https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91529
Bug ID: 91529
Summary: -fmerge-all-constants leads to corrupt output without
inlining
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: fiesh at zefix dot tv
Target Milestone: ---
(Filed this as C++ but don't think that's the right component.)
The following code compiles to a program that behaves as follows:
* Compiled with "g++ -std=c++17 -fmerge-all-constants": segfault
* Compiled with "g++ -std=c++17 -fmerge-all-constants -O1 -fno-inline":
segfault
* Compiled with "g++ -std=c++17 -fmerge-all-constants -O1": success
* Compiled with "g++ -std=c++17": success
It seems that for gcc-7, the program always succeeds, but for gcc-8, gcc-9, and
trunk, this behavior shows up. It was reduced from what I believe is valid
code using std::variant.
template <unsigned long>
struct e
{
};
template <long f>
e<f> h;
template <typename...>
class ad;
long bi;
struct i
{
static constexpr bool bm = 0;
};
template <typename...>
union ap {
};
template <typename ag, typename... ah>
union ap<ag, ah...> {
constexpr ap(e<0>) : aq() {}
template <unsigned long af>
constexpr ap(e<af>) : bt(h<af - 1>)
{
}
ag aq;
ap<ah...> bt;
};
template <bool, typename...>
struct as;
template <typename... bv>
struct as<false, bv...>
{
template <unsigned long af>
constexpr as(e<af>) : av(h<af>), aw(af)
{
}
void j() { aw = bi; }
~as() { j(); }
ap<bv...> av;
int aw;
};
template <typename... bv>
using az = as<i::bm, bv...>;
template <int, typename... bv>
struct k : az<bv...>
{
using bb = az<bv...>;
bb::bb;
};
template <typename... bv>
using ce = k<0, bv...>;
template <int, typename... bv>
struct m : ce<bv...>
{
using bb = ce<bv...>;
bb::bb;
};
template <typename... bv>
using be = m<0, bv...>;
template <int, typename... bv>
struct p : be<bv...>
{
using bb = be<bv...>;
bb::bb;
};
template <typename... bv>
using bg = p<0, bv...>;
template <int, typename... bv>
struct q : bg<bv...>
{
using bb = bg<bv...>;
bb::bb;
};
template <typename... bv>
using ck = q<0, bv...>;
template <typename... bv>
struct r : ck<bv...>
{
using bb = ck<bv...>;
template <unsigned long af>
constexpr r(e<af> s) : bb(s)
{
}
};
template <typename, typename>
struct l;
template <typename g, typename... bv>
struct l<g, ad<bv...>>
{
static constexpr long c = 1;
};
template <typename... bv>
class ad : r<bv...>
{
using bb = r<bv...>;
template <typename g>
static constexpr long l = l<g, ad>::c;
public:
template <typename g>
constexpr ad(g) : ad(h<l<g>>)
{
}
template <unsigned long af>
constexpr ad(e<af>) : bb(h<af>)
{
}
};
template <int>
struct n
{
double d = 1.;
};
using ch = ad<int, n<1>>;
main()
{
ch const o{n<0>()};
}
