Remove unused variables from REFERENCED_VARS list

[Jan Hubicka]

Hi,
this patch makes remove_unused_locals to prunt not only unexpanded_var_list but
also referenced_vars that are a lot more commonly traversed.  For temporaries
this also makes them available for ggc memory.  On tramp3d after early
optimization about 70% of local variables can be reclaimed to GGC this way
reducing peak memory usage from 720 to 630MB.

:ADDPATCH tree-optimization:
Bootstrapped/regtested i686-linux, OK?
Honza
	* tree-dfa.c (remove_referenced_var): New function.
	* tree-ssa-live.c (remove_unused_locals): Walk referenced vars and
	prune referenced vars list too.
	* tree-flow.h (remove_referenced_var): Declare.
Index: tree-dfa.c
===================================================================
*** tree-dfa.c	(revision 120681)
--- tree-dfa.c	(working copy)
*************** add_referenced_var (tree var)
*** 752,757 ****
--- 752,780 ----
      }
  }
  
+ /* Remove VAR from the list.  */
+ 
+ void
+ remove_referenced_var (tree var)
+ {
+   var_ann_t v_ann;
+   struct int_tree_map in;
+   void **loc;
+   unsigned int uid = DECL_UID (var);
+ 
+   clear_call_clobbered (var);
+   v_ann = get_var_ann (var);
+   ggc_free (v_ann);
+   var->base.ann = NULL;
+   gcc_assert (DECL_P (var));
+   in.uid = uid;
+   in.to = var;
+   loc = htab_find_slot_with_hash (gimple_referenced_vars (cfun), &in, uid,
+ 				  NO_INSERT);
+   ggc_free (*loc);
+   htab_clear_slot (gimple_referenced_vars (cfun), loc);
+ }
+ 
  
  /* Return the virtual variable associated to the non-scalar variable VAR.  */
  
Index: tree-ssa-live.c
===================================================================
*** tree-ssa-live.c	(revision 120681)
--- tree-ssa-live.c	(working copy)
*************** remove_unused_locals (void)
*** 449,463 ****
  {
    basic_block bb;
    tree t, *cell;
  
    /* Assume all locals are unused.  */
!   for (t = cfun->unexpanded_var_list; t; t = TREE_CHAIN (t))
!     {
!       tree var = TREE_VALUE (t);
!       if (TREE_CODE (var) != FUNCTION_DECL
! 	  && var_ann (var))
! 	var_ann (var)->used = false;
!     }
  
    /* Walk the CFG marking all referenced symbols.  */
    FOR_EACH_BB (bb)
--- 449,460 ----
  {
    basic_block bb;
    tree t, *cell;
+   referenced_var_iterator rvi;
+   var_ann_t ann;
  
    /* Assume all locals are unused.  */
!   FOR_EACH_REFERENCED_VAR (t, rvi)
!     var_ann (t)->used = false;
  
    /* Walk the CFG marking all referenced symbols.  */
    FOR_EACH_BB (bb)
*************** remove_unused_locals (void)
*** 493,503 ****
    for (cell = &cfun->unexpanded_var_list; *cell; )
      {
        tree var = TREE_VALUE (*cell);
-       var_ann_t ann;
  
        if (TREE_CODE (var) != FUNCTION_DECL
  	  && (!(ann = var_ann (var))
  	      || !ann->used))
  	{
  	  *cell = TREE_CHAIN (*cell);
  	  continue;
--- 490,499 ----
    for (cell = &cfun->unexpanded_var_list; *cell; )
      {
        tree var = TREE_VALUE (*cell);
  
        if (TREE_CODE (var) != FUNCTION_DECL
  	  && (!(ann = var_ann (var))
  	      || !ann->used))
  	{
  	  *cell = TREE_CHAIN (*cell);
  	  continue;
*************** remove_unused_locals (void)
*** 505,510 ****
--- 501,519 ----
  
        cell = &TREE_CHAIN (*cell);
      }
+ 
+   /* Remove unused variables from REFERENCED_VARs.  As an special exception
+      keep the variables that are believed to be aliased.  Those can't be
+      easilly removed from the alias sets and and operand caches.
+      They will be removed shortly after next may_alias pass is performed.  */
+   FOR_EACH_REFERENCED_VAR (t, rvi)
+     if (!is_global_var (t)
+ 	&& !MTAG_P (t)
+ 	&& TREE_CODE (t) != PARM_DECL
+ 	&& TREE_CODE (t) != RESULT_DECL
+ 	&& !(ann = var_ann (t))->used
+ 	&& !ann->is_aliased && !is_call_clobbered (t) && !ann->symbol_mem_tag)
+         remove_referenced_var (t);
  }
  
  
Index: tree-flow.h
===================================================================
*** tree-flow.h	(revision 120681)
--- tree-flow.h	(working copy)
*************** extern void dump_subvars_for (FILE *, tr
*** 698,703 ****
--- 698,704 ----
  extern void debug_subvars_for (tree);
  extern tree get_virtual_var (tree);
  extern void add_referenced_var (tree);
+ extern void remove_referenced_var (tree);
  extern void mark_symbols_for_renaming (tree);
  extern void find_new_referenced_vars (tree *);