Add support for empty hydrogen filter that matches only the top-level JSFunction.

src/objects.cc

 // Copyright 2013 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 9624 matching lines @@
 }
 
 
 Context* JSFunction::NativeContextFromLiterals(FixedArray* literals) {
   return Context::cast(literals->get(JSFunction::kLiteralNativeContextIndex));
 }
 
 
 bool JSFunction::PassesHydrogenFilter() {
   String* name = shared()->DebugName();
-  if (*FLAG_hydrogen_filter != '\0') {
+  // The filter string is a pattern that matches functions in this way:
+  //   "*"      all; the default
+  //   "-"      all but the top-level function
+  //   "-name"  all but the function "name"
+  //   ""       only the top-level function
+  //   "name"   only the function "name"
+  //   "name*"  only functions starting with "name"
+  if (*FLAG_hydrogen_filter != '*') {
     Vector<const char> filter = CStrVector(FLAG_hydrogen_filter);
+    if (filter.length() == 0) return name->length() == 0;
     if (filter[0] != '-' && name->IsUtf8EqualTo(filter)) return true;
     if (filter[0] == '-' &&
         !name->IsUtf8EqualTo(filter.SubVector(1, filter.length()))) {
       return true;
     }
     if (filter[filter.length() - 1] == '*' &&
         name->IsUtf8EqualTo(filter.SubVector(0, filter.length() - 1), true)) {
       return true;
     }
     return false;
@@ skipping 6291 matching lines @@
 
 void PropertyCell::AddDependentCode(Handle<Code> code) {
   Handle<DependentCode> codes = DependentCode::Insert(
       Handle<DependentCode>(dependent_code()),
       DependentCode::kPropertyCellChangedGroup, code);
   if (*codes != dependent_code()) set_dependent_code(*codes);
 }
 
 
 } }  // namespace v8::internal