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From: "thiago at kde dot org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/66671] New: Failure to create a new family of templates for template alias
Date: Thu, 25 Jun 2015 18:20:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D66671

            Bug ID: 66671
           Summary: Failure to create a new family of templates for
                    template alias
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thiago at kde dot org
  Target Milestone: ---

Whenever you use:

template <typename T>
using Z =3D Y<T>;

The template Z is different from Y and should be encoded separately. This c=
an
be seen in the example:

=3D=3D=3D=3D
#include <iostream>

template <template <typename> class>
struct X {
  X() { std::cout << "1"; }
};

template <typename>
struct Y {};

template <typename T>
using Z =3D Y<T>;

template <>
struct X<Y> {
  X() { std::cout << "2"; }
};

int main() {
  X<Y> x1;
  X<Z> x2;
}
=3D=3D=3D=3D
(from: http://cppquiz.org/quiz/giveup/117)

With GCC 5.1.1, the above prints "22", whereas it prints "21" with ICC 16,
Clang 3.7 and MSVC 2013. The explanation from the quiz site is given as:

> According to =C2=A714.5.7=C2=B61 in the standard, a template alias declar=
ation=20
> resolve to a new family of types. The specialization cannot be used,=20
> and the first template delcaration is used instead, printing 1.

Disassembly with -O2 -fno-inline shows that Clang and ICC both call differe=
nt
template specialisations of template class X:

        leaq    16(%rsp), %rdi
        callq   _ZN1XI1YEC2Ev          ; X<Y>::X()
        leaq    8(%rsp), %rdi
        callq   _ZN1XI1ZEC2Ev          ; X<Z>::X()

PS: should X<Z> count as a local type or a global one?
>>From gcc-bugs-return-490214-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 18:47:23 2015
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Subject: [Bug c++/66672] New: std::is_same wrong result for captured reference value inside a lambda
Date: Thu, 25 Jun 2015 18:47:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D66672

            Bug ID: 66672
           Summary: std::is_same wrong result for captured reference value
                    inside a lambda
           Product: gcc
           Version: 5.1.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: thiago at kde dot org
  Target Milestone: ---

Given the following code:

=3D=3D=3D=3D
#include <iostream>
#include <type_traits>

using namespace std;

int main()
{
  int i, &j =3D i;
  [=3D]
  {
    cout << is_same<decltype((j)), int      &>::value
         << is_same<decltype((j)), int const&>::value;
  }();
}
=3D=3D=3D=3D
(trimmed from http://cppquiz.org/quiz/question/127)

With GCC 5.1, the code will print 10, but it should be 01. Clang 3.6, ICC 16
and MSVC 2015 do compile this as expected. The output 10 would be correct if
the extra set of parentheses weren't there.

The explanation given on the quiz website is:

> Since the expression for decltype is a parenthesized lvalue=20
> expression, =C2=A77.1.6.2=C2=B64 has this to say: "The type denoted by=20
> decltype(e) is (...) T&, where T is the type of e;" As the
> expression occurs inside a const member function, the expression is
> const, and decltype((j)) denotes int const&. See also the example in=20
> =C2=A75.1.2=C2=B618.
[NB: it's paragraph 19 as of N4431]

The example in that paragraph of the standard matches almost exactly the co=
de
above.

The output is correct with a functor:

=3D=3D=3D=3D
struct S
{
  S(int &i) : j(i) {}
  void operator()() const
  {
    cout << is_same<decltype((j)), int      &>::value
         << is_same<decltype((j)), int const&>::value;
  };
  int j;    // captured by value
};
int main()
{
  int i;
  S{i}();
}
=3D=3D=3D=3D
>>From gcc-bugs-return-490215-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Thu Jun 25 18:49:06 2015
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From: "joe.carnuccio at qlogic dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c/39121] strange behavior in chained operations
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=39121

joe.carnuccio at qlogic dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |joe.carnuccio at qlogic dot com

--- Comment #4 from joe.carnuccio at qlogic dot com ---
I have found the following:

This works: c ^= d ^= c ^= d  (where c and d are not pointers)

This fails: *a ^= *b ^= *a ^= *b  (where a and b are pointers)

When compiling using -Os then the failed case now works.