Retaining path improvements.

runtime/vm/object_graph.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object_graph.h"
 
 #include "vm/dart.h"
 #include "vm/growable_array.h"
 #include "vm/isolate.h"
 #include "vm/object.h"
@@ skipping 243 matching lines @@
 class RetainingPathVisitor : public ObjectGraph::Visitor {
  public:
   // We cannot use a GrowableObjectArray, since we must not trigger GC.
   RetainingPathVisitor(RawObject* obj, const Array& path)
       : obj_(obj), path_(path), length_(0) {
     ASSERT(Thread::Current()->no_safepoint_scope_depth() != 0);
   }
 
   intptr_t length() const { return length_; }
 
+  bool ShouldSkip(RawObject* obj) {
+    // A retaining path through ICData is never the only retaining path,
+    // and it is less informative than its alternatives.
+    intptr_t cid = obj->GetClassId();
+    switch (cid) {
+    case kICDataCid:
+      return true;
+    default:
+      return false;
+    }
+  }
+
   virtual Direction VisitObject(ObjectGraph::StackIterator* it) {
     if (it->Get() != obj_) {
-      return kProceed;
+      if (ShouldSkip(it->Get())) {
+        return kBacktrack;
+      } else {
+        return kProceed;
+      }
     } else {
       HANDLESCOPE(Isolate::Current());
       Object& current = Object::Handle();
       Smi& offset_from_parent = Smi::Handle();
       do {
         intptr_t obj_index = length_ * 2;
         intptr_t offset_index = obj_index + 1;
         if (!path_.IsNull() && offset_index < path_.Length()) {
           current = it->Get();
           path_.SetAt(obj_index, current);
@@ skipping 180 matching lines @@
   {
     WritePointerVisitor ptr_writer(isolate(), stream);
     isolate()->IterateObjectPointers(&ptr_writer, false, false);
   }
   stream->WriteUnsigned(0);
   IterateObjects(&visitor);
   return visitor.count() + 1;  // + root
 }
 
 }  // namespace dart