Write buffer based write barrier for IA32 and Crankshaft. Currently...

src/write-buffer.cc

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 65 matching lines @@
 }
 
 
 void WriteBuffer::Compact() {
   memset(reinterpret_cast<void*>(hash_map_1_),
          0,
          sizeof(uintptr_t) * kHashMapLength);
   memset(reinterpret_cast<void*>(hash_map_2_),
          0,
          sizeof(uintptr_t) * kHashMapLength);
+  ASSERT(top_ <= limit_);
   Address* stop = top_;
   top_ = start_;
   // Goes through the addresses in the write buffer attempting to remove
   // duplicates.  In the interest of speed this is a lossy operation.  Some
   // duplicates will remain.  We have two hash tables with different hash
   // functions to reduce the number of unnecessary clashes.
   for (Address* current = start_; current < stop; current++) {
     uintptr_t int_addr = reinterpret_cast<uintptr_t>(*current);
     // Shift out the last bits including any tags.
     int_addr >>= kPointerSizeLog2;
@@ skipping 27 matching lines @@
     if (limit_ - top_ < (top_ - start_) >> 1) {
       // Compression did not free up at least one quarter.
       // TODO(gc): Set a flag to scan all of memory.
       top_ = start_;
       Counters::write_buffer_overflows.Increment();
     }
   }
 }
 
 } }  // namespace v8::internal