tree-ssa-alias.c (compute_flow_insensitive_aliasing): Reduce the number of…

tree-ssa-alias.c (compute_flow_insensitive_aliasing): Reduce the number of queries to random elements in the ai->written_vars bitmap.

        * tree-ssa-alias.c (compute_flow_insensitive_aliasing): Reduce
        the number of queries to random elements in the ai->written_vars
        bitmap.

From-SVN: r91271

gcc/ChangeLog

+2004-11-24  Jeff Law  <law@redhat.com>
+
+	* tree-ssa-alias.c (compute_flow_insensitive_aliasing): Reduce
+	the number of queries to random elements in the ai->written_vars
+	bitmap.
+
 2004-11-24  Roger Sayle  <roger@eyesopen.com>
 
 	* config/i386/i386.c (override_options): Disable x87 fancy math

gcc/tree-ssa-alias.c

@@ -921,11 +921,16 @@ compute_flow_insensitive_aliasing (struct alias_info *ai)
 	  /* Skip memory tags and variables that have never been
 	     written to.  We also need to check if the variables are
 	     call-clobbered because they may be overwritten by
-	     function calls.  */
-	  tag_stored_p = bitmap_bit_p (ai->written_vars, tag_ann->uid)
-			 || is_call_clobbered (tag);
-	  var_stored_p = bitmap_bit_p (ai->written_vars, v_ann->uid)
-			 || is_call_clobbered (var);
+	     function calls.
+
+	     Note this is effectively random accessing elements in
+	     the sparse bitset, which can be highly inefficient.
+	     So we first check the call_clobbered status of the
+	     tag and variable before querying the bitmap.  */
+	  tag_stored_p = is_call_clobbered (tag)
+			 || bitmap_bit_p (ai->written_vars, tag_ann->uid);
+	  var_stored_p = is_call_clobbered (var)
+			 || bitmap_bit_p (ai->written_vars, v_ann->uid);
 	  if (!tag_stored_p && !var_stored_p)
 	    continue;