[Bug bootstrap/79814] pass-instances.def:36:14: error: ‘*<unknown>.gcc::pass_manager::pass_warn_unused_result_1’ is used uninitialized in this function

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79814

--- Comment #3 from rguenther at suse dot de <rguenther at suse dot de> ---
On March 4, 2017 12:30:21 AM GMT+01:00, "dmalcolm at gcc dot gnu.org"
<gcc-bugzilla@gcc.gnu.org> wrote:
>https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79814
>
>--- Comment #2 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
>The code in question is:
>  do { ((void)(!(
> __null 
>== pass_warn_unused_result_1) ? fancy_abort ("./pass-instances.def",
>36,
>__FUNCTION__), 0 : 0)); if ((1) == 1) pass_warn_unused_result_1 =
>make_pass_warn_unused_result (m_ctxt); else {
>((void)(!(pass_warn_unused_result_1) ? fancy_abort
>("./pass-instances.def", 36,
>__FUNCTION__), 0 : 0)); pass_warn_unused_result_1 =
>pass_warn_unused_result_1->clone (); } p = next_pass_1 (p,
>pass_warn_unused_result_1, pass_warn_unused_result_1); } while (0);
>
>i.e. it's complaining about this assertion:
>
>  gcc_assert (NULL == PASS ## _ ## NUM); \
>
>within the definition of NEXT_PASS(PASS, NUM) supplied within the
>pass_manager
>ctor: it's asserting that a pointer field within the object is NULL.
>
>pass_manager::operator new ensures that the underlying memory of the
>pass
>manager is zero-initialized, but clearly the warning has no knowledge
>of this.

Well, the C++ frontend inserts CLOBBERs at the beginning of constructors so
either this zeroing is pointless (and likely optimized out) or the frontend
produces wrong-code in doing so.

>Eliminating the assertion fixes the warning, FWIW.