path: root/gcc/varpool.c

/* Callgraph handling code.
   Copyright (C) 2003, 2004, 2005, 2006, 2007 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 2, 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 COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "tree.h"
#include "cgraph.h"
#include "langhooks.h"
#include "diagnostic.h"
#include "hashtab.h"
#include "ggc.h"
#include "timevar.h"
#include "debug.h" 
#include "target.h"
#include "output.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_NNEDED_NODE points to the end of queue, so it can be maintained in forward
   order.  QTY is needed to make it friendly to PCH.
 
   During unit-at-a-time 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.  */
static 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.  Create new one when needed.  */
struct varpool_node *
varpool_node (tree decl)
{
  struct varpool_node key, *node, **slot;

  gcc_assert (DECL_P (decl) && TREE_CODE (decl) != FUNCTION_DECL);

  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_CNEW (struct varpool_node);
  node->decl = decl;
  node->order = cgraph_order++;
  node->next = varpool_nodes;
  varpool_nodes = node;
  *slot = node;
  return 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_INITIAL (node->decl))
    fprintf (f, " initialized");
  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");
  fprintf (f, "\n");
}

/* 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_needed)
    dump_varpool_node (f, node);
}

/* 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;
  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.  */
static 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, or (if not doing unit-at-a-time) to something we haven't
   seen yet.  */
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->externally_visible || node->force_output)
    return true;
  if (!flag_unit_at_a_time
      && lookup_attribute ("used", DECL_ATTRIBUTES (decl)))
    return true;

  /* ??? If the assembler name is set by hand, it is possible to assemble
     the name later after finalizing the function and the fact is noticed
     in assemble_name then.  This is arguably a bug.  */
  if (DECL_ASSEMBLER_NAME_SET_P (decl)
      && TREE_SYMBOL_REFERENCED (DECL_ASSEMBLER_NAME (decl)))
    return true;

  /* If we decided it was needed before, but at the time we didn't have
     the definition available, then it's still needed.  */
  if (node->needed)
    return true;

  /* Externally visible variables must be output.  The exception is
     COMDAT variables that must be output only when they are needed.  */
  if (TREE_PUBLIC (decl) && !flag_whole_program && !DECL_COMDAT (decl)
      && !DECL_EXTERNAL (decl))
    return true;

  /* When emulating tls, we actually see references to the control
     variable, rather than the user-level variable.  */
  if (!targetm.have_tls
      && TREE_CODE (decl) == VAR_DECL
      && DECL_THREAD_LOCAL_P (decl))
    {
      tree control = emutls_decl (decl);
      if (decide_is_variable_needed (varpool_node (control), control))
	return true;
    }

  /* When not reordering top level variables, we have to assume that
     we are going to keep everything.  */
  if (flag_unit_at_a_time && flag_toplevel_reorder)
    return false;

  /* We want to emit COMDAT variables only when absolutely necessary.  */
  if (DECL_COMDAT (decl))
    return false;
  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);

  /* 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 || (!flag_unit_at_a_time && !flag_openmp))
	varpool_assemble_pending_decls ();
      return;
    }
  if (node->needed)
    varpool_enqueue_needed_node (node);
  node->finalized = true;

  if (decide_is_variable_needed (node, decl))
    varpool_mark_needed_node (node);
  /* Since we reclaim unreachable nodes at the end of every language
     level unit, we need to be conservative about possible entry points
     there.  */
  else if (TREE_PUBLIC (decl) && !DECL_COMDAT (decl) && !DECL_EXTERNAL (decl))
    varpool_mark_needed_node (node);
  if (cgraph_global_info_ready || (!flag_unit_at_a_time && !flag_openmp))
    varpool_assemble_pending_decls ();
}

/* 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 (!(*targetm.binds_local_p) (node->decl) && !DECL_COMDAT (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_CGRAPH);

  while (varpool_first_unanalyzed_node)
    {
      tree decl = varpool_first_unanalyzed_node->decl;

      varpool_first_unanalyzed_node->analyzed = true;

      varpool_first_unanalyzed_node = varpool_first_unanalyzed_node->next_needed;

      /* Compute the alignment early so function body expanders are
	 already informed about increased alignment.  */
      align_variable (decl, 0);

      if (DECL_INITIAL (decl))
	record_references_in_initializer (decl);
      changed = true;
    }
  timevar_pop (TV_CGRAPH);
  return changed;
}

/* 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
      && !DECL_EXTERNAL (decl)
      && (TREE_CODE (decl) != VAR_DECL || !DECL_HAS_VALUE_EXPR_P (decl)))
    {
      assemble_variable (decl, 0, 1, 0);
      return TREE_ASM_WRITTEN (decl);
    }

  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 (errorcount || sorrycount)
    return;

  while (node)
    {
      tree decl = node->decl;
      next = node->next_needed;
      node->needed = 0;

      if (node->finalized
	  && (decide_is_variable_needed (node, decl)
	      /* ??? Cgraph does not yet rule the world with an iron hand,
		 and does not control the emission of debug information.
		 After a variable has its DECL_RTL set, we must assume that
		 it may be referenced by the debug information, and we can
		 no longer elide it.  */
	      || DECL_RTL_SET_P (decl)))
	varpool_mark_needed_node (node);

      node = next;
    }
  /* Make sure we mark alias targets as used targets.  */
  finish_aliases_1 ();
  varpool_analyze_pending_decls ();
}

/* Output all variables enqueued to be assembled.  */
bool
varpool_assemble_pending_decls (void)
{
  bool changed = false;

  if (errorcount || sorrycount)
    return false;

  /* 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;
      if (varpool_assemble_decl (node))
	{
	  changed = true;
	  node->next_needed = varpool_assembled_nodes_queue;
	  varpool_assembled_nodes_queue = node;
	  node->finalized = 1;
	}
      else
        node->next_needed = NULL;
    }
  return changed;
}

/* Output all variables enqueued to be assembled.  */
void
varpool_output_debug_info (void)
{
  timevar_push (TV_SYMOUT);
  if (errorcount == 0 && sorrycount == 0)
    while (varpool_assembled_nodes_queue)
      {
	struct varpool_node *node = varpool_assembled_nodes_queue;

	/* Local static variables are never seen by check_global_declarations
	   so we need to output debug info by hand.  */
	if (DECL_CONTEXT (node->decl)
	    && (TREE_CODE (DECL_CONTEXT (node->decl)) == BLOCK
		|| TREE_CODE (DECL_CONTEXT (node->decl)) == FUNCTION_DECL)
	    && errorcount == 0 && sorrycount == 0)
	     (*debug_hooks->global_decl) (node->decl);
	varpool_assembled_nodes_queue = node->next_needed;
	node->next_needed = 0;
      }
  timevar_pop (TV_SYMOUT);
}

#include "gt-varpool.h"