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@ -0,0 +1,387 @@
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/* Localize comdats.
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Copyright (C) 2014 Free Software Foundation, Inc.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it under
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the terms of the GNU General Public License as published by the Free
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Software Foundation; either version 3, or (at your option) any later
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version.
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GCC is distributed in the hope that it will be useful, but WITHOUT ANY
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WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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/* This is very simple pass that looks for static symbols that are used
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exlusively by symbol within one comdat group. In this case it makes
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sense to bring the symbol itself into the group to avoid dead code
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that would arrise when the comdat group from current unit is replaced
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by a different copy. Consider for example:
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static int q(void)
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{
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....
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}
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inline int t(void)
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{
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return q();
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}
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if Q is used only by T, it makes sense to put Q into T's comdat group.
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The pass solve simple dataflow across the callgraph trying to prove what
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symbols are used exclusively from a given comdat group.
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The implementation maintains a queue linked by AUX pointer terminated by
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pointer value 1. Lattice values are NULL for TOP, actual comdat group, or
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ERROR_MARK_NODE for bottom.
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TODO: When symbol is used only by comdat symbols, but from different groups,
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it would make sense to produce a new comdat group for it with anonymous name.
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TODO2: We can't mix variables and functions within one group. Currently
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we just give up on references of symbols of different types. We also should
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handle this by anonymous comdat group section. */
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#include "config.h"
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#include "system.h"
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#include "coretypes.h"
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#include "tm.h"
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#include "tree.h"
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#include "cgraph.h"
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#include "tree-pass.h"
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#include "pointer-set.h"
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/* Main dataflow loop propagating comdat groups across
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the symbol table. All references to SYMBOL are examined
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and NEWGROUP is updated accordingly. MAP holds current lattice
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values for individual symbols. */
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tree
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propagate_comdat_group (struct symtab_node *symbol,
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tree newgroup, pointer_map <tree> &map)
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{
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int i;
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struct ipa_ref *ref;
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/* Walk all references to SYMBOL, recursively dive into aliases. */
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for (i = 0;
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ipa_ref_list_referring_iterate (&symbol->ref_list, i, ref)
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&& newgroup != error_mark_node; i++)
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{
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struct symtab_node *symbol2 = ref->referring;
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if (ref->use == IPA_REF_ALIAS)
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{
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newgroup = propagate_comdat_group (symbol2, newgroup, map);
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continue;
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}
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/* One COMDAT group can not hold both variables and functions at
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a same time. For now we just go to BOTTOM, in future we may
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invent special comdat groups for this case. */
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if (symbol->type != symbol2->type)
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{
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newgroup = error_mark_node;
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break;
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}
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/* If we see inline clone, its comdat group actually
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corresponds to the comdat group of the function it is inlined
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to. */
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if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2))
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{
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if (cn->global.inlined_to)
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symbol2 = cn->global.inlined_to;
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}
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/* The actual merge operation. */
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tree *val2 = map.contains (symbol2);
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if (val2 && *val2 != newgroup)
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{
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if (!newgroup)
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newgroup = *val2;
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else
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newgroup = error_mark_node;
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}
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}
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/* If we analyze function, walk also callers. */
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cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol);
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if (cnode)
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for (struct cgraph_edge * edge = cnode->callers;
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edge && newgroup != error_mark_node; edge = edge->next_caller)
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{
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struct symtab_node *symbol2 = edge->caller;
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/* If we see inline clone, its comdat group actually
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corresponds to the comdat group of the function it is inlined
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to. */
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if (cgraph_node * cn = dyn_cast <cgraph_node *> (symbol2))
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{
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if (cn->global.inlined_to)
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symbol2 = cn->global.inlined_to;
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}
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/* The actual merge operation. */
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tree *val2 = map.contains (symbol2);
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if (val2 && *val2 != newgroup)
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{
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if (!newgroup)
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newgroup = *val2;
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else
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newgroup = error_mark_node;
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}
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}
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return newgroup;
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}
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/* Add all references of SYMBOL that are defined into queue started by FIRST
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and linked by AUX pointer (unless they are already enqueued).
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Walk recursively inlined functions. */
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void
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enqueue_references (symtab_node **first,
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symtab_node *symbol)
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{
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int i;
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struct ipa_ref *ref;
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for (i = 0; ipa_ref_list_reference_iterate (&symbol->ref_list, i, ref); i++)
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{
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symtab_node *node = symtab_alias_ultimate_target (ref->referred, NULL);
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if (!node->aux && node->definition)
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{
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node->aux = *first;
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*first = node;
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}
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}
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if (cgraph_node *cnode = dyn_cast <cgraph_node *> (symbol))
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{
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struct cgraph_edge *edge;
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for (edge = cnode->callees; edge; edge = edge->next_callee)
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if (!edge->inline_failed)
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enqueue_references (first, edge->callee);
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else
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{
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symtab_node *node = symtab_alias_ultimate_target (edge->callee,
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NULL);
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if (!node->aux && node->definition)
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{
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node->aux = *first;
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*first = node;
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}
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}
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}
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}
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/* Set comdat group of SYMBOL to GROUP.
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Callback for symtab_for_node_and_aliases. */
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bool
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set_comdat_group (symtab_node *symbol,
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void *head_p)
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{
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symtab_node *head = (symtab_node *)head_p;
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gcc_assert (!DECL_COMDAT_GROUP (symbol->decl));
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DECL_COMDAT_GROUP (symbol->decl) = DECL_COMDAT_GROUP (head->decl);
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symtab_add_to_same_comdat_group (symbol, head);
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return false;
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}
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/* The actual pass with the main dataflow loop. */
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static unsigned int
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ipa_comdats (void)
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{
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pointer_map<tree> map;
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pointer_map<symtab_node *> comdat_head_map;
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symtab_node *symbol;
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bool comdat_group_seen = false;
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symtab_node *first = (symtab_node *) (void *) 1;
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/* Start the dataflow by assigning comdat group to symbols that are in comdat
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groups already. All other externally visible symbols must stay, we use
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ERROR_MARK_NODE as bottom for the propagation. */
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FOR_EACH_DEFINED_SYMBOL (symbol)
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if (!symtab_real_symbol_p (symbol))
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;
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else if (DECL_COMDAT_GROUP (symbol->decl))
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{
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*map.insert (symbol) = DECL_COMDAT_GROUP (symbol->decl);
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*comdat_head_map.insert (DECL_COMDAT_GROUP (symbol->decl)) = symbol;
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comdat_group_seen = true;
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/* Mark the symbol so we won't waste time visiting it for dataflow. */
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symbol->aux = (symtab_node *) (void *) 1;
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}
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/* See symbols that can not be privatized to comdats; that is externally
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visible symbols or otherwise used ones. We also do not want to mangle
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user section names. */
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else if (symbol->externally_visible
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|| symbol->force_output
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|| symbol->used_from_other_partition
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|| TREE_THIS_VOLATILE (symbol->decl)
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|| DECL_SECTION_NAME (symbol->decl)
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|| (TREE_CODE (symbol->decl) == FUNCTION_DECL
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&& (DECL_STATIC_CONSTRUCTOR (symbol->decl)
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|| DECL_STATIC_DESTRUCTOR (symbol->decl))))
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{
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*map.insert (symtab_alias_ultimate_target (symbol, NULL)) = error_mark_node;
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/* Mark the symbol so we won't waste time visiting it for dataflow. */
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symbol->aux = (symtab_node *) (void *) 1;
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}
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else
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{
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/* Enqueue symbol for dataflow. */
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symbol->aux = first;
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first = symbol;
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}
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if (!comdat_group_seen)
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{
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FOR_EACH_DEFINED_SYMBOL (symbol)
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symbol->aux = NULL;
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return 0;
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}
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/* The actual dataflow. */
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while (first != (void *) 1)
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{
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tree group = NULL;
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tree newgroup, *val;
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symbol = first;
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first = (symtab_node *)first->aux;
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/* Get current lattice value of SYMBOL. */
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val = map.contains (symbol);
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if (val)
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group = *val;
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/* If it is bottom, there is nothing to do; do not clear AUX
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so we won't re-queue the symbol. */
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if (group == error_mark_node)
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continue;
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newgroup = propagate_comdat_group (symbol, group, map);
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/* If nothing changed, proceed to next symbol. */
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if (newgroup == group)
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{
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symbol->aux = NULL;
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continue;
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}
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/* Update lattice value and enqueue all references for re-visiting. */
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gcc_assert (newgroup);
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if (val)
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*val = newgroup;
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else
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*map.insert (symbol) = newgroup;
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enqueue_references (&first, symbol);
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/* We may need to revisit the symbol unless it is BOTTOM. */
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if (newgroup != error_mark_node)
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symbol->aux = NULL;
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}
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/* Finally assign symbols to the sections. */
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FOR_EACH_DEFINED_SYMBOL (symbol)
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{
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symbol->aux = NULL;
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if (!DECL_COMDAT_GROUP (symbol->decl)
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&& !symbol->alias
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&& symtab_real_symbol_p (symbol))
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{
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tree group = *map.contains (symbol);
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if (group == error_mark_node)
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continue;
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if (dump_file)
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{
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fprintf (dump_file, "Localizing symbol\n");
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dump_symtab_node (dump_file, symbol);
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fprintf (dump_file, "To group: %s\n", IDENTIFIER_POINTER (group));
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}
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symtab_for_node_and_aliases (symbol, set_comdat_group,
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*comdat_head_map.contains (group), true);
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}
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}
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return 0;
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}
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namespace {
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const pass_data pass_data_ipa_comdats =
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{
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IPA_PASS, /* type */
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"comdats", /* name */
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OPTGROUP_NONE, /* optinfo_flags */
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true, /* has_execute */
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TV_IPA_COMDATS, /* tv_id */
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0, /* properties_required */
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0, /* properties_provided */
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0, /* properties_destroyed */
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0, /* todo_flags_start */
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0, /* todo_flags_finish */
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};
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class pass_ipa_comdats : public ipa_opt_pass_d
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{
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public:
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pass_ipa_comdats (gcc::context *ctxt)
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: ipa_opt_pass_d (pass_data_ipa_comdats, ctxt,
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NULL, /* generate_summary */
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NULL, /* write_summary */
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NULL, /* read_summary */
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NULL, /* write_optimization_summary */
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NULL, /* read_optimization_summary */
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NULL, /* stmt_fixup */
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0, /* function_transform_todo_flags_start */
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NULL, /* function_transform */
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NULL) /* variable_transform */
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{}
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/* opt_pass methods: */
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virtual bool gate (function *);
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virtual unsigned int execute (function *) { return ipa_comdats (); }
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}; // class pass_ipa_comdats
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bool
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pass_ipa_comdats::gate (function *)
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{
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return optimize;
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}
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} // anon namespace
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ipa_opt_pass_d *
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make_pass_ipa_comdats (gcc::context *ctxt)
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{
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return new pass_ipa_comdats (ctxt);
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}
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