tree-ssa-dom.c (simplify_rhs_and_lookup_avail_expr): Remove reassociation code.

	* tree-ssa-dom.c (simplify_rhs_and_lookup_avail_expr): Remove
	reassociation code.
	* passes.c (init_optimization_passes): Run reassociation again
	after loop optimizations.

	* tree-ssa-dom.c (thread_across_edge): Canonicalize condition
	if necessary.
	(optimize_stmt): Ditto.
	(canonicalize_comparison): New function.
	* tree-ssa-operands.c (swap_tree_operands): Make external.
	(get_expr_operands): Stop auto-canonicalization.
	* tree-ssa-reassoc.c: Rewrite.
	(init_optimization_passes): 
	* tree-flow.h (swap_tree_operands): Prototype.
	* Makefile.in (tree-ssa-reassoc.o): Update dependencies.

	* gcc.dg/tree-ssa/ssa-pre-2.c: Update due to reassociation changes.
	* gcc.dg/tree-ssa/reassoc-1.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-2.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-3.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-4.c: Likewise.
	* gcc.dg/tree-ssa/reassoc-5.c: New.
	* gcc.dg/tree-ssa/reassoc-6.c: New.
	* gcc.dg/tree-ssa/reassoc-7.c: New.
	* gcc.dg/tree-ssa/reassoc-8.c: New.
	* gcc.dg/tree-ssa/reassoc-9.c: New.
	* gcc.dg/tree-ssa/reassoc-10.c: New.
	* gcc.dg/tree-ssa/reassoc-11.c: New.

From-SVN: r108425

1 files changed, 1284 insertions, 406 deletions

diff --git a/gcc/tree-ssa-reassoc.c b/gcc/tree-ssa-reassoc.c
index 5514c3d..6f19408 100644
--- a/gcc/tree-ssa-reassoc.c
+++ b/gcc/tree-ssa-reassoc.c
@@ -33,249 +33,219 @@ Boston, MA 02110-1301, USA.  */
 #include "tree-gimple.h"
 #include "tree-dump.h"
 #include "timevar.h"
-#include "hashtab.h"
 #include "tree-iterator.h"
 #include "tree-pass.h"
+#include "alloc-pool.h"
+#include "vec.h"
+#include "langhooks.h"
 
-/*  This is a simple global reassociation pass that uses a combination
-    of heuristics and a hashtable to try to expose more operations to
-    CSE.  
+/*  This is a simple global reassociation pass.  It is, in part, based
+    on the LLVM pass of the same name (They do some things more/less
+    than we do, in different orders, etc).
 
-    The basic idea behind the heuristic is to rank expressions by
-    depth of the computation tree and loop depth, and try to produce
-    expressions consisting of small rank operations, as they are more
-    likely to reoccur.  In addition, we use a hashtable to try to see
-    if we can transpose an operation into something we have seen
-    before.
+    It consists of five steps:
 
-    Note that the way the hashtable is structured will sometimes find
-    matches that will not expose additional redundancies, since it is
-    not unwound as we traverse back up one branch of the dominator
-    tree and down another.  However, the cost of improving this is
-    probably not worth the additional benefits it will bring.  */
+    1. Breaking up subtract operations into addition + negate, where
+    it would promote the reassociation of adds.
 
-/* Statistics */
-static struct
-{
-  int reassociated_by_rank;
-  int reassociated_by_match;
-} reassociate_stats;
+    2. Left linearization of the expression trees, so that (A+B)+(C+D)
+    becomes (((A+B)+C)+D), which is easier for us to rewrite later.
+    During linearization, we place the operands of the binary
+    expressions into a vector of operand_entry_t
 
+    3. Optimization of the operand lists, eliminating things like a +
+    -a, a & a, etc.
 
+    4. Rewrite the expression trees we linearized and optimized so
+    they are in proper rank order.
 
-/* Seen binary operator hashtable.  */
-static htab_t seen_binops;
+    5. Repropagate negates, as nothing else will clean it up ATM.
 
-/* Binary operator struct. */
+    A bit of theory on #4, since nobody seems to write anything down
+    about why it makes sense to do it the way they do it:
 
-typedef struct seen_binop_d
-{
-  tree op1;
-  tree op2;
-} *seen_binop_t;
+    We could do this much nicer theoretically, but don't (for reasons
+    explained after how to do it theoretically nice :P).
 
-/* Return a SEEN_BINOP_T if we have seen an associative binary
-   operator with OP1 and OP2 in it.  */
+    In order to promote the most redundancy elimination, you want
+    binary expressions whose operands are the same rank (or
+    preferrably, the same value) exposed to the redundancy eliminator,
+    for possible elimination.
 
-static seen_binop_t
-find_seen_binop (tree op1, tree op2)
-{
-  void **slot;
-  struct seen_binop_d sbd;
-  sbd.op1 = op1;
-  sbd.op2 = op2;
-  slot = htab_find_slot (seen_binops, &sbd, NO_INSERT);
-  if (!slot)
-    return NULL;
-  return ((seen_binop_t) *slot);
-}
+    So the way to do this if we really cared, is to build the new op
+    tree from the leaves to the roots, merging as you go, and putting the
+    new op on the end of the worklist, until you are left with one
+    thing on the worklist.
 
-/* Insert a binary operator consisting of OP1 and OP2 into the
-   SEEN_BINOP table.  */
+    IE if you have to rewrite the following set of operands (listed with
+    rank in parentheses), with opcode PLUS_EXPR:
 
-static void
-insert_seen_binop (tree op1, tree op2)
-{
-  void **slot;
-  seen_binop_t new_pair = xmalloc (sizeof (*new_pair));
-  new_pair->op1 = op1;
-  new_pair->op2 = op2;
-  slot = htab_find_slot (seen_binops, new_pair, INSERT);
-  if (*slot != NULL)
-    free (*slot);
-  *slot = new_pair;
-}
+    a (1),  b (1),  c (1),  d (2), e (2)
 
-/* Return the hash value for a seen binop structure pointed to by P.
-   Because all the binops we consider are associative, we just add the
-   hash value for op1 and op2.  */
 
-static hashval_t
-seen_binop_hash (const void *p)
-{
-  const seen_binop_t sb = (seen_binop_t) p;
-  return iterative_hash_expr (sb->op1, 0) + iterative_hash_expr (sb->op2, 0);
-}
+    We start with our merge worklist empty, and the ops list with all of
+    those on it.
 
-/* Return true if two seen binop structures pointed to by P1 and P2 are equal.
-   We have to check the operators both ways because we don't know what
-   order they appear in the table.  */
+    You want to first merge all leaves of the same rank, as much as
+    possible.
 
-static int
-seen_binop_eq (const void *p1, const void *p2)
-{
-  const seen_binop_t sb1 = (seen_binop_t) p1;
-  const seen_binop_t sb2 = (seen_binop_t) p2;
-  return (sb1->op1 == sb2->op1 && sb1->op2 == sb2->op2)
-    || (sb1->op2 == sb2->op1 && sb1->op1 == sb2->op2);
-}
+    So first build a binary op of
+
+    mergetmp = a + b, and put "mergetmp" on the merge worklist.
+
+    Because there is no three operand form of PLUS_EXPR, c is not going to
+    be exposed to redundancy elimination as a rank 1 operand.
+
+    So you might as well throw it on the merge worklist (you could also
+    consider it to now be a rank two operand, and merge it with d and e,
+    but in this case, you then have evicted e from a binary op. So at
+    least in this situation, you can't win.)
+
+    Then build a binary op of d + e
+    mergetmp2 = d + e
+
+    and put mergetmp2 on the merge worklist.
+    
+    so merge worklist = {mergetmp, c, mergetmp2}
+    
+    Continue building binary ops of these operations until you have only
+    one operation left on the worklist.
+    
+    So we have
+    
+    build binary op
+    mergetmp3 = mergetmp + c
+    
+    worklist = {mergetmp2, mergetmp3}
+    
+    mergetmp4 = mergetmp2 + mergetmp3
+    
+    worklist = {mergetmp4}
+    
+    because we have one operation left, we can now just set the original
+    statement equal to the result of that operation.
+    
+    This will at least expose a + b  and d + e to redundancy elimination
+    as binary operations.
+    
+    For extra points, you can reuse the old statements to build the
+    mergetmps, since you shouldn't run out.
 
-/* Value rank structure.  */
+    So why don't we do this?
+    
+    Because it's expensive, and rarely will help.  Most trees we are
+    reassociating have 3 or less ops.  If they have 2 ops, they already
+    will be written into a nice single binary op.  If you have 3 ops, a
+    single simple check suffices to tell you whether the first two are of the
+    same rank.  If so, you know to order it
+
+    mergetmp = op1 + op2
+    newstmt = mergetmp + op3
+    
+    instead of
+    mergetmp = op2 + op3
+    newstmt = mergetmp + op1
+    
+    If all three are of the same rank, you can't expose them all in a
+    single binary operator anyway, so the above is *still* the best you
+    can do.
+    
+    Thus, this is what we do.  When we have three ops left, we check to see
+    what order to put them in, and call it a day.  As a nod to vector sum
+    reduction, we check if any of ops are a really a phi node that is a
+    destructive update for the associating op, and keep the destructive
+    update together for vector sum reduction recognition.  */
 
-typedef struct valrank_d
+
+/* Statistics */
+static struct
+{
+  int linearized;
+  int constants_eliminated;
+  int ops_eliminated;
+  int rewritten;
+} reassociate_stats;
+
+/* Operator, rank pair.  */
+typedef struct operand_entry
 {
-  tree e;   
-  unsigned int rank;  
-} *valrank_t;
+  unsigned int rank;
+  tree op;
+} *operand_entry_t;
+
+static alloc_pool operand_entry_pool;
+
 
 /* Starting rank number for a given basic block, so that we can rank
    operations using unmovable instructions in that BB based on the bb
    depth.  */
 static unsigned int *bb_rank;
 
-/* Value rank hashtable.  */
-static htab_t value_rank;
+/* Operand->rank hashtable.  */
+static htab_t operand_rank;
 
 
-/* Look up the value rank structure for expression E.  */
+/* Look up the operand rank structure for expression E.  */
 
-static valrank_t
-find_value_rank (tree e)
+static operand_entry_t
+find_operand_rank (tree e)
 {
   void **slot;
-  struct valrank_d vrd;
-  vrd.e = e;
-  slot = htab_find_slot (value_rank, &vrd, NO_INSERT);
+  struct operand_entry vrd;
+
+  vrd.op = e;
+  slot = htab_find_slot (operand_rank, &vrd, NO_INSERT);
   if (!slot)
     return NULL;
-  return ((valrank_t) *slot);
+  return ((operand_entry_t) *slot);
 }
 
-/* Insert {E,RANK} into the value rank hashtable.  */
+/* Insert {E,RANK} into the operand rank hashtable.  */
 
 static void
-insert_value_rank (tree e, unsigned int rank)
+insert_operand_rank (tree e, unsigned int rank)
 {
   void **slot;
-  valrank_t new_pair = xmalloc (sizeof (*new_pair));
-  new_pair->e = e;
+  operand_entry_t new_pair = pool_alloc (operand_entry_pool);
+
+  new_pair->op = e;
   new_pair->rank = rank;
-  slot = htab_find_slot (value_rank, new_pair, INSERT);
+  slot = htab_find_slot (operand_rank, new_pair, INSERT);
   gcc_assert (*slot == NULL);
   *slot = new_pair;
-
 }
 
-
-/* Return the hash value for a value rank structure  */
+/* Return the hash value for a operand rank structure  */
 
 static hashval_t
-valrank_hash (const void *p)
+operand_entry_hash (const void *p)
 {
-  const valrank_t vr = (valrank_t) p;
-  return iterative_hash_expr (vr->e, 0);
+  const operand_entry_t vr = (operand_entry_t) p;
+  return iterative_hash_expr (vr->op, 0);
 }
 
-/* Return true if two value rank structures are equal.  */
+/* Return true if two operand rank structures are equal.  */
 
 static int
-valrank_eq (const void *p1, const void *p2)
+operand_entry_eq (const void *p1, const void *p2)
 {
-  const valrank_t vr1 = (valrank_t) p1;
-  const valrank_t vr2 = (valrank_t) p2;
-  return vr1->e == vr2->e;
+  const operand_entry_t vr1 = (operand_entry_t) p1;
+  const operand_entry_t vr2 = (operand_entry_t) p2;
+  return vr1->op == vr2->op;
 }
 
 
-/* Initialize the reassociation pass.  */
-
-static void
-init_reassoc (void)
-{
-  int i;
-  unsigned int rank = 2;
-  
-  tree param;
-  int *bbs = xmalloc ((last_basic_block + 1) * sizeof (int));
-  
-  memset (&reassociate_stats, 0, sizeof (reassociate_stats));
-
-  /* Reverse RPO (Reverse Post Order) will give us something where
-     deeper loops come later.  */
-  flow_reverse_top_sort_order_compute (bbs);
-  bb_rank = xcalloc (last_basic_block + 1, sizeof (unsigned int));
-  value_rank = htab_create (511, valrank_hash,
-			    valrank_eq, free);
-  seen_binops = htab_create (511, seen_binop_hash,
-			     seen_binop_eq, free);
-
-  /* Give each argument a distinct rank.   */
-  for (param = DECL_ARGUMENTS (current_function_decl);
-       param;
-       param = TREE_CHAIN (param))
-    {
-      if (default_def (param) != NULL)
-	{
-	  tree def = default_def (param);
-	  insert_value_rank (def, ++rank);
-	}
-    }
-  /* Give the chain decl a distinct rank. */
-  if (cfun->static_chain_decl != NULL)
-    {
-      tree def = default_def (cfun->static_chain_decl);
-      if (def != NULL)
-        insert_value_rank (def, ++rank);
-    }
-  
-  /* Set up rank for each BB  */
-  for (i = 0; i < n_basic_blocks; i++)
-    bb_rank[bbs[i]] = ++rank  << 16;
-
-  free (bbs);
-  calculate_dominance_info (CDI_DOMINATORS);
-
-}
-
-/* Cleanup after the reassociation pass, and print stats if
-   requested.  */
-
-static void
-fini_reassoc (void)
-{
-
-  if (dump_file && (dump_flags & TDF_STATS))
-    {
-      fprintf (dump_file, "Reassociation stats:\n");
-      fprintf (dump_file, "Reassociated by rank: %d\n", reassociate_stats.reassociated_by_rank);
-      fprintf (dump_file, "Reassociated by match: %d\n", reassociate_stats.reassociated_by_match);
-    }
-  htab_delete (value_rank);
-  htab_delete (seen_binops);
-  free (bb_rank);
-}
-
 /* Given an expression E, return the rank of the expression.  */
 
 static unsigned int
 get_rank (tree e)
 {
-  valrank_t vr;
+  operand_entry_t vr;
 
-  /* Constants have rank 0.  */  
+  /* Constants have rank 0.  */
   if (is_gimple_min_invariant (e))
     return 0;
-  
+
   /* SSA_NAME's have the rank of the expression they are the result
      of.
      For globals and uninitialized values, the rank is 0.
@@ -290,24 +260,24 @@ get_rank (tree e)
   if (TREE_CODE (e) == SSA_NAME)
     {
       tree stmt;
-      tree rhs;      
+      tree rhs;
       unsigned int rank, maxrank;
       int i;
-      
+
       if (TREE_CODE (SSA_NAME_VAR (e)) == PARM_DECL
 	  && e == default_def (SSA_NAME_VAR (e)))
-	return find_value_rank (e)->rank;
-      
+	return find_operand_rank (e)->rank;
+
       stmt = SSA_NAME_DEF_STMT (e);
       if (bb_for_stmt (stmt) == NULL)
 	return 0;
-      
+
       if (TREE_CODE (stmt) != MODIFY_EXPR
 	  || !ZERO_SSA_OPERANDS (stmt, SSA_OP_VIRTUAL_DEFS))
 	return bb_rank[bb_for_stmt (stmt)->index];
 
       /* If we already have a rank for this expression, use that.  */
-      vr = find_value_rank (e);
+      vr = find_operand_rank (e);
       if (vr)
 	return vr->rank;
 
@@ -318,24 +288,25 @@ get_rank (tree e)
       rhs = TREE_OPERAND (stmt, 1);
       if (TREE_CODE_LENGTH (TREE_CODE (rhs)) == 0)
 	rank = MAX (rank, get_rank (rhs));
-      else 
+      else
 	{
-	  for (i = 0; 
-	       i < TREE_CODE_LENGTH (TREE_CODE (rhs)) 
+	  for (i = 0;
+	       i < TREE_CODE_LENGTH (TREE_CODE (rhs))
 		 && TREE_OPERAND (rhs, i)
-		 && rank != maxrank; i++)
+		 && rank != maxrank;
+	       i++)
 	    rank = MAX(rank, get_rank (TREE_OPERAND (rhs, i)));
 	}
-      
+
       if (dump_file && (dump_flags & TDF_DETAILS))
 	{
 	  fprintf (dump_file, "Rank for ");
 	  print_generic_expr (dump_file, e, 0);
 	  fprintf (dump_file, " is %d\n", (rank + 1));
 	}
-      
+
       /* Note the rank in the hashtable so we don't recompute it.  */
-      insert_value_rank (e, (rank + 1));
+      insert_operand_rank (e, (rank + 1));
       return (rank + 1);
     }
 
@@ -343,274 +314,1179 @@ get_rank (tree e)
   return 0;
 }
 
+DEF_VEC_P(operand_entry_t);
+DEF_VEC_ALLOC_P(operand_entry_t, heap);
+
+/* We want integer ones to end up last no matter what, since they are
+   the ones we can do the most with.  */
+#define INTEGER_CONST_TYPE 1 << 3
+#define FLOAT_CONST_TYPE 1 << 2
+#define OTHER_CONST_TYPE 1 << 1
+
+/* Classify an invariant tree into integer, float, or other, so that
+   we can sort them to be near other constants of the same type.  */
+static inline int
+constant_type (tree t)
+{
+  if (INTEGRAL_TYPE_P (TREE_TYPE (t)))
+    return INTEGER_CONST_TYPE;
+  else if (SCALAR_FLOAT_TYPE_P (TREE_TYPE (t)))
+    return FLOAT_CONST_TYPE;
+  else
+    return OTHER_CONST_TYPE;
+}
+
+/* qsort comparison function to sort operand entries PA and PB by rank
+   so that the sorted array is ordered by rank in decreasing order.  */
+static int
+sort_by_operand_rank (const void *pa, const void *pb)
+{
+  const operand_entry_t oea = *(const operand_entry_t *)pa;
+  const operand_entry_t oeb = *(const operand_entry_t *)pb;
+
+  /* It's nicer for optimize_expression if constants that are likely
+     to fold when added/multiplied//whatever are put next to each
+     other.  Since all constants have rank 0, order them by type.  */
+  if (oeb->rank == 0 &&  oea->rank == 0)
+    return constant_type (oeb->op) - constant_type (oea->op);
+
+  /* Lastly, make sure the versions that are the same go next to each
+     other.  We use SSA_NAME_VERSION because it's stable.  */
+  if ((oeb->rank - oea->rank == 0)
+      && TREE_CODE (oea->op) == SSA_NAME
+      && TREE_CODE (oeb->op) == SSA_NAME)
+    return SSA_NAME_VERSION (oeb->op) - SSA_NAME_VERSION (oea->op);
+
+  return oeb->rank - oea->rank;
+}
+
+/* Add an operand entry to *OPS for the tree operand OP.  */
+
+static void
+add_to_ops_vec (VEC(operand_entry_t, heap) **ops, tree op)
+{
+  operand_entry_t oe = pool_alloc (operand_entry_pool);
+
+  oe->op = op;
+  oe->rank = get_rank (op);
+  VEC_safe_push (operand_entry_t, heap, *ops, oe);
+}
 
-/* Decide whether we should transpose RHS and some operand of
-   LHSDEFOP.
-   If yes, then return true and set TAKEOP to the operand number of LHSDEFOP to
-   switch RHS for.
-   Otherwise, return false.  */
+/* Return true if STMT is reassociable operation containing a binary
+   operation with tree code CODE.  */
 
 static bool
-should_transpose (tree rhs ATTRIBUTE_UNUSED, 
-		  unsigned int rhsrank,
-		  tree lhsdefop, unsigned int *takeop)
-{
-  /* Attempt to expose the low ranked
-     arguments to CSE if we have something like:
-     a = <rank 2> + c (rank 1)
-     b = a (rank 3) + d (rank 1)
-     We want to transform this into:
-     a = c + d
-     b = <rank 2> + <rank 3>
-     
-     The op finding part wouldn't be necessary if
-			 we could swap the operands above and not have
-			 update_stmt change them back on us.
-  */
-  unsigned int lowrankop;
-  unsigned int lowrank;
-  unsigned int highrank;
-  unsigned int highrankop;
-  unsigned int temp;
-  
-  lowrankop = 0;
-  *takeop = 1;
-  lowrank = get_rank (TREE_OPERAND (lhsdefop, 0));
-  temp = get_rank (TREE_OPERAND (lhsdefop, 1));
-  highrank = temp;
-  highrankop = 1;
-  if (temp < lowrank)
+is_reassociable_op (tree stmt, enum tree_code code)
+{
+  if (!IS_EMPTY_STMT (stmt)
+      && TREE_CODE (stmt) == MODIFY_EXPR
+      && TREE_CODE (TREE_OPERAND (stmt, 1)) == code
+      && has_single_use (TREE_OPERAND (stmt, 0)))
+    return true;
+  return false;
+}
+
+
+/* Given NAME, if NAME is defined by a unary operation OPCODE, return the
+   operand of the negate operation.  Otherwise, return NULL.  */
+
+static tree
+get_unary_op (tree name, enum tree_code opcode)
+{
+  tree stmt = SSA_NAME_DEF_STMT (name);
+  tree rhs;
+
+  if (TREE_CODE (stmt) != MODIFY_EXPR)
+    return NULL_TREE;
+
+  rhs = TREE_OPERAND (stmt, 1);
+  if (TREE_CODE (rhs) == opcode)
+    return TREE_OPERAND (rhs, 0);
+  return NULL_TREE;
+}
+
+/* If CURR and LAST are a pair of ops that OPCODE allows us to
+   eliminate through equivalences, do so, remove them from OPS, and
+   return true.  Otherwise, return false.  */
+
+static bool
+eliminate_duplicate_pair (enum tree_code opcode,
+			  VEC (operand_entry_t, heap) **ops,
+			  bool *all_done,
+			  unsigned int i,
+			  operand_entry_t curr,
+			  operand_entry_t last)
+{
+
+  /* If we have two of the same op, and the opcode is & or |, we can
+     eliminate one of them.
+     If we have two of the same op, and the opcode is ^, we can
+     eliminate both of them.  */
+
+  if (last && last->op == curr->op)
     {
-      lowrankop = 1;
-      highrankop = 0;
-      *takeop = 0;
-      highrank = lowrank;
-      lowrank = temp;
+      switch (opcode)
+	{
+	case BIT_IOR_EXPR:
+	case BIT_AND_EXPR:
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Equivalence: ");
+	      print_generic_expr (dump_file, curr->op, 0);
+	      fprintf (dump_file, " [&|] ");
+	      print_generic_expr (dump_file, last->op, 0);
+	      fprintf (dump_file, " -> ");
+	      print_generic_stmt (dump_file, last->op, 0);
+	    }
+
+	  VEC_ordered_remove (operand_entry_t, *ops, i);
+	  reassociate_stats.ops_eliminated ++;
+
+	  return true;
+
+	case BIT_XOR_EXPR:
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Equivalence: ");
+	      print_generic_expr (dump_file, curr->op, 0);
+	      fprintf (dump_file, " ^ ");
+	      print_generic_expr (dump_file, last->op, 0);
+	      fprintf (dump_file, " -> nothing\n");
+	    }
+
+	  reassociate_stats.ops_eliminated += 2;
+
+	  if (VEC_length (operand_entry_t, *ops) == 2)
+	    {
+	      VEC_free (operand_entry_t, heap, *ops);
+	      *ops = NULL;
+	      add_to_ops_vec (ops, fold_convert (TREE_TYPE (last->op), 
+						 integer_zero_node));
+	      *all_done = true;
+	    }
+	  else
+	    {
+	      VEC_ordered_remove (operand_entry_t, *ops, i-1);
+	      VEC_ordered_remove (operand_entry_t, *ops, i-1);
+	    }
+
+	  return true;
+
+	default:
+	  break;
+	}
     }
-  
-  /* If highrank == lowrank, then we had something
-     like:
-     a = <rank 1> + <rank 1> 
-     already, so there is no guarantee that
-     swapping our argument in is going to be
-     better.
-     If we run reassoc twice, we could probably
-     have a flag that switches this behavior on,
-     so that we try once without it, and once with
-     it, so that redundancy elimination sees it
-     both ways.
-  */		      
-  
-  if (lowrank == rhsrank && highrank != lowrank)
-    return true;
+  return false;
+}
+
+/* If OPCODE is PLUS_EXPR, CURR->OP is really a negate expression,
+   look in OPS for a corresponding positive operation to cancel it
+   out.  If we find one, remove the other from OPS, replace
+   OPS[CURRINDEX] with 0, and return true.  Otherwise, return
+   false. */
 
-  /* Also, see if the LHS's high ranked op should be switched with our
-     RHS simply because it is greater in rank than our current RHS.  */
-  if (TREE_CODE (TREE_OPERAND (lhsdefop, highrankop)) == SSA_NAME)
+static bool
+eliminate_plus_minus_pair (enum tree_code opcode,
+			   VEC (operand_entry_t, heap) **ops,
+			   unsigned int currindex,
+			   operand_entry_t curr)
+{
+  tree negateop;
+  unsigned int i;
+  operand_entry_t oe;
+
+  if (opcode != PLUS_EXPR || TREE_CODE (curr->op) != SSA_NAME)
+    return false;
+
+  negateop = get_unary_op (curr->op, NEGATE_EXPR);
+  if (negateop == NULL_TREE)
+    return false;
+
+  /* Any non-negated version will have a rank that is one less than
+     the current rank.  So once we hit those ranks, if we don't find
+     one, we can stop.  */
+
+  for (i = currindex + 1;
+       VEC_iterate (operand_entry_t, *ops, i, oe)
+       && oe->rank >= curr->rank - 1 ;
+       i++)
     {
-      tree iop = SSA_NAME_DEF_STMT (TREE_OPERAND (lhsdefop, highrankop));
-      if (TREE_CODE (iop) == MODIFY_EXPR)
-	iop = TREE_OPERAND (iop, 1);
-      if (TREE_CODE (iop) == TREE_CODE (lhsdefop))
-	*takeop = 1;
-      if (rhsrank < get_rank (TREE_OPERAND (lhsdefop, *takeop)))
-	return true;
-    }		  
-  
+      if (oe->op == negateop)
+	{
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Equivalence: ");
+	      print_generic_expr (dump_file, negateop, 0);
+	      fprintf (dump_file, " + -");
+	      print_generic_expr (dump_file, oe->op, 0);
+	      fprintf (dump_file, " -> 0\n");
+	    }
+
+	  VEC_ordered_remove (operand_entry_t, *ops, i);
+	  add_to_ops_vec (ops, fold_convert(TREE_TYPE (oe->op), 
+					    integer_zero_node));
+	  VEC_ordered_remove (operand_entry_t, *ops, currindex);
+	  reassociate_stats.ops_eliminated ++;
+
+	  return true;
+	}
+    }
+
   return false;
 }
 
-/* Attempt to reassociate the associative binary operator BEXPR, which
-   is in the statement pointed to by CURRBSI.  Return true if we
-   changed the statement.  */
+/* If OPCODE is BIT_IOR_EXPR, BIT_AND_EXPR, and, CURR->OP is really a
+   bitwise not expression, look in OPS for a corresponding operand to
+   cancel it out.  If we find one, remove the other from OPS, replace
+   OPS[CURRINDEX] with 0, and return true.  Otherwise, return
+   false. */
 
 static bool
-reassociate_expr (tree bexpr, block_stmt_iterator *currbsi)
-{
-  tree lhs = TREE_OPERAND (bexpr, 0);
-  tree rhs = TREE_OPERAND (bexpr, 1);
-  tree lhsdef;
-  tree lhsi;
-  bool changed = false;
-  unsigned int lhsrank = get_rank (lhs);
-  unsigned int rhsrank = get_rank (rhs);
-
-  /* If unsafe math optimizations we can do reassociation for non-integral
-     types.  */
-  if ((!INTEGRAL_TYPE_P (TREE_TYPE (lhs))
-       || !INTEGRAL_TYPE_P (TREE_TYPE (rhs)))
-      && (!SCALAR_FLOAT_TYPE_P (TREE_TYPE (rhs))
-	  || !SCALAR_FLOAT_TYPE_P (TREE_TYPE(lhs))
-	  || !flag_unsafe_math_optimizations))
+eliminate_not_pairs (enum tree_code opcode,
+		     VEC (operand_entry_t, heap) **ops,
+		     unsigned int currindex,
+		     operand_entry_t curr)
+{
+  tree notop;
+  unsigned int i;
+  operand_entry_t oe;
+
+  if ((opcode != BIT_IOR_EXPR && opcode != BIT_AND_EXPR)
+      || TREE_CODE (curr->op) != SSA_NAME)
     return false;
-    
-  /* We want the greater ranked operand to be our "LHS" for simplicity
-     sake.  There is no point in actually modifying the expression, as
-     update_stmt will simply resort the operands anyway. */
-  if (lhsrank < rhsrank)
+
+  notop = get_unary_op (curr->op, BIT_NOT_EXPR);
+  if (notop == NULL_TREE)
+    return false;
+
+  /* Any non-not version will have a rank that is one less than
+     the current rank.  So once we hit those ranks, if we don't find
+     one, we can stop.  */
+
+  for (i = currindex + 1;
+       VEC_iterate (operand_entry_t, *ops, i, oe)
+       && oe->rank >= curr->rank - 1;
+       i++)
     {
-      tree temp;
-      unsigned int temp1;
-      temp = lhs;
-      lhs = rhs;
-      rhs = temp;
-      temp1 = lhsrank;
-      lhsrank = rhsrank;
-      rhsrank = temp1;
+      if (oe->op == notop)
+	{
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Equivalence: ");
+	      print_generic_expr (dump_file, notop, 0);
+	      if (opcode == BIT_AND_EXPR)
+		fprintf (dump_file, " & ~");
+	      else if (opcode == BIT_IOR_EXPR)
+		fprintf (dump_file, " | ~");
+	      print_generic_expr (dump_file, oe->op, 0);
+	      if (opcode == BIT_AND_EXPR)
+		fprintf (dump_file, " -> 0\n");
+	      else if (opcode == BIT_IOR_EXPR)
+		fprintf (dump_file, " -> -1\n");
+	    }
+
+	  if (opcode == BIT_AND_EXPR)
+	    oe->op = fold_convert (TREE_TYPE (oe->op), integer_zero_node);
+	  else if (opcode == BIT_IOR_EXPR)
+	    oe->op = build_low_bits_mask (TREE_TYPE (oe->op),
+					  TYPE_PRECISION (TREE_TYPE (oe->op)));
+
+	  reassociate_stats.ops_eliminated 
+	    += VEC_length (operand_entry_t, *ops) - 1;
+	  VEC_free (operand_entry_t, heap, *ops);
+	  *ops = NULL;
+	  VEC_safe_push (operand_entry_t, heap, *ops, oe);
+	  return true;
+	}
     }
 
-  /* If the high ranked operand is an SSA_NAME, and the binary
-     operator is not something we've already seen somewhere else
-     (i.e., it may be redundant), attempt to reassociate it.
-     
-     We can't reassociate expressions unless the expression we are
-     going to reassociate with is only used in our current expression,
-     or else we may screw up other computations, like so:
-
-     a = b + c
-     e = a + d
-     
-     g = a + f
-     
-     We cannot reassociate and rewrite the "a = ..." , 
-     because that would change the value of the computation of 
-     "g = a + f".  */
-  if (TREE_CODE (lhs) == SSA_NAME && !find_seen_binop (lhs, rhs))
+  return false;
+}
+
+/* Use constant value that may be present in OPS to try to eliminate
+   operands.  Note that this function is only really used when we've
+   eliminated ops for other reasons, or merged constants.  Across
+   single statements, fold already does all of this, plus more.  There
+   is little point in duplicating logic, so I've only included the
+   identities that I could ever construct testcases to trigger.  */
+
+static void
+eliminate_using_constants (enum tree_code opcode,
+			   VEC(operand_entry_t, heap) **ops)
+{
+  operand_entry_t oelast = VEC_last (operand_entry_t, *ops);
+
+  if (oelast->rank == 0 && INTEGRAL_TYPE_P (TREE_TYPE (oelast->op)))
     {
-      lhsdef = SSA_NAME_DEF_STMT (lhs);
-      if (TREE_CODE (lhsdef) == MODIFY_EXPR)
+      switch (opcode)
 	{
-	  lhsi = TREE_OPERAND (lhsdef, 1);
-	  if (TREE_CODE (lhsi) == TREE_CODE (bexpr))
+	case BIT_AND_EXPR:
+	  if (integer_zerop (oelast->op))
 	    {
-	      use_operand_p use;
-	      tree usestmt;
-	      if (single_imm_use (lhs, &use, &usestmt))
+	      if (VEC_length (operand_entry_t, *ops) != 1)
 		{
-		  unsigned int takeop = 0;
-		  unsigned int otherop = 1;
-		  bool foundmatch = false;
-		  bool foundrank = false;
-
-		  /* If we can easily transpose this into an operation
-		     we've already seen, let's do that.
-		     otherwise, let's try to expose low ranked ops to
-		     CSE.  */
-		  if (find_seen_binop (TREE_OPERAND (lhsi, 1), rhs))
-		    {
-		      takeop = 0;
-		      otherop = 1;
-		      foundmatch = true;
-		    }
-		  else if (find_seen_binop (TREE_OPERAND (lhsi, 0),
-					    rhs))
-		    {
-		      takeop = 1;
-		      otherop = 0;
-		      foundmatch = true;
-		    }
-		  else if (should_transpose (rhs, rhsrank, lhsi,
-					     &takeop))
-		    {
-		      foundrank = true;
-		    }		  
-		  if (foundmatch || foundrank)
-		    {
-		      block_stmt_iterator lhsbsi = bsi_for_stmt (lhsdef);
-		      if (dump_file && (dump_flags & TDF_DETAILS))
-			{
-			  fprintf (dump_file, "Reassociating by %s\n",
-				   foundmatch ? "match" : "rank");
-			  fprintf (dump_file, "Before LHS:");
-			  print_generic_stmt (dump_file, lhsi, 0);
-			  fprintf (dump_file, "Before curr expr:");
-			  print_generic_stmt (dump_file, bexpr, 0);
-			}
-		      TREE_OPERAND (bexpr, 0) = TREE_OPERAND (lhsi, takeop);
-		      TREE_OPERAND (lhsi, takeop) = rhs;
-		      TREE_OPERAND (bexpr, 1) = TREE_OPERAND (lhsdef, 0);
-		      if (dump_file && (dump_flags & TDF_DETAILS))
-			{
-			  fprintf (dump_file, "After LHS:");
-			  print_generic_stmt (dump_file, lhsi, 0);
-			  fprintf (dump_file, "After curr expr:");
-			  print_generic_stmt (dump_file, bexpr, 0);
-			}
-		      bsi_move_before (&lhsbsi, currbsi);
-		      update_stmt (lhsdef);
-		      update_stmt (bsi_stmt (*currbsi));
-		      lhsbsi = bsi_for_stmt (lhsdef);
-		      update_stmt (bsi_stmt (lhsbsi));
-
-		      /* If update_stmt didn't reorder our operands,
-			 we'd like to recurse on the expression we
-			 just reassociated and reassociate it
-			 top-down, exposing further opportunities.
-			 Unfortunately, update_stmt does reorder them,
-			 so we can't do this cheaply.  */
-		      if (!foundmatch)
-			reassociate_stats.reassociated_by_rank++;
-		      else
-			reassociate_stats.reassociated_by_match++;
-		      return true;
-		    }
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found & 0, removing all other ops\n");
+
+		  reassociate_stats.ops_eliminated 
+		    += VEC_length (operand_entry_t, *ops) - 1;
+		  
+		  VEC_free (operand_entry_t, heap, *ops);
+		  *ops = NULL;
+		  VEC_safe_push (operand_entry_t, heap, *ops, oelast);
+		  return;
+		}
+	    }
+	  else if (integer_all_onesp (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found & -1, removing\n");
+		  VEC_pop (operand_entry_t, *ops);
+		  reassociate_stats.ops_eliminated++;
+		}
+	    }
+	  break;
+	case BIT_IOR_EXPR:
+	  if (integer_all_onesp (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found | -1, removing all other ops\n");
+
+		  reassociate_stats.ops_eliminated 
+		    += VEC_length (operand_entry_t, *ops) - 1;
+		  
+		  VEC_free (operand_entry_t, heap, *ops);
+		  *ops = NULL;
+		  VEC_safe_push (operand_entry_t, heap, *ops, oelast);
+		  return;
+		}
+	    }	  
+	  else if (integer_zerop (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found | 0, removing\n");
+		  VEC_pop (operand_entry_t, *ops);
+		  reassociate_stats.ops_eliminated++;
 		}
 	    }
+	  break;
+	case MULT_EXPR:
+	  if (integer_zerop (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found * 0, removing all other ops\n");
+		  
+		  reassociate_stats.ops_eliminated 
+		    += VEC_length (operand_entry_t, *ops) - 1;
+		  VEC_free (operand_entry_t, heap, *ops);
+		  *ops = NULL;
+		  VEC_safe_push (operand_entry_t, heap, *ops, oelast);
+		  return;
+		}
+	    }
+	  else if (integer_onep (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found * 1, removing\n");
+		  VEC_pop (operand_entry_t, *ops);
+		  reassociate_stats.ops_eliminated++;
+		  return;
+		}
+	    }
+	  break;
+	case BIT_XOR_EXPR:
+	case PLUS_EXPR:
+	case MINUS_EXPR:
+	  if (integer_zerop (oelast->op))
+	    {
+	      if (VEC_length (operand_entry_t, *ops) != 1)
+		{
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    fprintf (dump_file, "Found [|^+] 0, removing\n");
+		  VEC_pop (operand_entry_t, *ops);
+		  reassociate_stats.ops_eliminated++;
+		  return;
+		}
+	    }
+	  break;
+	default:
+	  break;
+	}
+    }
+}
+
+/* Perform various identities and other optimizations on the list of
+   operand entries, stored in OPS.  The tree code for the binary
+   operation between all the operands is OPCODE.  */
+
+static void
+optimize_ops_list (enum tree_code opcode,
+		   VEC (operand_entry_t, heap) **ops)
+{
+  unsigned int length = VEC_length (operand_entry_t, *ops);
+  unsigned int i;
+  operand_entry_t oe;
+  operand_entry_t oelast = NULL;
+  bool iterate = false;
+
+  if (length == 1)
+    return;
+
+  oelast = VEC_last (operand_entry_t, *ops);
+
+  /* If the last two are constants, pop the constants off, merge them
+     and try the next two.  */
+  if (oelast->rank == 0 && is_gimple_min_invariant (oelast->op))
+    {
+      operand_entry_t oelm1 = VEC_index (operand_entry_t, *ops, length - 2);
+
+      if (oelm1->rank == 0
+	  && is_gimple_min_invariant (oelm1->op)
+	  && lang_hooks.types_compatible_p (TREE_TYPE (oelm1->op),
+					    TREE_TYPE (oelast->op)))
+	{
+	  tree folded = fold_build2 (opcode, TREE_TYPE (oelm1->op),
+				     oelm1->op, oelast->op);
+
+	  if (is_gimple_min_invariant (folded))
+	    {
+	      if (dump_file && (dump_flags & TDF_DETAILS))
+		fprintf (dump_file, "Merging constants\n");
+
+	      VEC_pop (operand_entry_t, *ops);
+	      VEC_pop (operand_entry_t, *ops);
+
+	      add_to_ops_vec (ops, folded);
+	      reassociate_stats.constants_eliminated++;
+
+	      optimize_ops_list (opcode, ops);
+	      return;
+	    }
+	}
+    }
+
+  eliminate_using_constants (opcode, ops);
+  oelast = NULL;
+
+  for (i = 0; VEC_iterate (operand_entry_t, *ops, i, oe);)
+    {
+      bool done = false;
+
+      if (eliminate_not_pairs (opcode, ops, i, oe))
+	return;
+      if (eliminate_duplicate_pair (opcode, ops, &done, i, oe, oelast)
+	  || (!done && eliminate_plus_minus_pair (opcode, ops, i, oe)))
+	{
+	  if (done)
+	    return;
+	  iterate = true;
+	  oelast = NULL;
+	  continue;
+	}
+      oelast = oe;
+      i++;
+    }
+
+  length  = VEC_length (operand_entry_t, *ops);
+  oelast = VEC_last (operand_entry_t, *ops);
+
+  if (iterate)
+    optimize_ops_list (opcode, ops);
+}
+
+/* Return true if OPERAND is defined by a PHI node which uses the LHS
+   of STMT in it's operands.  This is also known as a "destructive
+   update" operation.  */
+
+static bool
+is_phi_for_stmt (tree stmt, tree operand)
+{
+  tree def_stmt;
+  tree lhs = TREE_OPERAND (stmt, 0);
+  use_operand_p arg_p;
+  ssa_op_iter i;
+
+  if (TREE_CODE (operand) != SSA_NAME)
+    return false;
+
+  def_stmt = SSA_NAME_DEF_STMT (operand);
+  if (TREE_CODE (def_stmt) != PHI_NODE)
+    return false;
+
+  FOR_EACH_PHI_ARG (arg_p, def_stmt, i, SSA_OP_USE)
+    if (lhs == USE_FROM_PTR (arg_p))
+      return true;
+  return false;
+}
+
+/* Recursively rewrite our linearized statements so that the operators
+   match those in OPS[OPINDEX], putting the computation in rank
+   order.  */
+
+static void
+rewrite_expr_tree (tree stmt, unsigned int opindex,
+		   VEC(operand_entry_t, heap) * ops)
+{
+  tree rhs = TREE_OPERAND (stmt, 1);
+  operand_entry_t oe;
+
+  /* If we have three operands left, then we want to make sure the one
+     that gets the double binary op are the ones with the same rank.
+
+     The alternative we try is to see if this is a destructive
+     update style statement, which is like:
+     b = phi (a, ...)
+     a = c + b;
+     In that case, we want to use the destructive update form to
+     expose the possible vectorizer sum reduction opportunity.
+     In that case, the third operand will be the phi node.
+
+     We could, of course, try to be better as noted above, and do a
+     lot of work to try to find these opportunities in >3 operand
+     cases, but it is unlikely to be worth it.  */
+  if (opindex + 3 == VEC_length (operand_entry_t, ops))
+    {
+      operand_entry_t oe1, oe2, oe3;
+
+      oe1 = VEC_index (operand_entry_t, ops, opindex);
+      oe2 = VEC_index (operand_entry_t, ops, opindex + 1);
+      oe3 = VEC_index (operand_entry_t, ops, opindex + 2);
+
+      if ((oe1->rank == oe2->rank
+	   && oe2->rank != oe3->rank)
+	  || (is_phi_for_stmt (stmt, oe3->op)
+	      && !is_phi_for_stmt (stmt, oe1->op)
+	      && !is_phi_for_stmt (stmt, oe2->op)))
+	{
+	  struct operand_entry temp = *oe3;
+	  oe3->op = oe1->op;
+	  oe3->rank = oe1->rank;
+	  oe1->op = temp.op;
+	  oe1->rank= temp.rank;
+	}
+    }
+
+  /* The final recursion case for this function is that you have
+     exactly two operations left.
+     If we had one exactly one op in the entire list to start with, we
+     would have never called this function, and the tail recursion
+     rewrites them one at a time.  */
+  if (opindex + 2 == VEC_length (operand_entry_t, ops))
+    {
+      operand_entry_t oe1, oe2;
+
+      oe1 = VEC_index (operand_entry_t, ops, opindex);
+      oe2 = VEC_index (operand_entry_t, ops, opindex + 1);
+
+      if (TREE_OPERAND (rhs, 0) != oe1->op
+	  || TREE_OPERAND (rhs, 1) != oe2->op)
+	{
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, "Transforming ");
+	      print_generic_expr (dump_file, rhs, 0);
+	    }
+
+	  TREE_OPERAND (rhs, 0) = oe1->op;
+	  TREE_OPERAND (rhs, 1) = oe2->op;
+	  update_stmt (stmt);
+
+	  if (dump_file && (dump_flags & TDF_DETAILS))
+	    {
+	      fprintf (dump_file, " into ");
+	      print_generic_stmt (dump_file, rhs, 0);
+	    }
+
 	}
+      return;
     }
-  return changed;
+
+  /* If we hit here, we should have 3 or more ops left.  */
+  gcc_assert (opindex + 2 < VEC_length (operand_entry_t, ops));
+
+  /* Rewrite the next operator.  */
+  oe = VEC_index (operand_entry_t, ops, opindex);
+
+  if (oe->op != TREE_OPERAND (rhs, 1))
+    {
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "Transforming ");
+	  print_generic_expr (dump_file, rhs, 0);
+	}
+
+      TREE_OPERAND (rhs, 1) = oe->op;
+      update_stmt (stmt);
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, " into ");
+	  print_generic_stmt (dump_file, rhs, 0);
+	}
+    }
+  /* Recurse on the LHS of the binary operator, which is guaranteed to
+     be the non-leaf side.  */
+  rewrite_expr_tree (SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 0)),
+		     opindex + 1, ops);
+}
+
+/* Transform STMT, which is really (A +B) + (C + D) into the left
+   linear form, ((A+B)+C)+D.
+   Recurse on D if necessary.  */
+
+static void
+linearize_expr (tree stmt)
+{
+  block_stmt_iterator bsinow, bsirhs;
+  tree rhs = TREE_OPERAND (stmt, 1);
+  enum tree_code rhscode = TREE_CODE (rhs);
+  tree binrhs = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 1));
+  tree binlhs = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 0));
+  tree newbinrhs = NULL_TREE;
+
+  gcc_assert (is_reassociable_op (binlhs, TREE_CODE (rhs))
+	      && is_reassociable_op (binrhs, TREE_CODE (rhs)));
+
+  bsinow = bsi_for_stmt (stmt);
+  bsirhs = bsi_for_stmt (binrhs);
+  bsi_move_before (&bsirhs, &bsinow);
+
+  TREE_OPERAND (rhs, 1) = TREE_OPERAND (TREE_OPERAND (binrhs, 1), 0);
+  if (TREE_CODE (TREE_OPERAND (rhs, 1)) == SSA_NAME)
+    newbinrhs = SSA_NAME_DEF_STMT (TREE_OPERAND (rhs, 1));
+  TREE_OPERAND (TREE_OPERAND (binrhs, 1), 0) = TREE_OPERAND (binlhs, 0);
+  TREE_OPERAND (rhs, 0) = TREE_OPERAND (binrhs, 0);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Linearized: ");
+      print_generic_stmt (dump_file, rhs, 0);
+    }
+
+  reassociate_stats.linearized++;
+  update_stmt (binrhs);
+  update_stmt (binlhs);
+  update_stmt (stmt);
+  TREE_VISITED (binrhs) = 1;
+  TREE_VISITED (binlhs) = 1;
+  TREE_VISITED (stmt) = 1;
+
+  /* Tail recurse on the new rhs if it still needs reassociation.  */
+  if (newbinrhs && is_reassociable_op (newbinrhs, rhscode))
+    linearize_expr (stmt);
+
 }
 
-/* Reassociate expressions in basic block BB and its dominator as
-   children , return true if any
-   expressions changed.  */
+/* If LHS has a single immediate use that is a MODIFY_EXPR, return
+   it.  Otherwise, return NULL.  */
+
+static tree
+get_single_immediate_use (tree lhs)
+{
+  use_operand_p immuse;
+  tree immusestmt;
+
+  if (TREE_CODE (lhs) == SSA_NAME
+      && single_imm_use (lhs, &immuse, &immusestmt))
+    {
+      if (TREE_CODE (immusestmt) == RETURN_EXPR)
+	immusestmt = TREE_OPERAND (immusestmt, 0);
+      if (TREE_CODE (immusestmt) == MODIFY_EXPR)
+	return immusestmt;
+    }
+  return NULL_TREE;
+}
+static VEC(tree, heap) *broken_up_subtracts;
+
+
+/* Recursively negate the value of TONEGATE, and return the SSA_NAME
+   representing the negated value.  Insertions of any necessary
+   instructions go before BSI.
+   This function is recursive in that, if you hand it "a_5" as the
+   value to negate, and a_5 is defined by "a_5 = b_3 + b_4", it will
+   transform b_3 + b_4 into a_5 = -b_3 + -b_4.  */
+
+static tree
+negate_value (tree tonegate, block_stmt_iterator *bsi)
+{
+  tree negatedef = tonegate;
+  tree resultofnegate;
+
+  if (TREE_CODE (tonegate) == SSA_NAME)
+    negatedef = SSA_NAME_DEF_STMT (tonegate);
+
+  /* If we are trying to negate a name, defined by an add, negate the
+     add operands instead.  */
+  if (TREE_CODE (tonegate) == SSA_NAME
+      && TREE_CODE (negatedef) == MODIFY_EXPR
+      && TREE_CODE (TREE_OPERAND (negatedef, 0)) == SSA_NAME
+      && num_imm_uses (TREE_OPERAND (negatedef, 0)) == 1
+      && TREE_CODE (TREE_OPERAND (negatedef, 1)) == PLUS_EXPR)
+    {
+      block_stmt_iterator bsi;
+      tree binop = TREE_OPERAND (negatedef, 1);
+
+      bsi = bsi_for_stmt (negatedef);
+      TREE_OPERAND (binop, 0) = negate_value (TREE_OPERAND (binop, 0),
+					      &bsi);
+      bsi = bsi_for_stmt (negatedef);
+      TREE_OPERAND (binop, 1) = negate_value (TREE_OPERAND (binop, 1),
+					      &bsi);
+      update_stmt (negatedef);
+      return TREE_OPERAND (negatedef, 0);
+    }
+
+  tonegate = fold_build1 (NEGATE_EXPR, TREE_TYPE (tonegate), tonegate);
+  resultofnegate = force_gimple_operand_bsi (bsi, tonegate, true,
+					     NULL_TREE);
+  VEC_safe_push (tree, heap, broken_up_subtracts, resultofnegate);
+  return resultofnegate;
+
+}
+
+/* Return true if we should break up the subtract in STMT into an add
+   with negate.  This is true when we the subtract operands are really
+   adds, or the subtract itself is used in an add expression.  In
+   either case, breaking up the subtract into an add with negate
+   exposes the adds to reassociation.  */
 
 static bool
-reassociate_bb (basic_block bb)
+should_break_up_subtract (tree stmt)
+{
+
+  tree lhs = TREE_OPERAND (stmt, 0);
+  tree rhs = TREE_OPERAND (stmt, 1);
+  tree binlhs = TREE_OPERAND (rhs, 0);
+  tree binrhs = TREE_OPERAND (rhs, 1);
+  tree immusestmt;
+
+  if (TREE_CODE (binlhs) == SSA_NAME
+      && is_reassociable_op (SSA_NAME_DEF_STMT (binlhs), PLUS_EXPR))
+    return true;
+
+  if (TREE_CODE (binrhs) == SSA_NAME
+      && is_reassociable_op (SSA_NAME_DEF_STMT (binrhs), PLUS_EXPR))
+    return true;
+
+  if (TREE_CODE (lhs) == SSA_NAME
+      && (immusestmt = get_single_immediate_use (lhs))
+      && TREE_CODE (TREE_OPERAND (immusestmt, 1)) == PLUS_EXPR)
+    return true;
+  return false;
+
+}
+
+/* Transform STMT from A - B into A + -B.  */
+
+static void
+break_up_subtract (tree stmt, block_stmt_iterator *bsi)
+{
+  tree rhs = TREE_OPERAND (stmt, 1);
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    {
+      fprintf (dump_file, "Breaking up subtract ");
+      print_generic_stmt (dump_file, stmt, 0);
+    }
+
+  TREE_SET_CODE (TREE_OPERAND (stmt, 1), PLUS_EXPR);
+  TREE_OPERAND (rhs, 1) = negate_value (TREE_OPERAND (rhs, 1), bsi);
+
+  update_stmt (stmt);
+}
+
+/* Recursively linearize a binary expression that is the RHS of STMT.
+   Place the operands of the expression tree in the vector named OPS.  */
+
+static void
+linearize_expr_tree (VEC(operand_entry_t, heap) **ops, tree stmt)
+{
+  block_stmt_iterator bsinow, bsilhs;
+  tree rhs = TREE_OPERAND (stmt, 1);
+  tree binrhs = TREE_OPERAND (rhs, 1);
+  tree binlhs = TREE_OPERAND (rhs, 0);
+  tree binlhsdef, binrhsdef;
+  bool binlhsisreassoc = false;
+  bool binrhsisreassoc = false;
+  enum tree_code rhscode = TREE_CODE (rhs);
+
+  TREE_VISITED (stmt) = 1;
+
+  if (TREE_CODE (binlhs) == SSA_NAME)
+    {
+      binlhsdef = SSA_NAME_DEF_STMT (binlhs);
+      binlhsisreassoc = is_reassociable_op (binlhsdef, rhscode);
+    }
+
+  if (TREE_CODE (binrhs) == SSA_NAME)
+    {
+      binrhsdef = SSA_NAME_DEF_STMT (binrhs);
+      binrhsisreassoc = is_reassociable_op (binrhsdef, rhscode);
+    }
+
+  /* If the LHS is not reassociable, but the RHS is, we need to swap
+     them.  If neither is reassociable, there is nothing we can do, so
+     just put them in the ops vector.  If the LHS is reassociable,
+     linearize it.  If both are reassociable, then linearize the RHS
+     and the LHS.  */
+
+  if (!binlhsisreassoc)
+    {
+      tree temp;
+
+      if (!binrhsisreassoc)
+	{
+	  add_to_ops_vec (ops, binrhs);
+	  add_to_ops_vec (ops, binlhs);
+	  return;
+	}
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, "swapping operands of ");
+	  print_generic_expr (dump_file, stmt, 0);
+	}
+
+      swap_tree_operands (stmt, &TREE_OPERAND (rhs, 0),
+			  &TREE_OPERAND (rhs, 1));
+      update_stmt (stmt);
+
+      if (dump_file && (dump_flags & TDF_DETAILS))
+	{
+	  fprintf (dump_file, " is now ");
+	  print_generic_stmt (dump_file, stmt, 0);
+	}
+
+      /* We want to make it so the lhs is always the reassociative op,
+	 so swap.  */
+      temp = binlhs;
+      binlhs = binrhs;
+      binrhs = temp;
+    }
+  else if (binrhsisreassoc)
+    {
+      linearize_expr (stmt);
+      gcc_assert (rhs == TREE_OPERAND (stmt, 1));
+      binlhs = TREE_OPERAND (rhs, 0);
+      binrhs = TREE_OPERAND (rhs, 1);
+    }
+
+  gcc_assert (TREE_CODE (binrhs) != SSA_NAME
+	      || !is_reassociable_op (SSA_NAME_DEF_STMT (binrhs), rhscode));
+  bsinow = bsi_for_stmt (stmt);
+  bsilhs = bsi_for_stmt (SSA_NAME_DEF_STMT (binlhs));
+  bsi_move_before (&bsilhs, &bsinow);
+  linearize_expr_tree (ops, SSA_NAME_DEF_STMT (binlhs));
+  add_to_ops_vec (ops, binrhs);
+}
+
+/* Repropagate the negates back into subtracts, since no other pass
+   currently does it.  */
+
+static void
+repropagate_negates (void)
+{
+  unsigned int i = 0;
+  tree negate;
+
+  for (i = 0; VEC_iterate (tree, broken_up_subtracts, i, negate); i++)
+    {
+      tree user = get_single_immediate_use (negate);
+
+      /* The negate operand can be either operand of a PLUS_EXPR
+	 (it can be the LHS if the RHS is a constant for example).
+
+	 Force the negate operand to the RHS of the PLUS_EXPR, then
+	 transform the PLUS_EXPR into a MINUS_EXPR.  */
+      if (user
+	  && TREE_CODE (user) == MODIFY_EXPR
+	  && TREE_CODE (TREE_OPERAND (user, 1)) == PLUS_EXPR)
+	{
+	  tree rhs = TREE_OPERAND (user, 1);
+
+	  /* If the negated operand appears on the LHS of the
+	     PLUS_EXPR, exchange the operands of the PLUS_EXPR
+	     to force the negated operand to the RHS of the PLUS_EXPR.  */
+	  if (TREE_OPERAND (TREE_OPERAND (user, 1), 0) == negate)
+	    {
+	      tree temp = TREE_OPERAND (rhs, 0);
+	      TREE_OPERAND (rhs, 0) = TREE_OPERAND (rhs, 1);
+	      TREE_OPERAND (rhs, 1) = temp;
+	    }
+
+	  /* Now transform the PLUS_EXPR into a MINUS_EXPR and replace
+	     the RHS of the PLUS_EXPR with the operand of the NEGATE_EXPR.  */
+	  if (TREE_OPERAND (TREE_OPERAND (user, 1), 1) == negate)
+	    {
+	      TREE_SET_CODE (rhs, MINUS_EXPR);
+	      TREE_OPERAND (rhs, 1) = get_unary_op (negate, NEGATE_EXPR);
+	      update_stmt (user);
+	    }
+	}
+    }
+}
+
+/* Break up subtract operations in block BB.
+
+   We do this top down because we don't know whether the subtract is
+   part of a possible chain of reassociation except at the top.
+ 
+   IE given
+   d = f + g
+   c = a + e
+   b = c - d
+   q = b - r
+   k = t - q
+   
+   we want to break up k = t - q, but we won't until we've transformed q
+   = b - r, which won't be broken up until we transform b = c - d.  */
+
+static void
+break_up_subtract_bb (basic_block bb)
 {
-  bool changed = false;
   block_stmt_iterator bsi;
   basic_block son;
 
   for (bsi = bsi_start (bb); !bsi_end_p (bsi); bsi_next (&bsi))
     {
       tree stmt = bsi_stmt (bsi);
-      
+
+      if (TREE_CODE (stmt) == MODIFY_EXPR)
+	{
+	  tree lhs = TREE_OPERAND (stmt, 0);
+	  tree rhs = TREE_OPERAND (stmt, 1);
+
+	  TREE_VISITED (stmt) = 0;
+	  /* If unsafe math optimizations we can do reassociation for
+	     non-integral types.  */
+	  if ((!INTEGRAL_TYPE_P (TREE_TYPE (lhs))
+	       || !INTEGRAL_TYPE_P (TREE_TYPE (rhs)))
+	      && (!SCALAR_FLOAT_TYPE_P (TREE_TYPE (rhs))
+		  || !SCALAR_FLOAT_TYPE_P (TREE_TYPE(lhs))
+		  || !flag_unsafe_math_optimizations))
+	    continue;
+
+	  /* Check for a subtract used only in an addition.  If this
+	     is the case, transform it into add of a negate for better
+	     reassociation.  IE transform C = A-B into C = A + -B if C
+	     is only used in an addition.  */
+	  if (TREE_CODE (rhs) == MINUS_EXPR)
+	    if (should_break_up_subtract (stmt))
+	      break_up_subtract (stmt, &bsi);
+	}
+    }
+  for (son = first_dom_son (CDI_DOMINATORS, bb);
+       son;
+       son = next_dom_son (CDI_DOMINATORS, son))
+    break_up_subtract_bb (son);
+}
+
+/* Reassociate expressions in basic block BB and its post-dominator as
+   children.  */
+
+static void
+reassociate_bb (basic_block bb)
+{
+  block_stmt_iterator bsi;
+  basic_block son;
+
+  for (bsi = bsi_last (bb); !bsi_end_p (bsi); bsi_prev (&bsi))
+    {
+      tree stmt = bsi_stmt (bsi);
+
       if (TREE_CODE (stmt) == MODIFY_EXPR)
 	{
+	  tree lhs = TREE_OPERAND (stmt, 0);
 	  tree rhs = TREE_OPERAND (stmt, 1);
+
+	  /* If this was part of an already processed tree, we don't
+	     need to touch it again. */
+	  if (TREE_VISITED (stmt))
+	    continue;
+
+	  /* If unsafe math optimizations we can do reassociation for
+	     non-integral types.  */
+	  if ((!INTEGRAL_TYPE_P (TREE_TYPE (lhs))
+	       || !INTEGRAL_TYPE_P (TREE_TYPE (rhs)))
+	      && (!SCALAR_FLOAT_TYPE_P (TREE_TYPE (rhs))
+		  || !SCALAR_FLOAT_TYPE_P (TREE_TYPE(lhs))
+		  || !flag_unsafe_math_optimizations))
+	    continue;
+
 	  if (associative_tree_code (TREE_CODE (rhs)))
 	    {
-	      if (reassociate_expr (rhs, &bsi))
+	      VEC(operand_entry_t, heap) *ops = NULL;
+
+	      /* There may be no immediate uses left by the time we
+		 get here because we may have eliminated them all.  */
+	      if (TREE_CODE (lhs) == SSA_NAME && num_imm_uses (lhs) == 0)
+		continue;
+
+	      TREE_VISITED (stmt) = 1;
+	      linearize_expr_tree (&ops, stmt);
+	      qsort (VEC_address (operand_entry_t, ops),
+		     VEC_length (operand_entry_t, ops),
+		     sizeof (operand_entry_t),
+		     sort_by_operand_rank);
+	      optimize_ops_list (TREE_CODE (rhs), &ops);
+
+	      if (VEC_length (operand_entry_t, ops) == 1)
 		{
-		  changed = true;
-		  update_stmt (stmt);		  
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    {
+		      fprintf (dump_file, "Transforming ");
+		      print_generic_expr (dump_file, rhs, 0);
+		    }
+		  TREE_OPERAND (stmt, 1) = VEC_last (operand_entry_t, ops)->op;
+		  update_stmt (stmt);
+
+		  if (dump_file && (dump_flags & TDF_DETAILS))
+		    {
+		      fprintf (dump_file, " into ");
+		      print_generic_stmt (dump_file,
+					  TREE_OPERAND (stmt, 1), 0);
+		    }
+		}
+	      else
+		{
+		  rewrite_expr_tree (stmt, 0, ops);
 		}
-	      insert_seen_binop (TREE_OPERAND (rhs, 0),
-				 TREE_OPERAND (rhs, 1));
+
+	      VEC_free (operand_entry_t, heap, ops);
 	    }
 	}
     }
-  for (son = first_dom_son (CDI_DOMINATORS, bb);
+  for (son = first_dom_son (CDI_POST_DOMINATORS, bb);
        son;
-       son = next_dom_son (CDI_DOMINATORS, son))
+       son = next_dom_son (CDI_POST_DOMINATORS, son))
+    reassociate_bb (son);
+}
+
+void dump_ops_vector (FILE *file, VEC (operand_entry_t, heap) *ops);
+void debug_ops_vector (VEC (operand_entry_t, heap) *ops);
+
+/* Dump the operand entry vector OPS to FILE.  */
+
+void
+dump_ops_vector (FILE *file, VEC (operand_entry_t, heap) *ops)
+{
+  operand_entry_t oe;
+  unsigned int i;
+
+  for (i = 0; VEC_iterate (operand_entry_t, ops, i, oe); i++)
     {
-      changed |= reassociate_bb (son);
+      fprintf (file, "Op %d -> rank: %d, tree: ", i, oe->rank);
+      print_generic_stmt (file, oe->op, 0);
     }
-  return changed;  
 }
 
-	
-static bool
+/* Dump the operand entry vector OPS to STDERR.  */
+
+void
+debug_ops_vector (VEC (operand_entry_t, heap) *ops)
+{
+  dump_ops_vector (stderr, ops);
+}
+
+static void
 do_reassoc (void)
-{  
-  bool changed = false;
+{
+  break_up_subtract_bb (ENTRY_BLOCK_PTR);
+  reassociate_bb (EXIT_BLOCK_PTR);
+}
+
+/* Initialize the reassociation pass.  */
+
+static void
+init_reassoc (void)
+{
+  int i;
+  unsigned int rank = 2;
+  tree param;
+  int *bbs = xmalloc ((last_basic_block + 1) * sizeof (int));
+
+  memset (&reassociate_stats, 0, sizeof (reassociate_stats));
+
+  operand_entry_pool = create_alloc_pool ("operand entry pool",
+					  sizeof (struct operand_entry), 30);
+
+  /* Reverse RPO (Reverse Post Order) will give us something where
+     deeper loops come later.  */
+  flow_depth_first_order_compute (NULL, bbs);
+  bb_rank = xcalloc (last_basic_block + 1, sizeof (unsigned int));
   
-  changed = reassociate_bb (ENTRY_BLOCK_PTR);
+  operand_rank = htab_create (511, operand_entry_hash,
+			      operand_entry_eq, 0);
 
-  return changed;  
+  /* Give each argument a distinct rank.   */
+  for (param = DECL_ARGUMENTS (current_function_decl);
+       param;
+       param = TREE_CHAIN (param))
+    {
+      if (default_def (param) != NULL)
+	{
+	  tree def = default_def (param);
+	  insert_operand_rank (def, ++rank);
+	}
+    }
+
+  /* Give the chain decl a distinct rank. */
+  if (cfun->static_chain_decl != NULL)
+    {
+      tree def = default_def (cfun->static_chain_decl);
+      if (def != NULL)
+	insert_operand_rank (def, ++rank);
+    }
+
+  /* Set up rank for each BB  */
+  for (i = 0; i < n_basic_blocks; i++)
+    bb_rank[bbs[i]] = ++rank  << 16;
+
+  free (bbs);
+  calculate_dominance_info (CDI_DOMINATORS);
+  calculate_dominance_info (CDI_POST_DOMINATORS);
+  broken_up_subtracts = NULL;
 }
 
+/* Cleanup after the reassociation pass, and print stats if
+   requested.  */
+
+static void
+fini_reassoc (void)
+{
+
+  if (dump_file && (dump_flags & TDF_STATS))
+    {
+      fprintf (dump_file, "Reassociation stats:\n");
+      fprintf (dump_file, "Linearized: %d\n", 
+	       reassociate_stats.linearized);
+      fprintf (dump_file, "Constants eliminated: %d\n",
+	       reassociate_stats.constants_eliminated);
+      fprintf (dump_file, "Ops eliminated: %d\n",
+	       reassociate_stats.ops_eliminated);
+      fprintf (dump_file, "Statements rewritten: %d\n",
+	       reassociate_stats.rewritten);
+    }
+  htab_delete (operand_rank);
+
+  free_alloc_pool (operand_entry_pool);
+  free (bb_rank);
+  VEC_free (tree, heap, broken_up_subtracts);
+  free_dominance_info (CDI_POST_DOMINATORS);
+}
 
 /* Gate and execute functions for Reassociation.  */
 
@@ -618,7 +1494,10 @@ static void
 execute_reassoc (void)
 {
   init_reassoc ();
+
   do_reassoc ();
+  repropagate_negates ();
+
   fini_reassoc ();
 }
 
@@ -635,7 +1514,6 @@ struct tree_opt_pass pass_reassoc =
   0,					/* properties_provided */
   0,					/* properties_destroyed */
   0,					/* todo_flags_start */
-  TODO_update_ssa | TODO_dump_func 
-  | TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */
+  TODO_dump_func | TODO_ggc_collect | TODO_verify_ssa, /* todo_flags_finish */
   0					/* letter */
 };