tree-pass.h (make_pass_ipa_comdats): New pass.

	* tree-pass.h (make_pass_ipa_comdats): New pass.
	* timevar.def (TV_IPA_COMDATS): New timevar.
	* passes.def (pass_ipa_comdats): Add.
	* Makefile.in (OBJS): Add ipa-comdats.o
	* ipa-comdats.c: New file.

	* g++.dg/ipa/comdat.C: New file.

From-SVN: r210597

1 files changed, 387 insertions, 0 deletions

diff --git a/gcc/ipa-comdats.c b/gcc/ipa-comdats.c
new file mode 100644
index 00000000000..d6840648fec
--- /dev/null
+++ b/gcc/ipa-comdats.c
@@ -0,0 +1,387 @@
+/* Localize comdats.
+   Copyright (C) 2014 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
+   exlusively 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 "cgraph.h"
+#include "tree-pass.h"
+#include "pointer-set.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, pointer_map <tree> &map)
+{
+  int i;
+  struct ipa_ref *ref;
+
+  /* Walk all references to SYMBOL, recursively dive into aliases.  */
+
+  for (i = 0;
+       ipa_ref_list_referring_iterate (&symbol->ref_list, 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 can not 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->global.inlined_to)
+	    symbol2 = cn->global.inlined_to;
+	}
+
+      /* The actual merge operation.  */
+
+      tree *val2 = map.contains (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 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->global.inlined_to)
+	      symbol2 = cn->global.inlined_to;
+	  }
+
+        /* The actual merge operation.  */
+
+	tree *val2 = map.contains (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;
+
+  for (i = 0; ipa_ref_list_reference_iterate (&symbol->ref_list, i, ref); i++)
+    {
+      symtab_node *node = symtab_alias_ultimate_target (ref->referred, NULL);
+      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 = symtab_alias_ultimate_target (edge->callee,
+							      NULL);
+	    if (!node->aux && node->definition)
+	      {
+		 node->aux = *first;
+		 *first = node;
+	      }
+	  }
+    }
+}
+
+/* Set comdat group of SYMBOL to GROUP.
+   Callback for symtab_for_node_and_aliases.  */
+
+bool
+set_comdat_group (symtab_node *symbol,
+	          void *head_p)
+{
+  symtab_node *head = (symtab_node *)head_p;
+
+  gcc_assert (!DECL_COMDAT_GROUP (symbol->decl));
+  DECL_COMDAT_GROUP (symbol->decl) = DECL_COMDAT_GROUP (head->decl);
+  symtab_add_to_same_comdat_group (symbol, head);
+  return false;
+}
+
+/* The actual pass with the main dataflow loop.  */
+
+static unsigned int
+ipa_comdats (void)
+{
+  pointer_map<tree> map;
+  pointer_map<symtab_node *> comdat_head_map;
+  symtab_node *symbol;
+  bool comdat_group_seen = false;
+  symtab_node *first = (symtab_node *) (void *) 1;
+
+  /* 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 (!symtab_real_symbol_p (symbol))
+      ;
+    else if (DECL_COMDAT_GROUP (symbol->decl))
+      {
+        *map.insert (symbol) = DECL_COMDAT_GROUP (symbol->decl);
+        *comdat_head_map.insert (DECL_COMDAT_GROUP (symbol->decl)) = 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 can not 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)
+	     || DECL_SECTION_NAME (symbol->decl)
+	     || (TREE_CODE (symbol->decl) == FUNCTION_DECL
+		 && (DECL_STATIC_CONSTRUCTOR (symbol->decl)
+		     || DECL_STATIC_DESTRUCTOR (symbol->decl))))
+      {
+	*map.insert (symtab_alias_ultimate_target (symbol, NULL)) = 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.contains (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.insert (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)
+    {
+      symbol->aux = NULL; 
+      if (!DECL_COMDAT_GROUP (symbol->decl)
+	  && !symbol->alias
+	  && symtab_real_symbol_p (symbol))
+	{
+	  tree group = *map.contains (symbol);
+
+	  if (group == error_mark_node)
+	    continue;
+	  if (dump_file)
+	    {
+	      fprintf (dump_file, "Localizing symbol\n");
+	      dump_symtab_node (dump_file, symbol);
+	      fprintf (dump_file, "To group: %s\n", IDENTIFIER_POINTER (group));
+	    }
+	  symtab_for_node_and_aliases (symbol, set_comdat_group,
+				       *comdat_head_map.contains (group), true);
+	}
+    }
+  return 0;
+}
+
+namespace {
+
+const pass_data pass_data_ipa_comdats =
+{
+  IPA_PASS, /* type */
+  "comdats", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  true, /* has_execute */
+  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: */
+  virtual bool gate (function *);
+  virtual unsigned int execute (function *) { return ipa_comdats (); }
+
+}; // class pass_ipa_comdats
+
+bool
+pass_ipa_comdats::gate (function *)
+{
+  return optimize;
+}
+
+} // anon namespace
+
+ipa_opt_pass_d *
+make_pass_ipa_comdats (gcc::context *ctxt)
+{
+  return new pass_ipa_comdats (ctxt);
+}