<table border="1" cellspacing="0" cellpadding="8">
    <tr>
        <th>Issue</th>
        <td>
            <a href=https://github.com/llvm/llvm-project/issues/127426>127426</a>
        </td>
    </tr>

    <tr>
        <th>Summary</th>
        <td>
            [Flang] Flang does not work correctly in file containing /* Old style C comments*/  in fixed source form
        </td>
    </tr>

    <tr>
      <th>Labels</th>
      <td>
            flang:frontend
      </td>
    </tr>

    <tr>
      <th>Assignees</th>
      <td>
      </td>
    </tr>

    <tr>
      <th>Reporter</th>
      <td>
          ohno-fj
      </td>
    </tr>
</table>

<pre>
    ```
Version of flang : 21.0.0(d2047242e6d0f0deb7634ff22ab164354c520c79)/AArch64
```

When building [Opium version 4.1](https://opium.sourceforge.net/), 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](https://flang.llvm.org/docs/Extensions.html#extensions-deletions-and-legacy-features-supported-by-default), 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:
```fortran
      subroutine foo ()
#include "inc.h"
       integer :: i
        i = VAL
        print *,i
      end subroutine foo
```

inc.h:
```fortran
/* 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:
```fortran
 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
$
```

</pre>
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