Fix exception for assignment to uninitialised const

src/x64/full-codegen-x64.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #if V8_TARGET_ARCH_X64
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 2650 matching lines @@
     Label assign;
     MemOperand location = VarOperand(var, rcx);
     __ movp(rdx, location);
     __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
     __ j(not_equal, &assign, Label::kNear);
     __ Push(var->name());
     __ CallRuntime(Runtime::kThrowReferenceError, 1);
     __ bind(&assign);
     EmitStoreToStackLocalOrContextSlot(var, location);
 
+  } else if (var->mode() == CONST && op != Token::INIT_CONST) {
+    // Assignment to const variable needs a write barrier.
+    DCHECK(!var->IsLookupSlot());
+    DCHECK(var->IsStackAllocated() || var->IsContextSlot());
+    Label const_error;
+    MemOperand location = VarOperand(var, rcx);
+    __ movp(rdx, location);
+    __ CompareRoot(rdx, Heap::kTheHoleValueRootIndex);
+    __ j(not_equal, &const_error, Label::kNear);
+    __ Push(var->name());
+    __ CallRuntime(Runtime::kThrowReferenceError, 1);
+    __ bind(&const_error);
+    __ CallRuntime(Runtime::kThrowConstAssignError, 0);
+
   } else if (!var->is_const_mode() || op == Token::INIT_CONST) {
     if (var->IsLookupSlot()) {
       // Assignment to var.
       __ Push(rax);  // Value.
       __ Push(rsi);  // Context.
       __ Push(var->name());
       __ Push(Smi::FromInt(language_mode()));
       __ CallRuntime(Runtime::kStoreLookupSlot, 4);
     } else {
       // Assignment to var or initializing assignment to let/const in harmony
@@ skipping 2705 matching lines @@
   DCHECK_EQ(isolate->builtins()->OsrAfterStackCheck()->entry(),
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64