Fix varpool confussion about what to remove and what not

[Jan Hubicka <hubicka at ucw dot cz>]

Hi,
this patch makes varpool less confused about removal of unreferenced variables.
This is done twice. First as part of cgraph_remove_unreachable_nodes that currently
contains a bug that makes it to remove unused vars even with -fno-toplevel-reorder
and at varpool_remove_unreferenced_decls (after function bodies has been assembled)
that gets -fno-toplevel-reorder but uses decide_is_variable_needed that is intended
for varpool_finalize_node use only and is completely confused about whole program
and LTO and consequently makes wore decisions with -fuse-linker-plugin than with
-fwhole-program.

I noticed another bug; we used to mark all variables referenced after late
GIMPLE optimization but we don't do this anymore.  This makes the dubious
DECL_RTL_SET_P neccesary.  This check was introduced to work around dwarf2out
referencing unreferenced vars. This problem was solved at dwarf2out side some
time ago. I will look into this problem incrementally.

Boostrapped/regtested x86_64-linux, will commit it later today.

	* cgraph.h (varpool_can_remove_if_no_refs): Move here from ...;
	when !flag_toplevel_reorder do not remove unless variable is
	COMDAT or ARTIFICIAL.
	* ipa.c (varpool_can_remove_if_no_refs): ... here.
	(cgraph_remove_unreachable_nodes): Only analyzed nodes needs to stay.
	* cgraphunit.c (cgraph_analyze_functions): Dump varpool, too.
	* varpool.c (decide_is_variable_needed): Do not handle visibility issues.
	(varpool_finalize_decl): Likewise.
	(varpool_remove_unreferenced_decls): Use varpool_mark_needed_node; update
	outdated comment on DECL_RTL_SET_P check.
Index: cgraph.h
===================================================================
--- cgraph.h	(revision 166777)
+++ cgraph.h	(working copy)
@@ -928,6 +928,18 @@ cgraph_can_remove_if_no_direct_calls_p (
   return !node->address_taken && cgraph_can_remove_if_no_direct_calls_and_refs_p (node);
 }
 
+/* Return true when function NODE can be removed from callgraph
+   if all direct calls are eliminated.  */
+
+static inline bool
+varpool_can_remove_if_no_refs (struct varpool_node *node)
+{
+  return (!node->force_output && !node->used_from_other_partition
+	  && (flag_toplevel_reorder || DECL_COMDAT (node->decl)
+	      || DECL_ARTIFICIAL (node->decl))
+  	  && (DECL_COMDAT (node->decl) || !node->externally_visible));
+}
+
 /* Return true when all references to VNODE must be visible in ipa_ref_list.
    i.e. if the variable is not externally visible or not used in some magic
    way (asm statement or such).
Index: cgraphunit.c
===================================================================
--- cgraphunit.c	(revision 166777)
+++ cgraphunit.c	(working copy)
@@ -943,6 +943,7 @@ cgraph_analyze_functions (void)
 	  fprintf (cgraph_dump_file, " %s", cgraph_node_name (node));
       fprintf (cgraph_dump_file, "\n\nInitial ");
       dump_cgraph (cgraph_dump_file);
+      dump_varpool (cgraph_dump_file);
     }
 
   if (cgraph_dump_file)
@@ -972,6 +973,7 @@ cgraph_analyze_functions (void)
     {
       fprintf (cgraph_dump_file, "\n\nReclaimed ");
       dump_cgraph (cgraph_dump_file);
+      dump_varpool (cgraph_dump_file);
     }
   bitmap_obstack_release (NULL);
   first_analyzed = cgraph_nodes;
@@ -1816,6 +1818,7 @@ cgraph_optimize (void)
     {
       fprintf (cgraph_dump_file, "\nFinal ");
       dump_cgraph (cgraph_dump_file);
+      dump_varpool (cgraph_dump_file);
     }
 #ifdef ENABLE_CHECKING
   verify_cgraph ();
Index: ipa.c
===================================================================
--- ipa.c	(revision 166777)
+++ ipa.c	(working copy)
@@ -188,16 +188,6 @@ process_references (struct ipa_ref_list 
     }
 }
 
-/* Return true when function NODE can be removed from callgraph
-   if all direct calls are eliminated.  */
-
-static inline bool
-varpool_can_remove_if_no_refs (struct varpool_node *node)
-{
-  return (!node->force_output && !node->used_from_other_partition
-  	  && (DECL_COMDAT (node->decl) || !node->externally_visible));
-}
-
 /* Return true when function can be marked local.  */
 
 static bool
@@ -269,7 +259,8 @@ cgraph_remove_unreachable_nodes (bool be
     {
       vnode->next_needed = NULL;
       vnode->prev_needed = NULL;
-      if (!varpool_can_remove_if_no_refs (vnode))
+      if (vnode->analyzed
+	  && !varpool_can_remove_if_no_refs (vnode))
 	{
 	  vnode->needed = false;
 	  varpool_mark_needed_node (vnode);
Index: varpool.c
===================================================================
--- varpool.c	(revision 166777)
+++ varpool.c	(working copy)
@@ -331,31 +331,24 @@ varpool_reset_queue (void)
 bool
 decide_is_variable_needed (struct varpool_node *node, tree decl)
 {
-  if (node->used_from_other_partition)
-    return true;
   /* If the user told us it is used, then it must be so.  */
-  if ((node->externally_visible && !DECL_COMDAT (decl))
-      || node->force_output)
+  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)
-      && !flag_whole_program
-      && !flag_lto
       && !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 false;
-
-  /* We want to emit COMDAT variables only when absolutely necessary.  */
-  if (DECL_COMDAT (decl))
-    return false;
-  return true;
+  if (!flag_toplevel_reorder)
+    return true;
+  return false;
 }
 
 /* Return if DECL is constant and its initial value is known (so we can do
@@ -427,11 +420,6 @@ varpool_finalize_decl (tree decl)
 
   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)
     varpool_assemble_pending_decls ();
 }
@@ -557,18 +545,14 @@ varpool_remove_unreferenced_decls (void)
 
   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)))
+      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;