[Bug libfortran/58020] Code for handling IEEE exceptions

["dominiq at lps dot ens.fr" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58020

--- Comment #7 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> I see your bug report. There are two matters to track down here. 
> The first one is the diagnostic of 'PR58027'. This may require you 
> to report a line number. That would be great. Testing that I have 
> done is with the gfortran compiler on Krogh's machine and my own 
> with the Intel compiler. I do not have access to the machine you 
> are using.

The ICE leading to PR58027 is

[macbook] bug/IEEE_1% gfc -c IEEE_tests_gfortran.f90
IEEE_tests_gfortran.f90: In function 'ieee_tests':
IEEE_tests_gfortran.f90:304:0: internal compiler error: in
gfc_conv_array_initializer, at fortran/trans-array.c:5512
     SA=transfer(ISCLASS(I),SA)

However any use of ISCLASS leads to the ICE because the parameter array is not
built. To understand why, I have compiled the following test

    integer, parameter :: isclass = Z'FF800000'
end

and got

isclass_2.f90:1.35:

    integer, parameter :: isclass = Z'FF800000'
                                   1
Error: Arithmetic overflow converting INTEGER(16) to INTEGER(4) at (1). This
check can be disabled with the option -fno-range-check

with -m64 and

isclass_2.f90:1.35:

    integer, parameter :: isclass = Z'FF800000'
                                   1
Error: Arithmetic overflow converting INTEGER(8) to INTEGER(4) at (1). This
check can be disabled with the option -fno-range-check

with -m32. The gfortran rationale is that Z'FF800000' is converted to the
highest integer kind (8 with -m32 or 16 with -m64) as 2**32-8388608, i.e., a
positive number larger that huge(1)=2**31-1.

> The second matter is the difference in a line of output. That is the
> printing of the 4 digit approximation to \pi. The internal constant \pi
> itself comes from the stored value in the x87. The output of the number
> comes from the routine messy. I expect the hardware value is correct. So
> one machine writes 3.141 wit messy, and the other 3.142.

Apparently 'CALL IEEE_SET_ROUNDING_MODE(IEEE_TO_ZERO)' propagates into

    call messy(E,'$N Double precision rounding mode IEEE_DOWN&
      & for \pi ~= $R agrees with IEEE_TO_ZERO.',rdat=[DA])

If I add

  CALL IEEE_SET_ROUNDING_MODE(IEEE_NEAREST)

before the line

  IF(DC == DA) THEN ! Round down should agree withround to zero, here.

then my output matches the one in list.