https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70844
TC <rs2740 at gmail dot com> changed:
What |Removed |Added
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CC| |rs2740 at gmail dot com
--- Comment #1 from TC <rs2740 at gmail dot com> ---
The attached test case doesn't reproduce in 6.2.0, presumably due to the fix
for 70972. The following (slightly modified) test case still produces a
-Wuseless-cast warning on trunk and 6.3.0:
struct base {
base (int const &);
};
struct derived : public base {
using base::base;
};
derived d(0);
What appears to be happening is that the inheriting constructor calls
forward_parm to perfectly forward the arguments, which in turn calls
build_static_cast to construct the equivalent of static_cast<const int&>(p)
where p is of type const int &, which emits a -Wuseless-cast warning.
Consistent with this hypothesis, 6.1 emits a warning for the original test case
because it was emitting the equivalent of static_cast<int>(p) where `p`'s type
is `int`; GCC >= 6.2, which has the 70972 fix, emits the equivalent of
static_cast<int&&>(p), which doesn't trigger the warning. GCC < 6 doesn't have
forward_parm and doesn't unconditionally build a static_cast, so doesn't hit
this warning either.
