Increase eval compilation cache hits.

src/compilation-cache.h

 // Copyright 2011 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 110 matching lines @@
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(CompilationCacheScript);
 };
 
 
 // Sub-cache for eval scripts. Two caches for eval are used. One for eval calls
 // in global contexts and one for eval calls in other contexts. The cache
 // considers the following pieces of information when checking for matching
 // entries:
 // 1. The source string.
-// 2. The shared function info of the calling function.
+// 2. The script of the calling function.
 // 3. Whether the source should be compiled as strict code or as non-strict
 //    code.
 //    Note: Currently there are clients of CompileEval that always compile
 //    non-strict code even if the calling function is a strict mode function.
 //    More specifically these are the CompileString, DebugEvaluate and
 //    DebugEvaluateGlobal runtime functions.
-// 4. The start position of the calling scope.
+// 4. The start position of the calling scope in the script source code.
+//    Note: The script plus the start position of the calling scope uniquely
+//    determine the shape of the outer scope of the eval call.
+//    Note: For eval calls in global context RelocInfo::kNoPosition is always
+//    used as the scope position to enable sharing between direct and indirect
+//    global eval calls.
 class CompilationCacheEval: public CompilationSubCache {
  public:
   CompilationCacheEval(Isolate* isolate, int generations)
       : CompilationSubCache(isolate, generations) { }
 
   Handle<SharedFunctionInfo> Lookup(Handle<String> source,
                                     Handle<Context> context,
                                     LanguageMode language_mode,
                                     int scope_position);
 
@@ skipping 138 matching lines @@
 
   friend class Isolate;
 
   DISALLOW_COPY_AND_ASSIGN(CompilationCache);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_COMPILATION_CACHE_H_