[Bug c++/66572] New: [6 Regression] Bogus Wlogical-op warning for operands coming from template instantiations

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66572

            Bug ID: 66572
           Summary: [6 Regression] Bogus Wlogical-op warning for operands
                    coming from template instantiations
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: miyuki at gcc dot gnu.org
  Target Milestone: ---

Consider this example:

$ cat ./test.cc 
struct false_type
{
    static constexpr bool value = false;
};

struct true_type
{
    static constexpr bool value = true;
};

template<typename T>
struct is_unsigned : false_type {};

template<>
struct is_unsigned<unsigned> : true_type {};

template<typename T1, typename T2>
bool foo()
{
    return is_unsigned<T1>::value && is_unsigned<T2>::value;
}

int main()
{
    foo<unsigned, unsigned>();
}

$ g++ -Wlogical-op -std=c++11 ./test.cc 
./test.cc: In instantiation of 'bool foo() [with T1 = unsigned int; T2 =
unsigned int]':
./test.cc:25:29:   required from here
./test.cc:20:35: warning: logical 'and' of equal expressions [-Wlogical-op]
     return is_unsigned<T1>::value && is_unsigned<T2>::value;

IMHO GCC should not issue this warning: in this instantiation
(is_unsigned<unsigned>::value && is_unsigned<unsigned>::value) operator && is
indeed redundant, but that is not true for general case.