Reviewers: Michael Starzinger,
Message:
As discussed offline, PTAL.
Description:
Skip write barrier if value and object originate from the same allocation.
Please review this at https://codereview.chromium.org/101993002/
SVN Base: https://v8.googlecode.com/svn/branches/bleeding_edge
Affected files (+20, -8 lines):
M src/hydrogen-instructions.h
Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index
d4beb6e1de2180b9fb903116a2d66b4dc7f21428..9f7605f628193b6c68d9cf06c7c53742ca8b050c
100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5652,11 +5652,10 @@ inline bool StoringValueNeedsWriteBarrier(HValue*
value) {
inline bool ReceiverObjectNeedsWriteBarrier(HValue* object,
+ HValue* value,
HValue* new_space_dominator) {
- if (object->IsInnerAllocatedObject()) {
- return ReceiverObjectNeedsWriteBarrier(
- HInnerAllocatedObject::cast(object)->base_object(),
- new_space_dominator);
+ while (object->IsInnerAllocatedObject()) {
+ object = HInnerAllocatedObject::cast(object)->base_object();
}
if (object->IsConstant() && HConstant::cast(object)->IsCell()) {
return false;
@@ -5668,7 +5667,17 @@ inline bool ReceiverObjectNeedsWriteBarrier(HValue*
object,
}
if (object != new_space_dominator) return true;
if (object->IsAllocate()) {
- return !HAllocate::cast(object)->IsNewSpaceAllocation();
+ // Stores to new space allocations require no write barriers if the
object
+ // is the new space dominator.
+ if (HAllocate::cast(object)->IsNewSpaceAllocation()) {
+ return false;
+ }
+ // Likewise we don't need a write barrier if we store a value that
+ // originates from the same allocation (via allocation folding).
+ while (value->IsInnerAllocatedObject()) {
+ value = HInnerAllocatedObject::cast(value)->base_object();
+ }
+ return object != value;
}
return true;
}
@@ -6589,12 +6598,14 @@ class HStoreNamedField V8_FINAL : public
HTemplateInstruction<3> {
if (field_representation().IsInteger32()) return false;
if (field_representation().IsExternal()) return false;
return StoringValueNeedsWriteBarrier(value()) &&
- ReceiverObjectNeedsWriteBarrier(object(), new_space_dominator());
+ ReceiverObjectNeedsWriteBarrier(object(), value(),
+ new_space_dominator());
}
bool NeedsWriteBarrierForMap() {
if (IsSkipWriteBarrier()) return false;
- return ReceiverObjectNeedsWriteBarrier(object(),
new_space_dominator());
+ return ReceiverObjectNeedsWriteBarrier(object(), transition(),
+ new_space_dominator());
}
Representation field_representation() const {
@@ -6756,7 +6767,8 @@ class HStoreKeyed V8_FINAL
return false;
} else {
return StoringValueNeedsWriteBarrier(value()) &&
- ReceiverObjectNeedsWriteBarrier(elements(),
new_space_dominator());
+ ReceiverObjectNeedsWriteBarrier(elements(), value(),
+ new_space_dominator());
}
}
--
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