On Thu, May 17, 2012 at 9:42 AM, Jan Hubicka <hubi...@ucw.cz> wrote: > Hi, > C++ virtual tables keyed to other compilation units are represented as > DECL_EXTERNAL > variables with constructor known. Knowhing the constructor helps constant > folding to do > devirtualization. > > At the moment these costructors are not seen by varpool and thus they are not > represented by ipa-ref and thus WHOPR partitioning is not seeing them and we > later in can_refer_decl_in_current_unit_p try to work out if the partitioning > was done in lucky or unlucky way. > > This patch makes external variables to be handled similarly to external > functions. > That is the variables gets finalized and analyzed by varpool. They go in > similar > way to partitioning as comdat functions. > > Code removing unreachable nodes treats them as normal variables until after > inlining when vars/funcions referred only by those are considred unreachable. > This also allows us to remove the constructors from memory when we know they > are no longer needed saving couple hundred KB on compiling Mozilla with LTO. > > The patch also enables aboud 3000 extra foldings on Mozilla LTO build. > Mostly those are devirtualized calls to libstdc++. > > Bootstrapped/regtested x86_64-linux, comitted. > Index: ChangeLog > =================================================================== > *** ChangeLog (revision 187630) > --- ChangeLog (working copy) > *************** > *** 1,3 **** > --- 1,26 ---- > + 2012-05-17 Jan Hubicka <j...@suse.cz> > + > + * lto-symtab.c (lto_symtab_resolve_symbols): Preffer decl with > constructor > + over decl without. > + * cgraph.c (cgraph_remove_node): Clear also body of unanalyzed nodes. > + * cgraph.h (varpool_can_remove_if_no_refs): Handle external correctly. > + * cgraphunit.c (process_function_and_variable_attributes): Finalize > + extrnal decls. > + (mark_functions_to_output): Also accept bodies for functions with > clones. > + (output_in_order): Skip external vars. > + * lto-cgraph.c (lto_output_node): External functions are never in > other > + partition. > + (lto_output_varpool_node): Likewise. > + * lto-streamer-out.c (lto_write_tree): Always use error_mark_nodes for > + forgotten initializers. > + * ipa.c (process_references): Handle external vars. > + (symtab_remove_unreachable_nodes): Update to handle external vars. > + (varpool_externally_visible_p): External vars are externally visible. > + * gimple-fold.c (can_refer_decl_in_current_unit_p): Update. > + * varpool.c (varpool_remove_node): Remove constructor. > + (decide_is_variable_needed): Handle externals. > + (varpool_remove_unreferenced_decls): Likewise. > +
This caused: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53428 -- H.J.
