[Bug c++/78908] [6/7 Regression] lto1: internal compiler error: in lto_read_decls, at lto/lto.c:1814

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78908

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
struct A { int a : 1; };
struct F { int foo (A const &); };
template <typename> struct O : F { int foo (A const &); };
struct S {} b;
template <typename L, typename T> int operator<< (L, T) { return (T) 123; }
template <class = int> struct V;
template <> struct V<> : O<long> { V () {} };
template <typename T> int O<T>::foo (A const &x) { return b << x.a; }

int
main ()
{
  A a = { 0 };
  O<int> o;
  if (o.foo (a) != 123)
    __builtin_abort ();
}

is smaller testcase that doesn't ICE, but results in wrong-code (T is signed
char : 1 rather than int as happens with G++ 5.x and earlier or current
clang++).
Or:

struct A { int a : 1; };
struct F { int foo (A const &); };
template <typename> struct O : F { int foo (A const &); };
struct S {} b;
template <typename L, typename T> int operator<< (L, T) { return (T) 123; }
template <class = int> struct V;
template <> struct V<> : O<long> { V () {} };
template <typename T> int O<T>::foo (A const &x) { return b << x.a; }

int
main ()
{
  A a = { 0 };
  O<int> o;
  if (o.foo (a) != 123)
    __builtin_abort ();
  signed char d = 2;
  if ((b << d) != 123)
    __builtin_abort ();
}

is another testcase that ICEs with the same error as the #c1 testcase.