[Bug libstdc++/67256] [C++11] Global scope contaminated with symbols from mathcalls.h

[Bug libstdc++/67256] [C++11] Global scope contaminated with symbols from mathcalls.h

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67256

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
          Component|c++                         |libstdc++
           Severity|major                       |normal

[Bug c++/67256] [C++11] Global scope contaminated with symbols from mathcalls.h

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67256

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
17.6.1.2 [headers] specifically says:

  It is unspecified whether these names are first declared within the global
  namespace scope and are then injected into namespace std by explicit using-
  declarations.

A conforming implementation can define ::log and ::sin when any standard header
is included, and so your code will never be portable if you reuse those names
for namespaces.

[Bug libstdc++/67256] [C++11] Global scope contaminated with symbols from mathcalls.h

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67256

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
N.B. the functions happen to be declared in <bits/mathcalls.h> but they are
standard functions declared in <math.h> and so your code would already have
failed to compile in C++03 if anyone included <math.h> (and the same applies
for <cmath> when that is implemented in terms of <math.h>, which is permitted
by the text I quoted from the standard).

[Bug libstdc++/67256] [C++11] Global scope contaminated with symbols from mathcalls.h

[michal.fita at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67256

--- Comment #3 from Michał Fita <michal.fita at gmail dot com> ---
Contrary to my expectations #include <cmath> doesn't work either. I would
expect these not declared in global if standard says unspecified, as my logic
whisper that would be more C++ way. I understand then I shouldn't expect to get
this fixed as removing these symbols from global scope would break existing
code?

Interesting thing about declaration in mathcalls.h is that they're surrounded
by _Mdouble_BEGIN_NAMESPACE and _Mdouble_END_NAMESPACE macros, which seem empty
when included from cmath (to my surprise that one redefines all functions in
std on top of what is in math.h). Whether these are empty or not the presence
of _GLIBCPP_USE_NAMESPACES decides.

Now I see it has been mindfully done with purpose: 
- https://gcc.gnu.org/bugzilla/show_bug.cgi?id=6257
- http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#456

Another point to the C++ list on the side "hate".
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https://gcc.gnu.org/bugzilla/show_bug.cgi?idg028

--- Comment #8 from Segher Boessenkool <segher at gcc dot gnu.org> ---
Author: segher
Date: Tue Aug 18 14:27:50 2015
New Revision: 226971

URL: https://gcc.gnu.org/viewcvs?rev"6971&root=gcc&view=rev
Log:
        PR rtl-optimization/67028
        * combine.c (simplify_comparison): Fix comment.  Rearrange code.
        Add test to see if a const_int fits in the new mode.

gcc/testsuite/
        PR rtl-optimization/67028
        * gcc.dg/pr67028.c: New testcase.

Added:
    branches/gcc-4_9-branch/gcc/testsuite/gcc.dg/pr67028.c
Modified:
    branches/gcc-4_9-branch/gcc/ChangeLog
    branches/gcc-4_9-branch/gcc/combine.c
    branches/gcc-4_9-branch/gcc/testsuite/ChangeLog