cc: Adding creation location to debug BeginFrameArgs objects.

cc/output/begin_frame_args.h

 // Copyright 2013 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 CC_OUTPUT_BEGIN_FRAME_ARGS_H_
 #define CC_OUTPUT_BEGIN_FRAME_ARGS_H_
 
+#include "base/location.h"
 #include "base/memory/ref_counted.h"
 #include "base/time/time.h"
 #include "base/values.h"
 #include "cc/base/cc_export.h"
 
 namespace base {
 namespace debug {
 class ConvertableToTraceFormat;
 class TracedValue;
 }
 }
 
+/**
+ * In debug builds we trace the creation origin of BeginFrameArgs objects. We
+ * reuse the tracked_objects::Location system to do that.
+ *
+ * However, in release builds we don't want this as it doubles the size of the
+ * BeginFrameArgs object. As well it adds a number of largish strings to the
+ * binary. Despite the argument being unused, most compilers are unable to
+ * optimise it away even when unused. Instead we use the BEGINFRAME_FROM_HERE
+ * macro to prevent the data even getting referenced.
+ */
+#ifdef NDEBUG
+#define BEGINFRAME_FROM_HERE nullptr
+#else
+#define BEGINFRAME_FROM_HERE (new FROM_HERE)

[Sami, 2014/11/20 11:36:13]

Do we need to allocate FROM_HEREs on the heap? They can usually be passed around
by value. I don't think creating a dummy location in release mode would add all
that much code if you consider that there aren't that many places that create
BeginFrames in non-test code.

Which compilers did you check that the strings cannot be pruned? At least gcc
4.8.2 with -flto was able to drop the strings even when they were passed between
compilation units.

[danakj, 2014/11/20 16:02:20]

I thought that too, but then you can't avoid allocating one in release builds.

[mithro-old, 2014/11/21 05:57:46]

I originally thought that too but with the typedef based solution it does work.

[mithro-old, 2014/11/21 05:57:46]

Actually, with the typedef approach I just added, these don't have to be heap
allocated anymore. See the updated change.
I'm using clang shipping with chrome and the binary definitely continued to
contain the strings when I checked with "strings".

+#endif
+
 namespace cc {
 
 struct CC_EXPORT BeginFrameArgs {
   enum BeginFrameArgsType {
     INVALID,
     NORMAL,
     SYNCHRONOUS,
     MISSED,
   };
+  static const char* TypeToString(BeginFrameArgsType type);
 
   // Creates an invalid set of values.
   BeginFrameArgs();
 
+#ifdef NDEBUG
+  typedef const void* CreationLocation;
+#else
+  typedef const tracked_objects::Location* CreationLocation;
+  tracked_objects::Location created_by;

[Sami, 2014/11/20 11:36:14]

bikeshed: created_from?

[mithro-old, 2014/11/21 05:57:46]

Done.

+#endif
+
   // You should be able to find all instances where a BeginFrame has been
   // created by searching for "BeginFrameArgs::Create".
-  static BeginFrameArgs Create(base::TimeTicks frame_time,
+  // The location argument should **always** be BEGINFRAME_FROM_HERE macro.
+  static BeginFrameArgs Create(CreationLocation location,
+                               base::TimeTicks frame_time,
                                base::TimeTicks deadline,
-                               base::TimeDelta interval);
-  static BeginFrameArgs CreateTyped(base::TimeTicks frame_time,
-                                    base::TimeTicks deadline,
-                                    base::TimeDelta interval,
-                                    BeginFrameArgsType type);
-  static BeginFrameArgs CreateForSynchronousCompositor(
-      base::TimeTicks now = base::TimeTicks());
+                               base::TimeDelta interval,
+                               BeginFrameArgsType type);
 
   // This is the default delta that will be used to adjust the deadline when
   // proper draw-time estimations are not yet available.
   static base::TimeDelta DefaultEstimatedParentDrawTime();
 
   // This is the default interval to use to avoid sprinkling the code with
   // magic numbers.
   static base::TimeDelta DefaultInterval();
 
   // This is the default amount of time after the frame_time to retroactively
@@ skipping 15 matching lines @@
  private:
   BeginFrameArgs(base::TimeTicks frame_time,
                  base::TimeTicks deadline,
                  base::TimeDelta interval,
                  BeginFrameArgsType type);
 };
 
 }  // namespace cc
 
 #endif  // CC_OUTPUT_BEGIN_FRAME_ARGS_H_