[Bug fortran/99609] New: Pure Function that has a Variable with Value Attribute that is modified

[Bug fortran/99609] New: Pure Function that has a Variable with Value Attribute that is modified

[Boyce at engineer dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

            Bug ID: 99609
           Summary: Pure Function that has a Variable with Value Attribute
                    that is modified
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Boyce at engineer dot com
  Target Milestone: ---

Created attachment 50392
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50392&action=edit
Module that replicates the error

This is a problem I found in all versions of gfortran.

The issue is with the value attribute for a pure function raises an error if
the variable is changed. gfortran assumes that the variable has an intent(in),
but with the value attribute the variable is a copy so the original is not
changed.

For example, the following module raises an error for func1, but not func2.
Functionally the two functions are equivalent, but one explicitly declares the
copy of a.

The attachment contains the same code as the following, but with a PROGRAM/END
PROGRAM driver.

MODULE ex_func
  contains
  !
  ! Does not recognize that value makes a copy of "a"
  !
  pure function func1(a) result(x)
    integer, value :: a
    integer :: x
    !
    a = a*a
    !
    x = a
    !
  end function
  !
  pure function func2(a) result(x)
    integer, intent(in) :: a
    integer :: x
    integer :: tmp
    !
    tmp = a
    tmp = tmp*tmp
    !
    x = tmp
    !
  end function
END MODULE

[Bug fortran/99609] Pure Function that has a Variable with Value Attribute that is modified

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kargl at gcc dot gnu.org
           Priority|P3                          |P4

--- Comment #1 from kargl at gcc dot gnu.org ---
Seems to fixed on main (aka 11.0.1).  Not sure if anyone did or will backport
the fix to the 10 or older branch.

[Bug fortran/99609] Pure Function that has a Variable with Value Attribute that is modified

[burnus at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

Tobias Burnus <burnus at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |DUPLICATE
                 CC|                            |burnus at gcc dot gnu.org

--- Comment #2 from Tobias Burnus <burnus at gcc dot gnu.org> ---
I believe this is a duplicate of PR fortran/97491, which has been fixed on
mainline (upcoming GCC 11) and also on the GCC 10 branch.

*** This bug has been marked as a duplicate of bug 97491 ***

[Bug fortran/99609] Pure Function that has a Variable with Value Attribute that is modified

[Boyce at engineer dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

--- Comment #3 from Scott Boyce <Boyce at engineer dot com> ---
Yeah that is the same bug request. Though it is for version 11, any chance of
back-porting to version 9 and 10?

[Bug fortran/99609] Pure Function that has a Variable with Value Attribute that is modified

[jvdelisle at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

Jerry DeLisle <jvdelisle at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jvdelisle at gcc dot gnu.org

--- Comment #4 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> ---
(In reply to Scott Boyce from comment #3)
> Yeah that is the same bug request. Though it is for version 11, any chance
> of back-porting to version 9 and 10?

It has been committed to version 10.

[Bug fortran/99609] Pure Function that has a Variable with Value Attribute that is modified

[anlauf at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99609

anlauf at gcc dot gnu.org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |anlauf at gcc dot gnu.org

--- Comment #5 from anlauf at gcc dot gnu.org ---
The patch for pr97491 appears simple and safe.  I could check if a "backport"
works unless there are objections.