[flang][runtime] Runtime error for INQUIRE with UNIT 64-bit integer

[NimishMishra]

INQUIRE statement with UNIT= specifier that is larger than default integer variable with a value larger than HUGE(1) results in a runtime error.

Reproducer:

Program test_inquire_int64
  Use Iso_Fortran_Env
  Implicit None
  Integer(int64) :: iunit
  Integer :: stat
  Logical :: is_open
  iunit = 10_int64
  Inquire(Unit=iunit, Opened=is_open)
  Print 2, is_open
  iunit = Huge(1) - 100_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
  iunit = Huge(1) + 1_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
1 Format(L4,I8)
2 Format(L4)
3 Format(I15)
End Program

flang-new test.f90 errs out with UNIT number 2147483648 is out of range and following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F    1029

gfortran test.f90 runs OK, with the following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F       0
   F       0

[llvmbot]

@llvm/issue-subscribers-bug

Author: None (NimishMishra)

INQUIRE statement with UNIT= specifier that is larger than default integer variable with a value larger than HUGE(1) results in a runtime error.

Reproducer:

Program test_inquire_int64
  Use Iso_Fortran_Env
  Implicit None
  Integer(int64) :: iunit
  Integer :: stat
  Logical :: is_open
  iunit = 10_int64
  Inquire(Unit=iunit, Opened=is_open)
  Print 2, is_open
  iunit = Huge(1) - 100_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
  iunit = Huge(1) + 1_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
1 Format(L4,I8)
2 Format(L4)
3 Format(I15)
End Program

flang-new test.f90 errs out with UNIT number 2147483648 is out of range and following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F    1029

gfortran test.f90 runs OK, with the following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F       0
   F       0

[llvmbot]

@llvm/issue-subscribers-flang-runtime

Author: None (NimishMishra)

INQUIRE statement with UNIT= specifier that is larger than default integer variable with a value larger than HUGE(1) results in a runtime error.

Reproducer:

Program test_inquire_int64
  Use Iso_Fortran_Env
  Implicit None
  Integer(int64) :: iunit
  Integer :: stat
  Logical :: is_open
  iunit = 10_int64
  Inquire(Unit=iunit, Opened=is_open)
  Print 2, is_open
  iunit = Huge(1) - 100_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
  iunit = Huge(1) + 1_int64
  Print 3, iunit
  Inquire(Unit=iunit, Opened=is_open, Iostat=stat)
  Print 1, is_open, stat
  Inquire(Unit=iunit, Opened=is_open)
  Print 1, is_open, stat
1 Format(L4,I8)
2 Format(L4)
3 Format(I15)
End Program

flang-new test.f90 errs out with UNIT number 2147483648 is out of range and following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F    1029

gfortran test.f90 runs OK, with the following output:

   F
     2147483547
   F       0
   F       0
     2147483648
   F       0
   F       0

[klausler]

Do you have an application that requires 64-bit unit numbers? Do you also want 128-bit unit numbers? Do you need 64-bit or wider unit numbers to work on I/O statements besides INQUIRE?

[NimishMishra]

Do you have an application that requires 64-bit unit numbers? Do you also want 128-bit unit numbers? Do you need 64-bit or wider unit numbers to work on I/O statements besides INQUIRE?

This came up while validating NAG test cases with llvm-flang.

[sihuan]

The Intel Fortran Compiler Developer Guide and Reference mentions the range of unit numbers:

The integer is in the range 0 through 2,147,483,647 (2**31-1)".

but it looks like ifrot (2021.11.0, https://godbolt.org/z/1zYve4EKG) supports a larger range than that. And for flang, commit c58c64d limits the unit number range to 32-bit.
I couldn't find a description of the unit number range in any other fortran specification document.

[NimishMishra]

Thank you @sihuan. So it seems like a compiler dependent choice?

I could ask Jean once on why 32-bit is the limit forced by flang.

[jeanPerier]

Thank you @sihuan. So it seems like a compiler dependent choice?

I could ask Jean once on why 32-bit is the limit forced by flang.

Because we need to set a limit in order to build the runtime interface and it is not clear what kind of Fortran applications would need more than 2,147,483,647 IO units. Before c58c64d, flang was just silently truncating the IO unit number, hence it was decided to add a runtime check and hard error / non zero stat number when hitting these cases.