make PRE constant value IDs negative

This separates constant and non-constant value-ids to allow for
a more efficient constant_value_id_p and for more efficient bit-packing
inside the bitmap sets which never contain any constant values.

There's further optimization opportunities but at this stage
I'll do small refactorings.

2020-11-06  Richard Biener  <rguenther@suse.de>

	* tree-ssa-sccvn.h (get_max_constant_value_id): Declare.
	(get_next_constant_value_id): Likewise.
	(value_id_constant_p): Inline and simplify.
	* tree-ssa-sccvn.c (constant_value_ids): Remove.
	(next_constant_value_id): Add.
	(get_or_alloc_constant_value_id): Adjust.
	(value_id_constant_p): Remove definition.
	(get_max_constant_value_id): Define.
	(get_next_value_id): Add assert for overflow.
	(get_next_constant_value_id): Define.
	(run_rpo_vn): Adjust.
	(free_rpo_vn): Likewise.
	(do_rpo_vn): Initialize next_constant_value_id.
	* tree-ssa-pre.c (constant_value_expressions): New.
	(add_to_value): Split into constant/non-constant value
	handling.  Avoid exact re-allocation.
	(vn_valnum_from_value_id): Adjust.
	(phi_translate_1): Remove spurious exact re-allocation.
	(bitmap_find_leader): Adjust.  Make sure we return
	a CONSTANT value for a constant value id.
	(do_pre_regular_insertion): Use 2 auto-elements for avail.
	(do_pre_partial_partial_insertion): Likewise.
	(init_pre): Allocate constant_value_expressions.
	(fini_pre): Release constant_value_expressions.

3 files changed, 69 insertions, 34 deletions

diff --git a/gcc/tree-ssa-pre.c b/gcc/tree-ssa-pre.c
index 39c52c9..65e8aaa 100644
--- a/gcc/tree-ssa-pre.c
+++ b/gcc/tree-ssa-pre.c
@@ -444,6 +444,9 @@ public:
 
 /* Mapping from value id to expressions with that value_id.  */
 static vec<bitmap> value_expressions;
+/* ???  We want to just record a single expression for each constant
+   value, one of kind CONSTANT.  */
+static vec<bitmap> constant_value_expressions;
 
 /* Sets that we need to keep track of.  */
 typedef struct bb_bitmap_sets
@@ -624,18 +627,30 @@ add_to_value (unsigned int v, pre_expr e)
 
   gcc_checking_assert (get_expr_value_id (e) == v);
 
-  if (v >= value_expressions.length ())
+  if (value_id_constant_p (v))
     {
-      value_expressions.safe_grow_cleared (v + 1, true);
-    }
+      if (-v >= constant_value_expressions.length ())
+	constant_value_expressions.safe_grow_cleared (-v + 1);
 
-  set = value_expressions[v];
-  if (!set)
-    {
-      set = BITMAP_ALLOC (&grand_bitmap_obstack);
-      value_expressions[v] = set;
+      set = constant_value_expressions[-v];
+      if (!set)
+	{
+	  set = BITMAP_ALLOC (&grand_bitmap_obstack);
+	  constant_value_expressions[-v] = set;
+	}
     }
+  else
+    {
+      if (v >= value_expressions.length ())
+	value_expressions.safe_grow_cleared (v + 1);
 
+      set = value_expressions[v];
+      if (!set)
+	{
+	  set = BITMAP_ALLOC (&grand_bitmap_obstack);
+	  value_expressions[v] = set;
+	}
+    }
   bitmap_set_bit (set, get_or_alloc_expression_id (e));
 }
 
@@ -687,7 +702,11 @@ vn_valnum_from_value_id (unsigned int val)
 {
   bitmap_iterator bi;
   unsigned int i;
-  bitmap exprset = value_expressions[val];
+  bitmap exprset;
+  if (value_id_constant_p (val))
+    exprset = constant_value_expressions[-val];
+  else
+    exprset = value_expressions[val];
   EXECUTE_IF_SET_IN_BITMAP (exprset, 0, i, bi)
     {
       pre_expr vexpr = expression_for_id (i);
@@ -1451,8 +1470,6 @@ phi_translate_1 (bitmap_set_t dest,
 	    else
 	      {
 		new_val_id = get_next_value_id ();
-		value_expressions.safe_grow_cleared (get_max_value_id () + 1,
-						     true);
 		nary = vn_nary_op_insert_pieces (newnary->length,
 						 newnary->opcode,
 						 newnary->type,
@@ -1603,11 +1620,7 @@ phi_translate_1 (bitmap_set_t dest,
 	    else
 	      {
 		if (changed || !same_valid)
-		  {
-		    new_val_id = get_next_value_id ();
-		    value_expressions.safe_grow_cleared
-		      (get_max_value_id () + 1, true);
-		  }
+		  new_val_id = get_next_value_id ();
 		else
 		  new_val_id = ref->value_id;
 		if (!newoperands.exists ())
@@ -1745,7 +1758,7 @@ bitmap_find_leader (bitmap_set_t set, unsigned int val)
     {
       unsigned int i;
       bitmap_iterator bi;
-      bitmap exprset = value_expressions[val];
+      bitmap exprset = constant_value_expressions[-val];
 
       EXECUTE_IF_SET_IN_BITMAP (exprset, 0, i, bi)
 	{
@@ -1753,6 +1766,7 @@ bitmap_find_leader (bitmap_set_t set, unsigned int val)
 	  if (expr->kind == CONSTANT)
 	    return expr;
 	}
+      gcc_unreachable ();
     }
   if (bitmap_set_contains_value (set, val))
     {
@@ -3190,7 +3204,7 @@ do_pre_regular_insertion (basic_block block, basic_block dom)
   bool new_stuff = false;
   vec<pre_expr> exprs;
   pre_expr expr;
-  auto_vec<pre_expr> avail;
+  auto_vec<pre_expr, 2> avail;
   int i;
 
   exprs = sorted_array_from_bitmap_set (ANTIC_IN (block));
@@ -3357,7 +3371,7 @@ do_pre_partial_partial_insertion (basic_block block, basic_block dom)
   bool new_stuff = false;
   vec<pre_expr> exprs;
   pre_expr expr;
-  auto_vec<pre_expr> avail;
+  auto_vec<pre_expr, 2> avail;
   int i;
 
   exprs = sorted_array_from_bitmap_set (PA_IN (block));
@@ -4111,7 +4125,9 @@ init_pre (void)
   expressions.create (0);
   expressions.safe_push (NULL);
   value_expressions.create (get_max_value_id () + 1);
-  value_expressions.safe_grow_cleared (get_max_value_id () + 1, true);
+  value_expressions.quick_grow_cleared (get_max_value_id () + 1);
+  constant_value_expressions.create (get_max_constant_value_id () + 1);
+  constant_value_expressions.quick_grow_cleared (get_max_constant_value_id () + 1);
   name_to_id.create (0);
 
   inserted_exprs = BITMAP_ALLOC (NULL);
@@ -4142,6 +4158,7 @@ static void
 fini_pre ()
 {
   value_expressions.release ();
+  constant_value_expressions.release ();
   expressions.release ();
   BITMAP_FREE (inserted_exprs);
   bitmap_obstack_release (&grand_bitmap_obstack);
diff --git a/gcc/tree-ssa-sccvn.c b/gcc/tree-ssa-sccvn.c
index c139adb..8c9880e 100644
--- a/gcc/tree-ssa-sccvn.c
+++ b/gcc/tree-ssa-sccvn.c
@@ -288,7 +288,6 @@ vn_constant_hasher::equal (const vn_constant_s *vc1, const vn_constant_s *vc2)
 }
 
 static hash_table<vn_constant_hasher> *constant_to_value_id;
-static bitmap constant_value_ids;
 
 
 /* Obstack we allocate the vn-tables elements from.  */
@@ -322,6 +321,7 @@ tree VN_TOP;
 /* Unique counter for our value ids.  */
 
 static unsigned int next_value_id;
+static int next_constant_value_id;
 
 
 /* Table of vn_ssa_aux_t's, one per ssa_name.  The vn_ssa_aux_t objects
@@ -611,20 +611,11 @@ get_or_alloc_constant_value_id (tree constant)
   vcp = XNEW (struct vn_constant_s);
   vcp->hashcode = vc.hashcode;
   vcp->constant = constant;
-  vcp->value_id = get_next_value_id ();
+  vcp->value_id = get_next_constant_value_id ();
   *slot = vcp;
-  bitmap_set_bit (constant_value_ids, vcp->value_id);
   return vcp->value_id;
 }
 
-/* Return true if V is a value id for a constant.  */
-
-bool
-value_id_constant_p (unsigned int v)
-{
-  return bitmap_bit_p (constant_value_ids, v);
-}
-
 /* Compute the hash for a reference operand VRO1.  */
 
 static void
@@ -5578,14 +5569,32 @@ get_max_value_id (void)
   return next_value_id;
 }
 
+/* Return the maximum constant value id we have ever seen.  */
+
+unsigned int
+get_max_constant_value_id (void)
+{
+  return -next_constant_value_id;
+}
+
 /* Return the next unique value id.  */
 
 unsigned int
 get_next_value_id (void)
 {
+  gcc_checking_assert ((int)next_value_id > 0);
   return next_value_id++;
 }
 
+/* Return the next unique value id for constants.  */
+
+unsigned int
+get_next_constant_value_id (void)
+{
+  gcc_checking_assert (next_constant_value_id < 0);
+  return next_constant_value_id--;
+}
+
 
 /* Compare two expressions E1 and E2 and return true if they are equal.  */
 
@@ -6654,7 +6663,6 @@ run_rpo_vn (vn_lookup_kind kind)
 
   /* ???  Prune requirement of these.  */
   constant_to_value_id = new hash_table<vn_constant_hasher> (23);
-  constant_value_ids = BITMAP_ALLOC (NULL);
 
   /* Initialize the value ids and prune out remaining VN_TOPs
      from dead code.  */
@@ -6721,7 +6729,6 @@ free_rpo_vn (void)
 
   delete constant_to_value_id;
   constant_to_value_id = NULL;
-  BITMAP_FREE (constant_value_ids);
 }
 
 /* Hook for maybe_push_res_to_seq, lookup the expression in the VN tables.  */
@@ -7446,6 +7453,7 @@ do_rpo_vn (function *fn, edge entry, bitmap exit_bbs,
 			  / (n_basic_blocks_for_fn (fn) - NUM_FIXED_BLOCKS));
   VN_TOP = create_tmp_var_raw (void_type_node, "vn_top");
   next_value_id = 1;
+  next_constant_value_id = -1;
 
   vn_ssa_aux_hash = new hash_table <vn_ssa_aux_hasher> (region_size * 2);
   gcc_obstack_init (&vn_ssa_aux_obstack);
diff --git a/gcc/tree-ssa-sccvn.h b/gcc/tree-ssa-sccvn.h
index 48701c3..3420e6b 100644
--- a/gcc/tree-ssa-sccvn.h
+++ b/gcc/tree-ssa-sccvn.h
@@ -269,11 +269,21 @@ bool vn_nary_op_eq (const_vn_nary_op_t const vno1,
 bool vn_nary_may_trap (vn_nary_op_t);
 bool vn_reference_may_trap (vn_reference_t);
 bool vn_reference_eq (const_vn_reference_t const, const_vn_reference_t const);
+
 unsigned int get_max_value_id (void);
+unsigned int get_max_constant_value_id (void);
 unsigned int get_next_value_id (void);
+unsigned int get_next_constant_value_id (void);
 unsigned int get_constant_value_id (tree);
 unsigned int get_or_alloc_constant_value_id (tree);
-bool value_id_constant_p (unsigned int);
+
+/* Return true if V is a value id for a constant.  */
+static inline bool
+value_id_constant_p (unsigned int v)
+{
+  return (int)v < 0;
+}
+
 tree fully_constant_vn_reference_p (vn_reference_t);
 tree vn_nary_simplify (vn_nary_op_t);