Fix load of potentially eval-shadowed let bindings.

src/x64/full-codegen-x64.cc

Index: src/x64/full-codegen-x64.cc
diff --git a/src/x64/full-codegen-x64.cc b/src/x64/full-codegen-x64.cc
index 1d9b8fffc2ba31442de8df8b9edddc25620ef549..afcf50a4b8feac962954ed2ab89122b807c8e760 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -1184,10 +1184,16 @@ void FullCodeGenerator::EmitDynamicLookupFastCase(Variable* var,
   } else if (var->mode() == Variable::DYNAMIC_LOCAL) {
     Variable* local = var->local_if_not_shadowed();
     __ movq(rax, ContextSlotOperandCheckExtensions(local, slow));
-    if (local->mode() == Variable::CONST) {
+    if (local->mode() == Variable::CONST ||
+        local->mode() == Variable::LET) {
       __ CompareRoot(rax, Heap::kTheHoleValueRootIndex);
       __ j(not_equal, done);
-      __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
+      if (local->mode() == Variable::CONST) {
+        __ LoadRoot(rax, Heap::kUndefinedValueRootIndex);
+      } else {  // Variable::LET
+        __ Push(var->name());
+        __ CallRuntime(Runtime::kThrowReferenceError, 1);
+      }
     }
     __ jmp(done);
   }