- Remove the from field from the the Scavenger class.

runtime/vm/scavenger.h

 // Copyright (c) 2012, 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.
 
 #ifndef VM_SCAVENGER_H_
 #define VM_SCAVENGER_H_
 
 #include "platform/assert.h"
 #include "platform/utils.h"
 #include "vm/dart.h"
@@ skipping 103 matching lines @@
   Scavenger(Heap* heap,
             intptr_t max_semi_capacity_in_words,
             uword object_alignment);
   ~Scavenger();
 
   // Check whether this Scavenger contains this address.
   // During scavenging both the to and from spaces contain "legal" objects.
   // During a scavenge this function only returns true for addresses that will
   // be part of the surviving objects.
   bool Contains(uword addr) const {
-    // No reasonable algorithm should be checking for objects in from space. At
-    // least unless it is debugging code. This might need to be relaxed later,
-    // but currently it helps prevent dumb bugs.
-    ASSERT(from_ == NULL || !from_->Contains(addr));
     return to_->Contains(addr);
   }
 
   RawObject* FindObject(FindObjectVisitor* visitor) const;
 
   uword TryAllocate(intptr_t size) {
     ASSERT(Utils::IsAligned(size, kObjectAlignment));
     ASSERT(heap_ != Dart::vm_isolate()->heap());
 #if defined(DEBUG)
     if (FLAG_gc_at_alloc && !scavenging_) {
@@ skipping 87 matching lines @@
     kProcessToSpace = 2,
     kIterateWeaks = 3,
     // Data
     kStoreBufferEntries = 0,
     kDataUnused1 = 1,
     kDataUnused2 = 2,
     kToKBAfterStoreBuffer = 3
   };
 
   uword FirstObjectStart() const { return to_->start() | object_alignment_; }
-  void Prologue(Isolate* isolate, bool invoke_api_callbacks);
+  SemiSpace* Prologue(Isolate* isolate, bool invoke_api_callbacks);
   void IterateStoreBuffers(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateObjectIdTable(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateRoots(Isolate* isolate,
                     ScavengerVisitor* visitor,
                     bool visit_prologue_weak_persistent_handles);
   void IterateWeakProperties(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateWeakReferences(Isolate* isolate, ScavengerVisitor* visitor);
   void IterateWeakRoots(Isolate* isolate,
                         HandleVisitor* visitor,
                         bool visit_prologue_weak_persistent_handles);
   void ProcessToSpace(ScavengerVisitor* visitor);
   uword ProcessWeakProperty(RawWeakProperty* raw_weak,
                             ScavengerVisitor* visitor);
-  void Epilogue(Isolate* isolate,
-                bool invoke_api_callbacks);
+  void Epilogue(Isolate* isolate, SemiSpace* from, bool invoke_api_callbacks);
 
   bool IsUnreachable(RawObject** p);
 
   // During a scavenge we need to remember the promoted objects.
   // This is implemented as a stack of objects at the end of the to space. As
   // object sizes are always greater than sizeof(uword) and promoted objects do
   // not consume space in the to space they leave enough room for this stack.
   void PushToPromotedStack(uword addr) {
     ASSERT(scavenging_);
     end_ -= sizeof(addr);
     ASSERT(end_ > top_);
     *reinterpret_cast<uword*>(end_) = addr;
   }
   uword PopFromPromotedStack() {
     ASSERT(scavenging_);
     uword result = *reinterpret_cast<uword*>(end_);
     end_ += sizeof(result);
     ASSERT(end_ <= to_->end());
     return result;
   }
   bool PromotedStackHasMore() const {
     ASSERT(scavenging_);
     return end_ < to_->end();
   }
 
   void ProcessWeakTables();
 
   intptr_t NewSizeInWords(intptr_t old_size_in_words) const;
 
-  SemiSpace* from_;
   SemiSpace* to_;
 
   Heap* heap_;
 
   // Current allocation top and end. These values are being accessed directly
   // from generated code.
   uword top_;
   uword end_;
 
   // A pointer to the first unscanned object.  Scanning completes when
@@ skipping 21 matching lines @@
 
   friend class ScavengerVisitor;
   friend class ScavengerWeakVisitor;
 
   DISALLOW_COPY_AND_ASSIGN(Scavenger);
 };
 
 }  // namespace dart
 
 #endif  // VM_SCAVENGER_H_