| /* Localize comdats. |
| Copyright (C) 2014-2022 Free Software Foundation, Inc. |
| |
| This file is part of GCC. |
| |
| GCC is free software; you can redistribute it and/or modify it under |
| the terms of the GNU General Public License as published by the Free |
| Software Foundation; either version 3, or (at your option) any later |
| version. |
| |
| GCC is distributed in the hope that it will be useful, but WITHOUT ANY |
| WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| for more details. |
| |
| You should have received a copy of the GNU General Public License |
| along with GCC; see the file COPYING3. If not see |
| <http://www.gnu.org/licenses/>. */ |
| |
| /* This is very simple pass that looks for static symbols that are used |
| exclusively by symbol within one comdat group. In this case it makes |
| sense to bring the symbol itself into the group to avoid dead code |
| that would arrise when the comdat group from current unit is replaced |
| by a different copy. Consider for example: |
| |
| static int q(void) |
| { |
| .... |
| } |
| inline int t(void) |
| { |
| return q(); |
| } |
| |
| if Q is used only by T, it makes sense to put Q into T's comdat group. |
| |
| The pass solve simple dataflow across the callgraph trying to prove what |
| symbols are used exclusively from a given comdat group. |
| |
| The implementation maintains a queue linked by AUX pointer terminated by |
| pointer value 1. Lattice values are NULL for TOP, actual comdat group, or |
| ERROR_MARK_NODE for bottom. |
| |
| TODO: When symbol is used only by comdat symbols, but from different groups, |
| it would make sense to produce a new comdat group for it with anonymous name. |
| |
| TODO2: We can't mix variables and functions within one group. Currently |
| we just give up on references of symbols of different types. We also should |
| handle this by anonymous comdat group section. */ |
| |
| #include "config.h" |
| #include "system.h" |
| #include "coretypes.h" |
| #include "tm.h" |
| #include "tree.h" |
| #include "tree-pass.h" |
| #include "cgraph.h" |
| |
| /* Main dataflow loop propagating comdat groups across |
| the symbol table. All references to SYMBOL are examined |
| and NEWGROUP is updated accordingly. MAP holds current lattice |
| values for individual symbols. */ |
| |
| tree |
| propagate_comdat_group (struct symtab_node *symbol, |
| tree newgroup, hash_map<symtab_node *, tree> &map) |
| { |
| int i; |
| struct ipa_ref *ref; |
| |
| /* Walk all references to SYMBOL, recursively dive into aliases. */ |
| |
| for (i = 0; |
| symbol->iterate_referring (i, ref) |
| && newgroup != error_mark_node; i++) |
| { |
| struct symtab_node *symbol2 = ref->referring; |
| |
| if (ref->use == IPA_REF_ALIAS) |
| { |
| newgroup = propagate_comdat_group (symbol2, newgroup, map); |
| continue; |
| } |
| |
| /* One COMDAT group cannot hold both variables and functions at |
| a same time. For now we just go to BOTTOM, in future we may |
| invent special comdat groups for this case. */ |
| |
| if (symbol->type != symbol2->type) |
| { |
| newgroup = error_mark_node; |
| break; |
| } |
| |
| /* If we see inline clone, its comdat group actually |
| corresponds to the comdat group of the function it is inlined |
| to. */ |
| |
| if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2)) |
| { |
| if (cn->inlined_to) |
| symbol2 = cn->inlined_to; |
| } |
| |
| /* The actual merge operation. */ |
| |
| tree *val2 = map.get (symbol2); |
| |
| if (val2 && *val2 != newgroup) |
| { |
| if (!newgroup) |
| newgroup = *val2; |
| else |
| newgroup = error_mark_node; |
| } |
| } |
| |
| /* If we analyze function, walk also callers. */ |
| |
| cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol); |
| |
| if (cnode) |
| for (struct cgraph_edge * edge = cnode->callers; |
| edge && newgroup != error_mark_node; edge = edge->next_caller) |
| { |
| struct symtab_node *symbol2 = edge->caller; |
| |
| if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2)) |
| { |
| /* Thunks cannot call across section boundary. */ |
| if (cn->thunk) |
| newgroup = propagate_comdat_group (symbol2, newgroup, map); |
| /* If we see inline clone, its comdat group actually |
| corresponds to the comdat group of the function it |
| is inlined to. */ |
| if (cn->inlined_to) |
| symbol2 = cn->inlined_to; |
| } |
| |
| /* The actual merge operation. */ |
| |
| tree *val2 = map.get (symbol2); |
| |
| if (val2 && *val2 != newgroup) |
| { |
| if (!newgroup) |
| newgroup = *val2; |
| else |
| newgroup = error_mark_node; |
| } |
| } |
| return newgroup; |
| } |
| |
| |
| /* Add all references of SYMBOL that are defined into queue started by FIRST |
| and linked by AUX pointer (unless they are already enqueued). |
| Walk recursively inlined functions. */ |
| |
| void |
| enqueue_references (symtab_node **first, |
| symtab_node *symbol) |
| { |
| int i; |
| struct ipa_ref *ref = NULL; |
| |
| for (i = 0; symbol->iterate_reference (i, ref); i++) |
| { |
| symtab_node *node = ref->referred->ultimate_alias_target (); |
| |
| /* Always keep thunks in same sections as target function. */ |
| if (is_a <cgraph_node *>(node)) |
| node = dyn_cast <cgraph_node *> (node)->function_symbol (); |
| if (!node->aux && node->definition) |
| { |
| node->aux = *first; |
| *first = node; |
| } |
| } |
| |
| if (cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol)) |
| { |
| struct cgraph_edge *edge; |
| |
| for (edge = cnode->callees; edge; edge = edge->next_callee) |
| if (!edge->inline_failed) |
| enqueue_references (first, edge->callee); |
| else |
| { |
| symtab_node *node = edge->callee->ultimate_alias_target (); |
| |
| /* Always keep thunks in same sections as target function. */ |
| if (is_a <cgraph_node *>(node)) |
| node = dyn_cast <cgraph_node *> (node)->function_symbol (); |
| if (!node->aux && node->definition) |
| { |
| node->aux = *first; |
| *first = node; |
| } |
| } |
| } |
| } |
| |
| /* Set comdat group of SYMBOL to GROUP. |
| Callback for for_node_and_aliases. */ |
| |
| bool |
| set_comdat_group (symtab_node *symbol, |
| void *head_p) |
| { |
| symtab_node *head = (symtab_node *)head_p; |
| |
| gcc_assert (!symbol->get_comdat_group ()); |
| if (symbol->real_symbol_p ()) |
| { |
| symbol->set_comdat_group (head->get_comdat_group ()); |
| symbol->add_to_same_comdat_group (head); |
| } |
| return false; |
| } |
| |
| /* Set comdat group of SYMBOL to GROUP. |
| Callback for for_node_thunks_and_aliases. */ |
| |
| bool |
| set_comdat_group_1 (cgraph_node *symbol, |
| void *head_p) |
| { |
| return set_comdat_group (symbol, head_p); |
| } |
| |
| /* The actual pass with the main dataflow loop. */ |
| |
| static unsigned int |
| ipa_comdats (void) |
| { |
| hash_map<symtab_node *, tree> map (251); |
| hash_map<tree, symtab_node *> comdat_head_map (251); |
| symtab_node *symbol; |
| bool comdat_group_seen = false; |
| symtab_node *first = (symtab_node *) (void *) 1; |
| tree group; |
| |
| /* Start the dataflow by assigning comdat group to symbols that are in comdat |
| groups already. All other externally visible symbols must stay, we use |
| ERROR_MARK_NODE as bottom for the propagation. */ |
| |
| FOR_EACH_DEFINED_SYMBOL (symbol) |
| if (!symbol->real_symbol_p ()) |
| ; |
| else if ((group = symbol->get_comdat_group ()) != NULL) |
| { |
| map.put (symbol, group); |
| comdat_head_map.put (group, symbol); |
| comdat_group_seen = true; |
| |
| /* Mark the symbol so we won't waste time visiting it for dataflow. */ |
| symbol->aux = (symtab_node *) (void *) 1; |
| } |
| /* See symbols that cannot be privatized to comdats; that is externally |
| visible symbols or otherwise used ones. We also do not want to mangle |
| user section names. */ |
| else if (symbol->externally_visible |
| || symbol->force_output |
| || symbol->used_from_other_partition |
| || TREE_THIS_VOLATILE (symbol->decl) |
| || symbol->get_section () |
| || (TREE_CODE (symbol->decl) == FUNCTION_DECL |
| && (DECL_STATIC_CONSTRUCTOR (symbol->decl) |
| || DECL_STATIC_DESTRUCTOR (symbol->decl)))) |
| { |
| symtab_node *target = symbol->ultimate_alias_target (); |
| |
| /* Always keep thunks in same sections as target function. */ |
| if (is_a <cgraph_node *>(target)) |
| target = dyn_cast <cgraph_node *> (target)->function_symbol (); |
| map.put (target, error_mark_node); |
| |
| /* Mark the symbol so we won't waste time visiting it for dataflow. */ |
| symbol->aux = (symtab_node *) (void *) 1; |
| } |
| else |
| { |
| /* Enqueue symbol for dataflow. */ |
| symbol->aux = first; |
| first = symbol; |
| } |
| |
| if (!comdat_group_seen) |
| { |
| FOR_EACH_DEFINED_SYMBOL (symbol) |
| symbol->aux = NULL; |
| return 0; |
| } |
| |
| /* The actual dataflow. */ |
| |
| while (first != (void *) 1) |
| { |
| tree group = NULL; |
| tree newgroup, *val; |
| |
| symbol = first; |
| first = (symtab_node *)first->aux; |
| |
| /* Get current lattice value of SYMBOL. */ |
| val = map.get (symbol); |
| if (val) |
| group = *val; |
| |
| /* If it is bottom, there is nothing to do; do not clear AUX |
| so we won't re-queue the symbol. */ |
| if (group == error_mark_node) |
| continue; |
| |
| newgroup = propagate_comdat_group (symbol, group, map); |
| |
| /* If nothing changed, proceed to next symbol. */ |
| if (newgroup == group) |
| { |
| symbol->aux = NULL; |
| continue; |
| } |
| |
| /* Update lattice value and enqueue all references for re-visiting. */ |
| gcc_assert (newgroup); |
| if (val) |
| *val = newgroup; |
| else |
| map.put (symbol, newgroup); |
| enqueue_references (&first, symbol); |
| |
| /* We may need to revisit the symbol unless it is BOTTOM. */ |
| if (newgroup != error_mark_node) |
| symbol->aux = NULL; |
| } |
| |
| /* Finally assign symbols to the sections. */ |
| |
| FOR_EACH_DEFINED_SYMBOL (symbol) |
| { |
| struct cgraph_node *fun; |
| symbol->aux = NULL; |
| if (!symbol->get_comdat_group () |
| && !symbol->alias |
| && (!(fun = dyn_cast <cgraph_node *> (symbol)) |
| || !fun->thunk) |
| && symbol->real_symbol_p ()) |
| { |
| tree *val = map.get (symbol); |
| |
| /* A NULL here means that SYMBOL is unreachable in the definition |
| of ipa-comdats. Either ipa-comdats is wrong about this or someone |
| forgot to cleanup and remove unreachable functions earlier. */ |
| gcc_assert (val); |
| |
| tree group = *val; |
| |
| if (group == error_mark_node) |
| continue; |
| if (dump_file) |
| { |
| fprintf (dump_file, "Localizing symbol\n"); |
| symbol->dump (dump_file); |
| fprintf (dump_file, "To group: %s\n", IDENTIFIER_POINTER (group)); |
| } |
| if (is_a <cgraph_node *> (symbol)) |
| dyn_cast <cgraph_node *>(symbol)->call_for_symbol_thunks_and_aliases |
| (set_comdat_group_1, |
| *comdat_head_map.get (group), |
| true); |
| else |
| symbol->call_for_symbol_and_aliases |
| (set_comdat_group, |
| *comdat_head_map.get (group), |
| true); |
| } |
| } |
| |
| #if 0 |
| /* Recompute calls comdat local flag. This need to be done after all changes |
| are made. */ |
| cgraph_node *function; |
| FOR_EACH_DEFINED_FUNCTION (function) |
| if (function->get_comdat_group ()) |
| function->calls_comdat_local = function->check_calls_comdat_local_p (); |
| #endif |
| return 0; |
| } |
| |
| namespace { |
| |
| const pass_data pass_data_ipa_comdats = |
| { |
| IPA_PASS, /* type */ |
| "comdats", /* name */ |
| OPTGROUP_NONE, /* optinfo_flags */ |
| TV_IPA_COMDATS, /* tv_id */ |
| 0, /* properties_required */ |
| 0, /* properties_provided */ |
| 0, /* properties_destroyed */ |
| 0, /* todo_flags_start */ |
| 0, /* todo_flags_finish */ |
| }; |
| |
| class pass_ipa_comdats : public ipa_opt_pass_d |
| { |
| public: |
| pass_ipa_comdats (gcc::context *ctxt) |
| : ipa_opt_pass_d (pass_data_ipa_comdats, ctxt, |
| NULL, /* generate_summary */ |
| NULL, /* write_summary */ |
| NULL, /* read_summary */ |
| NULL, /* write_optimization_summary */ |
| NULL, /* read_optimization_summary */ |
| NULL, /* stmt_fixup */ |
| 0, /* function_transform_todo_flags_start */ |
| NULL, /* function_transform */ |
| NULL) /* variable_transform */ |
| {} |
| |
| /* opt_pass methods: */ |
| bool gate (function *) final override; |
| unsigned int execute (function *) final override { return ipa_comdats (); } |
| |
| }; // class pass_ipa_comdats |
| |
| bool |
| pass_ipa_comdats::gate (function *) |
| { |
| return HAVE_COMDAT_GROUP; |
| } |
| |
| } // anon namespace |
| |
| ipa_opt_pass_d * |
| make_pass_ipa_comdats (gcc::context *ctxt) |
| { |
| return new pass_ipa_comdats (ctxt); |
| } |