Reviewers: Vyacheslav Egorov,
Description:
Rescan cells at the end of mark-sweep. This means they don't need a
write barrier.
Please review this at http://codereview.chromium.org/8816021/
SVN Base: http://v8.googlecode.com/svn/branches/bleeding_edge/
Affected files:
M src/ia32/code-stubs-ia32.cc
M src/ia32/lithium-codegen-ia32.cc
M src/ia32/stub-cache-ia32.cc
M src/mark-compact.cc
Index: src/ia32/code-stubs-ia32.cc
===================================================================
--- src/ia32/code-stubs-ia32.cc (revision 10174)
+++ src/ia32/code-stubs-ia32.cc (working copy)
@@ -4653,7 +4653,8 @@
// megamorphic.
__ cmp(ecx, Immediate(UninitializedSentinel(isolate)));
__ j(equal, &initialize, Label::kNear);
- // MegamorphicSentinel is a root so no write-barrier is needed.
+ // MegamorphicSentinel is an immortal immovable object (undefined) so
no
+ // write-barrier is needed.
__ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
Immediate(MegamorphicSentinel(isolate)));
__ jmp(&call, Label::kNear);
@@ -4661,14 +4662,7 @@
// An uninitialized cache is patched with the function.
__ bind(&initialize);
__ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset), edi);
- __ mov(ecx, edi);
- __ RecordWriteField(ebx,
- JSGlobalPropertyCell::kValueOffset,
- ecx,
- edx,
- kDontSaveFPRegs,
- OMIT_REMEMBERED_SET, // Cells are rescanned.
- OMIT_SMI_CHECK);
+ // No need for a write barrier here - cells are rescanned.
__ bind(&call);
}
@@ -4700,6 +4694,8 @@
// non-function case.
__ mov(ebx, Operand(esp, 0));
__ mov(ebx, Operand(ebx, 1));
+ // MegamorphicSentinel is an immortal immovable object (undefined) so
no
+ // write barrier is needed.
__ mov(FieldOperand(ebx, JSGlobalPropertyCell::kValueOffset),
Immediate(MegamorphicSentinel(isolate)));
}
Index: src/ia32/lithium-codegen-ia32.cc
===================================================================
--- src/ia32/lithium-codegen-ia32.cc (revision 10174)
+++ src/ia32/lithium-codegen-ia32.cc (working copy)
@@ -2144,20 +2144,7 @@
// Store the value.
__ mov(FieldOperand(object, offset), value);
-
- // Cells are always in the remembered set.
- if (instr->hydrogen()->NeedsWriteBarrier()) {
- HType type = instr->hydrogen()->value()->type();
- SmiCheck check_needed =
- type.IsHeapObject() ? OMIT_SMI_CHECK : INLINE_SMI_CHECK;
- __ RecordWriteField(object,
- offset,
- value,
- address,
- kSaveFPRegs,
- OMIT_REMEMBERED_SET,
- check_needed);
- }
+ // Cells are always rescanned, so no write barrier here.
}
Index: src/ia32/stub-cache-ia32.cc
===================================================================
--- src/ia32/stub-cache-ia32.cc (revision 10174)
+++ src/ia32/stub-cache-ia32.cc (working copy)
@@ -2522,23 +2522,9 @@
// Store the value in the cell.
__ mov(cell_operand, eax);
- Label done;
- __ test(eax, Immediate(kSmiTagMask));
- __ j(zero, &done);
+ // No write barrier here, because cells are always rescanned.
- __ mov(ecx, eax);
- __ lea(edx, cell_operand);
- // Cells are always in the remembered set.
- __ RecordWrite(ebx, // Object.
- edx, // Address.
- ecx, // Value.
- kDontSaveFPRegs,
- OMIT_REMEMBERED_SET,
- OMIT_SMI_CHECK);
-
// Return the value (register eax).
- __ bind(&done);
-
Counters* counters = isolate()->counters();
__ IncrementCounter(counters->named_store_global_inline(), 1);
__ ret(0);
Index: src/mark-compact.cc
===================================================================
--- src/mark-compact.cc (revision 10174)
+++ src/mark-compact.cc (working copy)
@@ -2081,6 +2081,22 @@
PrepareForCodeFlushing();
+ // There is no write barrier on cells so we have to scan them now at the
end
+ // of the incremental sweeping.
+ {
+ HeapObjectIterator cell_iterator(heap()->cell_space());
+ HeapObject* cell;
+ while ((cell = cell_iterator.Next()) != NULL) {
+ ASSERT(cell->IsJSGlobalPropertyCell());
+ if (IsMarked(cell)) {
+ int offset = JSGlobalPropertyCell::kValueOffset;
+ StaticMarkingVisitor::VisitPointer(
+ heap(),
+ reinterpret_cast<Object**>(cell->address() + offset));
+ }
+ }
+ }
+
RootMarkingVisitor root_visitor(heap());
MarkRoots(&root_visitor);
--
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