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/* LTO symbol table.

   Copyright 2009 Free Software Foundation, Inc.

   Contributed by CodeSourcery, 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/>.  */

#include "config.h"

#include "system.h"

#include "coretypes.h"

#include "toplev.h"

#include "tree.h"

#include "gimple.h"

#include "ggc.h"        /* lambda.h needs this */

#include "lambda.h"     /* gcd */

#include "hashtab.h"

#include "plugin-api.h"

#include "lto-streamer.h"

/* Vector to keep track of external variables we've seen so far.  */

VEC(tree,gc) *lto_global_var_decls;

/* Symbol table entry.  */

struct GTY(()) lto_symtab_entry_def

{

  /* The symbol table entry key, an IDENTIFIER.  */

  tree id;

  /* The symbol table entry, a DECL.  */

  tree decl;

  /* The cgraph node if decl is a function decl.  Filled in during the

     merging process.  */

  struct cgraph_node *node;

  /* LTO file-data and symbol resolution for this decl.  */

  struct lto_file_decl_data * GTY((skip (""))) file_data;

  enum ld_plugin_symbol_resolution resolution;

  /* Pointer to the next entry with the same key.  Before decl merging

     this links all symbols from the different TUs.  After decl merging

     this links merged but incompatible decls, thus all prevailing ones

     remaining.  */

  struct lto_symtab_entry_def *next;

};

typedef struct lto_symtab_entry_def *lto_symtab_entry_t;

/* A poor man's symbol table. This hashes identifier to prevailing DECL

   if there is one. */

static GTY ((if_marked ("lto_symtab_entry_marked_p"),

             param_is (struct lto_symtab_entry_def)))

  htab_t lto_symtab_identifiers;

/* Return the hash value of an lto_symtab_entry_t object pointed to by P.  */

static hashval_t

lto_symtab_entry_hash (const void *p)

{

  const struct lto_symtab_entry_def *base =

    (const struct lto_symtab_entry_def *) p;

  return htab_hash_string (IDENTIFIER_POINTER (base->id));

}

/* Return non-zero if P1 and P2 points to lto_symtab_entry_def structs

   corresponding to the same symbol.  */

static int

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

{

  const struct lto_symtab_entry_def *base1 =

     (const struct lto_symtab_entry_def *) p1;

  const struct lto_symtab_entry_def *base2 =

     (const struct lto_symtab_entry_def *) p2;

  return (base1->id == base2->id);

}

/* Returns non-zero if P points to an lto_symtab_entry_def struct that needs

   to be marked for GC.  */

static int

lto_symtab_entry_marked_p (const void *p)

{

  const struct lto_symtab_entry_def *base =

     (const struct lto_symtab_entry_def *) p;

  /* Keep this only if the common IDENTIFIER_NODE of the symtab chain

     is marked which it will be if at least one of the DECLs in the

     chain is marked.  */

  return ggc_marked_p (base->id);

}

/* Lazily initialize resolution hash tables.  */

static void

lto_symtab_maybe_init_hash_table (void)

{

  if (lto_symtab_identifiers)

    return;

  lto_symtab_identifiers =

    htab_create_ggc (1021, lto_symtab_entry_hash,

                     lto_symtab_entry_eq, NULL);

}

/* Registers DECL with the LTO symbol table as having resolution RESOLUTION

   and read from FILE_DATA. */

void

lto_symtab_register_decl (tree decl,

                          ld_plugin_symbol_resolution_t resolution,

                          struct lto_file_decl_data *file_data)

{

  lto_symtab_entry_t new_entry;

  void **slot;

  /* Check that declarations reaching this function do not have

     properties inconsistent with having external linkage.  If any of

     these asertions fail, then the object file reader has failed to

     detect these cases and issue appropriate error messages.  */

  gcc_assert (decl

              && TREE_PUBLIC (decl)

              && (TREE_CODE (decl) == VAR_DECL

                  || TREE_CODE (decl) == FUNCTION_DECL)

              && DECL_ASSEMBLER_NAME_SET_P (decl));

  if (TREE_CODE (decl) == VAR_DECL

      && DECL_INITIAL (decl))

    gcc_assert (!DECL_EXTERNAL (decl)

                || (TREE_STATIC (decl) && TREE_READONLY (decl)));

  if (TREE_CODE (decl) == FUNCTION_DECL)

    gcc_assert (!DECL_ABSTRACT (decl));

  new_entry = GGC_CNEW (struct lto_symtab_entry_def);

  new_entry->id = DECL_ASSEMBLER_NAME (decl);

  new_entry->decl = decl;

  new_entry->resolution = resolution;

  new_entry->file_data = file_data;

  lto_symtab_maybe_init_hash_table ();

  slot = htab_find_slot (lto_symtab_identifiers, new_entry, INSERT);

  new_entry->next = (lto_symtab_entry_t) *slot;

  *slot = new_entry;

}

/* Get the lto_symtab_entry_def struct associated with ID

   if there is one.  */

static lto_symtab_entry_t

lto_symtab_get (tree id)

{

  struct lto_symtab_entry_def temp;

  void **slot;

  lto_symtab_maybe_init_hash_table ();

  temp.id = id;

  slot = htab_find_slot (lto_symtab_identifiers, &temp, NO_INSERT);

  return slot ? (lto_symtab_entry_t) *slot : NULL;

}

/* Get the linker resolution for DECL.  */

enum ld_plugin_symbol_resolution

lto_symtab_get_resolution (tree decl)

{

  lto_symtab_entry_t e;

  gcc_assert (DECL_ASSEMBLER_NAME_SET_P (decl));

  e = lto_symtab_get (DECL_ASSEMBLER_NAME (decl));

  while (e && e->decl != decl)

    e = e->next;

  if (!e)

    return LDPR_UNKNOWN;

  return e->resolution;

}

/* Replace the cgraph node NODE with PREVAILING_NODE in the cgraph, merging

   all edges and removing the old node.  */

static void

lto_cgraph_replace_node (struct cgraph_node *node,

                         struct cgraph_node *prevailing_node)

{

  struct cgraph_edge *e, *next;

  /* Merge node flags.  */

  if (node->needed)

    cgraph_mark_needed_node (prevailing_node);

  if (node->reachable)

    cgraph_mark_reachable_node (prevailing_node);

  if (node->address_taken)

    {

      gcc_assert (!prevailing_node->global.inlined_to);

      cgraph_mark_address_taken_node (prevailing_node);

    }

  /* Redirect all incoming edges.  */

  for (e = node->callers; e; e = next)

    {

      next = e->next_caller;

      cgraph_redirect_edge_callee (e, prevailing_node);

    }

  /* There are not supposed to be any outgoing edges from a node we

     replace.  Still this can happen for multiple instances of weak

     functions.  */

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

    {

      next = e->next_callee;

      cgraph_remove_edge (e);

    }

  if (node->same_body)

    {

      struct cgraph_node *alias;

      for (alias = node->same_body; alias; alias = alias->next)

        if (DECL_ASSEMBLER_NAME_SET_P (alias->decl))

          {

            lto_symtab_entry_t se

              = lto_symtab_get (DECL_ASSEMBLER_NAME (alias->decl));

            for (; se; se = se->next)

              if (se->node == node)

                {

                  se->node = NULL;

                  break;

                }

          }

    }

  /* Finally remove the replaced node.  */

  cgraph_remove_node (node);

}

/* Merge two variable or function symbol table entries PREVAILING and ENTRY.

   Return false if the symbols are not fully compatible and a diagnostic

   should be emitted.  */

static bool

lto_symtab_merge (lto_symtab_entry_t prevailing, lto_symtab_entry_t entry)

{

  tree prevailing_decl = prevailing->decl;

  tree decl = entry->decl;

  tree prevailing_type, type;

  /* Merge decl state in both directions, we may still end up using

     the new decl.  */

  TREE_ADDRESSABLE (prevailing_decl) |= TREE_ADDRESSABLE (decl);

  TREE_ADDRESSABLE (decl) |= TREE_ADDRESSABLE (prevailing_decl);

  /* The linker may ask us to combine two incompatible symbols.

     Detect this case and notify the caller of required diagnostics.  */

  if (TREE_CODE (decl) == FUNCTION_DECL)

    {

      if (TREE_TYPE (prevailing_decl) != TREE_TYPE (decl))

        /* If we don't have a merged type yet...sigh.  The linker

           wouldn't complain if the types were mismatched, so we

           probably shouldn't either.  Just use the type from

           whichever decl appears to be associated with the

           definition.  If for some odd reason neither decl is, the

           older one wins.  */

        (void) 0;

      return true;

    }

  /* Now we exclusively deal with VAR_DECLs.  */

  /* Sharing a global symbol is a strong hint that two types are

     compatible.  We could use this information to complete

     incomplete pointed-to types more aggressively here, ignoring

     mismatches in both field and tag names.  It's difficult though

     to guarantee that this does not have side-effects on merging

     more compatible types from other translation units though.  */

  /* We can tolerate differences in type qualification, the

     qualification of the prevailing definition will prevail.

     ???  In principle we might want to only warn for structurally

     incompatible types here, but unless we have protective measures

     for TBAA in place that would hide useful information.  */

  prevailing_type = TYPE_MAIN_VARIANT (TREE_TYPE (prevailing_decl));

  type = TYPE_MAIN_VARIANT (TREE_TYPE (decl));

  /* We have to register and fetch canonical types here as the global

     fixup process didn't yet run.  */

  prevailing_type = gimple_register_type (prevailing_type);

  type = gimple_register_type (type);

  if (prevailing_type != type)

    {

      if (COMPLETE_TYPE_P (type))

        return false;

      /* If type is incomplete then avoid warnings in the cases

         that TBAA handles just fine.  */

      if (TREE_CODE (prevailing_type) != TREE_CODE (type))

        return false;

      if (TREE_CODE (prevailing_type) == ARRAY_TYPE)

        {

          tree tem1 = TREE_TYPE (prevailing_type);

          tree tem2 = TREE_TYPE (type);

          while (TREE_CODE (tem1) == ARRAY_TYPE

                 && TREE_CODE (tem2) == ARRAY_TYPE)

            {

              tem1 = TREE_TYPE (tem1);

              tem2 = TREE_TYPE (tem2);

            }

          if (TREE_CODE (tem1) != TREE_CODE (tem2))

            return false;

          if (gimple_register_type (tem1) != gimple_register_type (tem2))

            return false;

        }

      /* Fallthru.  Compatible enough.  */

    }

  /* ???  We might want to emit a warning here if type qualification

     differences were spotted.  Do not do this unconditionally though.  */

  /* There is no point in comparing too many details of the decls here.

     The type compatibility checks or the completing of types has properly

     dealt with most issues.  */

  /* The following should all not invoke fatal errors as in non-LTO

     mode the linker wouldn't complain either.  Just emit warnings.  */

  /* Report a warning if user-specified alignments do not match.  */

  if ((DECL_USER_ALIGN (prevailing_decl) && DECL_USER_ALIGN (decl))

      && DECL_ALIGN (prevailing_decl) < DECL_ALIGN (decl))

    return false;

  return true;

}

/* Return true if the symtab entry E can be replaced by another symtab

   entry.  */

static bool

lto_symtab_resolve_replaceable_p (lto_symtab_entry_t e)

{

  if (DECL_EXTERNAL (e->decl)

      || DECL_COMDAT (e->decl)

      || DECL_WEAK (e->decl))

    return true;

  if (TREE_CODE (e->decl) == VAR_DECL)

    return (DECL_COMMON (e->decl)

            || (!flag_no_common && !DECL_INITIAL (e->decl)));

  return false;

}

/* Return true if the symtab entry E can be the prevailing one.  */

static bool

lto_symtab_resolve_can_prevail_p (lto_symtab_entry_t e)

{

  /* The C++ frontend ends up neither setting TREE_STATIC nor

     DECL_EXTERNAL on virtual methods but only TREE_PUBLIC.

     So do not reject !TREE_STATIC here but only DECL_EXTERNAL.  */

  if (DECL_EXTERNAL (e->decl))

    return false;

  /* For functions we need a non-discarded body.  */

  if (TREE_CODE (e->decl) == FUNCTION_DECL)

    return (e->node && e->node->analyzed);

  /* A variable should have a size.  */

  else if (TREE_CODE (e->decl) == VAR_DECL)

    return (DECL_SIZE (e->decl) != NULL_TREE

            /* The C++ frontend retains TREE_STATIC on the declaration

               of foo_ in struct Foo { static Foo *foo_; }; but it is

               not a definition.  g++.dg/lto/20090315_0.C.  */

            && !DECL_EXTERNAL (e->decl));

  gcc_unreachable ();

}

/* Resolve the symbol with the candidates in the chain *SLOT and store

   their resolutions.  */

static void

lto_symtab_resolve_symbols (void **slot)

{

  lto_symtab_entry_t e;

  lto_symtab_entry_t prevailing = NULL;

  /* Always set e->node so that edges are updated to reflect decl merging. */

  for (e = (lto_symtab_entry_t) *slot; e; e = e->next)

    {

      if (TREE_CODE (e->decl) == FUNCTION_DECL)

        e->node = cgraph_get_node (e->decl);

      else if (TREE_CODE (e->decl) == VAR_DECL)

        {

          /* The LTO plugin for gold doesn't handle common symbols

             properly.  Let us choose manually.  */

          if (DECL_COMMON (e->decl))

            e->resolution = LDPR_UNKNOWN;

        }

    }

  e = (lto_symtab_entry_t) *slot;

  /* If the chain is already resolved there is nothing else to do.  */

  if (e->resolution != LDPR_UNKNOWN)

    return;

  /* Find the single non-replaceable prevailing symbol and

     diagnose ODR violations.  */

  for (e = (lto_symtab_entry_t) *slot; e; e = e->next)

    {

      if (!lto_symtab_resolve_can_prevail_p (e))

        {

          e->resolution = LDPR_RESOLVED_IR;

          continue;

        }

      /* Set a default resolution - the final prevailing one will get

         adjusted later.  */

      e->resolution = LDPR_PREEMPTED_IR;

      if (!lto_symtab_resolve_replaceable_p (e))

        {

          if (prevailing)

            {

              error_at (DECL_SOURCE_LOCATION (e->decl),

                        "%qD has already been defined", e->decl);

              inform (DECL_SOURCE_LOCATION (prevailing->decl),

                      "previously defined here");

            }

          prevailing = e;

        }

    }

  if (prevailing)

    goto found;

  /* Do a second round choosing one from the replaceable prevailing decls.  */

  for (e = (lto_symtab_entry_t) *slot; e; e = e->next)

    {

      if (e->resolution != LDPR_PREEMPTED_IR)

        continue;

      /* Choose the first function that can prevail as prevailing.  */

      if (TREE_CODE (e->decl) == FUNCTION_DECL)

        {

          prevailing = e;

          break;

        }

      /* From variables that can prevail choose the largest one.  */

      if (!prevailing

          || tree_int_cst_lt (DECL_SIZE (prevailing->decl),

                              DECL_SIZE (e->decl)))

        prevailing = e;

    }

  if (!prevailing)

    return;

found:

  if (TREE_CODE (prevailing->decl) == VAR_DECL

      && TREE_READONLY (prevailing->decl))

    prevailing->resolution = LDPR_PREVAILING_DEF_IRONLY;

  else

    prevailing->resolution = LDPR_PREVAILING_DEF;

}

/* Merge all decls in the symbol table chain to the prevailing decl and

   issue diagnostics about type mismatches.  */

static void

lto_symtab_merge_decls_2 (void **slot)

{

  lto_symtab_entry_t prevailing, e;

  VEC(tree, heap) *mismatches = NULL;

  unsigned i;

  tree decl;

  bool diagnosed_p = false;

  /* Nothing to do for a single entry.  */

  prevailing = (lto_symtab_entry_t) *slot;

  if (!prevailing->next)

    return;

  /* Try to merge each entry with the prevailing one.  */

  for (e = prevailing->next; e; e = e->next)

    {

      if (!lto_symtab_merge (prevailing, e))

        VEC_safe_push (tree, heap, mismatches, e->decl);

    }

  if (VEC_empty (tree, mismatches))

    return;

  /* Diagnose all mismatched re-declarations.  */

  for (i = 0; VEC_iterate (tree, mismatches, i, decl); ++i)

    {

      if (TREE_TYPE (prevailing->decl) != TREE_TYPE (decl))

        diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,

                                   "type of %qD does not match original "

                                   "declaration", decl);

      else if ((DECL_USER_ALIGN (prevailing->decl) && DECL_USER_ALIGN (decl))

               && DECL_ALIGN (prevailing->decl) < DECL_ALIGN (decl))

        {

          diagnosed_p |= warning_at (DECL_SOURCE_LOCATION (decl), 0,

                                     "alignment of %qD is bigger than "

                                     "original declaration", decl);

        }

    }

  if (diagnosed_p)

    inform (DECL_SOURCE_LOCATION (prevailing->decl),

            "previously declared here");

  VEC_free (tree, heap, mismatches);

}

/* Helper to process the decl chain for the symbol table entry *SLOT.  */

static int

lto_symtab_merge_decls_1 (void **slot, void *data ATTRIBUTE_UNUSED)

{

  lto_symtab_entry_t e, prevailing;

  bool diagnosed_p = false;

  /* Compute the symbol resolutions.  This is a no-op when using the

     linker plugin.  */

  lto_symtab_resolve_symbols (slot);

  /* Find the prevailing decl.  */

  for (prevailing = (lto_symtab_entry_t) *slot;

       prevailing

       && prevailing->resolution != LDPR_PREVAILING_DEF_IRONLY

       && prevailing->resolution != LDPR_PREVAILING_DEF;

       prevailing = prevailing->next)

    ;

  /* Assert it's the only one.  */

  if (prevailing)

    for (e = prevailing->next; e; e = e->next)

      gcc_assert (e->resolution != LDPR_PREVAILING_DEF_IRONLY

                  && e->resolution != LDPR_PREVAILING_DEF);

  /* If there's not a prevailing symbol yet it's an external reference.

     Happens a lot during ltrans.  Choose the first symbol with a

     cgraph or a varpool node.  */

  if (!prevailing)

    {

      prevailing = (lto_symtab_entry_t) *slot;

      /* For functions choose one with a cgraph node.  */

      if (TREE_CODE (prevailing->decl) == FUNCTION_DECL)

        while (!prevailing->node

               && prevailing->next)

          prevailing = prevailing->next;

      /* We do not stream varpool nodes, so the first decl has to

         be good enough for now.

         ???  For QOI choose a variable with readonly initializer

         if there is one.  This matches C++

         struct Foo { static const int i = 1; }; without a real

         definition.  */

      if (TREE_CODE (prevailing->decl) == VAR_DECL)

        while (!(TREE_READONLY (prevailing->decl)

                 && DECL_INITIAL (prevailing->decl))

               && prevailing->next)

          prevailing = prevailing->next;

    }

  /* Move it first in the list.  */

  if ((lto_symtab_entry_t) *slot != prevailing)

    {

      for (e = (lto_symtab_entry_t) *slot; e->next != prevailing; e = e->next)

        ;

      e->next = prevailing->next;

      prevailing->next = (lto_symtab_entry_t) *slot;

      *slot = (void *) prevailing;

    }

  /* Record the prevailing variable.  */

  if (TREE_CODE (prevailing->decl) == VAR_DECL)

    VEC_safe_push (tree, gc, lto_global_var_decls, prevailing->decl);

  /* Diagnose mismatched objects.  */

  for (e = prevailing->next; e; e = e->next)

    {

      if (TREE_CODE (prevailing->decl) == TREE_CODE (e->decl))

        continue;

      switch (TREE_CODE (prevailing->decl))

        {

        case VAR_DECL:

          gcc_assert (TREE_CODE (e->decl) == FUNCTION_DECL);

          error_at (DECL_SOURCE_LOCATION (e->decl),

                    "variable %qD redeclared as function", prevailing->decl);

          break;

        case FUNCTION_DECL:

          gcc_assert (TREE_CODE (e->decl) == VAR_DECL);

          error_at (DECL_SOURCE_LOCATION (e->decl),

                    "function %qD redeclared as variable", prevailing->decl);

          break;

        default:

          gcc_unreachable ();

        }

      diagnosed_p = true;

    }

  if (diagnosed_p)

      inform (DECL_SOURCE_LOCATION (prevailing->decl),

              "previously declared here");

  /* Register and adjust types of the entries.  */

  for (e = (lto_symtab_entry_t) *slot; e; e = e->next)

    TREE_TYPE (e->decl) = gimple_register_type (TREE_TYPE (e->decl));

  /* Merge the chain to the single prevailing decl and diagnose

     mismatches.  */

  lto_symtab_merge_decls_2 (slot);

  /* Drop all but the prevailing decl from the symtab.  */

  if (TREE_CODE (prevailing->decl) != FUNCTION_DECL)

    prevailing->next = NULL;

  return 1;

}

/* Resolve and merge all symbol table chains to a prevailing decl.  */

void

lto_symtab_merge_decls (void)

{

  lto_symtab_maybe_init_hash_table ();

  htab_traverse (lto_symtab_identifiers, lto_symtab_merge_decls_1, NULL);

}

/* Helper to process the decl chain for the symbol table entry *SLOT.  */

static int

lto_symtab_merge_cgraph_nodes_1 (void **slot, void *data ATTRIBUTE_UNUSED)

{

  lto_symtab_entry_t e, prevailing = (lto_symtab_entry_t) *slot;

  if (!prevailing->next)

    return 1;

  gcc_assert (TREE_CODE (prevailing->decl) == FUNCTION_DECL);

  /* Replace the cgraph node of each entry with the prevailing one.  */

  for (e = prevailing->next; e; e = e->next)

    {

      if (e->node != NULL)

        {

          if (e->node->decl != e->decl && e->node->same_body)

            {

              struct cgraph_node *alias;

              for (alias = e->node->same_body; alias; alias = alias->next)

                if (alias->decl == e->decl)

                  break;

              if (alias)

                {

                  cgraph_remove_same_body_alias (alias);

                  continue;

                }

            }

          lto_cgraph_replace_node (e->node, prevailing->node);

        }

    }

  /* Drop all but the prevailing decl from the symtab.  */

  prevailing->next = NULL;

  return 1;

}

/* Merge cgraph nodes according to the symbol merging done by

   lto_symtab_merge_decls.  */

void

lto_symtab_merge_cgraph_nodes (void)

{

  lto_symtab_maybe_init_hash_table ();

  htab_traverse (lto_symtab_identifiers, lto_symtab_merge_cgraph_nodes_1, NULL);

}

/* Given the decl DECL, return the prevailing decl with the same name. */

tree

lto_symtab_prevailing_decl (tree decl)

{

  lto_symtab_entry_t ret;

  /* Builtins and local symbols are their own prevailing decl.  */