[Bug fortran/57749] -ffpe-trap=zero or invalid produces SIGFPE on complex zero ** 1e0

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57749

--- Comment #8 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> And I still believe the result should not depend on the optimization level.

Well, it does and IMO it has to (see below).

> Note that compiling without -ffpe-trap the result
> with default optimization, -O0, is (  0.00000000    , -0.00000000    ),
> higher optimizations deliver (  0.00000000    ,  0.00000000    ).
> Another mystery.

IMO there is no mystery. zero is a constant that is propagated during the
optimization pass: looking at pr57749.f90.165t.optimized, I see

  D.1881 = __complex__ (0.0, 0.0);
  _gfortran_transfer_complex_write (&dt_parm.0, &D.1881, 4);

i.e., zero**1e0 is computed during the optimization (hence cannot generate
exception at run time). In pr57749.f90.003t.original, I see

     D.1881 = __builtin_cpowf (D.1880, __complex__ (1.0e+0, 0.0));
      _gfortran_transfer_complex_write (&dt_parm.0, &D.1881, 4);

so at run time you call a "buggy(?)" cpowf that generates the exception and
(0.0,-0.0). As said in comment #6, this is not a gfortran bug, but a
libgcc/libm one
to be reported upstrean.