https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66223
--- Comment #8 from Jan Hubicka <hubicka at gcc dot gnu.org> ---
Well, if you rely on undefined behaviour, you should not be surprised when your
program breaks with optimization. I am testing the following patch:
Index: ipa-devirt.c
===================================================================
--- ipa-devirt.c (revision 232555)
+++ ipa-devirt.c (working copy)
@@ -2326,6 +2326,14 @@ referenced_from_vtable_p (struct cgraph_
}
return found;
}
+static bool
+is_cxa_pure_virtual_p (tree target)
+{
+ return target && TREE_CODE (TREE_TYPE (target)) != METHOD_TYPE
+ && DECL_NAME (target)
+ && !strcmp (IDENTIFIER_POINTER (DECL_NAME (target)),
+ "__cxa_pure_virtual");
+}
/* If TARGET has associated node, record it in the NODES array.
CAN_REFER specify if program can refer to the target directly.
@@ -2341,11 +2349,12 @@ maybe_record_node (vec <cgraph_node *> &
{
struct cgraph_node *target_node, *alias_target;
enum availability avail;
+ bool pure_virtual = is_cxa_pure_virtual_p (target);
- /* cxa_pure_virtual and __builtin_unreachable do not need to be added into
+ /* __builtin_unreachable do not need to be added into
list of targets; the runtime effect of calling them is undefined.
Only "real" virtual methods should be accounted. */
- if (target && TREE_CODE (TREE_TYPE (target)) != METHOD_TYPE)
+ if (target && TREE_CODE (TREE_TYPE (target)) != METHOD_TYPE &&
!pure_virtual)
return;
if (!can_refer)
@@ -2388,6 +2397,7 @@ maybe_record_node (vec <cgraph_node *> &
??? Maybe it would make sense to be more aggressive for LTO even
elsewhere. */
if (!flag_ltrans
+ && !pure_virtual
&& type_in_anonymous_namespace_p (DECL_CONTEXT (target))
&& (!target_node
|| !referenced_from_vtable_p (target_node)))
@@ -2401,6 +2411,20 @@ maybe_record_node (vec <cgraph_node *> &
{
gcc_assert (!target_node->global.inlined_to);
gcc_assert (target_node->real_symbol_p ());
+ /* Only add pure virtual if it is the only possible target. This way
+ we will preserve the diagnostics about pure virtual called in many
+ cases without disabling optimization in other. */
+ if (pure_virtual)
+ {
+ if (nodes.length ())
+ return;
+ }
+ /* If we found a real target, take away cxa_pure_virtual. */
+ else if (!pure_virtual && nodes.length () == 1
+ && is_cxa_pure_virtual_p (nodes[0]->decl))
+ nodes.pop ();
+ if (pure_virtual && nodes.length ())
+ return;
if (!inserted->add (target))
{
cached_polymorphic_call_targets->add (target_node);
which attempts to preserve the call to cxa_pure_virtual in cases it is cheap to
do so (i.e. we know it is the only target of the call).
It is still more expensive to call cxa_pure_virtual compared to
bulitin_unreachable. I will try to get some stats on firefox how often it
matters in practice.
