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/* Callgraph handling code.

   Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2010, 2011

   Free Software Foundation, Inc.

   Contributed by Jan Hubicka

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/>.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "cgraph.h"

#include "langhooks.h"

#include "diagnostic-core.h"

#include "hashtab.h"

#include "ggc.h"

#include "timevar.h"

#include "debug.h"

#include "target.h"

#include "output.h"

#include "gimple.h"

#include "tree-flow.h"

#include "flags.h"

/*  This file contains basic routines manipulating variable pool.

    Varpool acts as interface in between the front-end and middle-end

    and drives the decision process on what variables and when are

    going to be compiled.

    The varpool nodes are allocated lazily for declarations

    either by frontend or at callgraph construction time.

    All variables supposed to be output into final file needs to be

    explicitly marked by frontend via VARPOOL_FINALIZE_DECL function.  */

/* Hash table used to convert declarations into nodes.  */

static GTY((param_is (struct varpool_node))) htab_t varpool_hash;

/* The linked list of cgraph varpool nodes.

   Linked via node->next pointer.  */

struct varpool_node *varpool_nodes;

/* Queue of cgraph nodes scheduled to be lowered and output.

   The queue is maintained via mark_needed_node, linked via node->next_needed

   pointer.

   LAST_NEEDED_NODE points to the end of queue, so it can be

   maintained in forward order.  GTY is needed to make it friendly to

   PCH.

   During compilation we construct the queue of needed variables

   twice: first time it is during cgraph construction, second time it is at the

   end of compilation in VARPOOL_REMOVE_UNREFERENCED_DECLS so we can avoid

   optimized out variables being output.

   Each variable is thus first analyzed and then later possibly output.

   FIRST_UNANALYZED_NODE points to first node in queue that was not analyzed

   yet and is moved via VARPOOL_ANALYZE_PENDING_DECLS.  */

struct varpool_node *varpool_nodes_queue;

static GTY(()) struct varpool_node *varpool_last_needed_node;

static GTY(()) struct varpool_node *varpool_first_unanalyzed_node;

/* Lists all assembled variables to be sent to debugger output later on.  */

static GTY(()) struct varpool_node *varpool_assembled_nodes_queue;

/* Return name of the node used in debug output.  */

const char *

varpool_node_name (struct varpool_node *node)

{

  return lang_hooks.decl_printable_name (node->decl, 2);

}

/* Returns a hash code for P.  */

static hashval_t

hash_varpool_node (const void *p)

{

  const struct varpool_node *n = (const struct varpool_node *) p;

  return (hashval_t) DECL_UID (n->decl);

}

/* Returns nonzero if P1 and P2 are equal.  */

static int

eq_varpool_node (const void *p1, const void *p2)

{

  const struct varpool_node *n1 =

    (const struct varpool_node *) p1;

  const struct varpool_node *n2 =

    (const struct varpool_node *) p2;

  return DECL_UID (n1->decl) == DECL_UID (n2->decl);

}

/* Return varpool node assigned to DECL without creating new one.  */

struct varpool_node *

varpool_get_node (const_tree decl)

{

  struct varpool_node key, **slot;

  gcc_assert (TREE_CODE (decl) == VAR_DECL

              && (TREE_STATIC (decl) || DECL_EXTERNAL (decl)));

  if (!varpool_hash)

    return NULL;

  key.decl = CONST_CAST2 (tree, const_tree, decl);

  slot = (struct varpool_node **)

    htab_find_slot (varpool_hash, &key, NO_INSERT);

  if (!slot)

    return NULL;

  return *slot;

}

/* Return varpool node assigned to DECL.  Create new one when needed.  */

struct varpool_node *

varpool_node (tree decl)

{

  struct varpool_node key, *node, **slot;

  gcc_assert (TREE_CODE (decl) == VAR_DECL

              && (TREE_STATIC (decl) || DECL_EXTERNAL (decl) || in_lto_p));

  if (!varpool_hash)

    varpool_hash = htab_create_ggc (10, hash_varpool_node,

                                           eq_varpool_node, NULL);

  key.decl = decl;

  slot = (struct varpool_node **)

    htab_find_slot (varpool_hash, &key, INSERT);

  if (*slot)

    return *slot;

  node = ggc_alloc_cleared_varpool_node ();

  node->decl = decl;

  node->order = cgraph_order++;

  node->next = varpool_nodes;

  ipa_empty_ref_list (&node->ref_list);

  if (varpool_nodes)

    varpool_nodes->prev = node;

  varpool_nodes = node;

  *slot = node;

  return node;

}

/* Remove node from the varpool.  */

void

varpool_remove_node (struct varpool_node *node)

{

  void **slot;

  slot = htab_find_slot (varpool_hash, node, NO_INSERT);

  gcc_assert (*slot == node);

  htab_clear_slot (varpool_hash, slot);

  gcc_assert (!varpool_assembled_nodes_queue);

  if (node->next)

    node->next->prev = node->prev;

  if (node->prev)

    node->prev->next = node->next;

  else

    {

      gcc_assert (varpool_nodes == node);

      varpool_nodes = node->next;

    }

  if (varpool_first_unanalyzed_node == node)

    varpool_first_unanalyzed_node = node->next_needed;

  if (node->next_needed)

    node->next_needed->prev_needed = node->prev_needed;

  else if (node->prev_needed)

    {

      gcc_assert (varpool_last_needed_node);

      varpool_last_needed_node = node->prev_needed;

    }

  if (node->prev_needed)

    node->prev_needed->next_needed = node->next_needed;

  else if (node->next_needed)

    {

      gcc_assert (varpool_nodes_queue == node);

      varpool_nodes_queue = node->next_needed;

    }

  if (node->same_comdat_group)

    {

      struct varpool_node *prev;

      for (prev = node->same_comdat_group;

           prev->same_comdat_group != node;

           prev = prev->same_comdat_group)

        ;

      if (node->same_comdat_group == prev)

        prev->same_comdat_group = NULL;

      else

        prev->same_comdat_group = node->same_comdat_group;

      node->same_comdat_group = NULL;

    }

  ipa_remove_all_references (&node->ref_list);

  ipa_remove_all_refering (&node->ref_list);

  ggc_free (node);

}

/* Dump given cgraph node.  */

void

dump_varpool_node (FILE *f, struct varpool_node *node)

{

  fprintf (f, "%s:", varpool_node_name (node));

  fprintf (f, " availability:%s",

           cgraph_function_flags_ready

           ? cgraph_availability_names[cgraph_variable_initializer_availability (node)]

           : "not-ready");

  if (DECL_ASSEMBLER_NAME_SET_P (node->decl))

    fprintf (f, " (asm: %s)", IDENTIFIER_POINTER (DECL_ASSEMBLER_NAME (node->decl)));

  if (DECL_INITIAL (node->decl))

    fprintf (f, " initialized");

  if (TREE_ASM_WRITTEN (node->decl))

    fprintf (f, " (asm written)");

  if (node->needed)

    fprintf (f, " needed");

  if (node->analyzed)

    fprintf (f, " analyzed");

  if (node->finalized)

    fprintf (f, " finalized");

  if (node->output)

    fprintf (f, " output");

  if (node->externally_visible)

    fprintf (f, " externally_visible");

  if (node->resolution != LDPR_UNKNOWN)

    fprintf (f, " %s",

             ld_plugin_symbol_resolution_names[(int)node->resolution]);

  if (node->in_other_partition)

    fprintf (f, " in_other_partition");

  else if (node->used_from_other_partition)

    fprintf (f, " used_from_other_partition");

  fprintf (f, "\n");

  fprintf (f, "  References: ");

  ipa_dump_references (f, &node->ref_list);

  fprintf (f, "  Refering this var: ");

  ipa_dump_refering (f, &node->ref_list);

}

/* Dump the variable pool.  */

void

dump_varpool (FILE *f)

{

  struct varpool_node *node;

  fprintf (f, "variable pool:\n\n");

  for (node = varpool_nodes; node; node = node->next)

    dump_varpool_node (f, node);

}

/* Dump the variable pool to stderr.  */

DEBUG_FUNCTION void

debug_varpool (void)

{

  dump_varpool (stderr);

}

/* Given an assembler name, lookup node.  */

struct varpool_node *

varpool_node_for_asm (tree asmname)

{

  struct varpool_node *node;

  for (node = varpool_nodes; node ; node = node->next)

    if (decl_assembler_name_equal (node->decl, asmname))

      return node;

  return NULL;

}

/* Helper function for finalization code - add node into lists so it will

   be analyzed and compiled.  */

static void

varpool_enqueue_needed_node (struct varpool_node *node)

{

  if (varpool_last_needed_node)

    {

      varpool_last_needed_node->next_needed = node;

      node->prev_needed = varpool_last_needed_node;

    }

  varpool_last_needed_node = node;

  node->next_needed = NULL;

  if (!varpool_nodes_queue)

    varpool_nodes_queue = node;

  if (!varpool_first_unanalyzed_node)

    varpool_first_unanalyzed_node = node;

  notice_global_symbol (node->decl);

}

/* Notify finalize_compilation_unit that given node is reachable

   or needed.  */

void

varpool_mark_needed_node (struct varpool_node *node)

{

  if (!node->needed && node->finalized

      && !TREE_ASM_WRITTEN (node->decl))

    varpool_enqueue_needed_node (node);

  node->needed = 1;

}

/* Reset the queue of needed nodes.  */

void

varpool_reset_queue (void)

{

  varpool_last_needed_node = NULL;

  varpool_nodes_queue = NULL;

  varpool_first_unanalyzed_node = NULL;

}

/* Determine if variable DECL is needed.  That is, visible to something

   either outside this translation unit, something magic in the system

   configury */

bool

decide_is_variable_needed (struct varpool_node *node, tree decl)

{

  /* If the user told us it is used, then it must be so.  */

  if (node->force_output)

    return true;

  gcc_assert (!DECL_EXTERNAL (decl));

  /* Externally visible variables must be output.  The exception is

     COMDAT variables that must be output only when they are needed.  */

  if (TREE_PUBLIC (decl)

      && !DECL_COMDAT (decl)

      && !DECL_EXTERNAL (decl))

    return true;

  /* When not reordering top level variables, we have to assume that

     we are going to keep everything.  */

  if (!flag_toplevel_reorder)

    return true;

  return false;

}

/* Return if DECL is constant and its initial value is known (so we can do

   constant folding using DECL_INITIAL (decl)).  */

bool

const_value_known_p (tree decl)

{

  if (TREE_CODE (decl) != VAR_DECL

      &&TREE_CODE (decl) != CONST_DECL)

    return false;

  if (TREE_CODE (decl) == CONST_DECL

      || DECL_IN_CONSTANT_POOL (decl))

    return true;

  gcc_assert (TREE_CODE (decl) == VAR_DECL);

  if (!TREE_READONLY (decl) || TREE_THIS_VOLATILE (decl))

    return false;

  /* Gimplifier takes away constructors of local vars  */

  if (!TREE_STATIC (decl) && !DECL_EXTERNAL (decl))

    return DECL_INITIAL (decl) != NULL;

  gcc_assert (TREE_STATIC (decl) || DECL_EXTERNAL (decl));

  /* Variables declared 'const' without an initializer

     have zero as the initializer if they may not be

     overridden at link or run time.  */

  if (!DECL_INITIAL (decl)

      && (DECL_EXTERNAL (decl)

          || decl_replaceable_p (decl)))

    return false;

  /* Variables declared `const' with an initializer are considered

     to not be overwritable with different initializer by default.

     ??? Previously we behaved so for scalar variables but not for array

     accesses.  */

  return true;

}

/* Mark DECL as finalized.  By finalizing the declaration, frontend instruct the

   middle end to output the variable to asm file, if needed or externally

   visible.  */

void

varpool_finalize_decl (tree decl)

{

  struct varpool_node *node = varpool_node (decl);

  gcc_assert (TREE_STATIC (decl));

  /* The first declaration of a variable that comes through this function

     decides whether it is global (in C, has external linkage)

     or local (in C, has internal linkage).  So do nothing more

     if this function has already run.  */

  if (node->finalized)

    {

      if (cgraph_global_info_ready)

        varpool_assemble_pending_decls ();

      return;

    }

  if (node->needed)

    varpool_enqueue_needed_node (node);

  node->finalized = true;

  if (TREE_THIS_VOLATILE (decl) || DECL_PRESERVE_P (decl))

    node->force_output = true;

  if (decide_is_variable_needed (node, decl))

    varpool_mark_needed_node (node);

  if (cgraph_global_info_ready)

    varpool_assemble_pending_decls ();

}

/* Add the variable DECL to the varpool.

   Unlike varpool_finalize_decl function is intended to be used

   by middle end and allows insertion of new variable at arbitrary point

   of compilation.  */

void

varpool_add_new_variable (tree decl)

{

  struct varpool_node *node;

  varpool_finalize_decl (decl);

  node = varpool_node (decl);

  if (varpool_externally_visible_p (node, false))

    node->externally_visible = true;

}

/* Return variable availability.  See cgraph.h for description of individual

   return values.  */

enum availability

cgraph_variable_initializer_availability (struct varpool_node *node)

{

  gcc_assert (cgraph_function_flags_ready);

  if (!node->finalized)

    return AVAIL_NOT_AVAILABLE;

  if (!TREE_PUBLIC (node->decl))

    return AVAIL_AVAILABLE;

  /* If the variable can be overwritten, return OVERWRITABLE.  Takes

     care of at least two notable extensions - the COMDAT variables

     used to share template instantiations in C++.  */

  if (!decl_replaceable_p (node->decl))

    return AVAIL_OVERWRITABLE;

  return AVAIL_AVAILABLE;

}

/* Walk the decls we marked as necessary and see if they reference new

   variables or functions and add them into the worklists.  */

bool

varpool_analyze_pending_decls (void)

{

  bool changed = false;

  timevar_push (TV_VARPOOL);

  while (varpool_first_unanalyzed_node)

    {

      struct varpool_node *node = varpool_first_unanalyzed_node, *next;

      tree decl = node->decl;

      bool analyzed = node->analyzed;

      varpool_first_unanalyzed_node->analyzed = true;

      varpool_first_unanalyzed_node = varpool_first_unanalyzed_node->next_needed;

      /* When reading back varpool at LTO time, we re-construct the queue in order

         to have "needed" list right by inserting all needed nodes into varpool.

         We however don't want to re-analyze already analyzed nodes.  */

      if (!analyzed)

        {

          gcc_assert (!in_lto_p || cgraph_function_flags_ready);

          /* Compute the alignment early so function body expanders are

             already informed about increased alignment.  */

          align_variable (decl, 0);

        }

      if (node->alias && node->alias_of)

        {

          struct varpool_node *tgt = varpool_node (node->alias_of);

          struct varpool_node *n;

          for (n = tgt; n && n->alias;

               n = n->analyzed ? varpool_alias_aliased_node (n) : NULL)

            if (n == node)

              {

                error ("variable %q+D part of alias cycle", node->decl);

                node->alias = false;

                continue;

              }

          if (!VEC_length (ipa_ref_t, node->ref_list.references))

            ipa_record_reference (NULL, node, NULL, tgt, IPA_REF_ALIAS, NULL);

          /* C++ FE sometimes change linkage flags after producing same body aliases.  */

          if (node->extra_name_alias)

            {

              DECL_WEAK (node->decl) = DECL_WEAK (node->alias_of);

              TREE_PUBLIC (node->decl) = TREE_PUBLIC (node->alias_of);

              DECL_EXTERNAL (node->decl) = DECL_EXTERNAL (node->alias_of);

              DECL_VISIBILITY (node->decl) = DECL_VISIBILITY (node->alias_of);

              if (TREE_PUBLIC (node->decl))

                {

                  DECL_COMDAT (node->decl) = DECL_COMDAT (node->alias_of);

                  DECL_COMDAT_GROUP (node->decl) = DECL_COMDAT_GROUP (node->alias_of);

                  if (DECL_ONE_ONLY (node->alias_of) && !node->same_comdat_group)

                    {

                      node->same_comdat_group = tgt;

                      if (!tgt->same_comdat_group)

                        tgt->same_comdat_group = node;

                      else

                        {

                          struct varpool_node *n;

                          for (n = tgt->same_comdat_group;

                               n->same_comdat_group != tgt;

                               n = n->same_comdat_group)

                            ;

                          n->same_comdat_group = node;

                        }

                    }

                }

            }

        }

      else if (DECL_INITIAL (decl))

        record_references_in_initializer (decl, analyzed);

      if (node->same_comdat_group)

        {

          for (next = node->same_comdat_group;

               next != node;

               next = next->same_comdat_group)

            varpool_mark_needed_node (next);

        }

      changed = true;

    }

  timevar_pop (TV_VARPOOL);

  return changed;

}

/* Assemble thunks and aliases asociated to NODE.  */

static void

assemble_aliases (struct varpool_node *node)

{

  int i;

  struct ipa_ref *ref;

  for (i = 0; ipa_ref_list_refering_iterate (&node->ref_list, i, ref); i++)

    if (ref->use == IPA_REF_ALIAS)

      {

        struct varpool_node *alias = ipa_ref_refering_varpool_node (ref);

        assemble_alias (alias->decl,

                        DECL_ASSEMBLER_NAME (alias->alias_of));

        assemble_aliases (alias);

      }

}

/* Output one variable, if necessary.  Return whether we output it.  */

bool

varpool_assemble_decl (struct varpool_node *node)

{

  tree decl = node->decl;

  if (!TREE_ASM_WRITTEN (decl)

      && !node->alias

      && !node->in_other_partition

      && !DECL_EXTERNAL (decl)

      && (TREE_CODE (decl) != VAR_DECL || !DECL_HAS_VALUE_EXPR_P (decl)))

    {

      assemble_variable (decl, 0, 1, 0);

      if (TREE_ASM_WRITTEN (decl))

        {

          node->next_needed = varpool_assembled_nodes_queue;

          node->prev_needed = NULL;

          if (varpool_assembled_nodes_queue)

            varpool_assembled_nodes_queue->prev_needed = node;

          varpool_assembled_nodes_queue = node;

          node->finalized = 1;

          assemble_aliases (node);

          return true;

        }

    }

  return false;

}

/* Optimization of function bodies might've rendered some variables as

   unnecessary so we want to avoid these from being compiled.

   This is done by pruning the queue and keeping only the variables that

   really appear needed (ie they are either externally visible or referenced

   by compiled function). Re-doing the reachability analysis on variables

   brings back the remaining variables referenced by these.  */

void

varpool_remove_unreferenced_decls (void)

{

  struct varpool_node *next, *node = varpool_nodes_queue;

  varpool_reset_queue ();

  if (seen_error ())

    return;

  while (node)

    {

      next = node->next_needed;

      node->needed = 0;

      if (node->analyzed

          && (!varpool_can_remove_if_no_refs (node)

              /* We just expanded all function bodies.  See if any of

                 them needed the variable.  */

              || DECL_RTL_SET_P (node->decl)))

        varpool_mark_needed_node (node);

      node = next;

    }

  /* Make sure we mark alias targets as used targets.  */

  finish_aliases_1 ();

  varpool_analyze_pending_decls ();

}

/* For variables in named sections make sure get_variable_section

   is called before we switch to those sections.  Then section

   conflicts between read-only and read-only requiring relocations

   sections can be resolved.  */

void

varpool_finalize_named_section_flags (struct varpool_node *node)

{

  if (!TREE_ASM_WRITTEN (node->decl)

      && !node->alias

      && !node->in_other_partition

      && !DECL_EXTERNAL (node->decl)

      && TREE_CODE (node->decl) == VAR_DECL

      && !DECL_HAS_VALUE_EXPR_P (node->decl)

      && DECL_SECTION_NAME (node->decl))

    get_variable_section (node->decl, false);

}

/* Output all variables enqueued to be assembled.  */

bool

varpool_assemble_pending_decls (void)

{

  bool changed = false;

  struct varpool_node *node;

  if (seen_error ())

    return false;

  timevar_push (TV_VAROUT);

  /* EH might mark decls as needed during expansion.  This should be safe since

     we don't create references to new function, but it should not be used

     elsewhere.  */

  varpool_analyze_pending_decls ();

  for (node = varpool_nodes_queue; node; node = node->next_needed)

    varpool_finalize_named_section_flags (node);

  while (varpool_nodes_queue)

    {

      struct varpool_node *node = varpool_nodes_queue;

      varpool_nodes_queue = varpool_nodes_queue->next_needed;

      if (varpool_assemble_decl (node))

        changed = true;

      else

        {

          node->prev_needed = NULL;

          node->next_needed = NULL;

        }

    }

  /* varpool_nodes_queue is now empty, clear the pointer to the last element

     in the queue.  */

  varpool_last_needed_node = NULL;

  timevar_pop (TV_VAROUT);

  return changed;

}

/* Remove all elements from the queue so we can re-use it for debug output.  */

void

varpool_empty_needed_queue (void)

{

  /* EH might mark decls as needed during expansion.  This should be safe since

     we don't create references to new function, but it should not be used

     elsewhere.  */

  varpool_analyze_pending_decls ();

  while (varpool_nodes_queue)

    {

      struct varpool_node *node = varpool_nodes_queue;

      varpool_nodes_queue = varpool_nodes_queue->next_needed;

      node->next_needed = NULL;

      node->prev_needed = NULL;

    }

  /* varpool_nodes_queue is now empty, clear the pointer to the last element

     in the queue.  */

  varpool_last_needed_node = NULL;

}