Re: [tree-ssa] Re-use SSA_NAME expressions

[law at redhat dot com]

In message <20031119225506.GB1138@redhat.com>, Richard Henderson writes:
 >On Wed, Nov 19, 2003 at 01:07:56PM -0700, law@redhat.com wrote:
 >> + /* Free list of SSA_NAMEs.  This list is wiped at the end of each functio
 >n
 >> +    after we leave SSA form.  */
 >> + static varray_type free_ssanames = NULL;
 >
 >A varray is truely wasteful here.  I suggest instead:
 >
 >  static GTY ((deletable (""))) tree free_ssanames;
 >
 >and chain the nodes via TREE_CHAIN.
 >
 >The deletable tag means that we'll zap the list if we GC in the middle
 >of optimization some day.  Ordinarily you wouldn't want one of these
 >cached free nodes preventing a page from being freed, but that would
 >also prevent you from re-using SSA numbers that were freed so it might
 >not be best here.

Bootstrapped and regression tested and of course I verified that we continued
to re-use SSA_NAMES :-)

        * tree-ssanames.c (free_ssanames): No longer a varray.
        (init_ssanames, make_ssa_name, release_ssa_name): Corresponding 
changes.


Index: tree-ssanames.c 
===================================================================
RCS file: /cvs/gcc/gcc/gcc/Attic/tree-ssanames.c,v
retrieving revision 1.1.2.2
diff -c -3 -p -r1.1.2.2 tree-ssanames.c
*** tree-ssanames.c	20 Nov 2003 11:52:19 -0000	1.1.2.2
--- tree-ssanames.c	20 Nov 2003 15:34:42 -0000
*************** unsigned int highest_ssa_version;
*** 61,68 ****
                                                                               

  /* Free list of SSA_NAMEs.  This list is wiped at the end of each function
     after we leave SSA form.  */
! static varray_type free_ssanames = NULL;
!                                                                              

  /* Version numbers with special meanings.  We start allocating new version
     numbers after the special ones.  */
  #define UNUSED_NAME_VERSION 0
--- 61,68 ----
                                                                               

  /* Free list of SSA_NAMEs.  This list is wiped at the end of each function
     after we leave SSA form.  */
! static GTY ((deletable (""))) tree free_ssanames;
! 
  /* Version numbers with special meanings.  We start allocating new version
     numbers after the special ones.  */
  #define UNUSED_NAME_VERSION 0
*************** void
*** 78,84 ****
  init_ssanames (void)
  {
    highest_ssa_version = UNUSED_NAME_VERSION + 1;
!   VARRAY_TREE_INIT (free_ssanames, 1, "Free List of SSA_NAME exprs");
  }
  
  /* Finalize management of SSA_NAMEs.  */
--- 78,84 ----
  init_ssanames (void)
  {
    highest_ssa_version = UNUSED_NAME_VERSION + 1;
!   free_ssanames = NULL;
  }
  
  /* Finalize management of SSA_NAMEs.  */
*************** make_ssa_name (tree var, tree stmt)
*** 121,132 ****
    /* If our free list has an element, then use it.  Also reuse the
       SSA version number of the element on the free list which helps
       keep sbitmaps and arrays sized HIGHEST_SSA_VERSION smaller.  */
!   if (VARRAY_ACTIVE_SIZE (free_ssanames) > 0)
      {
        unsigned int save_version;
  
!       t = VARRAY_TOP_TREE (free_ssanames);
!       VARRAY_POP (free_ssanames);
  #ifdef GATHER_STATISTICS
        ssa_name_nodes_reused++;
  #endif
--- 121,132 ----
    /* If our free list has an element, then use it.  Also reuse the
       SSA version number of the element on the free list which helps
       keep sbitmaps and arrays sized HIGHEST_SSA_VERSION smaller.  */
!   if (free_ssanames)
      {
        unsigned int save_version;
  
!       t = free_ssanames;
!       free_ssanames = TREE_CHAIN (free_ssanames);
  #ifdef GATHER_STATISTICS
        ssa_name_nodes_reused++;
  #endif
*************** release_ssa_name (tree var)
*** 170,175 ****
    if (SSA_NAME_DEF_STMT (var) != NULL)
      {
        SSA_NAME_DEF_STMT (var) = NULL;
!       VARRAY_PUSH_TREE (free_ssanames, var);
      }
  }
--- 170,176 ----
    if (SSA_NAME_DEF_STMT (var) != NULL)
      {
        SSA_NAME_DEF_STMT (var) = NULL;
!       TREE_CHAIN (var) = free_ssanames;
!       free_ssanames = var;
      }
  }