Disable g++ inlining of eager-tracing mark() method.

third_party/WebKit/Source/platform/heap/TraceTraits.h

 // Copyright 2015 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 TraceTraits_h
 #define TraceTraits_h
 
 #include "platform/heap/GCInfo.h"
 #include "platform/heap/Heap.h"
 #include "platform/heap/InlinedGlobalMarkingVisitor.h"
@@ skipping 21 matching lines @@
 class Member;
 template <typename T>
 class TraceEagerlyTrait;
 template <typename T>
 class TraceTrait;
 template <typename T>
 class WeakMember;
 template <typename T>
 class WeakPersistent;
 
+// "g++ -Os" reasonably considers the mark() eager-tracing specialization
+// as an inlinable method. Its optimization pipeline will however trigger
+// unconditional uses of that inlining inside trace() methods, i.e., without
+// consideration for resulting code size, so one for each use of
+// "visitor->trace(..)". This results in an unwanted amount of extra code
+// across all trace methods. Address the issue indirectly by turning off
+// inlining for the method. See crbug.com/681991 for further details.
+//
+// TODO(sof): revisit with later g++ versions, or when g++ is no
+// longer used for production builds.
+#if !defined(__clang__) && defined(__GNUC__)
+#define NOINLINE_GXX_ONLY NOINLINE
+#else
+#define NOINLINE_GXX_ONLY
+#endif
+
 template <typename T, bool = NeedsAdjustAndMark<T>::value>
 class AdjustAndMarkTrait;
 
 template <typename T>
 class AdjustAndMarkTrait<T, false> {
   STATIC_ONLY(AdjustAndMarkTrait);
 
  public:
   template <typename VisitorDispatcher>
-  static void mark(VisitorDispatcher visitor, const T* t) {
+  static NOINLINE_GXX_ONLY void mark(VisitorDispatcher visitor, const T* t) {
 #if DCHECK_IS_ON()
     assertObjectHasGCInfo(const_cast<T*>(t), GCInfoTrait<T>::index());
 #endif
     // Default mark method of the trait just calls the two-argument mark
     // method on the visitor. The second argument is the static trace method
     // of the trait, which by default calls the instance method
     // trace(Visitor*) on the object.
     //
     // If the trait allows it, invoke the trace callback right here on the
     // not-yet-marked object.
@@ skipping 729 matching lines @@
     // since iterating over the hash table backing will find the whole
     // chain.
     visitor->markNoTracing(node);
     return false;
   }
 };
 
 }  // namespace WTF
 
 #endif