Strict mode arguments do not share binding with formal parameters.

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 780f4b027fa6a9507ce28429f321cbd5ddf74881..b52e6bb937c1f9069aa6ea3fe2ae5c6e520b1850 100644
--- a/src/x64/full-codegen-x64.cc
+++ b/src/x64/full-codegen-x64.cc
@@ -200,11 +200,18 @@ void FullCodeGenerator::Generate(CompilationInfo* info) {
     // stack frame was an arguments adapter frame.
     ArgumentsAccessStub stub(ArgumentsAccessStub::NEW_OBJECT);
     __ CallStub(&stub);
-    // Store new arguments object in both "arguments" and ".arguments" slots.
-    __ movq(rcx, rax);
-    Move(arguments->AsSlot(), rax, rbx, rdx);
-    Slot* dot_arguments_slot = scope()->arguments_shadow()->AsSlot();
-    Move(dot_arguments_slot, rcx, rbx, rdx);
+
+    Variable* arguments_shadow = scope()->arguments_shadow();
+    if (arguments_shadow != NULL) {
+      // Store new arguments object in both "arguments" and ".arguments" slots.
+      __ movq(rcx, rax);
+      Move(arguments->AsSlot(), rax, rbx, rdx);
+      Move(arguments_shadow->AsSlot(), rcx, rbx, rdx);
+    } else {
+      // arguments are allocated without shadow only in strict mode.
+      ASSERT(scope()->is_strict_mode());
+      Move(arguments->AsSlot(), rax, rbx, rdx);
+    }
   }
 
   if (FLAG_trace) {