Make sure DCHECK compiles out completely if DCHECKS aren't enabled.

base/logging.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_LOGGING_H_
 #define BASE_LOGGING_H_
 
 #include <stddef.h>
 
 #include <cassert>
@@ skipping 710 matching lines @@
   LAZY_STREAM(LOG_STREAM(DCHECK), false)                                \
   << "Check failed: " #condition ". "
 
 #define DPCHECK(condition)                                              \
   __analysis_assume(!!(condition)),                                     \
   LAZY_STREAM(PLOG_STREAM(DCHECK), false)                               \
   << "Check failed: " #condition ". "
 
 #else  // _PREFAST_
 
-#define DCHECK(condition)                                                \
-  LAZY_STREAM(LOG_STREAM(DCHECK), DCHECK_IS_ON() ? !(condition) : false) \
+#if DCHECK_IS_ON()
+
+#define DCHECK(condition)                       \
+  LAZY_STREAM(LOG_STREAM(DCHECK), !(condition)) \
+      << "Check failed: " #condition ". "
+#define DPCHECK(condition)                       \
+  LAZY_STREAM(PLOG_STREAM(DCHECK), !(condition)) \
       << "Check failed: " #condition ". "
 
-#define DPCHECK(condition)                                                \
-  LAZY_STREAM(PLOG_STREAM(DCHECK), DCHECK_IS_ON() ? !(condition) : false) \
-      << "Check failed: " #condition ". "
+#else  // DCHECK_IS_ON()
+
+#define DCHECK(condition) EAT_STREAM_PARAMETERS << !(condition)
+#define DPCHECK(condition) EAT_STREAM_PARAMETERS << !(condition)
+
+#endif  // DCHECK_IS_ON()
 
 #endif  // _PREFAST_
 
 // Helper macro for binary operators.
 // Don't use this macro directly in your code, use DCHECK_EQ et al below.
 // The 'switch' is used to prevent the 'else' from being ambiguous when the
 // macro is used in an 'if' clause such as:
 // if (a == 1)
 //   DCHECK_EQ(2, a);
+#if DCHECK_IS_ON()
+
 #define DCHECK_OP(name, op, val1, val2)                                \
   switch (0) case 0: default:                                          \
   if (::logging::CheckOpResult true_if_passed =                        \
       DCHECK_IS_ON() ?                                                 \
       ::logging::Check##name##Impl((val1), (val2),                     \
                                    #val1 " " #op " " #val2) : nullptr) \
    ;                                                                   \
   else                                                                 \
     ::logging::LogMessage(__FILE__, __LINE__, ::logging::LOG_DCHECK,   \
                           true_if_passed.message()).stream()
 
+#else  // DCHECK_IS_ON()
+
+#define DCHECK_OP(name, op, val1, val2)                             \
+  EAT_STREAM_PARAMETERS << (::logging::MakeCheckOpValueString(      \
+                                ::logging::g_swallow_stream, val1), \
+                            ::logging::MakeCheckOpValueString(      \
+                                ::logging::g_swallow_stream, val2), \

[Wez, 2017/01/25 01:57:24]

nit: Add a comment to clarify why we're doing this weird
(MakeCheckOpValueString, MCOVS, (val1)op(val2)) thing here?

[dcheng, 2017/01/25 03:11:58]

Done.

+                            (val1)op(val2))
+
+#endif  // DCHECK_IS_ON()
+
 // Equality/Inequality checks - compare two values, and log a
 // LOG_DCHECK message including the two values when the result is not
 // as expected.  The values must have operator<<(ostream, ...)
 // defined.
 //
 // You may append to the error message like so:
 //   DCHECK_NE(1, 2) << "The world must be ending!";
 //
 // We are very careful to ensure that each argument is evaluated exactly
 // once, and that anything which is legal to pass as a function argument is
@@ skipping 250 matching lines @@
 #elif NOTIMPLEMENTED_POLICY == 5
 #define NOTIMPLEMENTED() do {\
   static bool logged_once = false;\
   LOG_IF(ERROR, !logged_once) << NOTIMPLEMENTED_MSG;\
   logged_once = true;\
 } while(0);\
 EAT_STREAM_PARAMETERS
 #endif
 
 #endif  // BASE_LOGGING_H_