------- Comment #9 from rguenth at gcc dot gnu dot org 2009-08-27 15:43 -------
In fact the code generated by the C++ frontend (or the library) looks bogus.
other.1157_15 = (const struct hash_eq_fn *) D.107435_2;
this.1158_16 = (struct hash_eq_fn *) D.107436_4;
other.1161_17 = (struct equal_to *) other.1157_15;
this.1162_18 = (struct equal_to *) this.1158_16;
__tmp = *this.1162_18;
*this.1162_18 = *other.1161_17;
*other.1161_17 = __tmp;
this swaps the first byte(!) of the struct which contains the vtable pointer.
In fact gp_hash_table::swap(gp_hash_table&) seems to cause this. Forcing
to not inline that function fixes the issue as well.
(so the dead store really is not dead - but only because of that bogus swap).
Thus, things like
void
_M_swap(_Hash_code_base& __x)
{
std::swap(_M_extract, __x._M_extract);
std::swap(_M_eq, __x._M_eq);
std::swap(_M_h1, __x._M_h1);
std::swap(_M_h2, __x._M_h2);
}
protected:
_ExtractKey _M_extract;
_Equal _M_eq;
_H1 _M_h1;
_H2 _M_h2;
};
seem to corrupt the vtable pointer as the empty function classes are
tail-packed into that field. OTOH std::swap should do nothing for
empty classes, but instead it does
;; Function void std::swap(_Tp&, _Tp&) [with _Tp =
std::equal_to<__gnu_pbds::test::basic_type>] (null)
;; enabled by -tree-original
{
struct equal_to __tmp;
struct equal_to __tmp;
<<cleanup_point <<< Unknown tree: expr_stmt
(void) (__tmp = TARGET_EXPR <D.100064, *(const struct equal_to &) (const
struct equal_to *) __a>) >>>
>>;
<<cleanup_point <<< Unknown tree: expr_stmt
(void) (*(struct equal_to *) __a = *(const struct equal_to &) (const struct
equal_to *) __b) >>>
>>;
<<cleanup_point <<< Unknown tree: expr_stmt
(void) (*(struct equal_to *) __b = *(const struct equal_to &) (const struct
equal_to *) &__tmp) >>>
>>;
}
bah. Paolo, who is at fault here? The library or the frontend? The
issue must be latent on trunk.
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |paolo dot carlini at oracle
| |dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41058
