Add support for enabling DCHECKs in release mode

src/x64/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/codegen.h"
 #include "src/macro-assembler.h"
@@ skipping 638 matching lines @@
   // following boilerplate stack-building prologue that is found both in
   // FUNCTION and OPTIMIZED_FUNCTION code:
   CodePatcher patcher(young_sequence_.start(), young_sequence_.length());
   patcher.masm()->pushq(rbp);
   patcher.masm()->movp(rbp, rsp);
   patcher.masm()->Push(rsi);
   patcher.masm()->Push(rdi);
 }
 
 
-#ifdef DEBUG
+#if DCHECK_IS_ON
 bool CodeAgingHelper::IsOld(byte* candidate) const {
   return *candidate == kCallOpcode;
 }
 #endif
 
 
 bool Code::IsYoungSequence(Isolate* isolate, byte* sequence) {
   bool result = isolate->code_aging_helper()->IsYoung(sequence);
   DCHECK(result || isolate->code_aging_helper()->IsOld(sequence));
   return result;
@@ skipping 50 matching lines @@
     // argument_count_reg_ * times_pointer_size + (receiver - 1) * kPointerSize.
     return Operand(base_reg_, argument_count_reg_, times_pointer_size,
         displacement_to_last_argument + (receiver - 1 - index) * kPointerSize);
   }
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64