bool InferredType::set(const ConcurrentJSLocker& locker, VM& vm, Descriptor newDescriptor)
{
// We will trigger write barriers while holding our lock. Currently, write barriers don't GC, but that
// could change. If it does, we don't want to deadlock. Note that we could have used
// GCSafeConcurrentJSLocker in the caller, but the caller is on a fast path so maybe that wouldn't be
// a good idea.
DeferGCForAWhile deferGC(vm.heap);
// Be defensive: if we're not really changing the type, then we don't have to do anything.
if (descriptor(locker) == newDescriptor)
return false;
bool shouldFireWatchpointSet = false;
// The new descriptor must be more general than the previous one.
ASSERT(newDescriptor.subsumes(descriptor(locker)));
// If the new descriptors have different structures, then it can only be because one is null.
if (descriptor(locker).structure() != newDescriptor.structure())
ASSERT(!descriptor(locker).structure() || !newDescriptor.structure());
// We are changing the type, so make sure that if anyone was watching, they find out about it now. If
// anyone is watching, we make sure to go to Top so that we don't do this sort of thing again.
if (m_watchpointSet.state() != ClearWatchpoint) {
// We cannot have been invalidated, since if we were, then we'd already be at Top.
ASSERT(m_watchpointSet.state() != IsInvalidated);
// We're about to do expensive things because some compiler thread decided to watch this type and
// then the type changed. Assume that this property is crazy, and don't ever do any more things for
// it.
newDescriptor = Top;
shouldFireWatchpointSet = true;
}
// Remove the old InferredStructure object if we no longer need it.
if (!newDescriptor.structure())
m_structure = nullptr;
// Add a new InferredStructure object if we need one now.
if (newDescriptor.structure()) {
if (m_structure) {
// We should agree on the structures if we get here.
ASSERT(newDescriptor.structure() == m_structure->structure());
} else {
m_structure = adoptRef(new InferredStructure(vm, this, newDescriptor.structure()));
newDescriptor.structure()->addTransitionWatchpoint(&m_structure->m_watchpoint);
}
}
// Finally, set the descriptor kind.
m_kind = newDescriptor.kind();
// Assert that we did things.
ASSERT(descriptor(locker) == newDescriptor);
return shouldFireWatchpointSet;
}
void InferredType::Descriptor::merge(const Descriptor& other)
{
// Filter out common things to simplify the switch statement below.
if (*this == other)
return;
if (other.m_kind == Bottom)
return;
switch (m_kind) {
case Bottom:
*this = other;
return;
case Boolean:
case String:
case Symbol:
*this = Top;
return;
case Other:
switch (other.m_kind) {
case ObjectWithStructure:
case ObjectWithStructureOrOther:
*this = Descriptor(ObjectWithStructureOrOther, other.structure());
return;
case Object:
case ObjectOrOther:
*this = ObjectOrOther;
return;
default:
*this = Top;
return;
}
case Int32:
switch (other.m_kind) {
case Number:
*this = Number;
return;
default:
*this = Top;
return;
}
case Number:
switch (other.m_kind) {
case Int32:
return;
default:
*this = Top;
return;
}
case ObjectWithStructure:
switch (other.m_kind) {
case ObjectWithStructure: // If we see this here, then we know that the structures didn't match.
case Object:
*this = Object;
return;
case ObjectWithStructureOrOther:
if (m_structure == other.m_structure) {
*this = other;
return;
}
*this = ObjectOrOther;
return;
case ObjectOrOther:
*this = ObjectOrOther;
return;
case Other:
m_kind = ObjectWithStructureOrOther;
return;
default:
*this = Top;
return;
}
case ObjectWithStructureOrOther:
switch (other.m_kind) {
case ObjectWithStructure:
if (m_structure == other.m_structure)
return;
*this = ObjectOrOther;
return;
case Object:
case ObjectWithStructureOrOther: // If we see this here, then we know that the structures didn't match.
case ObjectOrOther:
*this = ObjectOrOther;
return;
case Other:
return;
default:
*this = Top;
return;
}
case Object:
switch (other.m_kind) {
case ObjectWithStructure:
return;
case ObjectWithStructureOrOther:
case ObjectOrOther:
case Other:
*this = ObjectOrOther;
return;
default:
*this = Top;
return;
}
case ObjectOrOther:
switch (other.m_kind) {
case ObjectWithStructure:
case ObjectWithStructureOrOther:
case Object:
case Other:
return;
default:
*this = Top;
return;
}
case Top:
return;
}
RELEASE_ASSERT_NOT_REACHED();
}