Reverting r4703.

src/x64/macro-assembler-x64.cc

Index: src/x64/macro-assembler-x64.cc
===================================================================
--- src/x64/macro-assembler-x64.cc	(revision 4703)
+++ src/x64/macro-assembler-x64.cc	(working copy)
@@ -90,21 +90,58 @@
     bind(&not_in_new_space);
   }
 
+  Label fast;
+
   // Compute the page start address from the heap object pointer, and reuse
   // the 'object' register for it.
-  and_(object, Immediate(~Page::kPageAlignmentMask));
+  ASSERT(is_int32(~Page::kPageAlignmentMask));
+  and_(object,
+       Immediate(static_cast<int32_t>(~Page::kPageAlignmentMask)));
+  Register page_start = object;
 
-  // Compute number of region covering addr. See Page::GetRegionNumberForAddress
-  // method for more details.
-  and_(addr, Immediate(Page::kPageAlignmentMask));
-  shrl(addr, Immediate(Page::kRegionSizeLog2));
+  // Compute the bit addr in the remembered set/index of the pointer in the
+  // page. Reuse 'addr' as pointer_offset.
+  subq(addr, page_start);
+  shr(addr, Immediate(kPointerSizeLog2));
+  Register pointer_offset = addr;
 
-  // Set dirty mark for region.
-  bts(Operand(object, Page::kDirtyFlagOffset), addr);
+  // If the bit offset lies beyond the normal remembered set range, it is in
+  // the extra remembered set area of a large object.
+  cmpq(pointer_offset, Immediate(Page::kPageSize / kPointerSize));
+  j(below, &fast);
+
+  // We have a large object containing pointers. It must be a FixedArray.
+
+  // Adjust 'page_start' so that addressing using 'pointer_offset' hits the
+  // extra remembered set after the large object.
+
+  // Load the array length into 'scratch'.
+  movl(scratch,
+       Operand(page_start,
+               Page::kObjectStartOffset + FixedArray::kLengthOffset));
+  Register array_length = scratch;
+
+  // Extra remembered set starts right after the large object (a FixedArray), at
+  //   page_start + kObjectStartOffset + objectSize
+  // where objectSize is FixedArray::kHeaderSize + kPointerSize * array_length.
+  // Add the delta between the end of the normal RSet and the start of the
+  // extra RSet to 'page_start', so that addressing the bit using
+  // 'pointer_offset' hits the extra RSet words.
+  lea(page_start,
+      Operand(page_start, array_length, times_pointer_size,
+              Page::kObjectStartOffset + FixedArray::kHeaderSize
+                  - Page::kRSetEndOffset));
+
+  // NOTE: For now, we use the bit-test-and-set (bts) x86 instruction
+  // to limit code size. We should probably evaluate this decision by
+  // measuring the performance of an equivalent implementation using
+  // "simpler" instructions
+  bind(&fast);
+  bts(Operand(page_start, Page::kRSetOffset), pointer_offset);
 }
 
 
-// For page containing |object| mark region covering [object+offset] dirty.
+// Set the remembered set bit for [object+offset].
 // object is the object being stored into, value is the object being stored.
 // If offset is zero, then the smi_index register contains the array index into
 // the elements array represented as a smi. Otherwise it can be used as a
@@ -119,8 +156,9 @@
   // registers are rsi.
   ASSERT(!object.is(rsi) && !value.is(rsi) && !smi_index.is(rsi));
 
-  // First, check if a write barrier is even needed. The tests below
-  // catch stores of Smis and stores into young gen.
+  // First, check if a remembered set write is even needed. The tests below
+  // catch stores of Smis and stores into young gen (which does not have space
+  // for the remembered set bits).
   Label done;
   JumpIfSmi(value, &done);
 
@@ -153,8 +191,8 @@
     bind(&okay);
   }
 
-  // Test that the object address is not in the new space. We cannot
-  // update page dirty marks for new space pages.
+  // Test that the object address is not in the new space.  We cannot
+  // set remembered set bits in the new space.
   InNewSpace(object, scratch, equal, &done);
 
   // The offset is relative to a tagged or untagged HeapObject pointer,
@@ -163,19 +201,48 @@
   ASSERT(IsAligned(offset, kPointerSize) ||
          IsAligned(offset + kHeapObjectTag, kPointerSize));
 
-  Register dst = smi_index;
-  if (offset != 0) {
-    lea(dst, Operand(object, offset));
+  // We use optimized write barrier code if the word being written to is not in
+  // a large object page, or is in the first "page" of a large object page.
+  // We make sure that an offset is inside the right limits whether it is
+  // tagged or untagged.
+  if ((offset > 0) && (offset < Page::kMaxHeapObjectSize - kHeapObjectTag)) {
+    // Compute the bit offset in the remembered set, leave it in 'scratch'.
+    lea(scratch, Operand(object, offset));
+    ASSERT(is_int32(Page::kPageAlignmentMask));
+    and_(scratch, Immediate(static_cast<int32_t>(Page::kPageAlignmentMask)));
+    shr(scratch, Immediate(kPointerSizeLog2));
+
+    // Compute the page address from the heap object pointer, leave it in
+    // 'object' (immediate value is sign extended).
+    and_(object, Immediate(~Page::kPageAlignmentMask));
+
+    // NOTE: For now, we use the bit-test-and-set (bts) x86 instruction
+    // to limit code size. We should probably evaluate this decision by
+    // measuring the performance of an equivalent implementation using
+    // "simpler" instructions
+    bts(Operand(object, Page::kRSetOffset), scratch);
   } else {
-    // array access: calculate the destination address in the same manner as
-    // KeyedStoreIC::GenerateGeneric.
-    SmiIndex index = SmiToIndex(smi_index, smi_index, kPointerSizeLog2);
-    lea(dst, FieldOperand(object,
-                          index.reg,
-                          index.scale,
-                          FixedArray::kHeaderSize));
+    Register dst = smi_index;
+    if (offset != 0) {
+      lea(dst, Operand(object, offset));
+    } else {
+      // array access: calculate the destination address in the same manner as
+      // KeyedStoreIC::GenerateGeneric.
+      SmiIndex index = SmiToIndex(smi_index, smi_index, kPointerSizeLog2);
+      lea(dst, FieldOperand(object,
+                            index.reg,
+                            index.scale,
+                            FixedArray::kHeaderSize));
+    }
+    // If we are already generating a shared stub, not inlining the
+    // record write code isn't going to save us any memory.
+    if (generating_stub()) {
+      RecordWriteHelper(object, dst, scratch);
+    } else {
+      RecordWriteStub stub(object, dst, scratch);
+      CallStub(&stub);
+    }
   }
-  RecordWriteHelper(object, dst, scratch);
 
   bind(&done);
 
@@ -577,18 +644,6 @@
 }
 
 
-void MacroAssembler::PositiveSmiDivPowerOfTwoToInteger32(Register dst,
-                                                         Register src,
-                                                         int power) {
-  ASSERT((0 <= power) && (power < 32));
-  if (dst.is(src)) {
-    shr(dst, Immediate(power + kSmiShift));
-  } else {
-    UNIMPLEMENTED();  // Not used.
-  }
-}
-
-
 Condition MacroAssembler::CheckSmi(Register src) {
   ASSERT_EQ(0, kSmiTag);
   testb(src, Immediate(kSmiTagMask));
@@ -2552,7 +2607,7 @@
   movq(FieldOperand(result, HeapObject::kMapOffset), kScratchRegister);
   Integer32ToSmi(scratch1, length);
   movq(FieldOperand(result, String::kLengthOffset), scratch1);
-  movq(FieldOperand(result, String::kHashFieldOffset),
+  movl(FieldOperand(result, String::kHashFieldOffset),
        Immediate(String::kEmptyHashField));
 }
 
@@ -2590,7 +2645,7 @@
   movq(FieldOperand(result, HeapObject::kMapOffset), kScratchRegister);
   Integer32ToSmi(scratch1, length);
   movq(FieldOperand(result, String::kLengthOffset), scratch1);
-  movq(FieldOperand(result, String::kHashFieldOffset),
+  movl(FieldOperand(result, String::kHashFieldOffset),
        Immediate(String::kEmptyHashField));
 }