Optimize loads from variables that might be shadowed by variables...

src/variables.h

Index: src/variables.h
===================================================================
--- src/variables.h	(revision 1289)
+++ src/variables.h	(working copy)
@@ -113,13 +113,27 @@
   enum Mode {
     // User declared variables:
     VAR,       // declared via 'var', and 'function' declarations
+
     CONST,     // declared via 'const' declarations
 
     // Variables introduced by the compiler:
-    DYNAMIC,   // always require dynamic lookup (we don't know the declaration)
-    INTERNAL,  // like VAR, but not user-visible (may or may not be in a
-               // context)
-    TEMPORARY  // temporary variables (not user-visible), never in a context
+    DYNAMIC,         // always require dynamic lookup (we don't know
+                     // the declaration)
+
+    DYNAMIC_GLOBAL,  // requires dynamic lookup, but we know that the
+                     // variable is global unless it has been shadowed
+                     // by an eval-introduced variable
+
+    DYNAMIC_LOCAL,   // requires dynamic lookup, but we know that the
+                     // variable is local and where it is unless it
+                     // has been shadowed by an eval-introduced
+                     // variable
+
+    INTERNAL,        // like VAR, but not user-visible (may or may not
+                     // be in a context)
+
+    TEMPORARY        // temporary variables (not user-visible), never
+                     // in a context
   };
 
   // Printing support
@@ -150,9 +164,24 @@
     return !is_this() && name().is_identical_to(n);
   }
 
+  bool is_dynamic() const {
+    return (mode_ == DYNAMIC ||
+            mode_ == DYNAMIC_GLOBAL ||
+            mode_ == DYNAMIC_LOCAL);
+  }
+
   bool is_global() const;
   bool is_this() const { return is_this_; }
 
+  Variable* local_if_not_shadowed() const {
+    ASSERT(mode_ == DYNAMIC_LOCAL && local_if_not_shadowed_ != NULL);
+    return local_if_not_shadowed_;
+  }
+
+  void set_local_if_not_shadowed(Variable* local) {
+    local_if_not_shadowed_ = local;
+  }
+
   Expression* rewrite() const  { return rewrite_; }
   Slot* slot() const;
 
@@ -168,6 +197,8 @@
   bool is_valid_LHS_;
   bool is_this_;
 
+  Variable* local_if_not_shadowed_;
+
   // Usage info.
   bool is_accessed_from_inner_scope_;  // set by variable resolver
   UseCount var_uses_;  // uses of the variable value