Hi,
this patch fixes ICE in ipa-devirt that is caused by get_binfo_at_offset
reporting NULL for a valid query. This is because how virtual inheritance
is represented.
Here we have chain A<-B<-C where A is a virtual base. We look for A within
C that is there at offset 64. On this query get_binfo_at_offset walks
fields of C and it finds A, it matches it and it looks for BINFO. The
catch is that BINFO represents only direct bases and A is not direct base.
Conseuqentely it returns NULL. In the past this only prevented us from
devirtualizing here, now we ICE, since ipa-devirt depends on fact that
it can resolve all possible queries. get_binfo_at_offset needs to make a hop
through B.
This patch is kind of minimal change needed to get get_binfo_at_offset to
look into B: when base is not found, it finds a base that contains A
and dives into it.
I plan to rewrite the function for next stage1: the walk of fields is already
done by ipa-devirt separately, so it really should do only BINFO walk. For
that we however need to retire other uses of get_binfo_at_offset that are still
used by ipa-devirt. That is on the TODO list to switch it to be basically a
propagation engine for ipa-devirt's polymorphic_call_context structures.
(basically I want to have one local pass doing non-trivial propagation and
one IPA pass propagation across function boundaries, both sharing
polymorphic_call_context structure and a lattice operations)
Bootstrapped/regtested x86_64-linux, OK with the testcase?
struct A
{
virtual void foo () = 0;
void bar () { foo (); }
bool a;
};
struct B : public virtual A
{
virtual void foo ();
};
struct C : public B
{
C ();
};
void
baz ()
{
C c;
c.bar ();
}
PR ipa/59775
* tree.c (get_binfo_at_offset): Look harder for virtual bases.
Index: tree.c
===================================================================
--- tree.c (revision 206617)
+++ tree.c (working copy)
@@ -11995,16 +11995,35 @@ get_binfo_at_offset (tree binfo, HOST_WI
represented in the binfo for the derived class. */
else if (offset != 0)
{
- tree base_binfo, found_binfo = NULL_TREE;
- for (i = 0; BINFO_BASE_ITERATE (binfo, i, base_binfo); i++)
- if (types_same_for_odr (TREE_TYPE (base_binfo), TREE_TYPE (fld)))
- {
- found_binfo = base_binfo;
- break;
- }
- if (!found_binfo)
- return NULL_TREE;
- binfo = found_binfo;
+ tree base_binfo, binfo2 = binfo;
+
+ /* Find BINFO corresponding to FLD. This is bit harder
+ by a fact that in virtual inheritance we may need to walk down
+ the non-virtual inheritance chain. */
+ while (true)
+ {
+ tree containing_binfo = NULL, found_binfo = NULL;
+ for (i = 0; BINFO_BASE_ITERATE (binfo2, i, base_binfo); i++)
+ if (types_same_for_odr (TREE_TYPE (base_binfo), TREE_TYPE
(fld)))
+ {
+ found_binfo = base_binfo;
+ break;
+ }
+ else
+ if (BINFO_OFFSET (base_binfo) - BINFO_OFFSET (binfo) < pos
+ && (!containing_binfo
+ || (BINFO_OFFSET (containing_binfo)
+ < BINFO_OFFSET (base_binfo))))
+ containing_binfo = base_binfo;
+ if (found_binfo)
+ {
+ binfo = found_binfo;
+ break;
+ }
+ if (!containing_binfo)
+ return NULL_TREE;
+ binfo2 = containing_binfo;
+ }
}
type = TREE_TYPE (fld);
