PR c++/42317
* cgraph.h (struct cgraph_node): Add same_comdat_group field.
* cgraph.c (cgraph_remove_node): Unchain node from same_comdat_group
circular list.
(cgraph_node_can_be_local_p): Return false for DECL_COMDAT with
node->same_comdat_group.
* ipa.c (cgraph_remove_unreachable_nodes): For any reachable node
mark all its same_comdat_group nodes as also reachable.
(cgraph_externally_visible_p): Return true even if any of
same_comdat_group nodes has address taken.
* lto-cgraph.c (lto_output_node): Stream out same_comdat_group.
(output_cgraph): Ensure other same_comdat_group nodes are also
included.
(input_node): Stream in same_comdat_group.
(input_cgraph_1): Fix up same_comdat_group fields from references
to pointers.
* cgraphunit.c (cgraph_analyze_functions): Mark all other
same_comdat_group nodes as reachable.
(cgraph_mark_functions_to_output): For each node->process process
also other same_comdat_group nodes.
* ipa-inline.c (cgraph_clone_inlined_nodes): Don't reuse nodes
with same_comdat_group non-NULL.
(cgraph_mark_inline_edge): Likewise.
* decl2.c (cp_write_global_declarations): Clear DECL_EXTERNAL
also on all other functions in the same comdat group.
* optimize.c (maybe_clone_body): Also optimize virtual implicit
dtors. For virtual comdat dtors tell cgraph that base and deleting
dtor are in the same comdat group.
* config/abi/pre/gnu.ver: Don't export certain base dtors that
weren't previously exported.
* g++.dg/opt/dtor2.C: New test.
* g++.dg/opt/dtor2.h: New file.
* g++.dg/opt/dtor2-aux.cc: New file.
From-SVN: r155143
