[Bug fortran/27866] New: Warn when casting, e.g. assigning a double precision to a real

[Bug fortran/27866] New: Warn when casting, e.g. assigning a double precision to a real

[tobias dot burnus at physik dot fu-berlin dot de]

In the following program there is clearly a problem with the "r = d"
assignment. In most real programs such drastic case does not happen. However,
simple precision loss or worse things may occure.

gfortran -Wall should warn, but it does not deserve a default warning.

program test
  double precision :: d
  real   :: r
  d = 4d99
  r = d
  print *, d, r
end program test

g95 -Wall shows:
  r = d
       1
Warning (140): Implicit conversion at (1) may cause precision loss


-- 
           Summary: Warn when casting, e.g. assigning a double precision to
                    a real
           Product: gcc
           Version: 4.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: tobias dot burnus at physik dot fu-berlin dot de


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[tkoenig at gcc dot gnu dot org]

------- Comment #1 from tkoenig at gcc dot gnu dot org  2006-06-01 21:09 -------
(In reply to comment #0)
> In the following program there is clearly a problem with the "r = d"
> assignment. In most real programs such drastic case does not happen. However,
> simple precision loss or worse things may occure.
> 
> gfortran -Wall should warn, but it does not deserve a default warning.

There is -Wconversion, but this also warns the wrong way around.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |tkoenig at gcc dot gnu dot
                   |                            |org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[tkoenig at gcc dot gnu dot org]

------- Comment #2 from tkoenig at gcc dot gnu dot org  2006-06-07 19:32 -------
Yes, this would be useful.

Confirmed as an enhancement.


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2006-06-07 19:32:09
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[manu at gcc dot gnu dot org]

------- Comment #3 from manu at gcc dot gnu dot org  2007-02-14 15:47 -------
(In reply to comment #1)
> (In reply to comment #0)
> > In the following program there is clearly a problem with the "r = d"
> > assignment. In most real programs such drastic case does not happen. However,
> > simple precision loss or worse things may occure.
> > 
> > gfortran -Wall should warn, but it does not deserve a default warning.
> 
> There is -Wconversion, but this also warns the wrong way around.

There is a new -Wconversion implementation. Perhaps you could do the same for
fortran as I did for C/C++. Take a look at c-common.c (conversion_warnings). It
would be great if -Wconversion behaves the same way (more or less) in all
front-ends.



-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |manu at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[tkoenig at gcc dot gnu dot org]

------- Comment #4 from tkoenig at gcc dot gnu dot org  2007-02-16 20:50 -------
(In reply to comment #3)

> There is a new -Wconversion implementation. Perhaps you could do the same for
> fortran as I did for C/C++. Take a look at c-common.c (conversion_warnings). It
> would be great if -Wconversion behaves the same way (more or less) in all
> front-ends.

This would be a good idea.

Looking at the code from c-common.c, we should warn about

  real(kind=4) :: a
  real(kind=8) :: b
  integer(kind=1) :: i1
  integer(kind=4) :: i4
  i4 = 2.3               ! Not exact
  i1 = 500               ! doesn't fit
  a = 2**26-1          ! Loses bits of precision
  b = 1d99             ! Doesn't fit the type

  a = i4               ! may lose extra digits
  b = i4               ! This is OK (enough digits in the kind=8 var)
  i1 = i4              ! i1 may not be able to represent the values in i4
  a = b                ! precision loss

For Fortran, we should also warn about

  b = 2.5
  print *,b**(3/2)      ! identical to b**1, usually unintended

and maybe even about

  print *,4/3           ! constant integer division


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[manu at gcc dot gnu dot org]

------- Comment #5 from manu at gcc dot gnu dot org  2007-02-16 21:08 -------
(In reply to comment #4)
> (In reply to comment #3)
> 
> > There is a new -Wconversion implementation. Perhaps you could do the same for
> > fortran as I did for C/C++. Take a look at c-common.c (conversion_warnings). It
> > would be great if -Wconversion behaves the same way (more or less) in all
> > front-ends.
> 
> This would be a good idea.
> 
> Looking at the code from c-common.c, we should warn about
> 

That is up to you. I don't know so much about fortran. I was just pointing to
the middle-end functions used in c-common.c to detect whether a value is
changed by the conversion. However, be careful about not warning in excess. For
example, constant integer division does not change any value, so I think it is
not appropriate for -Wconversion. But I guess that it is up to fortran
maintainers to make this decision.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[tkoenig at gcc dot gnu dot org]

------- Comment #6 from tkoenig at gcc dot gnu dot org  2007-02-18 21:18 -------
*** Bug 28399 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[pinskia at gcc dot gnu dot org]

------- Comment #7 from pinskia at gcc dot gnu dot org  2007-04-19 21:45 -------
*** Bug 31637 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vivekrao4 at yahoo dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[tkoenig at gcc dot gnu dot org]

------- Comment #8 from tkoenig at gcc dot gnu dot org  2008-04-17 22:00 -------
*** Bug 35962 has been marked as a duplicate of this bug. ***


-- 

tkoenig at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |J dot Hogg at rl dot ac dot
                   |                            |uk


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[dfranke at gcc dot gnu dot org]

------- Comment #9 from dfranke at gcc dot gnu dot org  2010-05-10 17:11 -------
Subject: Bug 27866

Author: dfranke
Date: Mon May 10 17:10:53 2010
New Revision: 159238

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=159238
Log:
gcc/fortran/:
2010-05-10  Daniel Franke  <franke.daniel@gmail.com>

        PR fortran/27866
        PR fortran/35003
        PR fortran/42809
        * intrinsic.c (gfc_convert_type_warn): Be more discriminative
        about conversion warnings.

gcc/testsuite/:
2010-05-08  Daniel Franke  <franke.daniel@gmail.com>

        PR fortran/27866
        PR fortran/35003
        PR fortran/42809
        * gfortran.dg/array_constructor_type_17.f03: Updated match string.
        * gfortran.dg/warn_conversion.f90: New.


Added:
    trunk/gcc/testsuite/gfortran.dg/warn_conversion.f90
Modified:
    trunk/gcc/fortran/ChangeLog
    trunk/gcc/fortran/intrinsic.c
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gfortran.dg/array_constructor_type_17.f03


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866

[Bug fortran/27866] Warn when casting, e.g. assigning a double precision to a real

[dfranke at gcc dot gnu dot org]

------- Comment #10 from dfranke at gcc dot gnu dot org  2010-05-10 19:29 -------
We should now have about the same behaviour as with C.

The additional requests in comment #4 (integer division) are not handled by the
patch in #9. These are special cases and not necessarily related to
-Wconversion. Please open another PR if this should be pursued.

Closing as fixed.


-- 

dfranke at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED
   Target Milestone|---                         |4.6.0


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27866