[turbofan] Initial version of allocation folding and write barrier elimination.

src/heap/spaces.cc

 // Copyright 2011 the V8 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.
 
 #include "src/heap/spaces.h"
 
 #include "src/base/bits.h"
 #include "src/base/platform/platform.h"
 #include "src/base/platform/semaphore.h"
 #include "src/full-codegen/full-codegen.h"
@@ skipping 2453 matching lines @@
   const int kThreshold = IncrementalMarking::kAllocatedThreshold;
 
   // Memory in the linear allocation area is counted as allocated.  We may free
   // a little of this again immediately - see below.
   owner_->Allocate(new_node_size);
 
   if (owner_->heap()->inline_allocation_disabled()) {
     // Keep the linear allocation area empty if requested to do so, just
     // return area back to the free list instead.
     owner_->Free(new_node->address() + size_in_bytes, bytes_left);
-    DCHECK(owner_->top() == NULL && owner_->limit() == NULL);
+    owner_->SetTopAndLimit(new_node->address() + size_in_bytes,
+                           new_node->address() + size_in_bytes);
   } else if (bytes_left > kThreshold &&
              owner_->heap()->incremental_marking()->IsMarkingIncomplete() &&
              FLAG_incremental_marking) {
     int linear_size = owner_->RoundSizeDownToObjectAlignment(kThreshold);
     // We don't want to give too large linear areas to the allocator while
     // incremental marking is going on, because we won't check again whether
     // we want to do another increment until the linear area is used up.
     owner_->Free(new_node->address() + size_in_bytes + linear_size,
                  new_node_size - size_in_bytes - linear_size);
     owner_->SetTopAndLimit(new_node->address() + size_in_bytes,
                            new_node->address() + size_in_bytes + linear_size);
-  } else if (bytes_left > 0) {
+  } else if (bytes_left >= 0) {
     // Normally we give the rest of the node to the allocator as its new
     // linear allocation area.
     owner_->SetTopAndLimit(new_node->address() + size_in_bytes,
                            new_node->address() + new_node_size);
   }
 
   owner_->AllocationStep(new_node->address(), size_in_bytes);
 
   return new_node;
 }
@@ skipping 725 matching lines @@
     object->ShortPrint();
     PrintF("\n");
   }
   printf(" --------------------------------------\n");
   printf(" Marked: %x, LiveCount: %x\n", mark_size, LiveBytes());
 }
 
 #endif  // DEBUG
 }  // namespace internal
 }  // namespace v8