cat test.f90
module m
 use iso_c_binding, only : c_int
 integer(c_int), bind(c) :: global_var=9
end module




> cat main.c
#include <stdio.h>
extern int global_var;
int main () {
 fprintf(stdout,"%d\n",global_var);
}




> pgfortran -V

pgfortran 20.4-0 LLVM 64-bit target on x86-64 Linux -tp nehalem
PGI Compilers and Tools
Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.




> pgcc -V

pgcc (aka pgcc18) 20.4-0 LLVM 64-bit target on x86-64 Linux -tp nehalem
PGI Compilers and Tools
Copyright (c) 2020, NVIDIA CORPORATION.  All rights reserved.

Of course this is a highly unusual case in that the variable is not referenced at all from the Fortran.

2

Hi Andy,

It looks like you just forgot to add “test.o” to the link for the pgcc case.

% pgfortran -V20.4 -c test.f90
% pgcc -V20.4 main.c test.o
main.c:
% a.out
9

You get the same error GNU when test.o is missing.

% gfortran -c test.f90
% gcc main.c
/tmp/ccNfQxRT.o: In function `main':
main.c:(.text+0x6): undefined reference to `global_var'
collect2: error: ld returned 1 exit status

-Mat

3

Apologies, I made a mistake in haste to get a cut-down reproducer. This hopefully shows the issue:

> cat test.f90 
module m
 use iso_c_binding, only : c_int
 integer(c_int), bind(c) :: global_var
end module




> cat main.c 
extern int global_var;
int main () {
 global_var=9;
}




> pgfortran -c test.f90
> pgcc main.c test.o
main.c:
/usr/bin/ld: main.o: in function `main':
/home/andy/a/main.c:3: undefined reference to `global_var'




> gfortran -c test.f90
> gcc main.c test.o
>
4

Thanks, I’m able to recreate the problem and have filed TPR #28525. We’ll have our engineers take a look.

The obvious work around is to set the variable in the module to a default value.

-Mat