https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71675
Bug ID: 71675
Summary: __atomic_compare_exchange_n returns wrong type for
typed enum
Product: gcc
Version: 5.3.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: js at alien8 dot de
Target Milestone: ---
Consider the following code:
enum class foo : unsigned char {
FOO, BAR
};
foo v;
bool bar(foo old_v, foo new_v)
{
return __atomic_compare_exchange_n(&v, &old_v, new_v, true,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
}
This fails to compile with
% g++ -std=c++14 -c problem.cpp
reader.cpp: In function ‘bool bar(foo, foo)’:
reader.cpp:10:99: error: cannot convert ‘foo’ to ‘bool’ in return
return __atomic_compare_exchange_n(&v, &old_v, new_v, true,
__ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST);
According to the manual __atomic_compare_exchange_n returns a bool, so this
error is bogus. The expected behavior is for __atomic_compare_exchange_n to
return a bool in the first place.
Manually casting the result of __atomic_compare_exchange_n to bool generates
the expected result.
The issue appears with gcc 5.3.1 20160406 (Red Hat 5.3.1-6) on Fedora 23 x86_64
and also with gcc 6.1 (tested using https://gcc.godbolt.org/)
