https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82207
Lionel GUEZ <guez at lmd dot ens.fr> changed:
What |Removed |Added
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CC| |guez at lmd dot ens.fr
--- Comment #6 from Lionel GUEZ <guez at lmd dot ens.fr> ---
I think this is a bug. A consequence of this bug is that gfortran signals an
exception with the option -ffpe-trap=invalid when it encounters a quiet NaN.
Here is a test program:
$ gfortran --version
GNU Fortran (GCC) 7.1.0
$ cat test_qnan.f90
use, intrinsic:: ieee_arithmetic, only: IEEE_SUPPORT_DATATYPE, &
ieee_support_nan, ieee_value, IEEE_QUIET_NAN
real x
if (.not. IEEE_SUPPORT_DATATYPE(0.) .or. .not. ieee_support_nan(0.)) stop 1
x = ieee_value(0., IEEE_QUIET_NAN)
end
$ gfortran -ffpe-trap=invalid test_qnan.f90
$ a.out
Program received signal SIGFPE: Floating-point exception - erroneous arithmetic
operation.
Backtrace for this error:
#0 0x2b67f141250f in ???
#1 0x2b67f0ad8628 in __ieee_arithmetic_MOD_ieee_value_4
at ../../../libgfortran/ieee/ieee_arithmetic.F90:868
#2 0x4009ae in ???
#3 0x400a01 in ???
#4 0x2b67f13fed1c in ???
#5 0x4007f8 in ???
Floating point exception
A quiet NaN should not raise the exception. See for example Adams (2009, The
Fortran 2003 Handbook, ยง 14.2.4):
"For a processor that supports NaNs and for an operation that returns a
floating-point result, a quiet NaN propagates through the operation without
raising an invalid exception."
For comparison, the ifort compiler behaves correctly here:
$ ifort -fpe-all=0 test_qnan.f90
$ a.out
produces no error.
This behaviour of gfortran is a problem because it prevents the use of qnan as
a normal missing value and the debugging option at the same time.
