Fix arrow functions requiring context without slots.

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 165 matching lines @@
       // Emit the remaining pushes.
       for (int i  = 0; i < remaining; i++) {
         __ Push(rdx);
       }
     }
   }
 
   bool function_in_register = true;
 
   // Possibly allocate a local context.
-  int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
-  if (heap_slots > 0) {
+  if (info->scope()->num_heap_slots() > 0) {
     Comment cmnt(masm_, "[ Allocate context");
     bool need_write_barrier = true;
+    int slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
     // Argument to NewContext is the function, which is still in rdi.
     if (info->scope()->is_script_scope()) {
       __ Push(rdi);
       __ Push(info->scope()->GetScopeInfo(info->isolate()));
       __ CallRuntime(Runtime::kNewScriptContext, 2);
-    } else if (heap_slots <= FastNewContextStub::kMaximumSlots) {
-      FastNewContextStub stub(isolate(), heap_slots);
+    } else if (slots <= FastNewContextStub::kMaximumSlots) {
+      FastNewContextStub stub(isolate(), slots);
       __ CallStub(&stub);
       // Result of FastNewContextStub is always in new space.
       need_write_barrier = false;
     } else {
       __ Push(rdi);
       __ CallRuntime(Runtime::kNewFunctionContext, 1);
     }
     function_in_register = false;
     // Context is returned in rax.  It replaces the context passed to us.
     // It's saved in the stack and kept live in rsi.
@@ skipping 5245 matching lines @@
             Assembler::target_address_at(call_target_address,
                                          unoptimized_code));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_X64