[Bug libstdc++/48760] [4.6 / 4.7 Regression (?)] std::complex constructor buggy in the face of NaN's

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

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48760

--- Comment #14 from Gabriel Dos Reis <gdr at gcc dot gnu.org> 2011-04-26 14:12:35 UTC ---
(In reply to comment #12)
> (In reply to comment #9)
> > I guess, in the 4.6.1 time frame we can only workaround the issue in C++03 mode
> > by doing the piecewise work in the body. I can maybe help for the compiler work
> > too but I need more guidance: is there an agreement about the C1X inspired
> > builtin suggested by Joseph? In case, can I have a more specific reference?
> > 
> > I'm adding in CC Richi too, in case he has additional tips and/or hints about
> > the builtin work..
> 
> A __builtin_complex builtin should be almost trivial.  It would be purely
> frontend sugar for frontends that lack a way to specify a complex value
> component-wise.  The frontend would be resposible for lowering it to
> a COMPLEX_EXPR.  I don't think the middle-end wants to deal with
> __builtin_complex as it already has a perfect matching tree code.

Agreed -- except since __builtin_complex is already a perfect match, 
the front-end should just accept either

     _M_value{r,i}

or

    _M_value(r,i)

if it wanted to be C++03 compatible too.  Either way, you say, there
is no need to involve the middle end.


> 
> Now I understand C++0x might have a proper syntax already, so I'm not sure
> how it relates to this (C++) bug.
> 
> What changed in 4.6 is that we put complex values in registers even at -O0.

that is fine (and appreciated!).  It is unrelated to the bug though.

> You should be able to reproduce any issue in this bug in older releases
> with optimization turned on (given that the library implementation didn't
> change).

The bug is a source-level bug; the source code is written that way because
we don't have yet a good way to initialize at once GCC builtin COMPLEX_EXPR.

-- Gaby