* tree-into-ssa.c: Re-organize internal functions.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@95499 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 726 insertions, 712 deletions

diff --git a/gcc/tree-into-ssa.c b/gcc/tree-into-ssa.c
index 05229470901..bdc7623e87f 100644
--- a/gcc/tree-into-ssa.c
+++ b/gcc/tree-into-ssa.c
@@ -54,7 +54,6 @@ Boston, MA 02111-1307, USA.  */
    Graph. ACM Transactions on Programming Languages and Systems,
    13(4):451-490, October 1991.  */
 
-
 /* Structure to map a variable VAR to the set of blocks that contain
    definitions for VAR.  */
 struct def_blocks_d
@@ -66,7 +65,7 @@ struct def_blocks_d
      Ith block contains a definition of VAR.  */
   bitmap def_blocks;
 
-  /* Blocks that contain a phi node for VAR.  */
+  /* Blocks that contain a PHI node for VAR.  */
   bitmap phi_blocks;
 
   /* Blocks where VAR is live-on-entry.  Similar semantics as
@@ -74,6 +73,7 @@ struct def_blocks_d
   bitmap livein_blocks;
 };
 
+
 /* Each entry in DEF_BLOCKS contains an element of type STRUCT
    DEF_BLOCKS_D, mapping a variable VAR to a bitmap describing all the
    basic blocks where VAR is defined (assigned a new value).  It also
@@ -87,19 +87,18 @@ static htab_t def_blocks;
    state after completing rewriting of a block and its dominator children.
 
    This vector is used in two contexts.  The first is rewriting of _DECL
-   nodes into SSA_NAMEs.  In that context it's elements have the
+   nodes into SSA_NAMEs.  In that context its elements have the
    following properties:
 
      An SSA_NAME indicates that the current definition of the underlying
      variable should be set to the given SSA_NAME.
-                                                                                
+
      A _DECL node indicates that the underlying variable has no current
      definition.
-                                                                                
+
      A NULL node is used to mark the last node associated with the
      current block. 
 
-
    This vector is also used when rewriting an SSA_NAME which has multiple
    definition sites into multiple SSA_NAMEs.  In that context entries come
    in pairs.
@@ -127,8 +126,8 @@ struct mark_def_sites_global_data
   sbitmap names_to_rename;
 };
 
-/* Information stored for ssa names.  */
 
+/* Information stored for ssa names.  */
 struct ssa_name_info
 {
   /* This field indicates whether or not the variable may need PHI nodes.
@@ -140,31 +139,6 @@ struct ssa_name_info
   tree current_def;
 };
 
-/* Local functions.  */
-static void rewrite_finalize_block (struct dom_walk_data *, basic_block);
-static void rewrite_initialize_block (struct dom_walk_data *, basic_block);
-static void rewrite_add_phi_arguments (struct dom_walk_data *, basic_block);
-static void mark_def_sites (struct dom_walk_data *walk_data,
-			    basic_block bb, block_stmt_iterator);
-static void mark_def_sites_initialize_block (struct dom_walk_data *walk_data,
-					     basic_block bb);
-static void set_def_block (tree, basic_block, bool, bool);
-static void set_livein_block (tree, basic_block);
-static bool prepare_use_operand_for_rename (use_operand_p, size_t *uid_p);
-static bool prepare_def_operand_for_rename (tree def, size_t *uid_p);
-static void insert_phi_nodes (bitmap *, bitmap);
-static void rewrite_stmt (struct dom_walk_data *, basic_block,
-			  block_stmt_iterator);
-static inline void rewrite_operand (use_operand_p);
-static void insert_phi_nodes_for (tree, bitmap *, VEC(basic_block) **);
-static tree get_reaching_def (tree);
-static hashval_t def_blocks_hash (const void *);
-static int def_blocks_eq (const void *, const void *);
-static void def_blocks_free (void *);
-static int debug_def_blocks_r (void **, void *);
-static inline struct def_blocks_d *get_def_blocks_for (tree);
-static inline struct def_blocks_d *find_def_blocks_for (tree);
-static void htab_statistics (FILE *, htab_t);
 
 /* Use TREE_VISITED to keep track of which statements we want to
    rename.  When renaming a subset of the variables, not all
@@ -183,6 +157,7 @@ get_ssa_name_ann (tree name)
   return SSA_NAME_AUX (name);
 }
 
+
 /* Gets phi_state field for VAR.  */
 
 static inline enum need_phi_state
@@ -194,6 +169,7 @@ get_phi_state (tree var)
     return var_ann (var)->need_phi_state;
 }
 
+
 /* Sets phi_state field for VAR to STATE.  */
 
 static inline void
@@ -205,6 +181,7 @@ set_phi_state (tree var, enum need_phi_state state)
     var_ann (var)->need_phi_state = state;
 }
 
+
 /* Return the current definition for VAR.  */
 
 static inline tree
@@ -216,6 +193,7 @@ get_current_def (tree var)
     return var_ann (var)->current_def;
 }
 
+
 /* Sets current definition of VAR to DEF.  */
 
 static inline void
@@ -227,6 +205,7 @@ set_current_def (tree var, tree def)
     var_ann (var)->current_def = def;
 }
 
+
 /* Compute global livein information given the set of blockx where
    an object is locally live at the start of the block (LIVEIN)
    and the set of blocks where the object is defined (DEF_BLOCKS).
@@ -280,78 +259,154 @@ compute_global_livein (bitmap livein, bitmap def_blocks)
 }
 
 
-/* Block initialization routine for mark_def_sites.  Clear the 
-   KILLS bitmap at the start of each block.  */
+/* Return the set of blocks where variable VAR is defined and the blocks
+   where VAR is live on entry (livein).  If no entry is found in
+   DEF_BLOCKS, a new one is created and returned.  */
 
-static void
-mark_def_sites_initialize_block (struct dom_walk_data *walk_data,
-				 basic_block bb ATTRIBUTE_UNUSED)
+static inline struct def_blocks_d *
+get_def_blocks_for (tree var)
 {
-  struct mark_def_sites_global_data *gd = walk_data->global_data;
-  bitmap kills = gd->kills;
+  struct def_blocks_d db, *db_p;
+  void **slot;
 
-  bitmap_clear (kills);
+  db.var = var;
+  slot = htab_find_slot (def_blocks, (void *) &db, INSERT);
+  if (*slot == NULL)
+    {
+      db_p = xmalloc (sizeof (*db_p));
+      db_p->var = var;
+      db_p->def_blocks = BITMAP_ALLOC (NULL);
+      db_p->phi_blocks = BITMAP_ALLOC (NULL);
+      db_p->livein_blocks = BITMAP_ALLOC (NULL);
+      *slot = (void *) db_p;
+    }
+  else
+    db_p = (struct def_blocks_d *) *slot;
+
+  return db_p;
 }
 
-/* Block initialization routine for mark_def_sites.  Clear the 
-   KILLS bitmap at the start of each block.  */
+
+/* Mark block BB as the definition site for variable VAR.  PHI_P is true if
+   VAR is defined by a PHI node.  IS_UPDATE is true if the caller is
+   updating an existing SSA form.  */
 
 static void
-ssa_mark_def_sites_initialize_block (struct dom_walk_data *walk_data,
-				     basic_block bb)
+set_def_block (tree var, basic_block bb, bool phi_p, bool is_update)
 {
-  struct mark_def_sites_global_data *gd = walk_data->global_data;
-  bitmap kills = gd->kills;
-  tree phi, def;
-  unsigned def_uid;
+  struct def_blocks_d *db_p;
+  enum need_phi_state state;
 
-  bitmap_clear (kills);
+  if (!is_update && TREE_CODE (var) == SSA_NAME)
+    var = SSA_NAME_VAR (var);
 
-  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
-    {
-      def = PHI_RESULT (phi);
-      def_uid = SSA_NAME_VERSION (def);
+  state = get_phi_state (var);
+  db_p = get_def_blocks_for (var);
 
-      if (!TEST_BIT (gd->names_to_rename, def_uid))
-	continue;
+  /* Set the bit corresponding to the block where VAR is defined.  */
+  bitmap_set_bit (db_p->def_blocks, bb->index);
+  if (phi_p)
+    bitmap_set_bit (db_p->phi_blocks, bb->index);
 
-      set_def_block (def, bb, true, true);
-      bitmap_set_bit (kills, def_uid);
-    }
+  /* Keep track of whether or not we may need to insert PHI nodes.
+
+     If we are in the UNKNOWN state, then this is the first definition
+     of VAR.  Additionally, we have not seen any uses of VAR yet, so
+     we do not need a PHI node for this variable at this time (i.e.,
+     transition to NEED_PHI_STATE_NO).
+
+     If we are in any other state, then we either have multiple definitions
+     of this variable occurring in different blocks or we saw a use of the
+     variable which was not dominated by the block containing the
+     definition(s).  In this case we may need a PHI node, so enter
+     state NEED_PHI_STATE_MAYBE.  */
+  if (state == NEED_PHI_STATE_UNKNOWN)
+    set_phi_state (var, NEED_PHI_STATE_NO);
+  else
+    set_phi_state (var, NEED_PHI_STATE_MAYBE);
 }
 
-/* Marks ssa names used as arguments of phis at the end of BB.  */
+
+/* Mark block BB as having VAR live at the entry to BB.  */
 
 static void
-ssa_mark_phi_uses (struct dom_walk_data *walk_data, basic_block bb)
+set_livein_block (tree var, basic_block bb)
 {
-  struct mark_def_sites_global_data *gd = walk_data->global_data;
-  bitmap kills = gd->kills;
-  edge e;
-  tree phi, use;
-  unsigned uid;
-  edge_iterator ei;
+  struct def_blocks_d *db_p;
+  enum need_phi_state state = get_phi_state (var);
 
-  FOR_EACH_EDGE (e, ei, bb->succs)
-    {
-      if (e->dest == EXIT_BLOCK_PTR)
-	continue;
+  db_p = get_def_blocks_for (var);
 
-      for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
-	{
-	  use = PHI_ARG_DEF_FROM_EDGE (phi, e);
-	  if (TREE_CODE (use) != SSA_NAME)
-	    continue;
+  /* Set the bit corresponding to the block where VAR is live in.  */
+  bitmap_set_bit (db_p->livein_blocks, bb->index);
 
-	  uid = SSA_NAME_VERSION (use);
+  /* Keep track of whether or not we may need to insert PHI nodes.
 
-	  if (TEST_BIT (gd->names_to_rename, uid)
-	      && !bitmap_bit_p (kills, uid))
-	    set_livein_block (use, bb);
-	}
+     If we reach here in NEED_PHI_STATE_NO, see if this use is dominated
+     by the single block containing the definition(s) of this variable.  If
+     it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to
+     NEED_PHI_STATE_MAYBE.  */
+  if (state == NEED_PHI_STATE_NO)
+    {
+      int def_block_index = bitmap_first_set_bit (db_p->def_blocks);
+
+      if (def_block_index == -1
+	  || ! dominated_by_p (CDI_DOMINATORS, bb,
+	                       BASIC_BLOCK (def_block_index)))
+	set_phi_state (var, NEED_PHI_STATE_MAYBE);
     }
+  else
+    set_phi_state (var, NEED_PHI_STATE_MAYBE);
+}
+
+
+/* If the use operand pointed to by OP_P needs to be renamed, then strip away 
+   any SSA_NAME wrapping the operand, set *UID_P to the underlying variable's 
+   uid, and return true.  Otherwise return false.  If the operand was an 
+   SSA_NAME, change it to the stripped name.  */
+
+static bool
+prepare_use_operand_for_rename (use_operand_p op_p, size_t *uid_p)
+{
+  tree use = USE_FROM_PTR (op_p);
+  tree var = (TREE_CODE (use) != SSA_NAME) ? use : SSA_NAME_VAR (use);
+  *uid_p = var_ann (var)->uid;
+
+  /* Ignore variables that don't need to be renamed.  */
+  if (vars_to_rename && !bitmap_bit_p (vars_to_rename, *uid_p))
+    return false;
+
+  /* The variable needs to be renamed.  If this is a use which already
+     has an SSA_NAME, then strip it off.
+
+     By not throwing away SSA_NAMEs on assignments, we avoid a lot of 
+     useless churn of SSA_NAMEs without having to overly complicate the
+     renamer.  */
+  if (TREE_CODE (use) == SSA_NAME)
+    SET_USE (op_p, var);
+
+  return true;
+}
+
+
+/* If the def variable DEF needs to be renamed, then strip away any SSA_NAME 
+   wrapping the operand, set *UID_P to the underlying variable's uid and return
+   true.  Otherwise return false.  */
+
+static bool
+prepare_def_operand_for_rename (tree def, size_t *uid_p)
+{
+  tree var = (TREE_CODE (def) != SSA_NAME) ? def : SSA_NAME_VAR (def);
+  *uid_p = var_ann (var)->uid;
+
+  /* Ignore variables that don't need to be renamed.  */
+  if (vars_to_rename && !bitmap_bit_p (vars_to_rename, *uid_p))
+    return false;
+
+  return true;
 }
 
+
 /* Call back for walk_dominator_tree used to collect definition sites
    for every variable in the function.  For every statement S in block
    BB:
@@ -434,179 +489,136 @@ mark_def_sites (struct dom_walk_data *walk_data,
 }
 
 
-/* Same as mark_def_sites, but works over SSA names.  */
+/* Given a set of blocks with variable definitions (DEF_BLOCKS),
+   return a bitmap with all the blocks in the iterated dominance
+   frontier of the blocks in DEF_BLOCKS.  DFS contains dominance
+   frontier information as returned by compute_dominance_frontiers.
+   
+   The resulting set of blocks are the potential sites where PHI nodes
+   are needed.  The caller is responsible from freeing the memory
+   allocated for the return value.  */
 
-static void
-ssa_mark_def_sites (struct dom_walk_data *walk_data,
-		    basic_block bb,
-		    block_stmt_iterator bsi)
+static bitmap
+find_idf (bitmap def_blocks, bitmap *dfs)
 {
-  struct mark_def_sites_global_data *gd = walk_data->global_data;
-  bitmap kills = gd->kills;
-  size_t uid, def_uid;
-  tree stmt, use, def;
-  ssa_op_iter iter;
+  bitmap_iterator bi;
+  unsigned bb_index;
+  VEC(basic_block) *work_stack;
+  bitmap phi_insertion_points;
 
-  /* Mark all the blocks that have definitions for each variable in the
-     names_to_rename bitmap.  */
-  stmt = bsi_stmt (bsi);
-  get_stmt_operands (stmt);
+  work_stack = VEC_alloc (basic_block, n_basic_blocks);
+  phi_insertion_points = BITMAP_ALLOC (NULL);
 
-  /* If a variable is used before being set, then the variable is live
-     across a block boundary, so mark it live-on-entry to BB.  */
-  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
-    {
-      uid = SSA_NAME_VERSION (use);
+  /* Seed the work list with all the blocks in DEF_BLOCKS.  */
+  EXECUTE_IF_SET_IN_BITMAP (def_blocks, 0, bb_index, bi)
+    VEC_safe_push (basic_block, work_stack, BASIC_BLOCK (bb_index));
 
-      if (TEST_BIT (gd->names_to_rename, uid)
-	  && !bitmap_bit_p (kills, uid))
-	set_livein_block (use, bb);
-    }
-	  
-  /* Now process the definition made by this statement.  Mark the
-     variables in KILLS.  */
-  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
+  /* Pop a block off the worklist, add every block that appears in
+     the original block's DF that we have not already processed to
+     the worklist.  Iterate until the worklist is empty.   Blocks
+     which are added to the worklist are potential sites for
+     PHI nodes.  */
+  while (VEC_length (basic_block, work_stack) > 0)
     {
-      def_uid = SSA_NAME_VERSION (def);
-
-      if (TEST_BIT (gd->names_to_rename, def_uid))
+      basic_block bb = VEC_pop (basic_block, work_stack);
+      bb_index = bb->index;
+      
+      EXECUTE_IF_AND_COMPL_IN_BITMAP (dfs[bb_index], phi_insertion_points,
+				      0, bb_index, bi)
 	{
-	  set_def_block (def, bb, false, true);
-	  bitmap_set_bit (kills, def_uid);
+	  bb = BASIC_BLOCK (bb_index);
+
+	  /* Use a safe push because if there is a definition of VAR
+	     in every basic block, then WORK_STACK may eventually have
+	     more than N_BASIC_BLOCK entries.  */
+	  VEC_safe_push (basic_block, work_stack, bb);
+	  bitmap_set_bit (phi_insertion_points, bb_index);
 	}
     }
-}
-
-/* Mark block BB as the definition site for variable VAR.  PHI_P is true if
-   VAR is defined by a phi node.  SSA_P is true if we are called from
-   rewrite_ssa_into_ssa.  */
-
-static void
-set_def_block (tree var, basic_block bb, bool phi_p, bool ssa_p)
-{
-  struct def_blocks_d *db_p;
-  enum need_phi_state state;
-
-  if (!ssa_p
-      && TREE_CODE (var) == SSA_NAME)
-    var = SSA_NAME_VAR (var);
 
-  state = get_phi_state (var);
-  db_p = get_def_blocks_for (var);
+  VEC_free (basic_block, work_stack);
 
-  /* Set the bit corresponding to the block where VAR is defined.  */
-  bitmap_set_bit (db_p->def_blocks, bb->index);
-  if (phi_p)
-    bitmap_set_bit (db_p->phi_blocks, bb->index);
+  return phi_insertion_points;
+}
 
-  /* Keep track of whether or not we may need to insert phi nodes.
 
-     If we are in the UNKNOWN state, then this is the first definition
-     of VAR.  Additionally, we have not seen any uses of VAR yet, so
-     we do not need a phi node for this variable at this time (i.e.,
-     transition to NEED_PHI_STATE_NO).
+/* Return the set of blocks where variable VAR is defined and the blocks
+   where VAR is live on entry (livein).  Return NULL, if no entry is
+   found in DEF_BLOCKS.  */
 
-     If we are in any other state, then we either have multiple definitions
-     of this variable occurring in different blocks or we saw a use of the
-     variable which was not dominated by the block containing the
-     definition(s).  In this case we may need a PHI node, so enter
-     state NEED_PHI_STATE_MAYBE.  */
-  if (state == NEED_PHI_STATE_UNKNOWN)
-    set_phi_state (var, NEED_PHI_STATE_NO);
-  else
-    set_phi_state (var, NEED_PHI_STATE_MAYBE);
+static inline struct def_blocks_d *
+find_def_blocks_for (tree var)
+{
+  struct def_blocks_d dm;
+  dm.var = var;
+  return (struct def_blocks_d *) htab_find (def_blocks, &dm);
 }
 
 
-/* Mark block BB as having VAR live at the entry to BB.  */
+/* Insert PHI nodes for variable VAR using the iterated dominance
+   frontier given in PHI_INSERTION_POINTS.  */
 
 static void
-set_livein_block (tree var, basic_block bb)
+insert_phi_nodes_for (tree var, bitmap phi_insertion_points)
 {
-  struct def_blocks_d *db_p;
-  enum need_phi_state state = get_phi_state (var);
+  unsigned bb_index;
+  edge e;
+  tree phi;
+  basic_block bb;
+  bitmap_iterator bi;
+  struct def_blocks_d *def_map;
 
-  db_p = get_def_blocks_for (var);
+  def_map = find_def_blocks_for (var);
 
-  /* Set the bit corresponding to the block where VAR is live in.  */
-  bitmap_set_bit (db_p->livein_blocks, bb->index);
+  /* Remove the blocks where we already have PHI nodes for VAR.  */
+  bitmap_and_compl_into (phi_insertion_points, def_map->phi_blocks);
 
-  /* Keep track of whether or not we may need to insert phi nodes.
+  /* Now compute global livein for this variable.  Note this modifies
+     def_map->livein_blocks.  */
+  compute_global_livein (def_map->livein_blocks, def_map->def_blocks);
 
-     If we reach here in NEED_PHI_STATE_NO, see if this use is dominated
-     by the single block containing the definition(s) of this variable.  If
-     it is, then we remain in NEED_PHI_STATE_NO, otherwise we transition to
-     NEED_PHI_STATE_MAYBE.  */
-  if (state == NEED_PHI_STATE_NO)
+  /* And insert the PHI nodes.  */
+  EXECUTE_IF_AND_IN_BITMAP (phi_insertion_points, def_map->livein_blocks,
+			    0, bb_index, bi)
     {
-      int def_block_index = bitmap_first_set_bit (db_p->def_blocks);
+      bb = BASIC_BLOCK (bb_index);
+      phi = create_phi_node (var, bb);
 
-      if (def_block_index == -1
-	  || ! dominated_by_p (CDI_DOMINATORS, bb,
-	                       BASIC_BLOCK (def_block_index)))
-	set_phi_state (var, NEED_PHI_STATE_MAYBE);
+      /* If we are rewriting SSA names, add also the PHI arguments.  */
+      if (TREE_CODE (var) == SSA_NAME)
+	{
+	  edge_iterator ei;
+	  FOR_EACH_EDGE (e, ei, bb->preds)
+	    add_phi_arg (phi, var, e);
+	}
+
+      /* Mark this PHI node as interesting for the rename process.  */
+      REWRITE_THIS_STMT (phi) = 1;
     }
-  else
-    set_phi_state (var, NEED_PHI_STATE_MAYBE);
 }
 
 
-/* If the use operand pointed to by OP_P needs to be renamed, then strip away 
-   any SSA_NAME wrapping the operand, set *UID_P to the underlying variable's 
-   uid, and return true.  Otherwise return false.  If the operand was an 
-   SSA_NAME, change it to the stripped name.  */
+/* Helper for insert_phi_nodes.  If VAR needs PHI nodes, insert them
+   at the dominance frontier (DFS) of blocks defining VAR.  */
 
-static bool
-prepare_use_operand_for_rename (use_operand_p op_p, size_t *uid_p)
+static inline void
+insert_phi_nodes_1 (tree var, bitmap *dfs)
 {
-  tree use = USE_FROM_PTR (op_p);
-  tree var = (TREE_CODE (use) != SSA_NAME) ? use : SSA_NAME_VAR (use);
-  *uid_p = var_ann (var)->uid;
-
-  /* Ignore variables that don't need to be renamed.  */
-  if (vars_to_rename && !bitmap_bit_p (vars_to_rename, *uid_p))
-    return false;
-
-  /* The variable needs to be renamed.  If this is a use which already
-     has an SSA_NAME, then strip it off.
-
-     By not throwing away SSA_NAMEs on assignments, we avoid a lot of 
-     useless churn of SSA_NAMEs without having to overly complicate the
-     renamer.  */
-  if (TREE_CODE (use) == SSA_NAME)
-    SET_USE (op_p, var);
+  struct def_blocks_d *def_map;
+  bitmap idf;
 
-  return true;
-}
+  def_map = find_def_blocks_for (var);
+  if (def_map == NULL)
+    return;
 
-/* If the def variable DEF needs to be renamed, then strip away any SSA_NAME 
-   wrapping the operand, set *UID_P to the underlying variable's uid and return
-   true.  Otherwise return false.  */
+  idf = find_idf (def_map->def_blocks, dfs);
 
-static bool
-prepare_def_operand_for_rename (tree def, size_t *uid_p)
-{
-  tree var = (TREE_CODE (def) != SSA_NAME) ? def : SSA_NAME_VAR (def);
-  *uid_p = var_ann (var)->uid;
-
-  /* Ignore variables that don't need to be renamed.  */
-  if (vars_to_rename && !bitmap_bit_p (vars_to_rename, *uid_p))
-    return false;
+  if (get_phi_state (var) != NEED_PHI_STATE_NO)
+    insert_phi_nodes_for (var, idf);
 
-  return true;
+  BITMAP_FREE (idf);
 }
 
-/* Helper for insert_phi_nodes.  If VAR needs PHI nodes, insert them
-   at the dominance frontier (DFS) of blocks defining VAR.
-   WORK_STACK is the vector used to implement the worklist of basic
-   blocks.  */
-
-static inline void
-insert_phi_nodes_1 (tree var, bitmap *dfs, VEC(basic_block) **work_stack)
-{
-  if (get_phi_state (var) != NEED_PHI_STATE_NO)
-    insert_phi_nodes_for (var, dfs, work_stack);
-}
 
 /* Insert PHI nodes at the dominance frontier of blocks with variable
    definitions.  DFS contains the dominance frontier information for
@@ -620,15 +632,10 @@ static void
 insert_phi_nodes (bitmap *dfs, bitmap names_to_rename)
 {
   unsigned i;
-  VEC(basic_block) *work_stack;
   bitmap_iterator bi;
 
   timevar_push (TV_TREE_INSERT_PHI_NODES);
 
-  /* Vector WORK_STACK is a stack of CFG blocks.  Each block that contains
-     an assignment or PHI node will be pushed to this stack.  */
-  work_stack = VEC_alloc (basic_block, n_basic_blocks);
-
   /* Iterate over all variables in VARS_TO_RENAME.  For each variable, add
      to the work list all the blocks that have a definition for the
      variable.  PHI nodes will be added to the dominance frontier blocks of
@@ -636,26 +643,62 @@ insert_phi_nodes (bitmap *dfs, bitmap names_to_rename)
   if (names_to_rename)
     {
       EXECUTE_IF_SET_IN_BITMAP (names_to_rename, 0, i, bi)
-	{
-	  if (ssa_name (i))
-	    insert_phi_nodes_1 (ssa_name (i), dfs, &work_stack);
-	}
+	if (ssa_name (i))
+	  insert_phi_nodes_1 (ssa_name (i), dfs);
     }
   else if (vars_to_rename)
-    EXECUTE_IF_SET_IN_BITMAP (vars_to_rename, 0, i, bi)
-      {
-	insert_phi_nodes_1 (referenced_var (i), dfs, &work_stack);
-      }
+    {
+      EXECUTE_IF_SET_IN_BITMAP (vars_to_rename, 0, i, bi)
+	insert_phi_nodes_1 (referenced_var (i), dfs);
+    }
   else
-    for (i = 0; i < num_referenced_vars; i++)
-      insert_phi_nodes_1 (referenced_var (i), dfs, &work_stack);
-
-  VEC_free (basic_block, work_stack);
+    {
+      for (i = 0; i < num_referenced_vars; i++)
+	insert_phi_nodes_1 (referenced_var (i), dfs);
+    }
 
   timevar_pop (TV_TREE_INSERT_PHI_NODES);
 }
 
 
+/* Register DEF (an SSA_NAME) to be a new definition for its underlying
+   variable (SSA_NAME_VAR (DEF)) and push VAR's current reaching definition
+   into the stack pointed by BLOCK_DEFS_P.  */
+
+void
+register_new_def (tree def, VEC (tree_on_heap) **block_defs_p)
+{
+  tree var = SSA_NAME_VAR (def);
+  tree currdef;
+   
+  /* If this variable is set in a single basic block and all uses are
+     dominated by the set(s) in that single basic block, then there is
+     no reason to record anything for this variable in the block local
+     definition stacks.  Doing so just wastes time and memory.
+
+     This is the same test to prune the set of variables which may
+     need PHI nodes.  So we just use that information since it's already
+     computed and available for us to use.  */
+  if (get_phi_state (var) == NEED_PHI_STATE_NO)
+    {
+      set_current_def (var, def);
+      return;
+    }
+
+  currdef = get_current_def (var);
+
+  /* Push the current reaching definition into *BLOCK_DEFS_P.  This stack is
+     later used by the dominator tree callbacks to restore the reaching
+     definitions for all the variables defined in the block after a recursive
+     visit to all its immediately dominated blocks.  If there is no current
+     reaching definition, then just record the underlying _DECL node.  */
+  VEC_safe_push (tree_on_heap, *block_defs_p, currdef ? currdef : var);
+
+  /* Set the current reaching definition for VAR to be DEF.  */
+  set_current_def (var, def);
+}
+
+
 /* Perform a depth-first traversal of the dominator tree looking for
    variables to rename.  BB is the block where to start searching.
    Renaming is a five step process:
@@ -702,84 +745,124 @@ rewrite_initialize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
   for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
     {
       tree result = PHI_RESULT (phi);
-
-      register_new_def (result, &block_defs_stack);
+      if (REWRITE_THIS_STMT (phi))
+	register_new_def (result, &block_defs_stack);
     }
 }
 
-/* Register DEF (an SSA_NAME) to be a new definition for the original
-   ssa name VAR and push VAR's current reaching definition
-   into the stack pointed by BLOCK_DEFS_P.  */
 
-static void
-ssa_register_new_def (tree var, tree def)
+/* Return the current definition for variable VAR.  If none is found,
+   create a new SSA name to act as the zeroth definition for VAR.  If VAR
+   is call clobbered and there exists a more recent definition of
+   GLOBAL_VAR, return the definition for GLOBAL_VAR.  This means that VAR
+   has been clobbered by a function call since its last assignment.  */
+
+static tree
+get_reaching_def (tree var)
 {
-  tree currdef;
-   
-  /* If this variable is set in a single basic block and all uses are
-     dominated by the set(s) in that single basic block, then there is
-     nothing to do.  TODO we should not be called at all, and just
-     keep the original name.  */
-  if (get_phi_state (var) == NEED_PHI_STATE_NO)
+  tree default_d, currdef_var, avar;
+  
+  /* Lookup the current reaching definition for VAR.  */
+  default_d = NULL_TREE;
+  currdef_var = get_current_def (var);
+
+  /* If there is no reaching definition for VAR, create and register a
+     default definition for it (if needed).  */
+  if (currdef_var == NULL_TREE)
     {
-      set_current_def (var, def);
-      return;
+      if (TREE_CODE (var) == SSA_NAME)
+	avar = SSA_NAME_VAR (var);
+      else
+	avar = var;
+
+      default_d = default_def (avar);
+      if (default_d == NULL_TREE)
+	{
+	  default_d = make_ssa_name (avar, build_empty_stmt ());
+	  set_default_def (avar, default_d);
+	}
+      set_current_def (var, default_d);
     }
 
-  currdef = get_current_def (var);
+  /* Return the current reaching definition for VAR, or the default
+     definition, if we had to create one.  */
+  return (currdef_var) ? currdef_var : default_d;
+}
 
-  /* Push the current reaching definition into *BLOCK_DEFS_P.  This stack is
-     later used by the dominator tree callbacks to restore the reaching
-     definitions for all the variables defined in the block after a recursive
-     visit to all its immediately dominated blocks.  */
-  VEC_safe_push (tree_on_heap, block_defs_stack, currdef);
-  VEC_safe_push (tree_on_heap, block_defs_stack, var);
 
-  /* Set the current reaching definition for VAR to be DEF.  */
-  set_current_def (var, def);
+/* Replace the operand pointed by OP_P with its immediate reaching
+   definition.  */
+
+static inline void
+rewrite_operand (use_operand_p op_p)
+{
+  tree var = USE_FROM_PTR (op_p);
+  if (TREE_CODE (var) != SSA_NAME)
+    SET_USE (op_p, get_reaching_def (var));
+  else
+    {
+#if defined ENABLE_CHECKING
+      /* If we get to this point, VAR is an SSA_NAME.  If VAR's symbol
+	 was marked for renaming, make sure that its reaching
+	 definition is VAR itself.  Otherwise, something has gone
+	 wrong.  */
+      tree sym = SSA_NAME_VAR (var);
+      if (bitmap_bit_p (vars_to_rename, var_ann (sym)->uid))
+	gcc_assert (var == get_reaching_def (SSA_NAME_VAR (var)));
+#endif
+    }
 }
 
-/* Ditto, for rewriting ssa names.  */
+
+/* SSA Rewriting Step 2.  Rewrite every variable used in each statement in
+   the block with its immediate reaching definitions.  Update the current
+   definition of a variable when a new real or virtual definition is found.  */
 
 static void
-ssa_rewrite_initialize_block (struct dom_walk_data *walk_data, basic_block bb)
+rewrite_stmt (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+	      basic_block bb ATTRIBUTE_UNUSED,
+	      block_stmt_iterator si)
 {
-  tree phi, new_name;
-  sbitmap names_to_rename = walk_data->global_data;
-  edge e;
-  bool abnormal_phi;
-  edge_iterator ei;
+  stmt_ann_t ann;
+  tree stmt;
+  use_operand_p use_p;
+  def_operand_p def_p;
+  ssa_op_iter iter;
+
+  stmt = bsi_stmt (si);
+  ann = stmt_ann (stmt);
+
+  /* If mark_def_sites decided that we don't need to rewrite this
+     statement, ignore it.  */
+  if (!REWRITE_THIS_STMT (stmt))
+    return;
 
   if (dump_file && (dump_flags & TDF_DETAILS))
-    fprintf (dump_file, "\n\nRenaming block #%d\n\n", bb->index);
+    {
+      fprintf (dump_file, "Renaming statement ");
+      print_generic_stmt (dump_file, stmt, TDF_SLIM);
+      fprintf (dump_file, "\n");
+    }
 
-  /* Mark the unwind point for this block.  */
-  VEC_safe_push (tree_on_heap, block_defs_stack, NULL_TREE);
+  get_stmt_operands (stmt);
 
-  FOR_EACH_EDGE (e, ei, bb->preds)
-    if (e->flags & EDGE_ABNORMAL)
-      break;
-  abnormal_phi = (e != NULL);
+  /* Step 1.  Rewrite USES and VUSES in the statement.  */
+  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
+    rewrite_operand (use_p);
 
-  /* Step 1.  Register new definitions for every PHI node in the block.
-     Conceptually, all the PHI nodes are executed in parallel and each PHI
-     node introduces a new version for the associated variable.  */
-  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+  /* Step 2.  Register the statement's DEF and VDEF operands.  */
+  FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS)
     {
-      tree result = PHI_RESULT (phi);
-
-      if (TEST_BIT (names_to_rename, SSA_NAME_VERSION (result)))
-	{
-	  new_name = duplicate_ssa_name (result, phi);
-	  SET_PHI_RESULT (phi, new_name);
+      if (TREE_CODE (DEF_FROM_PTR (def_p)) != SSA_NAME)
+	SET_DEF (def_p, make_ssa_name (DEF_FROM_PTR (def_p), stmt));
 
-	  if (abnormal_phi)
-	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (new_name) = 1;
-	  ssa_register_new_def (result, new_name);
-	}
+      /* FIXME: We shouldn't be registering new defs if the variable
+	 doesn't need to be renamed.  */
+      register_new_def (DEF_FROM_PTR (def_p), &block_defs_stack);
     }
 }
 
+
 /* SSA Rewriting Step 3.  Visit all the successor blocks of BB looking for
    PHI nodes.  For every PHI node found, add a new argument containing the
    current reaching definition for the variable and the edge through which
@@ -812,9 +895,10 @@ rewrite_add_phi_arguments (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
     }
 }
 
+
 /*  Rewrite existing virtual PHI arguments so that they have the correct
     reaching definitions.  BB is the basic block whose successors contain the
-    phi nodes we want to add arguments for.  */
+    PHI nodes we want to add arguments for.  */
 
 static void
 rewrite_virtual_phi_arguments (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
@@ -848,42 +932,10 @@ rewrite_virtual_phi_arguments (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
     }
 }
 
-/* Ditto, for ssa name rewriting.  */
-
-static void
-ssa_rewrite_phi_arguments (struct dom_walk_data *walk_data, basic_block bb)
-{
-  edge e;
-  sbitmap names_to_rename = walk_data->global_data;
-  use_operand_p op;
-  edge_iterator ei;
-
-  FOR_EACH_EDGE (e, ei, bb->succs)
-    {
-      tree phi;
-
-      if (e->dest == EXIT_BLOCK_PTR)
-	continue;
-
-      for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
-	{
-	  op = PHI_ARG_DEF_PTR_FROM_EDGE (phi, e);
-	  if (TREE_CODE (USE_FROM_PTR (op)) != SSA_NAME)
-	    continue;
-	  
-	  if (!TEST_BIT (names_to_rename, SSA_NAME_VERSION (USE_FROM_PTR (op))))
-	    continue; 
-
-	  SET_USE (op, get_reaching_def (USE_FROM_PTR (op)));
-	  if (e->flags & EDGE_ABNORMAL)
-	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (op)) = 1;
-	}
-    }
-}
 
+/* Called after visiting basic block BB.  Restore CURRDEFS to its
+   original value.  */
 
-/* Similar to restore_vars_to_original_value, except that it restores 
-   CURRDEFS to its original value.  */
 static void
 rewrite_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
 			basic_block bb ATTRIBUTE_UNUSED)
@@ -916,28 +968,6 @@ rewrite_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
     }
 }
 
-/* Ditto, for rewriting ssa names.  */
-
-static void
-ssa_rewrite_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
-			    basic_block bb ATTRIBUTE_UNUSED)
-{
-
-  /* Step 5.  Restore the current reaching definition for each variable
-     referenced in the block (in reverse order).  */
-  while (VEC_length (tree_on_heap, block_defs_stack) > 0)
-    {
-      tree var = VEC_pop (tree_on_heap, block_defs_stack);
-      tree saved_def;
-      
-      if (var == NULL)
-	break;
-
-      saved_def = VEC_pop (tree_on_heap, block_defs_stack);
-
-      set_current_def (var, saved_def);
-    }
-}
 
 /* Dump SSA information to FILE.  */
 
@@ -969,29 +999,6 @@ debug_tree_ssa (void)
 }
 
 
-/* Dump SSA statistics on FILE.  */
-
-void
-dump_tree_ssa_stats (FILE *file)
-{
-  fprintf (file, "\nHash table statistics:\n");
-
-  fprintf (file, "    def_blocks: ");
-  htab_statistics (file, def_blocks);
-
-  fprintf (file, "\n");
-}
-
-
-/* Dump SSA statistics on stderr.  */
-
-void
-debug_tree_ssa_stats (void)
-{
-  dump_tree_ssa_stats (stderr);
-}
-
-
 /* Dump statistics for the hash table HTAB.  */
 
 static void
@@ -1004,288 +1011,26 @@ htab_statistics (FILE *file, htab_t htab)
 }
 
 
-/* Insert PHI nodes for variable VAR using the dominance frontier
-   information given in DFS.  WORK_STACK is the vector used to
-   implement the worklist of basic blocks.  */
-
-static void
-insert_phi_nodes_for (tree var, bitmap *dfs, VEC(basic_block) **work_stack)
-{
-  struct def_blocks_d *def_map;
-  bitmap phi_insertion_points;
-  unsigned bb_index;
-  edge e;
-  tree phi;
-  basic_block bb;
-  bitmap_iterator bi;
-
-  def_map = find_def_blocks_for (var);
-  if (def_map == NULL)
-    return;
-
-  phi_insertion_points = BITMAP_ALLOC (NULL);
-
-  EXECUTE_IF_SET_IN_BITMAP (def_map->def_blocks, 0, bb_index, bi)
-    {
-      VEC_safe_push (basic_block, *work_stack, BASIC_BLOCK (bb_index));
-    }
-
-  /* Pop a block off the worklist, add every block that appears in
-     the original block's dfs that we have not already processed to
-     the worklist.  Iterate until the worklist is empty.   Blocks
-     which are added to the worklist are potential sites for
-     PHI nodes. 
-
-     The iteration step could be done during PHI insertion just as
-     easily.  We do it here for historical reasons -- we used to have
-     a heuristic which used the potential PHI insertion points to
-     determine if fully pruned or semi pruned SSA form was appropriate.
-
-     We now always use fully pruned SSA form.  */
-  while (VEC_length (basic_block, *work_stack) > 0)
-    {
-      unsigned dfs_index;
-      bitmap_iterator bi;
-
-      bb = VEC_pop (basic_block, *work_stack);
-      bb_index = bb->index;
-      
-      EXECUTE_IF_AND_COMPL_IN_BITMAP (dfs[bb_index],
-				      phi_insertion_points,
-				      0, dfs_index, bi)
-	{
-	  basic_block bb = BASIC_BLOCK (dfs_index);
-
-	  /* Use a safe push because if there is a definition of VAR
-	     in every basic block, then WORK_STACK may eventually have
-	     more than N_BASIC_BLOCK entries.  */
-	  VEC_safe_push (basic_block, *work_stack, bb);
-	  bitmap_set_bit (phi_insertion_points, dfs_index);
-	}
-    }
-
-  /* Remove the blocks where we already have the phis.  */
-  bitmap_and_compl_into (phi_insertion_points, def_map->phi_blocks);
-
-  /* Now compute global livein for this variable.  Note this modifies
-     def_map->livein_blocks.  */
-  compute_global_livein (def_map->livein_blocks, def_map->def_blocks);
-
-  /* And insert the PHI nodes.  */
-  EXECUTE_IF_AND_IN_BITMAP (phi_insertion_points, def_map->livein_blocks,
-			    0, bb_index, bi)
-    {
-      bb = BASIC_BLOCK (bb_index);
-
-      phi = create_phi_node (var, bb);
-
-      /* If we are rewriting ssa names, add also the phi arguments.  */
-      if (TREE_CODE (var) == SSA_NAME)
-	{
-	  edge_iterator ei;
-	  FOR_EACH_EDGE (e, ei, bb->preds)
-	    add_phi_arg (phi, var, e);
-	}
-    }
-
-  BITMAP_FREE (phi_insertion_points);
-}
-
-/* SSA Rewriting Step 2.  Rewrite every variable used in each statement in
-   the block with its immediate reaching definitions.  Update the current
-   definition of a variable when a new real or virtual definition is found.  */
-
-static void
-rewrite_stmt (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
-	      basic_block bb ATTRIBUTE_UNUSED,
-	      block_stmt_iterator si)
-{
-  stmt_ann_t ann;
-  tree stmt;
-  use_operand_p use_p;
-  def_operand_p def_p;
-  ssa_op_iter iter;
-
-  stmt = bsi_stmt (si);
-  ann = stmt_ann (stmt);
-
-  /* If mark_def_sites decided that we don't need to rewrite this
-     statement, ignore it.  */
-  if (!REWRITE_THIS_STMT (stmt))
-    return;
-
-  if (dump_file && (dump_flags & TDF_DETAILS))
-    {
-      fprintf (dump_file, "Renaming statement ");
-      print_generic_stmt (dump_file, stmt, TDF_SLIM);
-      fprintf (dump_file, "\n");
-    }
-
-  /* We have just scanned the code for operands.  No statement should
-     be modified.  */
-  gcc_assert (!ann->modified);
-
-  /* Step 1.  Rewrite USES and VUSES in the statement.  */
-  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
-    rewrite_operand (use_p);
-
-  /* Step 2.  Register the statement's DEF and VDEF operands.  */
-  FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS)
-    {
-      if (TREE_CODE (DEF_FROM_PTR (def_p)) != SSA_NAME)
-	SET_DEF (def_p, make_ssa_name (DEF_FROM_PTR (def_p), stmt));
-
-      /* FIXME: We shouldn't be registering new defs if the variable
-	 doesn't need to be renamed.  */
-      register_new_def (DEF_FROM_PTR (def_p), &block_defs_stack);
-    }
-}
-
-
-/* Same as rewrite_stmt, for rewriting ssa names.  */
+/* Dump SSA statistics on FILE.  */
 
-static void
-ssa_rewrite_stmt (struct dom_walk_data *walk_data,
-		  basic_block bb ATTRIBUTE_UNUSED,
-		  block_stmt_iterator si)
+void
+dump_tree_ssa_stats (FILE *file)
 {
-  stmt_ann_t ann;
-  tree stmt, var;
-  ssa_op_iter iter;
-  use_operand_p use_p;
-  def_operand_p def_p;
-  sbitmap names_to_rename = walk_data->global_data;
-
-  stmt = bsi_stmt (si);
-  ann = stmt_ann (stmt);
-
-  if (dump_file && (dump_flags & TDF_DETAILS))
-    {
-      fprintf (dump_file, "Renaming statement ");
-      print_generic_stmt (dump_file, stmt, TDF_SLIM);
-      fprintf (dump_file, "\n");
-    }
-
-  /* We have just scanned the code for operands.  No statement should
-     be modified.  */
-  gcc_assert (!ann->modified);
-
-  /* Step 1.  Rewrite USES and VUSES in the statement.  */
-  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
-    {
-      if (TEST_BIT (names_to_rename, SSA_NAME_VERSION (USE_FROM_PTR (use_p))))
-	SET_USE (use_p, get_reaching_def (USE_FROM_PTR (use_p)));
-    }
-
-  /* Step 2.  Register the statement's DEF and VDEF operands.  */
-  FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS)
-    {
-      var = DEF_FROM_PTR (def_p);
+  fprintf (file, "\nHash table statistics:\n");
 
-      if (!TEST_BIT (names_to_rename, SSA_NAME_VERSION (var)))
-	continue;
+  fprintf (file, "    def_blocks: ");
+  htab_statistics (file, def_blocks);
 
-      SET_DEF (def_p, duplicate_ssa_name (var, stmt));
-      ssa_register_new_def (var, DEF_FROM_PTR (def_p));
-    }
+  fprintf (file, "\n");
 }
 
-/* Replace the operand pointed by OP_P with its immediate reaching
-   definition.  */
 
-static inline void
-rewrite_operand (use_operand_p op_p)
-{
-  tree var = USE_FROM_PTR (op_p);
-  if (TREE_CODE (var) != SSA_NAME)
-    SET_USE (op_p, get_reaching_def (var));
-  else
-    {
-#if defined ENABLE_CHECKING
-      /* If we get to this point, VAR is an SSA_NAME.  If VAR's symbol
-	 was marked for renaming, make sure that its reaching
-	 definition is VAR itself.  Otherwise, something has gone
-	 wrong.  */
-      tree sym = SSA_NAME_VAR (var);
-      if (bitmap_bit_p (vars_to_rename, var_ann (sym)->uid))
-	gcc_assert (var == get_reaching_def (SSA_NAME_VAR (var)));
-#endif
-    }
-}
-
-/* Register DEF (an SSA_NAME) to be a new definition for its underlying
-   variable (SSA_NAME_VAR (DEF)) and push VAR's current reaching definition
-   into the stack pointed by BLOCK_DEFS_P.  */
+/* Dump SSA statistics on stderr.  */
 
 void
-register_new_def (tree def, VEC (tree_on_heap) **block_defs_p)
-{
-  tree var = SSA_NAME_VAR (def);
-  tree currdef;
-   
-  /* If this variable is set in a single basic block and all uses are
-     dominated by the set(s) in that single basic block, then there is
-     no reason to record anything for this variable in the block local
-     definition stacks.  Doing so just wastes time and memory.
-
-     This is the same test to prune the set of variables which may
-     need PHI nodes.  So we just use that information since it's already
-     computed and available for us to use.  */
-  if (get_phi_state (var) == NEED_PHI_STATE_NO)
-    {
-      set_current_def (var, def);
-      return;
-    }
-
-  currdef = get_current_def (var);
-
-  /* Push the current reaching definition into *BLOCK_DEFS_P.  This stack is
-     later used by the dominator tree callbacks to restore the reaching
-     definitions for all the variables defined in the block after a recursive
-     visit to all its immediately dominated blocks.  If there is no current
-     reaching definition, then just record the underlying _DECL node.  */
-  VEC_safe_push (tree_on_heap, *block_defs_p, currdef ? currdef : var);
-
-  /* Set the current reaching definition for VAR to be DEF.  */
-  set_current_def (var, def);
-}
-
-/* Return the current definition for variable VAR.  If none is found,
-   create a new SSA name to act as the zeroth definition for VAR.  If VAR
-   is call clobbered and there exists a more recent definition of
-   GLOBAL_VAR, return the definition for GLOBAL_VAR.  This means that VAR
-   has been clobbered by a function call since its last assignment.  */
-
-static tree
-get_reaching_def (tree var)
+debug_tree_ssa_stats (void)
 {
-  tree default_d, currdef_var, avar;
-  
-  /* Lookup the current reaching definition for VAR.  */
-  default_d = NULL_TREE;
-  currdef_var = get_current_def (var);
-
-  /* If there is no reaching definition for VAR, create and register a
-     default definition for it (if needed).  */
-  if (currdef_var == NULL_TREE)
-    {
-      if (TREE_CODE (var) == SSA_NAME)
-	avar = SSA_NAME_VAR (var);
-      else
-	avar = var;
-
-      default_d = default_def (avar);
-      if (default_d == NULL_TREE)
-	{
-	  default_d = make_ssa_name (avar, build_empty_stmt ());
-	  set_default_def (avar, default_d);
-	}
-      set_current_def (var, default_d);
-    }
-
-  /* Return the current reaching definition for VAR, or the default
-     definition, if we had to create one.  */
-  return (currdef_var) ? currdef_var : default_d;
+  dump_tree_ssa_stats (stderr);
 }
 
 
@@ -1305,6 +1050,7 @@ def_blocks_eq (const void *p1, const void *p2)
 	 == ((const struct def_blocks_d *)p2)->var;
 }
 
+
 /* Free memory allocated by one entry in DEF_BLOCKS.  */
 
 static void
@@ -1318,14 +1064,6 @@ def_blocks_free (void *p)
 }
 
 
-/* Dump the DEF_BLOCKS hash table on stderr.  */
-
-void
-debug_def_blocks (void)
-{
-  htab_traverse (def_blocks, debug_def_blocks_r, NULL);
-}
-
 /* Callback for htab_traverse to dump the DEF_BLOCKS hash table.  */
 
 static int
@@ -1342,46 +1080,15 @@ debug_def_blocks_r (void **slot, void *data ATTRIBUTE_UNUSED)
 }
 
 
-/* Return the set of blocks where variable VAR is defined and the blocks
-   where VAR is live on entry (livein).  Return NULL, if no entry is
-   found in DEF_BLOCKS.  */
+/* Dump the DEF_BLOCKS hash table on stderr.  */
 
-static inline struct def_blocks_d *
-find_def_blocks_for (tree var)
+void
+debug_def_blocks (void)
 {
-  struct def_blocks_d dm;
-  dm.var = var;
-  return (struct def_blocks_d *) htab_find (def_blocks, &dm);
+  htab_traverse (def_blocks, debug_def_blocks_r, NULL);
 }
 
 
-/* Return the set of blocks where variable VAR is defined and the blocks
-   where VAR is live on entry (livein).  If no entry is found in
-   DEF_BLOCKS, a new one is created and returned.  */
-
-static inline struct def_blocks_d *
-get_def_blocks_for (tree var)
-{
-  struct def_blocks_d db, *db_p;
-  void **slot;
-
-  db.var = var;
-  slot = htab_find_slot (def_blocks, (void *) &db, INSERT);
-  if (*slot == NULL)
-    {
-      db_p = xmalloc (sizeof (*db_p));
-      db_p->var = var;
-      db_p->def_blocks = BITMAP_ALLOC (NULL);
-      db_p->phi_blocks = BITMAP_ALLOC (NULL);
-      db_p->livein_blocks = BITMAP_ALLOC (NULL);
-      *slot = (void *) db_p;
-    }
-  else
-    db_p = (struct def_blocks_d *) *slot;
-
-  return db_p;
-}
-
 /* If a variable V in VARS_TO_RENAME is a pointer, the renaming
    process will cause us to lose the name memory tags that may have
    been associated with the various SSA_NAMEs of V.  This means that
@@ -1433,12 +1140,12 @@ invalidate_name_tags (bitmap vars_to_rename)
       }
 }
 
-/* Rewrite the actual blocks, statements, and phi arguments, to be in SSA
+
+/* Rewrite the actual blocks, statements, and PHI arguments, to be in SSA
    form.  FIX_VIRTUAL_PHIS is true if we should only be fixing up virtual
-   phi arguments, instead of adding new phi arguments for just added phi
+   PHI arguments, instead of adding new PHI arguments for just added PHI
    nodes.  */
 
-
 static void
 rewrite_blocks (bool fix_virtual_phis)
 {
@@ -1493,6 +1200,20 @@ rewrite_blocks (bool fix_virtual_phis)
   timevar_pop (TV_TREE_SSA_REWRITE_BLOCKS);
 }
 
+
+/* Block initialization routine for mark_def_sites.  Clear the 
+   KILLS bitmap at the start of each block.  */
+
+static void
+mark_def_sites_initialize_block (struct dom_walk_data *walk_data,
+				 basic_block bb ATTRIBUTE_UNUSED)
+{
+  struct mark_def_sites_global_data *gd = walk_data->global_data;
+  bitmap kills = gd->kills;
+  bitmap_clear (kills);
+}
+
+
 /* Mark the definition site blocks for each variable, so that we know where
    the variable is actually live.  */
 
@@ -1513,7 +1234,6 @@ mark_def_site_blocks (void)
   /* Ensure that the dominance information is OK.  */
   calculate_dominance_info (CDI_DOMINATORS);
 
-
   /* Setup callbacks for the generic dominator tree walker to find and
      mark definition sites.  */
   walk_data.walk_stmts_backward = false;
@@ -1628,8 +1348,35 @@ rewrite_into_ssa (bool all)
   timevar_pop (TV_TREE_SSA_OTHER);
 }
 
-/* Rewrite the def-def chains so that they have the correct reaching
-   definitions.  */
+
+/* Rewrites all variables into SSA.  */
+
+static void
+rewrite_all_into_ssa (void)
+{
+  rewrite_into_ssa (true);
+}
+
+struct tree_opt_pass pass_build_ssa = 
+{
+  "ssa",				/* name */
+  NULL,					/* gate */
+  rewrite_all_into_ssa,			/* execute */
+  NULL,					/* sub */
+  NULL,					/* next */
+  0,					/* static_pass_number */
+  0,					/* tv_id */
+  PROP_cfg | PROP_referenced_vars,	/* properties_required */
+  PROP_ssa,				/* properties_provided */
+  0,					/* properties_destroyed */
+  0,					/* todo_flags_start */
+  TODO_dump_func | TODO_verify_ssa,	/* todo_flags_finish */
+  0					/* letter */
+};
+
+
+/* Rewrite the def-def chains of virtual operands so that they have
+   the correct reaching definitions.  */
 
 void
 rewrite_def_def_chains (void)
@@ -1638,10 +1385,302 @@ rewrite_def_def_chains (void)
   calculate_dominance_info (CDI_DOMINATORS);
   mark_def_site_blocks ();
   rewrite_blocks (true);
+}
+
+
 
+/*---------------------------------------------------------------------------
+    Functions to fix a program in invalid SSA form into valid SSA
+    form.  The main entry point here is rewrite_ssa_into_ssa.
+---------------------------------------------------------------------------*/
+
+/* Called after visiting basic block BB.  Restore CURRDEFS to its
+   original value.  */
+
+static void
+ssa_rewrite_finalize_block (struct dom_walk_data *walk_data ATTRIBUTE_UNUSED,
+			    basic_block bb ATTRIBUTE_UNUSED)
+{
+
+  /* Step 5.  Restore the current reaching definition for each variable
+     referenced in the block (in reverse order).  */
+  while (VEC_length (tree_on_heap, block_defs_stack) > 0)
+    {
+      tree var = VEC_pop (tree_on_heap, block_defs_stack);
+      tree saved_def;
+      
+      if (var == NULL)
+	break;
+
+      saved_def = VEC_pop (tree_on_heap, block_defs_stack);
+      set_current_def (var, saved_def);
+    }
 }
+
+
+/* Register DEF (an SSA_NAME) to be a new definition for the original
+   ssa name VAR and push VAR's current reaching definition
+   into the stack pointed by BLOCK_DEFS_P.  */
+
+static void
+ssa_register_new_def (tree var, tree def)
+{
+  tree currdef;
+   
+  /* If this variable is set in a single basic block and all uses are
+     dominated by the set(s) in that single basic block, then there is
+     nothing to do.  TODO we should not be called at all, and just
+     keep the original name.  */
+  if (get_phi_state (var) == NEED_PHI_STATE_NO)
+    {
+      set_current_def (var, def);
+      return;
+    }
+
+  currdef = get_current_def (var);
+
+  /* Push the current reaching definition into *BLOCK_DEFS_P.  This stack is
+     later used by the dominator tree callbacks to restore the reaching
+     definitions for all the variables defined in the block after a recursive
+     visit to all its immediately dominated blocks.  */
+  VEC_safe_push (tree_on_heap, block_defs_stack, currdef);
+  VEC_safe_push (tree_on_heap, block_defs_stack, var);
+
+  /* Set the current reaching definition for VAR to be DEF.  */
+  set_current_def (var, def);
+}
+
+
+/* Same as rewrite_stmt, for rewriting ssa names.  */
+
+static void
+ssa_rewrite_stmt (struct dom_walk_data *walk_data,
+		  basic_block bb ATTRIBUTE_UNUSED,
+		  block_stmt_iterator si)
+{
+  stmt_ann_t ann;
+  tree stmt, var;
+  ssa_op_iter iter;
+  use_operand_p use_p;
+  def_operand_p def_p;
+  sbitmap names_to_rename = walk_data->global_data;
+
+  stmt = bsi_stmt (si);
+  ann = stmt_ann (stmt);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Renaming statement ");
+      print_generic_stmt (dump_file, stmt, TDF_SLIM);
+      fprintf (dump_file, "\n");
+    }
+
+  /* We have just scanned the code for operands.  No statement should
+     be modified.  */
+  gcc_assert (!ann->modified);
+
+  /* Step 1.  Rewrite USES and VUSES in the statement.  */
+  FOR_EACH_SSA_USE_OPERAND (use_p, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
+    {
+      if (TEST_BIT (names_to_rename, SSA_NAME_VERSION (USE_FROM_PTR (use_p))))
+	SET_USE (use_p, get_reaching_def (USE_FROM_PTR (use_p)));
+    }
+
+  /* Step 2.  Register the statement's DEF and VDEF operands.  */
+  FOR_EACH_SSA_DEF_OPERAND (def_p, stmt, iter, SSA_OP_ALL_DEFS)
+    {
+      var = DEF_FROM_PTR (def_p);
+
+      if (!TEST_BIT (names_to_rename, SSA_NAME_VERSION (var)))
+	continue;
+
+      SET_DEF (def_p, duplicate_ssa_name (var, stmt));
+      ssa_register_new_def (var, DEF_FROM_PTR (def_p));
+    }
+}
+
+
+/* Ditto, for ssa name rewriting.  */
+
+static void
+ssa_rewrite_phi_arguments (struct dom_walk_data *walk_data, basic_block bb)
+{
+  edge e;
+  sbitmap names_to_rename = walk_data->global_data;
+  use_operand_p op;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->succs)
+    {
+      tree phi;
+
+      if (e->dest == EXIT_BLOCK_PTR)
+	continue;
+
+      for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
+	{
+	  op = PHI_ARG_DEF_PTR_FROM_EDGE (phi, e);
+	  if (TREE_CODE (USE_FROM_PTR (op)) != SSA_NAME)
+	    continue;
+	  
+	  if (!TEST_BIT (names_to_rename, SSA_NAME_VERSION (USE_FROM_PTR (op))))
+	    continue; 
+
+	  SET_USE (op, get_reaching_def (USE_FROM_PTR (op)));
+	  if (e->flags & EDGE_ABNORMAL)
+	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (USE_FROM_PTR (op)) = 1;
+	}
+    }
+}
+
+/* Ditto, for rewriting ssa names.  */
+
+static void
+ssa_rewrite_initialize_block (struct dom_walk_data *walk_data, basic_block bb)
+{
+  tree phi, new_name;
+  sbitmap names_to_rename = walk_data->global_data;
+  edge e;
+  bool abnormal_phi;
+  edge_iterator ei;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    fprintf (dump_file, "\n\nRenaming block #%d\n\n", bb->index);
+
+  /* Mark the unwind point for this block.  */
+  VEC_safe_push (tree_on_heap, block_defs_stack, NULL_TREE);
+
+  FOR_EACH_EDGE (e, ei, bb->preds)
+    if (e->flags & EDGE_ABNORMAL)
+      break;
+  abnormal_phi = (e != NULL);
+
+  /* Step 1.  Register new definitions for every PHI node in the block.
+     Conceptually, all the PHI nodes are executed in parallel and each PHI
+     node introduces a new version for the associated variable.  */
+  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+    {
+      tree result = PHI_RESULT (phi);
+
+      if (TEST_BIT (names_to_rename, SSA_NAME_VERSION (result)))
+	{
+	  new_name = duplicate_ssa_name (result, phi);
+	  SET_PHI_RESULT (phi, new_name);
+
+	  if (abnormal_phi)
+	    SSA_NAME_OCCURS_IN_ABNORMAL_PHI (new_name) = 1;
+	  ssa_register_new_def (result, new_name);
+	}
+    }
+}
+
+
+/* Same as mark_def_sites, but works over SSA names.  */
+
+static void
+ssa_mark_def_sites (struct dom_walk_data *walk_data,
+		    basic_block bb,
+		    block_stmt_iterator bsi)
+{
+  struct mark_def_sites_global_data *gd = walk_data->global_data;
+  bitmap kills = gd->kills;
+  size_t uid, def_uid;
+  tree stmt, use, def;
+  ssa_op_iter iter;
+
+  /* Mark all the blocks that have definitions for each variable in the
+     names_to_rename bitmap.  */
+  stmt = bsi_stmt (bsi);
+  get_stmt_operands (stmt);
+
+  /* If a variable is used before being set, then the variable is live
+     across a block boundary, so mark it live-on-entry to BB.  */
+  FOR_EACH_SSA_TREE_OPERAND (use, stmt, iter, SSA_OP_ALL_USES | SSA_OP_ALL_KILLS)
+    {
+      uid = SSA_NAME_VERSION (use);
+
+      if (TEST_BIT (gd->names_to_rename, uid)
+	  && !bitmap_bit_p (kills, uid))
+	set_livein_block (use, bb);
+    }
+	  
+  /* Now process the definition made by this statement.  Mark the
+     variables in KILLS.  */
+  FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
+    {
+      def_uid = SSA_NAME_VERSION (def);
+
+      if (TEST_BIT (gd->names_to_rename, def_uid))
+	{
+	  set_def_block (def, bb, false, true);
+	  bitmap_set_bit (kills, def_uid);
+	}
+    }
+}
+
+
+/* Block initialization routine for mark_def_sites.  Clear the 
+   KILLS bitmap at the start of each block.  */
+
+static void
+ssa_mark_def_sites_initialize_block (struct dom_walk_data *walk_data,
+				     basic_block bb)
+{
+  struct mark_def_sites_global_data *gd = walk_data->global_data;
+  bitmap kills = gd->kills;
+  tree phi, def;
+  unsigned def_uid;
+
+  bitmap_clear (kills);
+
+  for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
+    {
+      def = PHI_RESULT (phi);
+      def_uid = SSA_NAME_VERSION (def);
+
+      if (!TEST_BIT (gd->names_to_rename, def_uid))
+	continue;
+
+      set_def_block (def, bb, true, true);
+      bitmap_set_bit (kills, def_uid);
+    }
+}
+
+/* Marks ssa names used as arguments of phis at the end of BB.  */
+
+static void
+ssa_mark_phi_uses (struct dom_walk_data *walk_data, basic_block bb)
+{
+  struct mark_def_sites_global_data *gd = walk_data->global_data;
+  bitmap kills = gd->kills;
+  edge e;
+  tree phi, use;
+  unsigned uid;
+  edge_iterator ei;
+
+  FOR_EACH_EDGE (e, ei, bb->succs)
+    {
+      if (e->dest == EXIT_BLOCK_PTR)
+	continue;
+
+      for (phi = phi_nodes (e->dest); phi; phi = PHI_CHAIN (phi))
+	{
+	  use = PHI_ARG_DEF_FROM_EDGE (phi, e);
+	  if (TREE_CODE (use) != SSA_NAME)
+	    continue;
+
+	  uid = SSA_NAME_VERSION (use);
+
+	  if (TEST_BIT (gd->names_to_rename, uid)
+	      && !bitmap_bit_p (kills, uid))
+	    set_livein_block (use, bb);
+	}
+    }
+}
+       
+   
 /* The marked ssa names may have more than one definition;
-   add phi nodes and rewrite them to fix this.  */
+   add PHI nodes and rewrite them to fix this.  */
 
 void
 rewrite_ssa_into_ssa (void)
@@ -1796,28 +1835,3 @@ rewrite_ssa_into_ssa (void)
   block_defs_stack = NULL;
   timevar_pop (TV_TREE_SSA_OTHER);
 }
-
-/* Rewrites all variables into ssa.  */
-
-static void
-rewrite_all_into_ssa (void)
-{
-  rewrite_into_ssa (true);
-}
-
-struct tree_opt_pass pass_build_ssa = 
-{
-  "ssa",				/* name */
-  NULL,					/* gate */
-  rewrite_all_into_ssa,			/* execute */
-  NULL,					/* sub */
-  NULL,					/* next */
-  0,					/* static_pass_number */
-  0,					/* tv_id */
-  PROP_cfg | PROP_referenced_vars,	/* properties_required */
-  PROP_ssa,				/* properties_provided */
-  0,					/* properties_destroyed */
-  0,					/* todo_flags_start */
-  TODO_dump_func | TODO_verify_ssa,			/* todo_flags_finish */
-  0					/* letter */
-};