Fix arrow functions requiring context without slots.

src/arm64/full-codegen-arm64.cc

 // Copyright 2013 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_ARM64
 
 #include "src/code-factory.h"
 #include "src/code-stubs.h"
@@ skipping 174 matching lines @@
         }
         int remaining = locals_count % kMaxPushes;
         // Emit the remaining pushes.
         __ PushMultipleTimes(x10 , remaining);
       }
     }
   }
 
   bool function_in_register_x1 = true;
 
-  int heap_slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
-  if (heap_slots > 0) {
+  if (info->scope()->num_heap_slots() > 0) {
     // Argument to NewContext is the function, which is still in x1.
     Comment cmnt(masm_, "[ Allocate context");
     bool need_write_barrier = true;
+    int slots = info->scope()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
     if (info->scope()->is_script_scope()) {
       __ Mov(x10, Operand(info->scope()->GetScopeInfo(info->isolate())));
       __ Push(x1, x10);
       __ 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(x1);
       __ CallRuntime(Runtime::kNewFunctionContext, 1);
     }
     function_in_register_x1 = false;
     // Context is returned in x0.  It replaces the context passed to us.
     // It's saved in the stack and kept live in cp.
@@ skipping 5322 matching lines @@
   }
 
   return INTERRUPT;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM64