folly::Optional<AliasClass> AliasClass::precise_union(AliasClass o) const {
if (o <= *this) return *this;
if (*this <= o) return o;
auto const unioned = static_cast<rep>(m_bits | o.m_bits);
// For a precise union, we need to make sure the returned class is not any
// bigger than it should be. This means we can't deal with situations where
// we have disjoint stags, and right now we also don't try to deal with
// situations that have the same stag in a combinable way. (E.g. two
// adjacent AStack ranges.)
auto const stag1 = m_stag;
auto const stag2 = o.m_stag;
if (stag1 == STag::None && stag2 == STag::None) {
return AliasClass{unioned};
}
if (stag1 == STag::None && stag2 != STag::None) {
return o.precise_union(*this); // flip args
}
assertx(stag1 != STag::None);
if (stag2 != STag::None) return folly::none;
if (o.m_bits & stagBit(stag1)) return folly::none;
// Keep the data and stag from this, but change its bits.
auto ret = *this;
ret.m_bits = unioned;
assertx(ret.m_stag == stag1);
return ret;
}
bool AliasClass::operator<=(AliasClass o) const {
if (m_bits == BEmpty) return true;
auto const isect = static_cast<rep>(m_bits & o.m_bits);
if (isect != m_bits) return false;
// If they have the same specialized tag, then since isect is equal to
// m_bits, the stagBit must be part of the intersection or be BEmpty. This
// means they can only be in a subclass relationship if that specialized data
// is.
if (m_stag == o.m_stag) return subclassData(o);
/*
* Disjoint stags. The stagBit for m_stag must be part of the intersection
* (or be BEmpty), since isect == m_bits above. This breaks down into the
* following cases:
*
* If the osbit is part of the intersection, then this can't be a subclass of
* `o', because this has only generic information for that bit but it is set
* in isect. If the osbit is BEmpty, osbit & isect is zero, which avoids
* this case.
*
* The remaining situations are that m_stag is STag::None, in which case it
* is a subclass since osbit wasn't in the intersection. Or that m_stag has
* a bit that is in the isect (since m_bits == isect), and that bit is set in
* o.m_bits. In either case this is a subclass, so we can just return true.
*/
auto const osbit = stagBit(o.m_stag);
if (osbit & isect) return false;
return true;
}
bool AliasClass::checkInvariants() const {
switch (m_stag) {
case STag::None: break;
case STag::Frame: break;
case STag::Prop: break;
case STag::ElemI: break;
case STag::Stack:
assertx(m_stack.base->type() <= TStkPtr ||
m_stack.base->type() <= TFramePtr);
assertx(m_stack.size != 0); // use AEmpty if you want that
assertx(m_stack.size > 0);
break;
case STag::ElemS:
assertx(m_elemS.key->isStatic());
break;
case STag::MIState:
break;
case STag::Ref:
assertx(m_ref.boxed->isA(TBoxedCell));
break;
}
assertx(m_bits & stagBit(m_stag));
return true;
}
AliasClass AliasClass::operator|(AliasClass o) const {
if (auto const c = precise_union(o)) return *c;
auto const unioned = static_cast<rep>(m_bits | o.m_bits);
// If they have the same stag, try to merge them with unionData.
auto stag1 = m_stag;
auto stag2 = o.m_stag;
if (stag1 == stag2) return unionData(unioned, *this, o);
// If one of the alias classes have a non-None stag, we can only keep it if
// the other doesn't have the corresponding bit set.
if (stag1 != STag::None && (o.m_bits & stagBit(stag1))) stag1 = STag::None;
if (stag2 != STag::None && (m_bits & stagBit(stag2))) stag2 = STag::None;
auto ret = AliasClass{unioned};
if (stag1 == stag2) return ret; // both None.
// Note: union operations are guaranteed to be commutative, so if there are
// two non-None stags, we have to consistently choose between them. For now
// we keep the one with a smaller `rep' value, instead of discarding both.
const AliasClass* chosen = &o;
auto stag = stag2;
if (stag1 != STag::None) {
if (stag2 == STag::None || stagBit(stag1) < stagBit(stag2)) {
chosen = this;
stag = stag1;
}
}
switch (stag) {
case STag::None:
break;
case STag::Frame: new (&ret.m_frame) AFrame(chosen->m_frame); break;
case STag::Prop: new (&ret.m_prop) AProp(chosen->m_prop); break;
case STag::ElemI: new (&ret.m_elemI) AElemI(chosen->m_elemI); break;
case STag::ElemS: new (&ret.m_elemS) AElemS(chosen->m_elemS); break;
case STag::Stack: new (&ret.m_stack) AStack(chosen->m_stack); break;
case STag::MIState: new (&ret.m_mis) AMIState(chosen->m_mis); break;
case STag::Ref: new (&ret.m_ref) ARef(chosen->m_ref); break;
}
ret.m_stag = stag;
return ret;
}
/*
* TODO(#2884927): we probably need to be aware of possibly-integer-like string
* keys here before we can start using ElemS for anything. (Or else ensure
* that we never use ElemS with an integer-like string.)
*/
bool AliasClass::maybe(AliasClass o) const {
auto const isect = static_cast<rep>(m_bits & o.m_bits);
if (isect == 0) return false;
if (*this <= o || o <= *this) return true;
/*
* If we have the same stag, then the cases are either the stag is in the
* intersection or not. If it's not (including if it was BEmpty), we already
* know the intersection is non-empty and return true.
*
* If it is in the intersection, and it is not the only relevant bit, then we
* still have a non-empty intersection.
*
* Finally if it's in the intersection and the only isect bit, then we need
* to see if the data is in a maybe relationship.
*/
if (m_stag == o.m_stag) {
auto const bit = stagBit(m_stag);
assertx(isect != 0);
if ((bit & isect) == isect) return maybeData(o);
return true;
}
/*
* The stags are different. However, since isect is non-empty, there are
* three cases:
*
* o One of the stag bits is not in the intersection, and thus not
* relevant. Since the other stag bit is in the intersection, but
* didn't have specialized information from one of the intersectees, the
* intersection is non-empty and we should return true.
*
* o Both of the stag bits are not in the intersection, and thus not
* relevant. Some other bit was set, since we already checked that
* isect was non-zero, so we should return true.
*
* o Both of the stag bits are in the intersection. But each intersectee
* therefore had only generic information for the bit of the other, so
* the intersection is non-empty, and we should return true.
*
* All of these cases are handled by the following statement:
*/
return true;
}
bool AliasClass::checkInvariants() const {
switch (m_stag) {
case STag::None: break;
case STag::Frame: break;
case STag::Prop: break;
case STag::ElemI: break;
case STag::Stack:
assertx(m_stack.size > 0);
break;
case STag::ElemS:
assertx(m_elemS.key->isStatic());
break;
case STag::MIState:
break;
case STag::Ref:
assertx(m_ref.boxed->isA(TBoxedCell));
break;
}
assertx(m_bits & stagBit(m_stag));
return true;
}
AliasClass AliasClass::operator|(AliasClass o) const {
if (o <= *this) return *this;
if (*this <= o) return o;
auto const unioned = static_cast<rep>(m_bits | o.m_bits);
// Note: union operations are guaranteed to be commutative, so if there are
// two non-None stags, we have to consistently choose between them. For now
// we throw both away in any case where they differ, and try to merge them
// with unionData if they are the same. If only one had an stag, we can keep
// it only if the other didn't have that bit set.
auto const stag1 = m_stag;
auto const stag2 = o.m_stag;
if (stag1 == stag2) return unionData(unioned, *this, o);
if (stag1 != STag::None && stag2 != STag::None) {
return AliasClass{unioned};
}
if (stag2 != STag::None) return o | *this;
if (o.m_bits & stagBit(stag1)) {
return AliasClass{unioned};
}
auto ret = AliasClass{unioned};
switch (stag1) {
case STag::None:
break;
case STag::Frame: new (&ret.m_frame) AFrame(m_frame); break;
case STag::Prop: new (&ret.m_prop) AProp(m_prop); break;
case STag::ElemI: new (&ret.m_elemI) AElemI(m_elemI); break;
case STag::ElemS: new (&ret.m_elemS) AElemS(m_elemS); break;
case STag::Stack: new (&ret.m_stack) AStack(m_stack); break;
case STag::MIState: new (&ret.m_mis) AMIState(m_mis); break;
}
ret.m_stag = stag1;
return ret;
}
