Revert r4715.

src/spaces-inl.h

Index: src/spaces-inl.h
===================================================================
--- src/spaces-inl.h	(revision 4722)
+++ src/spaces-inl.h	(working copy)
@@ -66,173 +66,99 @@
 }
 
 
-Address Page::AllocationWatermark() {
-  PagedSpace* owner = MemoryAllocator::PageOwner(this);
-  if (this == owner->AllocationTopPage()) {
-    return owner->top();
-  }
-  return address() + AllocationWatermarkOffset();
+void Page::ClearRSet() {
+  // This method can be called in all rset states.
+  memset(RSetStart(), 0, kRSetEndOffset - kRSetStartOffset);
 }
 
 
-uint32_t Page::AllocationWatermarkOffset() {
-  return static_cast<uint32_t>((flags_ & kAllocationWatermarkOffsetMask) >>
-                               kAllocationWatermarkOffsetShift);
-}
+// Given a 32-bit address, separate its bits into:
+// | page address | words (6) | bit offset (5) | pointer alignment (2) |
+// The address of the rset word containing the bit for this word is computed as:
+//    page_address + words * 4
+// For a 64-bit address, if it is:
+// | page address | words(5) | bit offset(5) | pointer alignment (3) |
+// The address of the rset word containing the bit for this word is computed as:
+//    page_address + words * 4 + kRSetOffset.
+// The rset is accessed as 32-bit words, and bit offsets in a 32-bit word,
+// even on the X64 architecture.
 
+Address Page::ComputeRSetBitPosition(Address address, int offset,
+                                     uint32_t* bitmask) {
+  ASSERT(Page::is_rset_in_use());
 
-void Page::SetAllocationWatermark(Address allocation_watermark) {
-  if ((Heap::gc_state() == Heap::SCAVENGE) && IsWatermarkValid()) {
-    // When iterating intergenerational references during scavenge
-    // we might decide to promote an encountered young object.
-    // We will allocate a space for such an object and put it
-    // into the promotion queue to process it later.
-    // If space for object was allocated somewhere beyond allocation
-    // watermark this might cause garbage pointers to appear under allocation
-    // watermark. To avoid visiting them during dirty regions iteration
-    // which might be still in progress we store a valid allocation watermark
-    // value and mark this page as having an invalid watermark.
-    SetCachedAllocationWatermark(AllocationWatermark());
-    InvalidateWatermark(true);
-  }
+  Page* page = Page::FromAddress(address);
+  uint32_t bit_offset = ArithmeticShiftRight(page->Offset(address) + offset,
+                                             kPointerSizeLog2);
+  *bitmask = 1 << (bit_offset % kBitsPerInt);
 
-  flags_ = (flags_ & kFlagsMask) |
-           Offset(allocation_watermark) << kAllocationWatermarkOffsetShift;
-  ASSERT(AllocationWatermarkOffset()
-         == static_cast<uint32_t>(Offset(allocation_watermark)));
-}
+  Address rset_address =
+      page->address() + kRSetOffset + (bit_offset / kBitsPerInt) * kIntSize;
+  // The remembered set address is either in the normal remembered set range
+  // of a page or else we have a large object page.
+  ASSERT((page->RSetStart() <= rset_address && rset_address < page->RSetEnd())
+         || page->IsLargeObjectPage());
 
+  if (rset_address >= page->RSetEnd()) {
+    // We have a large object page, and the remembered set address is actually
+    // past the end of the object.
 
-void Page::SetCachedAllocationWatermark(Address allocation_watermark) {
-  mc_first_forwarded = allocation_watermark;
+    // The first part of the remembered set is still located at the start of
+    // the page, but anything after kRSetEndOffset must be relocated to after
+    // the large object, i.e. after
+    //   (page->ObjectAreaStart() + object size)
+    // We do that by adding the difference between the normal RSet's end and
+    // the object's end.
+    ASSERT(HeapObject::FromAddress(address)->IsFixedArray());
+    int fixedarray_length =
+        FixedArray::SizeFor(Memory::int_at(page->ObjectAreaStart()
+                                           + Array::kLengthOffset));
+    rset_address += kObjectStartOffset - kRSetEndOffset + fixedarray_length;
+  }
+  return rset_address;
 }
 
 
-Address Page::CachedAllocationWatermark() {
-  return mc_first_forwarded;
-}
+void Page::SetRSet(Address address, int offset) {
+  uint32_t bitmask = 0;
+  Address rset_address = ComputeRSetBitPosition(address, offset, &bitmask);
+  Memory::uint32_at(rset_address) |= bitmask;
 
-
-uint32_t Page::GetRegionMarks() {
-  return dirty_regions_;
+  ASSERT(IsRSetSet(address, offset));
 }
 
 
-void Page::SetRegionMarks(uint32_t marks) {
-  dirty_regions_ = marks;
-}
+// Clears the corresponding remembered set bit for a given address.
+void Page::UnsetRSet(Address address, int offset) {
+  uint32_t bitmask = 0;
+  Address rset_address = ComputeRSetBitPosition(address, offset, &bitmask);
+  Memory::uint32_at(rset_address) &= ~bitmask;
 
-
-int Page::GetRegionNumberForAddress(Address addr) {
-  // Each page is divided into 256 byte regions. Each region has a corresponding
-  // dirty mark bit in the page header. Region can contain intergenerational
-  // references iff its dirty mark is set.
-  // A normal 8K page contains exactly 32 regions so all region marks fit
-  // into 32-bit integer field. To calculate a region number we just divide
-  // offset inside page by region size.
-  // A large page can contain more then 32 regions. But we want to avoid
-  // additional write barrier code for distinguishing between large and normal
-  // pages so we just ignore the fact that addr points into a large page and
-  // calculate region number as if addr pointed into a normal 8K page. This way
-  // we get a region number modulo 32 so for large pages several regions might
-  // be mapped to a single dirty mark.
-  ASSERT_PAGE_ALIGNED(this->address());
-  STATIC_ASSERT((kPageAlignmentMask >> kRegionSizeLog2) < kBitsPerInt);
-
-  // We are using masking with kPageAlignmentMask instead of Page::Offset()
-  // to get an offset to the beginning of 8K page containing addr not to the
-  // beginning of actual page which can be bigger then 8K.
-  intptr_t offset_inside_normal_page = OffsetFrom(addr) & kPageAlignmentMask;
-  return static_cast<int>(offset_inside_normal_page >> kRegionSizeLog2);
+  ASSERT(!IsRSetSet(address, offset));
 }
 
 
-uint32_t Page::GetRegionMaskForAddress(Address addr) {
-  return 1 << GetRegionNumberForAddress(addr);
-}
-
-
-void Page::MarkRegionDirty(Address address) {
-  SetRegionMarks(GetRegionMarks() | GetRegionMaskForAddress(address));
-}
-
-
-bool Page::IsRegionDirty(Address address) {
-  return GetRegionMarks() & GetRegionMaskForAddress(address);
-}
-
-
-void Page::ClearRegionMarks(Address start, Address end, bool reaches_limit) {
-  int rstart = GetRegionNumberForAddress(start);
-  int rend = GetRegionNumberForAddress(end);
-
-  if (reaches_limit) {
-    end += 1;
-  }
-
-  if ((rend - rstart) == 0) {
-    return;
-  }
-
+bool Page::IsRSetSet(Address address, int offset) {
   uint32_t bitmask = 0;
-
-  if ((OffsetFrom(start) & kRegionAlignmentMask) == 0
-      || (start == ObjectAreaStart())) {
-    // First region is fully covered
-    bitmask = 1 << rstart;
-  }
-
-  while (++rstart < rend) {
-    bitmask |= 1 << rstart;
-  }
-
-  if (bitmask) {
-    SetRegionMarks(GetRegionMarks() & ~bitmask);
-  }
+  Address rset_address = ComputeRSetBitPosition(address, offset, &bitmask);
+  return (Memory::uint32_at(rset_address) & bitmask) != 0;
 }
 
 
-void Page::FlipMeaningOfInvalidatedWatermarkFlag() {
-  watermark_invalidated_mark_ ^= WATERMARK_INVALIDATED;
-}
-
-
-bool Page::IsWatermarkValid() {
-  return (flags_ & WATERMARK_INVALIDATED) != watermark_invalidated_mark_;
-}
-
-
-void Page::InvalidateWatermark(bool value) {
-  if (value) {
-    flags_ = (flags_ & ~WATERMARK_INVALIDATED) | watermark_invalidated_mark_;
-  } else {
-    flags_ = (flags_ & ~WATERMARK_INVALIDATED) |
-             (watermark_invalidated_mark_ ^ WATERMARK_INVALIDATED);
-  }
-
-  ASSERT(IsWatermarkValid() == !value);
-}
-
-
 bool Page::GetPageFlag(PageFlag flag) {
-  return (flags_ & flag) != 0;
+  return (flags & flag) != 0;
 }
 
 
 void Page::SetPageFlag(PageFlag flag, bool value) {
   if (value) {
-    flags_ |= flag;
+    flags |= flag;
   } else {
-    flags_ &= ~flag;
+    flags &= ~flag;
   }
 }
 
 
-void Page::ClearPageFlags() {
-  flags_ = 0;
-}
-
-
 bool Page::WasInUseBeforeMC() {
   return GetPageFlag(WAS_IN_USE_BEFORE_MC);
 }
@@ -417,6 +343,14 @@
 // -----------------------------------------------------------------------------
 // LargeObjectSpace
 
+int LargeObjectSpace::ExtraRSetBytesFor(int object_size) {
+  int extra_rset_bits =
+      RoundUp((object_size - Page::kObjectAreaSize) / kPointerSize,
+              kBitsPerInt);
+  return extra_rset_bits / kBitsPerByte;
+}
+
+
 Object* NewSpace::AllocateRawInternal(int size_in_bytes,
                                       AllocationInfo* alloc_info) {
   Address new_top = alloc_info->top + size_in_bytes;