[Flang] IARGC can't be used in a range loop

[arrowd]

Trying to compile https://github.com/loriab/dftd3/blob/8e5463eafbaa0130a1aa26b8ee8ed57b1c3ffef0/dftd3.f#L268C14-L268C19 with Flang 21 I get the following error:

/usr/local/bin/flang21   -O -O3 -c /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f -o CMakeFiles/dftd3.dir/dftd3.f.o
error: Semantic errors in /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f
/wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f:268:14: error: No explicit type declared for 'iargc'
        do i=1,iargc()
               ^^^^^

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Gleb Popov (arrowd)

Trying to compile https://github.com/loriab/dftd3/blob/8e5463eafbaa0130a1aa26b8ee8ed57b1c3ffef0/dftd3.f#L268C14-L268C19 with Flang 21 I get the following error:

/usr/local/bin/flang21   -O -O3 -c /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f -o CMakeFiles/dftd3.dir/dftd3.f.o
error: Semantic errors in /wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f
/wrkdirs/usr/ports/science/dftd3/work/dftd3-3.2.0-3-g8e5463e/dftd3.f:268:14: error: No explicit type declared for 'iargc'
        do i=1,iargc()
               ^^^^^

[eugeneepshteyn]

iargc() is available as extension in flang runtime, but it's not hooked up as intrinsic.

Smaller reproducer:

implicit none
integer i
character(len=40) arg
print *, "Number of arguments:", iargc()
do i = 1, iargc()
  call getarg(i, arg)
  print *, "Arg", i, ": ", arg
end do
end

Output:

$ flang iargc.f90 && ./a.out a b c
error: Semantic errors in iargc.f90
./iargc.f90:4:34: error: No explicit type declared for 'iargc'
  print *, "Number of arguments:", iargc()
                                   ^^^^^

If I remove implicit none, then get the expected output:

$ flang iargc.f90 && ./a.out a b c
 Number of arguments: 3
 Arg 1 : a                                       
 Arg 2 : b                                       
 Arg 3 : c  

@mlir-maiden , would you like to hook up iargc() and getarg() as proper intrinsics and document them?

[eugeneepshteyn]

Documentation for gfortran extensions:

• https://gcc.gnu.org/onlinedocs/gfortran/IARGC.html
• https://gcc.gnu.org/onlinedocs/gfortran/GETARG.html

[mlir-maiden]

@eugeneepshteyn , yes, I’d be glad to take this on! :)