On Tue, Mar 14, 2017 at 8:24 AM, Pierre-Marie de Rodat
<dero...@adacore.com> wrote:
> Hello,
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79542 reports an ICE in
> dwarf2out.c for an Ada testcase built with optimization.
>
> This crash happens during the late generation pass because
> add_gnat_descriptive_type cannot find the type DIE corresponding to some
> descriptive type after having tried to generate it. This is because the
> DIE was generated during the early generation pass, but then pruned by
> the type pruning machinery. So why was it pruned?
>
> We are in a situation where we have cloned types (because of inlining,
> IIUC) whose TYPE_NAME have non-null DECL_ABSTRACT_ORIGIN attributes. As
> a consequence:
>
> * In modified_type_die, the "handle C typedef types" part calls
> gen_type_die on the cloned type.
>
> * gen_type_die matches a typedef variant, and then calls gen_decl_die
> on its TYPE_NAME, which will end up calling gen_typedef_die.
>
> * gen_typedef_die checks decl_ultimate_origin for this TYPE_DECL, and
> finds one, so it only adds a DW_AT_abstract_origin attribute to the
> DW_TAG_typedef DIE, but the cloned type itself does not get its own
> DIE.
That seems like a bug; if gen_typedef_die is going to generate a DIE
for a cloned typedef, it needs to associate the type with the DIE.
> * Back in modified_type_die, the call to lookup_type_die on the type
> passed to gen_type_die returns NULL.
> In the end, whole type trees, i.e. the ones referenced by
> DECL_ABSTRACT_ORIGIN attributes, are never referenced from type pruning
> "roots" and are thus pruned. The descriptive type at stake here is one
> of them, hence the assertion failure.
>
> This patch attemps to fix that with what seems to be the most sensible
> thing to do in my opinion: updating the "handle C typedef types" part in
> modified_type_die to check decl_ultimate_origin before calling
> gen_type_die: if that function returns something not null, then we know
> that gen_type_die/gen_typedef_die will not generate a DIE for the input
> type, so we try to process the ultimate origin instead.
This soundsn good; the DWARF standard says that we don't need to have
a die at all for the cloned typedef.
> @@ -12496,6 +12496,18 @@ modified_type_die (tree type, int cv_quals, bool
> reverse,
>
> if (qualified_type == dtype)
> {
> + tree origin
> + = TYPE_NAME (qualified_type) == NULL
> + ? NULL
> + : decl_ultimate_origin (TYPE_NAME (qualified_type));
This is unnecessarily complicated; at this point we already know that
TYPE_NAME (qualified_type) is non-null and in the variable "name".
> + /* Typedef variants that have an abstract origin don't get their own
> + type DIE (see gen_typedef_die), so fall back on the ultimate
gen_typedef_die does create a DIE for them, it just doesn't do it
properly. But we could change gen_typedef_die to abort in that case,
making this comment correct.
Jason
