[Bug fortran/47659] -Wconversion[-extra] should emit warning for constant expressions

[tkoenig at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47659

--- Comment #3 from Thomas Koenig <tkoenig at gcc dot gnu.org> 2011-08-07 21:20:36 UTC ---
Created attachment 24945
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=24945
Proposed patch

Here's a patch.

For

    real a
    a = 2.3d0

it checks for truncation correctly and only warns if digits are lost.

Unfortunately, for the case of

   double precision a
   a = 1.2

I don't see a good way of getting at the original string of numbers to
see if the 1.2 would have been interpreted differently if it had been
a double precision number.

What should we do?  Not warn for integers (like I did here) or warn
unconditionally?