Only invoke reaching definitions if there are >0 variables and >0 definitions...

src/compiler.cc

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 77 matching lines @@
     }
   }
 
   if (FLAG_use_flow_graph) {
     FlowGraphBuilder builder;
     builder.Build(function);
 
     if (!builder.HasStackOverflow()) {
       int variable_count =
           function->num_parameters() + function->scope()->num_stack_slots();
-      ReachingDefinitions rd(builder.postorder(),
-                             builder.definitions(),
-                             variable_count);
-      rd.Compute();
+      if (variable_count > 0 && builder.definitions()->length() > 0) {

[Kevin Millikin (Chromium), 2010/03/12 14:58:16]

Hmm.  I'd let the ReachingDefinitions class check the definitions() length
itself.

+        ReachingDefinitions rd(builder.postorder(),
+                               builder.definitions(),
+                               variable_count);
+        rd.Compute();
+      }
     }
 
 #ifdef DEBUG
     if (FLAG_print_graph_text && !builder.HasStackOverflow()) {
       builder.graph()->PrintText(builder.postorder());
     }
 #endif
   }
 
   // Generate code and return it.  Code generator selection is governed by
@@ skipping 378 matching lines @@
       }
     }
 
     if (FLAG_use_flow_graph) {
       FlowGraphBuilder builder;
       builder.Build(literal);
 
     if (!builder.HasStackOverflow()) {
       int variable_count =
           literal->num_parameters() + literal->scope()->num_stack_slots();
-      ReachingDefinitions rd(builder.postorder(),
-                             builder.definitions(),
-                             variable_count);
-      rd.Compute();
+      if (variable_count > 0 && builder.definitions()->length() > 0) {
+        ReachingDefinitions rd(builder.postorder(),
+                               builder.definitions(),
+                               variable_count);
+        rd.Compute();
+      }
     }
 
 #ifdef DEBUG
       if (FLAG_print_graph_text && !builder.HasStackOverflow()) {
         builder.graph()->PrintText(builder.postorder());
       }
 #endif
     }
 
     // Generate code and return it.  The way that the compilation mode
@@ skipping 115 matching lines @@
       LOG(CodeCreateEvent(tag, *code, *func_name));
       OProfileAgent::CreateNativeCodeRegion(*func_name,
                                             code->instruction_start(),
                                             code->instruction_size());
     }
   }
 }
 #endif
 
 } }  // namespace v8::internal