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[turbofan] Instance types don't change, so no need to watch for side effects.

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The instance type of an object cannot change, only the concrete map
might. So when searching for an instance type witness, we don't need
to pay attention to potentially side-effecting nodes.

R=mstarzinger@chromium.org

Review-Url: https://codereview.chromium.org/2652893011
Cr-Commit-Position: refs/heads/master@{#42699}
This commit is contained in:
bmeurer 2017-01-26 06:14:54 -08:00 committed by Commit bot
parent 169b85673f
commit 7f441a5e1b
1 changed files with 9 additions and 21 deletions
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30
src/compiler/js-builtin-reducer.cc
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@ -915,27 +915,15 @@ bool HasInstanceTypeWitness(Node* receiver, Node* effect,
}
return true;
}
switch (dominator->opcode()) {
case IrOpcode::kStoreField: {
FieldAccess const& access = FieldAccessOf(dominator->op());
if (access.base_is_tagged == kTaggedBase &&
access.offset == HeapObject::kMapOffset) {
return false;
}
break;
}
case IrOpcode::kStoreElement:
case IrOpcode::kStoreTypedElement:
break;
default: {
DCHECK_EQ(1, dominator->op()->EffectOutputCount());
if (dominator->op()->EffectInputCount() != 1 ||
!dominator->op()->HasProperty(Operator::kNoWrite)) {
// Didn't find any appropriate CheckMaps node.
return false;
}
break;
}
// The instance type doesn't change for JSReceiver values, so we
// don't need to pay attention to potentially side-effecting nodes
// here. Strings and internal structures like FixedArray and
// FixedDoubleArray are weird here, but we don't use this function then.
DCHECK_LE(FIRST_JS_RECEIVER_TYPE, instance_type);
DCHECK_EQ(1, dominator->op()->EffectOutputCount());
if (dominator->op()->EffectInputCount() != 1) {
// Didn't find any appropriate CheckMaps node.
return false;
}
dominator = NodeProperties::GetEffectInput(dominator);
}