[Bug fortran/40675] Support -fnosign-zero for SIGN intrinsic for Fortran 77 compatibility

["burnus at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #10 from burnus at gcc dot gnu dot org  2009-07-08 08:00 -------
I think one can consider supporting non-signed zeros as extension, similar to
ifort which has:
    -assume nominus0            The compiler uses Fortran 90/77 standard
                                semantics in the SIGN intrinsic to treat
                                -0.0 and +0.0 as 0.0, and writes a value
                                of 0.0 with no sign on formatted output.

(Default as of ifort 11.1 is the F77/F90 behaviour while gfortran defaults to
the F95/F2003/F2008 behaviour.)

Currently, gfortran only has such a flag for I/O and not for the sign
intrinsic:
       -fsign-zero
           When writing zero values, show the negative sign if the sign
           bit is set.  "fno-sign-zero" does not print the negative
           sign of zero values for compatibility with F77.  Default
           behavior is to show the negative sign.


I think one can extends this to the SIGN intrinsic. One needs to modify
("if (gfc_option.flag_sign_zero)") trans-intrinsic.c's gfc_conv_intrinsic_sign.

Currently,
  test = sign(x, y)
produces (-fdump-tree-original)
  test = __builtin_copysignf (x, y)
that would have to be replaced by
  test = (y == 0) ? abs(x) : __builtin_copysignf (x, y)

This can be further optimized by using MODE_HAS_SIGNED_ZEROS (or
HONOR_SIGNED_ZEROS?).


Actually, one also needs to modify simplify.c's gfc_simplify_sign: Either -0.0
is not correctly handled or the comment is wrong.


-- 

burnus at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Severity|normal                      |enhancement
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
  GCC build triplet|x86_64-unknown-linux-gnu    |
   GCC host triplet|x86_64-unknown-linux-gnu    |
 GCC target triplet|x86_64-unknown-linux-gnu    |
   Last reconfirmed|0000-00-00 00:00:00         |2009-07-08 08:00:23
               date|                            |
            Summary|sign intrinsic fails for    |Support -fnosign-zero for
                   |value of 0.0                |SIGN intrinsic for Fortran
                   |                            |77 compatibility


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40675