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

Review URL: http://codereview.chromium.org/885004

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4120 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/compiler.cc

@@ -95,11 +95,13 @@ static Handle<Code> MakeCode(Handle<Context> context, CompilationInfo* info) {
     if (!builder.HasStackOverflow()) {
       int variable_count =
           function->num_parameters() + function->scope()->num_stack_slots();
+      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()) {
@@ -497,11 +499,13 @@ Handle<JSFunction> Compiler::BuildBoilerplate(FunctionLiteral* literal,
     if (!builder.HasStackOverflow()) {
       int variable_count =
           literal->num_parameters() + literal->scope()->num_stack_slots();
+      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()) {

src/data-flow.cc

@@ -2061,7 +2061,7 @@ void JoinNode::UpdateRDIn(WorkList<Node>* worklist, bool mark) {
 
 
 void ReachingDefinitions::Compute() {
-  if (definitions_->is_empty()) return;
+  ASSERT(!definitions_->is_empty());
 
   int variable_count = variables_.length();
   int definition_count = definitions_->length();