Add map-based read barrier to WeakCell

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index b69ce7952dd917a918beb470806486b1637e4708..98616fa9c32c7b61c7f768d36a2d4f8f73658f34 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -6049,6 +6049,8 @@ class HObjectAccess FINAL {
     return ExistingInobjectPropertyField::decode(value_);
   }
 
+  inline bool read_barrier() const { return ReadBarrierField::decode(value_); }
+
   inline HObjectAccess WithRepresentation(Representation representation) {
     return HObjectAccess(portion(), offset(), representation, name(),
                          immutable(), existing_inobject_property());
@@ -6215,16 +6217,10 @@ class HObjectAccess FINAL {
                          Representation::UInteger16());
   }
 
-  static HObjectAccess ForPropertyCellValue() {
-    return HObjectAccess(kInobject, PropertyCell::kValueOffset);
-  }
-
-  static HObjectAccess ForCellValue() {
-    return HObjectAccess(kInobject, Cell::kValueOffset);
-  }
-
   static HObjectAccess ForWeakCellValue() {

[Erik Corry Chromium.org, 2015/02/03 17:42:53]

I suspect some or perhaps all of the uses of this are for checks and should not
trigger the read barrier.

[ulan, 2015/02/04 09:35:04]

Yesterday I landed a change in StoreGlobal hydrogen stub that loads and uses
weak value.

[Erik Corry, 2015/02/04 10:49:42]

OK, we probably need both.

-    return HObjectAccess(kInobject, WeakCell::kValueOffset);
+    return HObjectAccess(
+        kInobject, WeakCell::kValueOffsetDontForgetTheReadBarrier,
+        Representation::Tagged(), Handle<String>::null(), false, true, true);
   }
 
   static HObjectAccess ForAllocationMementoSite() {
@@ -6398,15 +6394,16 @@ class HObjectAccess FINAL {
   HObjectAccess(Portion portion, int offset,
                 Representation representation = Representation::Tagged(),
                 Handle<String> name = Handle<String>::null(),
-                bool immutable = false,
-                bool existing_inobject_property = true)
-    : value_(PortionField::encode(portion) |
-             RepresentationField::encode(representation.kind()) |
-             ImmutableField::encode(immutable ? 1 : 0) |
-             ExistingInobjectPropertyField::encode(
-                 existing_inobject_property ? 1 : 0) |
-             OffsetField::encode(offset)),
-      name_(name) {
+                bool immutable = false, bool existing_inobject_property = true,
+                bool read_barrier = false)
+      : value_(PortionField::encode(portion) |
+               RepresentationField::encode(representation.kind()) |
+               ImmutableField::encode(immutable ? 1 : 0) |
+               ExistingInobjectPropertyField::encode(
+                   existing_inobject_property ? 1 : 0) |
+               ReadBarrierField::encode(read_barrier ? 1 : 0) |

[Hannes Payer (out of office), 2015/02/04 12:45:59]

I like that.

+               OffsetField::encode(offset)),
+        name_(name) {
     // assert that the fields decode correctly
     DCHECK(this->offset() == offset);
     DCHECK(this->portion() == portion);
@@ -6420,7 +6417,8 @@ class HObjectAccess FINAL {
   class RepresentationField : public BitField<Representation::Kind, 3, 4> {};
   class ImmutableField : public BitField<bool, 7, 1> {};
   class ExistingInobjectPropertyField : public BitField<bool, 8, 1> {};
-  class OffsetField : public BitField<int, 9, 23> {};
+  class ReadBarrierField : public BitField<bool, 9, 1> {};
+  class OffsetField : public BitField<int, 10, 22> {};
 
   uint32_t value_;  // encodes portion, representation, immutable, and offset
   Handle<String> name_;