[Flang] Flang does not work correctly in file containing /* Old style C comments*/ in fixed source form

[ohno-fj]

Version of flang : 21.0.0(d2047242e6d0f0deb7634ff22ab164354c520c79)/AArch64

When building Opium version 4.1, the preprocessor does not work correctly.
File containing /* Old style C comments */ in fixed source form cannot be included.

According to Fortran Extensions supported by Flang, the attached program is correct because:

• Classic C-style /*comments*/ are skipped, so multi-language header files are easier to write and use.

The above program is z001.F.

When fixed source form is changed to free source form, it is included correctly.
The above program is z002.F90.

The following are the test program, Flang, Gfortran and ifx compilation/execution result.

z001.F:

      subroutine foo ()
#include "inc.h"
       integer :: i
        i = VAL
        print *,i
      end subroutine foo

inc.h:

/* Old style C comments
 *comments
 */
#define VAL 1

$ flang z001.F -c
error: Could not parse z001.F
./inc.h:1:1: warning: Character in fixed-form label field must be a digit
  /* Old style C comments
  ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:2:2: warning: Character in fixed-form label field must be a digit
   *comments
   ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:3:2: warning: Character in fixed-form label field must be a digit
   */
   ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:2: error: expected declaration construct
  /* Old style C comments
   ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
./inc.h:2:3: error: expected declaration construct
   *comments
    ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
./inc.h:3:3: error: expected declaration construct
   */
    ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
$

$ gfortran z001.F -c -save-temps
$ cat z001.f90
# 1 "z001.F"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "z001.F"
      subroutine foo ()

# 1 "inc.h" 1

# 3 "z001.F" 2
       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

$ ifx z001.F -c -P
$ cat z001.i
# 1 "z001.F"
      subroutine foo ()
# 1 "./inc.h" 1
# 3


# 3 "z001.F" 2
       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

z002.F90:

      subroutine foo ()
#include "inc.h"
       integer :: i
        i = VAL
        print *,i
      end subroutine foo

$ flang z002.F90 -c
$
$ flang z002.F90 -c -save-temps
#line "./z002.F90" 1
      subroutine foo ()

       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: None (ohno-fj)

``` Version of flang : 21.0.0(d204724)/AArch64 ```

When building Opium version 4.1, the preprocessor does not work correctly.
File containing /* Old style C comments */ in fixed source form cannot be included.

According to Fortran Extensions supported by Flang, the attached program is correct because:

• Classic C-style /comments/ are skipped, so multi-language header files are easier to write and use.

The above program is z001.F.

When fixed source form is changed to free source form, it is included correctly.
The above program is z002.F90.

The following are the test program, Flang, Gfortran and ifx compilation/execution result.

z001.F:

      subroutine foo ()
#include "inc.h"
       integer :: i
        i = VAL
        print *,i
      end subroutine foo

inc.h:

/* Old style C comments
 *comments
 */
#define VAL 1

$ flang z001.F -c
error: Could not parse z001.F
./inc.h:1:1: warning: Character in fixed-form label field must be a digit
  /* Old style C comments
  ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:2:2: warning: Character in fixed-form label field must be a digit
   *comments
   ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:3:2: warning: Character in fixed-form label field must be a digit
   */
   ^
./z001.F:2:1: warning: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:2: error: expected declaration construct
  /* Old style C comments
   ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
./inc.h:2:3: error: expected declaration construct
   *comments
    ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
./inc.h:3:3: error: expected declaration construct
   */
    ^
./z001.F:2:1: error: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./inc.h:1:1: in the context: specification part
  /* Old style C comments
  ^
./z001.F:2:1: in the context: included here
  #include "inc.h"
  ^^^^^^^^^^^^^^^^
./z001.F:1:7: in the context: SUBROUTINE subprogram
        subroutine foo ()
        ^
$

$ gfortran z001.F -c -save-temps
$ cat z001.f90
# 1 "z001.F"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "z001.F"
      subroutine foo ()

# 1 "inc.h" 1

# 3 "z001.F" 2
       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

$ ifx z001.F -c -P
$ cat z001.i
# 1 "z001.F"
      subroutine foo ()
# 1 "./inc.h" 1
# 3


# 3 "z001.F" 2
       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

z002.F90:

      subroutine foo ()
#include "inc.h"
       integer :: i
        i = VAL
        print *,i
      end subroutine foo

$ flang z002.F90 -c
$
$ flang z002.F90 -c -save-temps
#line "./z002.F90" 1
      subroutine foo ()

       integer :: i
        i = 1
        print *,i
      end subroutine foo
$

[ohno-fj]

There was a mistake in the description.
Incorrect :

• Classic C-style /comments/ are skipped, so multi-language header files are easier to write and use.

Fixed :

• Classic C-style /*comments*/ are skipped, so multi-language header files are easier to write and use.

[ohno-fj]

I also corrected the mistake in the main body.