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

[rguenth at gcc dot gnu.org]

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

--- Comment #12 from Richard Guenther <rguenth at gcc dot gnu.org> 2011-04-26 08:44:18 UTC ---
(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.

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.
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).