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

["tkoenig at gcc dot gnu dot org" <gcc-bugzilla 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


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