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/* Callgraph based analysis of static variables.

   Copyright (C) 2004, 2005, 2007, 2008, 2009, 2010

   Free Software Foundation, Inc.

   Contributed by Kenneth Zadeck <zadeck@naturalbridge.com>

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 file gathers information about how variables whose scope is

   confined to the compilation unit are used.

   The transitive call site specific clobber effects are computed

   for the variables whose scope is contained within this compilation

   unit.

   First each function and static variable initialization is analyzed

   to determine which local static variables are either read, written,

   or have their address taken.  Any local static that has its address

   taken is removed from consideration.  Once the local read and

   writes are determined, a transitive closure of this information is

   performed over the call graph to determine the worst case set of

   side effects of each call.  In later parts of the compiler, these

   local and global sets are examined to make the call clobbering less

   traumatic, promote some statics to registers, and improve aliasing

   information.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "tm.h"

#include "tree.h"

#include "tree-flow.h"

#include "tree-inline.h"

#include "tree-pass.h"

#include "langhooks.h"

#include "pointer-set.h"

#include "splay-tree.h"

#include "ggc.h"

#include "ipa-utils.h"

#include "ipa-reference.h"

#include "gimple.h"

#include "cgraph.h"

#include "output.h"

#include "flags.h"

#include "timevar.h"

#include "diagnostic.h"

#include "langhooks.h"

#include "data-streamer.h"

#include "lto-streamer.h"

static void remove_node_data (struct cgraph_node *node,

                              void *data ATTRIBUTE_UNUSED);

static void duplicate_node_data (struct cgraph_node *src,

                                 struct cgraph_node *dst,

                                 void *data ATTRIBUTE_UNUSED);

/* The static variables defined within the compilation unit that are

   loaded or stored directly by function that owns this structure.  */

struct ipa_reference_local_vars_info_d

{

  bitmap statics_read;

  bitmap statics_written;

};

/* Statics that are read and written by some set of functions. The

   local ones are based on the loads and stores local to the function.

   The global ones are based on the local info as well as the

   transitive closure of the functions that are called. */

struct ipa_reference_global_vars_info_d

{

  bitmap statics_read;

  bitmap statics_written;

};

/* Information we save about every function after ipa-reference is completed.  */

struct ipa_reference_optimization_summary_d

{

  bitmap statics_not_read;

  bitmap statics_not_written;

};

typedef struct ipa_reference_local_vars_info_d *ipa_reference_local_vars_info_t;

typedef struct ipa_reference_global_vars_info_d *ipa_reference_global_vars_info_t;

typedef struct ipa_reference_optimization_summary_d *ipa_reference_optimization_summary_t;

struct ipa_reference_vars_info_d

{

  struct ipa_reference_local_vars_info_d local;

  struct ipa_reference_global_vars_info_d global;

};

typedef struct ipa_reference_vars_info_d *ipa_reference_vars_info_t;

/* This splay tree contains all of the static variables that are

   being considered by the compilation level alias analysis.  */

static splay_tree reference_vars_to_consider;

/* A bit is set for every module static we are considering.  This is

   ored into the local info when asm code is found that clobbers all

   memory. */

static bitmap all_module_statics;

/* Obstack holding bitmaps of local analysis (live from analysis to

   propagation)  */

static bitmap_obstack local_info_obstack;

/* Obstack holding global analysis live forever.  */

static bitmap_obstack optimization_summary_obstack;

/* Holders of ipa cgraph hooks: */

static struct cgraph_2node_hook_list *node_duplication_hook_holder;

static struct cgraph_node_hook_list *node_removal_hook_holder;

/* Vector where the reference var infos are actually stored. */

DEF_VEC_P (ipa_reference_vars_info_t);

DEF_VEC_ALLOC_P (ipa_reference_vars_info_t, heap);

static VEC (ipa_reference_vars_info_t, heap) *ipa_reference_vars_vector;

DEF_VEC_P (ipa_reference_optimization_summary_t);

DEF_VEC_ALLOC_P (ipa_reference_optimization_summary_t, heap);

static VEC (ipa_reference_optimization_summary_t, heap) *ipa_reference_opt_sum_vector;

/* Return the ipa_reference_vars structure starting from the cgraph NODE.  */

static inline ipa_reference_vars_info_t

get_reference_vars_info (struct cgraph_node *node)

{

  if (!ipa_reference_vars_vector

      || VEC_length (ipa_reference_vars_info_t,

                     ipa_reference_vars_vector) <= (unsigned int) node->uid)

    return NULL;

  return VEC_index (ipa_reference_vars_info_t, ipa_reference_vars_vector,

                    node->uid);

}

/* Return the ipa_reference_vars structure starting from the cgraph NODE.  */

static inline ipa_reference_optimization_summary_t

get_reference_optimization_summary (struct cgraph_node *node)

{

  if (!ipa_reference_opt_sum_vector

      || (VEC_length (ipa_reference_optimization_summary_t,

                      ipa_reference_opt_sum_vector)

          <= (unsigned int) node->uid))

    return NULL;

  return VEC_index (ipa_reference_optimization_summary_t, ipa_reference_opt_sum_vector,

                    node->uid);

}

/* Return the ipa_reference_vars structure starting from the cgraph NODE.  */

static inline void

set_reference_vars_info (struct cgraph_node *node,

                         ipa_reference_vars_info_t info)

{

  if (!ipa_reference_vars_vector

      || VEC_length (ipa_reference_vars_info_t,

                     ipa_reference_vars_vector) <= (unsigned int) node->uid)

    VEC_safe_grow_cleared (ipa_reference_vars_info_t, heap,

                           ipa_reference_vars_vector, node->uid + 1);

  VEC_replace (ipa_reference_vars_info_t, ipa_reference_vars_vector,

               node->uid, info);

}

/* Return the ipa_reference_vars structure starting from the cgraph NODE.  */

static inline void

set_reference_optimization_summary (struct cgraph_node *node,

                                    ipa_reference_optimization_summary_t info)

{

  if (!ipa_reference_opt_sum_vector

      || (VEC_length (ipa_reference_optimization_summary_t,

                      ipa_reference_opt_sum_vector)

          <= (unsigned int) node->uid))

    VEC_safe_grow_cleared (ipa_reference_optimization_summary_t,

                           heap, ipa_reference_opt_sum_vector, node->uid + 1);

  VEC_replace (ipa_reference_optimization_summary_t,

               ipa_reference_opt_sum_vector, node->uid, info);

}

/* Return a bitmap indexed by_DECL_UID uid for the static variables

   that are not read during the execution of the function FN.  Returns

   NULL if no data is available.  */

bitmap

ipa_reference_get_not_read_global (struct cgraph_node *fn)

{

  ipa_reference_optimization_summary_t info;

  info = get_reference_optimization_summary (cgraph_function_node (fn, NULL));

  if (info)

    return info->statics_not_read;

  else if (flags_from_decl_or_type (fn->decl) & ECF_LEAF)

    return all_module_statics;

  else

    return NULL;

}

/* Return a bitmap indexed by DECL_UID uid for the static variables

   that are not written during the execution of the function FN.  Note

   that variables written may or may not be read during the function

   call.  Returns NULL if no data is available.  */

bitmap

ipa_reference_get_not_written_global (struct cgraph_node *fn)

{

  ipa_reference_optimization_summary_t info;

  info = get_reference_optimization_summary (fn);

  if (info)

    return info->statics_not_written;

  else if (flags_from_decl_or_type (fn->decl) & ECF_LEAF)

    return all_module_statics;

  else

    return NULL;

}

/* Add VAR to all_module_statics and the two

   reference_vars_to_consider* sets.  */

static inline void

add_static_var (tree var)

{

  int uid = DECL_UID (var);

  gcc_assert (TREE_CODE (var) == VAR_DECL);

  if (dump_file)

    splay_tree_insert (reference_vars_to_consider,

                       uid, (splay_tree_value)var);

  bitmap_set_bit (all_module_statics, uid);

}

/* Return true if the variable T is the right kind of static variable to

   perform compilation unit scope escape analysis.  */

static inline bool

is_proper_for_analysis (tree t)

{

  /* We handle only variables whose address is never taken.  */

  if (TREE_ADDRESSABLE (t))

    return false;

  /* If the variable has the "used" attribute, treat it as if it had a

     been touched by the devil.  */

  if (DECL_PRESERVE_P (t))

    return false;

  /* Do not want to do anything with volatile except mark any

     function that uses one to be not const or pure.  */

  if (TREE_THIS_VOLATILE (t))

    return false;

  /* We do not need to analyze readonly vars, we already know they do not

     alias.  */

  if (TREE_READONLY (t))

    return false;

  /* We cannot touch decls where the type needs constructing.  */

  if (TYPE_NEEDS_CONSTRUCTING (TREE_TYPE (t)))

    return false;

  /* This is a variable we care about.  Check if we have seen it

     before, and if not add it the set of variables we care about.  */

  if (all_module_statics

      && !bitmap_bit_p (all_module_statics, DECL_UID (t)))

    add_static_var (t);

  return true;

}

/* Lookup the tree node for the static variable that has UID and

   convert the name to a string for debugging.  */

static const char *

get_static_name (int index)

{

  splay_tree_node stn =

    splay_tree_lookup (reference_vars_to_consider, index);

  if (stn)

    return lang_hooks.decl_printable_name ((tree)(stn->value), 2);

  return NULL;

}

/* Or in all of the bits from every callee of X into X_GLOBAL, the caller's cycle,

   bit vector.  There are several cases to check to avoid the sparse

   bitmap oring.  */

static void

propagate_bits (ipa_reference_global_vars_info_t x_global, struct cgraph_node *x)

{

  struct cgraph_edge *e;

  for (e = x->callees; e; e = e->next_callee)

    {

      enum availability avail;

      struct cgraph_node *y = cgraph_function_node (e->callee, &avail);

      if (!y)

        continue;

      /* Only look into nodes we can propagate something.  */

      if (avail > AVAIL_OVERWRITABLE

          || (avail == AVAIL_OVERWRITABLE

              && (flags_from_decl_or_type (y->decl) & ECF_LEAF)))

        {

          int flags = flags_from_decl_or_type (y->decl);

          if (get_reference_vars_info (y))

            {

              ipa_reference_vars_info_t y_info

                = get_reference_vars_info (y);

              ipa_reference_global_vars_info_t y_global = &y_info->global;

              /* Calls in current cycle do not have global computed yet.  */

              if (!y_global->statics_read)

                continue;

              /* If function is declared const, it reads no memory even if it

                 seems so to local analysis.  */

              if (flags & ECF_CONST)

                continue;

              if (x_global->statics_read

                  != all_module_statics)

                {

                  if (y_global->statics_read

                      == all_module_statics)

                    {

                      BITMAP_FREE (x_global->statics_read);

                      x_global->statics_read

                        = all_module_statics;

                    }

                  /* Skip bitmaps that are pointer equal to node's bitmap

                     (no reason to spin within the cycle).  */

                  else if (x_global->statics_read

                           != y_global->statics_read)

                    bitmap_ior_into (x_global->statics_read,

                                     y_global->statics_read);

                }

              /* If function is declared pure, it has no stores even if it

                 seems so to local analysis; If we can not return from here,

                 we can safely ignore the call.  */

              if ((flags & ECF_PURE)

                  || cgraph_edge_cannot_lead_to_return (e))

                continue;

              if (x_global->statics_written

                  != all_module_statics)

                {

                  if (y_global->statics_written

                      == all_module_statics)

                    {

                      BITMAP_FREE (x_global->statics_written);

                      x_global->statics_written

                        = all_module_statics;

                    }

                  /* Skip bitmaps that are pointer equal to node's bitmap

                     (no reason to spin within the cycle).  */

                  else if (x_global->statics_written

                           != y_global->statics_written)

                    bitmap_ior_into (x_global->statics_written,

                                     y_global->statics_written);

                }

            }

          else

            gcc_unreachable ();

        }

    }

}

/* The init routine for analyzing global static variable usage.  See

   comments at top for description.  */

static void

ipa_init (void)

{

  static bool init_p = false;

  if (init_p)

    return;

  init_p = true;

  if (dump_file)

    reference_vars_to_consider = splay_tree_new (splay_tree_compare_ints, 0, 0);

  bitmap_obstack_initialize (&local_info_obstack);

  bitmap_obstack_initialize (&optimization_summary_obstack);

  all_module_statics = BITMAP_ALLOC (&optimization_summary_obstack);

  node_removal_hook_holder =

      cgraph_add_node_removal_hook (&remove_node_data, NULL);

  node_duplication_hook_holder =

      cgraph_add_node_duplication_hook (&duplicate_node_data, NULL);

}

/* Set up the persistent info for FN.  */

static ipa_reference_local_vars_info_t

init_function_info (struct cgraph_node *fn)

{

  ipa_reference_vars_info_t info

    = XCNEW (struct ipa_reference_vars_info_d);

  /* Add the info to the tree's annotation.  */

  set_reference_vars_info (fn, info);

  info->local.statics_read = BITMAP_ALLOC (&local_info_obstack);

  info->local.statics_written = BITMAP_ALLOC (&local_info_obstack);

  return &info->local;

}

/* This is the main routine for finding the reference patterns for

   global variables within a function FN.  */

static void

analyze_function (struct cgraph_node *fn)

{

  ipa_reference_local_vars_info_t local;

  struct ipa_ref *ref;

  int i;

  tree var;

  local = init_function_info (fn);

  for (i = 0; ipa_ref_list_reference_iterate (&fn->ref_list, i, ref); i++)

    {

      if (ref->refered_type != IPA_REF_VARPOOL)

        continue;

      var = ipa_ref_varpool_node (ref)->decl;

      if (ipa_ref_varpool_node (ref)->externally_visible

          || !ipa_ref_varpool_node (ref)->analyzed

          || !is_proper_for_analysis (var))

        continue;

      switch (ref->use)

        {

        case IPA_REF_LOAD:

          bitmap_set_bit (local->statics_read, DECL_UID (var));

          break;

        case IPA_REF_STORE:

          if (ipa_ref_cannot_lead_to_return (ref))

            break;

          bitmap_set_bit (local->statics_written, DECL_UID (var));

          break;

        case IPA_REF_ADDR:

          gcc_unreachable ();

          break;

        }

    }

  if (cgraph_node_cannot_return (fn))

    bitmap_clear (local->statics_written);

}

static bitmap

copy_global_bitmap (bitmap src)

{

  bitmap dst;

  if (!src)

    return NULL;

  if (src == all_module_statics)

    return all_module_statics;

  dst = BITMAP_ALLOC (&optimization_summary_obstack);

  bitmap_copy (dst, src);

  return dst;

}

/* Called when new clone is inserted to callgraph late.  */

static void

duplicate_node_data (struct cgraph_node *src, struct cgraph_node *dst,

                     void *data ATTRIBUTE_UNUSED)

{

  ipa_reference_optimization_summary_t ginfo;

  ipa_reference_optimization_summary_t dst_ginfo;

  ginfo = get_reference_optimization_summary (src);

  if (!ginfo)

    return;

  dst_ginfo = XCNEW (struct ipa_reference_optimization_summary_d);

  set_reference_optimization_summary (dst, dst_ginfo);

  dst_ginfo->statics_not_read = copy_global_bitmap (ginfo->statics_not_read);

  dst_ginfo->statics_not_written = copy_global_bitmap (ginfo->statics_not_written);

}

/* Called when node is removed.  */

static void

remove_node_data (struct cgraph_node *node, void *data ATTRIBUTE_UNUSED)

{

  ipa_reference_optimization_summary_t ginfo;

  ginfo = get_reference_optimization_summary (node);

  if (ginfo)

    {

      if (ginfo->statics_not_read

          && ginfo->statics_not_read != all_module_statics)

        BITMAP_FREE (ginfo->statics_not_read);

      if (ginfo->statics_not_written

          && ginfo->statics_not_written != all_module_statics)

        BITMAP_FREE (ginfo->statics_not_written);

      free (ginfo);

      set_reference_optimization_summary (node, NULL);

    }

}

/* Analyze each function in the cgraph to see which global or statics

   are read or written.  */

static void

generate_summary (void)

{

  struct cgraph_node *node;

  unsigned int index;

  bitmap_iterator bi;

  bitmap bm_temp;

  ipa_init ();

  bm_temp = BITMAP_ALLOC (&local_info_obstack);

  /* Process all of the functions next.  */

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

    if (node->analyzed)

      analyze_function (node);

  if (dump_file)

    EXECUTE_IF_SET_IN_BITMAP (all_module_statics, 0, index, bi)

      {

        fprintf (dump_file, "\nPromotable global:%s",

                 get_static_name (index));

      }

  BITMAP_FREE(bm_temp);

  if (dump_file)

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

      if (cgraph_function_body_availability (node) >= AVAIL_OVERWRITABLE)

        {

          ipa_reference_local_vars_info_t l;

          unsigned int index;

          bitmap_iterator bi;

          l = &get_reference_vars_info (node)->local;

          fprintf (dump_file,

                   "\nFunction name:%s/%i:",

                   cgraph_node_name (node), node->uid);

          fprintf (dump_file, "\n  locals read: ");

          if (l->statics_read)

            EXECUTE_IF_SET_IN_BITMAP (l->statics_read,

                                      0, index, bi)

              {

                fprintf (dump_file, "%s ",

                         get_static_name (index));

              }

          fprintf (dump_file, "\n  locals written: ");

          if (l->statics_written)

            EXECUTE_IF_SET_IN_BITMAP (l->statics_written,

                                      0, index, bi)

              {

                fprintf(dump_file, "%s ",

                        get_static_name (index));

              }

        }

}

/* Set READ_ALL/WRITE_ALL based on decl flags of NODE.  */

static void

read_write_all_from_decl (struct cgraph_node *node, bool * read_all,

                          bool * write_all)

{

  tree decl = node->decl;

  int flags = flags_from_decl_or_type (decl);

  if ((flags & ECF_LEAF)

      && cgraph_function_body_availability (node) <= AVAIL_OVERWRITABLE)

    ;

  else if (flags & ECF_CONST)

    ;

  else if ((flags & ECF_PURE)

           || cgraph_node_cannot_return (node))

    {

      *read_all = true;

      if (dump_file && (dump_flags & TDF_DETAILS))

         fprintf (dump_file, "   %s/%i -> read all\n",

                  cgraph_node_name (node), node->uid);

    }

  else

    {

       /* TODO: To be able to produce sane results, we should also handle

          common builtins, in particular throw.  */

      *read_all = true;

      *write_all = true;

      if (dump_file && (dump_flags & TDF_DETAILS))

         fprintf (dump_file, "   %s/%i -> read all, write all\n",

                  cgraph_node_name (node), node->uid);

    }

}

/* Produce the global information by preforming a transitive closure

   on the local information that was produced by ipa_analyze_function */

static unsigned int

propagate (void)

{

  struct cgraph_node *node;

  struct cgraph_node *w;

  struct cgraph_node **order =

    XCNEWVEC (struct cgraph_node *, cgraph_n_nodes);

  int order_pos;

  int i;

  if (dump_file)

    dump_cgraph (dump_file);

  ipa_discover_readonly_nonaddressable_vars ();

  generate_summary ();

  /* Propagate the local information thru the call graph to produce

     the global information.  All the nodes within a cycle will have

     the same info so we collapse cycles first.  Then we can do the

     propagation in one pass from the leaves to the roots.  */

  order_pos = ipa_reduced_postorder (order, true, true, NULL);

  if (dump_file)

    ipa_print_order (dump_file, "reduced", order, order_pos);

  for (i = 0; i < order_pos; i++ )

    {

      ipa_reference_vars_info_t node_info;

      ipa_reference_global_vars_info_t node_g;

      ipa_reference_local_vars_info_t node_l;

      struct cgraph_edge *e, *ie;

      bool read_all;

      bool write_all;

      struct ipa_dfs_info * w_info;

      node = order[i];

      if (node->alias)

        continue;

      node_info = get_reference_vars_info (node);

      gcc_assert (node_info);

      if (dump_file && (dump_flags & TDF_DETAILS))

        fprintf (dump_file, "Starting cycle with %s/%i\n",

                  cgraph_node_name (node), node->uid);

      node_l = &node_info->local;

      node_g = &node_info->global;

      read_all = false;

      write_all = false;

      /* When function is overwritable, we can not assume anything.  */

      if (cgraph_function_body_availability (node) <= AVAIL_OVERWRITABLE)

        read_write_all_from_decl (node, &read_all, &write_all);

      for (e = node->callees; e; e = e->next_callee)

        {

          enum availability avail;

          struct cgraph_node *callee = cgraph_function_node (e->callee, &avail);

          if (!callee || avail <= AVAIL_OVERWRITABLE)

            read_write_all_from_decl (callee, &read_all, &write_all);

        }

      for (ie = node->indirect_calls; ie; ie = ie->next_callee)

        if (!(ie->indirect_info->ecf_flags & ECF_CONST))

          {

            read_all = true;

            if (dump_file && (dump_flags & TDF_DETAILS))

               fprintf (dump_file, "   indirect call -> read all\n");

            if (!cgraph_edge_cannot_lead_to_return (ie)

                && !(ie->indirect_info->ecf_flags & ECF_PURE))

              {

                if (dump_file && (dump_flags & TDF_DETAILS))

                   fprintf (dump_file, "   indirect call -> write all\n");

                write_all = true;

              }

          }

      /* If any node in a cycle is read_all or write_all

         they all are. */

      w_info = (struct ipa_dfs_info *) node->aux;

      w = w_info->next_cycle;

      while (w && (!read_all || !write_all))

        {

          if (dump_file && (dump_flags & TDF_DETAILS))

            fprintf (dump_file, "  Visiting %s/%i\n",

                      cgraph_node_name (w), w->uid);

          /* When function is overwritable, we can not assume anything.  */

          if (cgraph_function_body_availability (w) <= AVAIL_OVERWRITABLE)

            read_write_all_from_decl (w, &read_all, &write_all);

          for (e = w->callees; e; e = e->next_callee)

            {

              enum availability avail;

              struct cgraph_node *callee = cgraph_function_node (e->callee, &avail);