[Bug target/70117] ppc long double isinf() is wrong?

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70117

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |powerpc*
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2016-03-14
     Ever confirmed|0                           |1

--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
So another way to "fix" this would be to stop the simplification of isinf
to isgreater(fabs(x),DBL_MAX) by providing patterns for isinf and friends
(isfinite, isnormal), see fold_builtin_interclass_mathfn.  Though neither
isfinite nor isnormal have associated optabs - breaking testcases for them
could be easily constructed.

For the long double case more optimal implementation should be possible in
the backend.  Given we can't easily expose long double implementation
details on GENERIC/GIMPLE it needs to be done there (well, in theory
we could use sth. like VIEW_CONVERT <struct doubledouble> (ldbl_1).d[0]
or so ... or REALPART (V_C_E <_Complex double> (ldbl_1)) whatever would
work better.  But then struct realformat needs to expose this fact
(real.c checks fmt->pnan < fmt->p for this!?).

Confirmed anyway.

The question remains whether the long double value from gnulib is "valid"
(it's a valid bit pattern that is _not_ inf after all).  I still somewhat
think that GCC is at fault here and not gnulib - even if it is technically
not LDBL_MAX that is wrong but the folding to isgreater(fabs(x),DBL_MAX).