Use RTC_UNUSED instead of conditional compilation in BWE simulator tool.

webrtc/typedefs.h

 /*
  *  Copyright (c) 2012 The WebRTC 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 in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 62 matching lines @@
 #if defined(__GNUC__) || defined(__clang__)
 #define WARN_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
 #else
 #define WARN_UNUSED_RESULT
 #endif
 #endif  // WARN_UNUSED_RESULT
 
 // Put after a variable that might not be used, to prevent compiler warnings:
 //   int result ATTRIBUTE_UNUSED = DoSomething();
 //   assert(result == 17);
+// Deprecated since it only works with GCC & clang. See RTC_UNUSED below.
+// TODO(terelius): Remove.
 #ifndef ATTRIBUTE_UNUSED
 #if defined(__GNUC__) || defined(__clang__)
 #define ATTRIBUTE_UNUSED __attribute__ ((__unused__))
 #else
 #define ATTRIBUTE_UNUSED
 #endif
 #endif
 
 // Macro to be used for switch-case fallthrough (required for enabling
 // -Wimplicit-fallthrough warning on Clang).
 #ifndef FALLTHROUGH
 #if defined(__clang__)
 #define FALLTHROUGH() [[clang::fallthrough]]
 #else
 #define FALLTHROUGH() do { } while (0)
 #endif
 #endif
 
 #ifndef NO_RETURN
 // Annotate a function that will not return control flow to the caller.
 #if defined(_MSC_VER)
 #define NO_RETURN __declspec(noreturn)
 #elif defined(__GNUC__)
 #define NO_RETURN __attribute__ ((__noreturn__))
 #else
 #define NO_RETURN
 #endif
 #endif
 
+// Prevent compiler from warning about an unused variable.
+//   int result = DoSomething();
+//   assert(result == 17);

[nisse-webrtc, 2017/03/17 10:16:37]

I think the example is misleading, we don't use assert, and there's no need to
use RTC_UNUSED together with RTC_DCHECK.

[terelius, 2017/03/17 10:28:54]

I based this on the example for ATTRIBUTE_UNUSED. Do you have any better
suggestion?

[nisse-webrtc, 2017/03/17 10:41:42]

There's rarely a good reason to use RTC_UNUSED, so maybe it's best to just
delete the example.

If you want an example, maybe you can cook one up from how it's actually used? 

int foo = get_foo();
FOO_LOGGING(foo);  // Expanding to empty in some builds
RTC_UNUSED(foo);

[terelius, 2017/03/17 11:59:15]

I like having an example that shows how to use the macro and in particular where
it should be placed compared to ATTRIBUTE_UNUSED. I also prefer using constructs
that'll be familiar to the reader (e.g. assert) over more obscure logging macros
in the example.

I have added a note in the comment that discourages use of RTC_UNUSED though.

+//   RTC_UNUSED(result);
+#ifndef RTC_UNUSED
+#define RTC_UNUSED(x) RtcUnused(static_cast<const void*>(&x))

[nisse-webrtc, 2017/03/17 10:16:37]

Please try out this simpler definition:

  #define RTC_UNUSED(x) (static_cast<void>(x))

[terelius, 2017/03/17 10:28:54]

Already tried. It does not work on Android bots.

[nisse-webrtc, 2017/03/17 10:41:42]

Where's the failure? I see you tried 

#define RTC_UNUSED(x) static_cast<const void*>(&x)

in patchset #2, but that's quite different from what I'm suggesting.

[terelius, 2017/03/17 11:59:15]

Sorry, I misread your comment. Yeah, that seems to work.

+static inline void RtcUnused(const void* dummy) {}
+#endif  // RTC_UNUSED
+
 #endif  // WEBRTC_TYPEDEFS_H_