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ConstraintGraph.cpp
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//===--- ConstraintGraph.cpp - Constraint Graph ---------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file implements the \c ConstraintGraph class, which describes the
// relationships among the type variables within a constraint system.
//
//===----------------------------------------------------------------------===//
#include "swift/Basic/Defer.h"
#include "swift/Basic/Statistic.h"
#include "swift/Sema/ConstraintGraph.h"
#include "swift/Sema/ConstraintSystem.h"
#include "swift/Sema/CSTrail.h"
#include "swift/Basic/Assertions.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/SaveAndRestore.h"
#include <algorithm>
#include <memory>
#include <numeric>
using namespace swift;
using namespace constraints;
#define DEBUG_TYPE "ConstraintGraph"
#pragma mark Graph construction/destruction
ConstraintGraph::ConstraintGraph(ConstraintSystem &cs) : CS(cs) { }
ConstraintGraph::~ConstraintGraph() {
for (unsigned i = 0, n = TypeVariables.size(); i != n; ++i) {
auto &impl = TypeVariables[i]->getImpl();
delete impl.getGraphNode();
impl.setGraphNode(nullptr);
}
for (auto *node : FreeList) {
delete node;
}
}
#pragma mark Graph accessors
std::pair<ConstraintGraphNode &, unsigned>
ConstraintGraph::lookupNode(TypeVariableType *typeVar) {
// Check whether we've already created a node for this type variable.
auto &impl = typeVar->getImpl();
if (auto nodePtr = impl.getGraphNode()) {
assert(impl.getGraphIndex() < TypeVariables.size() && "Out-of-bounds index");
assert(TypeVariables[impl.getGraphIndex()] == typeVar &&
"Type variable mismatch");
ASSERT(nodePtr->TypeVar == typeVar &&
"Use-after-free");
return { *nodePtr, impl.getGraphIndex() };
}
// Allocate the new node.
ConstraintGraphNode *nodePtr;
if (FreeList.empty())
nodePtr = new ConstraintGraphNode(*this, typeVar);
else {
nodePtr = FreeList.back();
FreeList.pop_back();
nodePtr->initTypeVariable(typeVar);
}
unsigned index = TypeVariables.size();
impl.setGraphNode(nodePtr);
impl.setGraphIndex(index);
// Record this type variable.
TypeVariables.push_back(typeVar);
// Record the change, if there are active scopes. Note that we specifically
// check CS.solverState and not CS.isRecordingChanges(), because we want
// recordChange() to assert if there's an active undo. It is not valid to
// create new nodes during an undo.
if (CS.solverState)
CS.recordChange(SolverTrail::Change::AddedTypeVariable(typeVar));
// If this type variable is not the representative of its equivalence class,
// add it to its representative's set of equivalences.
auto typeVarRep = CS.getRepresentative(typeVar);
if (typeVar != typeVarRep)
mergeNodes(typeVar, typeVarRep);
else if (auto fixed = CS.getFixedType(typeVarRep)) {
// Bind the type variable.
bindTypeVariable(typeVar, fixed);
}
return { *nodePtr, index };
}
void ConstraintGraphNode::reset() {
ASSERT(TypeVar);
TypeVar = nullptr;
Bindings.reset();
Constraints.clear();
ConstraintIndex.clear();
ReferencedBy.clear();
References.clear();
EquivalenceClass.clear();
}
bool ConstraintGraphNode::forRepresentativeVar() const {
auto *typeVar = getTypeVariable();
return typeVar == typeVar->getImpl().getRepresentative(nullptr);
}
ArrayRef<TypeVariableType *> ConstraintGraphNode::getEquivalenceClass() const{
assert(forRepresentativeVar() &&
"Can't request equivalence class from non-representative type var");
return getEquivalenceClassUnsafe();
}
ArrayRef<TypeVariableType *>
ConstraintGraphNode::getEquivalenceClassUnsafe() const{
if (EquivalenceClass.empty())
EquivalenceClass.push_back(TypeVar);
return EquivalenceClass;
}
#pragma mark Node mutation
static bool isUsefulForReferencedVars(Constraint *constraint) {
switch (constraint->getKind()) {
// Don't attempt to propagate information about `Bind`s and
// `BindOverload`s to referenced variables since they are
// adjacent through that binding already, and there is no
// useful information in trying to process that kind of
// constraint.
case ConstraintKind::Bind:
case ConstraintKind::BindOverload:
return false;
default:
return true;
}
}
void ConstraintGraphNode::addConstraint(Constraint *constraint) {
assert(ConstraintIndex.count(constraint) == 0 && "Constraint re-insertion");
ConstraintIndex[constraint] = Constraints.size();
Constraints.push_back(constraint);
}
void ConstraintGraphNode::removeConstraint(Constraint *constraint) {
auto pos = ConstraintIndex.find(constraint);
assert(pos != ConstraintIndex.end());
// Remove this constraint from the constraint mapping.
auto index = pos->second;
ConstraintIndex.erase(pos);
assert(Constraints[index] == constraint && "Mismatched constraint");
// If this is the last constraint, just pop it off the list and we're done.
unsigned lastIndex = Constraints.size()-1;
if (index == lastIndex) {
Constraints.pop_back();
return;
}
// This constraint is somewhere in the middle; swap it with the last
// constraint, so we can remove the constraint from the vector in O(1)
// time rather than O(n) time.
auto lastConstraint = Constraints[lastIndex];
Constraints[index] = lastConstraint;
ConstraintIndex[lastConstraint] = index;
Constraints.pop_back();
}
void ConstraintGraphNode::notifyReferencingVars(
llvm::function_ref<void(ConstraintGraphNode &,
Constraint *)> notification) const {
SmallVector<TypeVariableType *, 4> stack;
stack.push_back(TypeVar);
auto updateAdjacencies = [&](TypeVariableType *typeVar) {
for (auto *constraint : CG[typeVar].getConstraints()) {
if (constraint->getClassification() !=
ConstraintClassification::Relational)
continue;
auto lhsTy = constraint->getFirstType();
auto rhsTy = constraint->getSecondType();
Type affectedTy =
ConstraintSystem::typeVarOccursInType(typeVar, lhsTy) ? rhsTy : lhsTy;
if (auto *affectedVar = affectedTy->getAs<TypeVariableType>()) {
auto *repr =
affectedVar->getImpl().getRepresentative(/*record=*/nullptr);
if (!repr->getImpl().getFixedType(/*record=*/nullptr))
notification(CG[repr], constraint);
}
}
};
while (!stack.empty()) {
auto *typeVar = stack.pop_back_val();
// All of the relational constraints associated with this
// variable need to get re-introduced to other mentioned
// type variable to update their bindings.
//
// If variable is a representative of an equivalence class
// it means that all members have been modified together
// with their representative and their adjacencies have to
// get updated as well.
if (CG[typeVar].forRepresentativeVar()) {
for (auto *eqVar : CG[typeVar].getEquivalenceClass()) {
updateAdjacencies(eqVar);
for (auto *referrer : CG[eqVar].getReferencedBy())
stack.push_back(referrer);
}
} else {
updateAdjacencies(typeVar);
// If current type variable is referenced by some other
// type variable as part of its fixed type it means that
// all of the adjacencies of that variable have to be
// notified as well otherwise they'll miss change in type.
for (auto *referrer : CG[typeVar].getReferencedBy())
stack.push_back(referrer);
}
}
}
void ConstraintGraphNode::notifyReferencedVars(
llvm::function_ref<void(ConstraintGraphNode &)> notification) const {
for (auto *fixedBinding : getReferencedVars()) {
notification(CG[fixedBinding]);
}
}
void ConstraintGraphNode::addToEquivalenceClass(
ArrayRef<TypeVariableType *> typeVars) {
assert(forRepresentativeVar() &&
"Can't extend equivalence class of non-representative type var");
if (EquivalenceClass.empty())
EquivalenceClass.push_back(getTypeVariable());
EquivalenceClass.append(typeVars.begin(), typeVars.end());
{
for (auto *newMember : typeVars) {
auto &node = CG[newMember];
for (auto *constraint : node.getConstraints()) {
introduceToInference(constraint);
if (!isUsefulForReferencedVars(constraint))
continue;
notifyReferencedVars([&](ConstraintGraphNode &referencedVar) {
referencedVar.introduceToInference(constraint);
});
}
// FIXME: Perhaps this also needs to be split up into two stages,
// where the first stage runs before we merge the equivalence
// classes
node.notifyReferencingVars(
[&](ConstraintGraphNode &node, Constraint *constraint) {
node.retractFromInference(constraint);
node.introduceToInference(constraint);
});
}
}
}
void ConstraintGraphNode::truncateEquivalenceClass(unsigned prevSize) {
EquivalenceClass.erase(EquivalenceClass.begin() + prevSize,
EquivalenceClass.end());
}
void ConstraintGraphNode::addReferencedVar(TypeVariableType *typeVar) {
bool inserted = References.insert(typeVar);
if (!inserted) {
llvm::errs() << "$T" << TypeVar->getImpl().getID() << " already "
<< "references $T" << typeVar->getImpl().getID() << "\n";
abort();
}
}
void ConstraintGraphNode::addReferencedBy(TypeVariableType *typeVar) {
bool inserted = ReferencedBy.insert(typeVar);
if (!inserted) {
llvm::errs() << "$T" << TypeVar->getImpl().getID() << " already "
<< "referenced by $T" << typeVar->getImpl().getID() << "\n";
abort();
}
}
void ConstraintGraphNode::removeReference(TypeVariableType *typeVar) {
auto removed = References.remove(typeVar);
if (!removed) {
llvm::errs() << "$T" << TypeVar->getImpl().getID() << " does not "
<< "reference $T" << typeVar->getImpl().getID() << "\n";
abort();
}
}
void ConstraintGraphNode::removeReferencedBy(TypeVariableType *typeVar) {
auto removed = ReferencedBy.remove(typeVar);
if (!removed) {
llvm::errs() << "$T" << TypeVar->getImpl().getID() << " not "
<< "referenced by $T" << typeVar->getImpl().getID() << "\n";
abort();
}
}
inference::PotentialBindings &ConstraintGraphNode::getCurrentBindings() {
assert(forRepresentativeVar());
if (!Bindings)
Bindings.emplace(CG.getConstraintSystem(), TypeVar);
return *Bindings;
}
void ConstraintGraphNode::introduceToInference(Constraint *constraint) {
if (forRepresentativeVar()) {
auto fixedType = TypeVar->getImpl().getFixedType(/*record=*/nullptr);
if (!fixedType)
getCurrentBindings().infer(constraint);
} else {
auto *repr =
getTypeVariable()->getImpl().getRepresentative(/*record=*/nullptr);
CG[repr].introduceToInference(constraint);
}
}
void ConstraintGraphNode::retractFromInference(Constraint *constraint) {
if (forRepresentativeVar()) {
auto fixedType = TypeVar->getImpl().getFixedType(/*record=*/nullptr);
if (!fixedType)
getCurrentBindings().retract(constraint);
} else {
auto *repr =
getTypeVariable()->getImpl().getRepresentative(/*record=*/nullptr);
CG[repr].retractFromInference(constraint);
}
}
void ConstraintGraphNode::introduceToInference(Type fixedType) {
// Notify all of the type variables that reference this one.
//
// Since this type variable has been replaced with a fixed type
// all of the concrete types that reference it are going to change,
// which means that all of the not-yet-attempted bindings should
// change as well.
notifyReferencingVars(
[&](ConstraintGraphNode &node, Constraint *constraint) {
node.retractFromInference(constraint);
node.introduceToInference(constraint);
});
if (!fixedType->hasTypeVariable())
return;
SmallPtrSet<TypeVariableType *, 4> referencedVars;
fixedType->getTypeVariables(referencedVars);
for (auto *referencedVar : referencedVars) {
auto &node = CG[referencedVar];
// Newly referred vars need to re-introduce all constraints associated
// with this type variable since they are now going to be used in
// all of the constraints that reference bound type variable.
for (auto *constraint : getConstraints()) {
if (isUsefulForReferencedVars(constraint)) {
node.retractFromInference(constraint);
node.introduceToInference(constraint);
}
}
}
}
#pragma mark Graph mutation
void ConstraintGraph::removeNode(TypeVariableType *typeVar) {
// Remove this node.
auto &impl = typeVar->getImpl();
unsigned index = impl.getGraphIndex();
auto *node = impl.getGraphNode();
node->reset();
FreeList.push_back(node);
impl.setGraphNode(nullptr);
// Remove this type variable from the list.
unsigned lastIndex = TypeVariables.size()-1;
if (index < lastIndex)
TypeVariables[index] = TypeVariables[lastIndex];
TypeVariables.pop_back();
}
void ConstraintGraph::addConstraint(Constraint *constraint) {
// For the nodes corresponding to each type variable...
auto referencedTypeVars = constraint->getTypeVariables();
for (auto typeVar : referencedTypeVars) {
// Record the change, if there are active scopes.
if (CS.solverState)
CS.recordChange(SolverTrail::Change::AddedConstraint(typeVar, constraint));
addConstraint(typeVar, constraint);
auto &node = (*this)[typeVar];
node.introduceToInference(constraint);
if (isUsefulForReferencedVars(constraint)) {
node.notifyReferencedVars([&](ConstraintGraphNode &referencedVar) {
referencedVar.introduceToInference(constraint);
});
}
}
// If the constraint doesn't reference any type variables, it's orphaned;
// track it as such.
if (referencedTypeVars.empty()) {
// Record the change, if there are active scopes.
if (CS.solverState)
CS.recordChange(SolverTrail::Change::AddedConstraint(nullptr, constraint));
addConstraint(nullptr, constraint);
}
}
void ConstraintGraph::addConstraint(TypeVariableType *typeVar,
Constraint *constraint) {
if (typeVar) {
(*this)[typeVar].addConstraint(constraint);
return;
}
// If the constraint doesn't reference any type variables, it's orphaned;
// track it as such.
OrphanedConstraints.push_back(constraint);
}
void ConstraintGraph::removeConstraint(Constraint *constraint) {
// For the nodes corresponding to each type variable...
auto referencedTypeVars = constraint->getTypeVariables();
for (auto typeVar : referencedTypeVars) {
// Find the node for this type variable.
auto &node = (*this)[typeVar];
node.retractFromInference(constraint);
if (isUsefulForReferencedVars(constraint)) {
node.notifyReferencedVars([&](ConstraintGraphNode &referencedVar) {
referencedVar.retractFromInference(constraint);
});
}
// Record the change, if there are active scopes.
if (CS.solverState)
CS.recordChange(SolverTrail::Change::RemovedConstraint(typeVar, constraint));
removeConstraint(typeVar, constraint);
}
// If this is an orphaned constraint, remove it from the list.
if (referencedTypeVars.empty()) {
// Record the change, if there are active scopes.
if (CS.solverState)
CS.recordChange(SolverTrail::Change::RemovedConstraint(nullptr, constraint));
removeConstraint(nullptr, constraint);
}
}
void ConstraintGraph::removeConstraint(TypeVariableType *typeVar,
Constraint *constraint) {
if (typeVar) {
(*this)[typeVar].removeConstraint(constraint);
return;
}
// If this is an orphaned constraint, remove it from the list.
auto known = std::find(OrphanedConstraints.begin(),
OrphanedConstraints.end(),
constraint);
assert(known != OrphanedConstraints.end() && "missing orphaned constraint");
*known = OrphanedConstraints.back();
OrphanedConstraints.pop_back();
}
void ConstraintGraph::mergeNodes(TypeVariableType *typeVar1,
TypeVariableType *typeVar2) {
assert(CS.getRepresentative(typeVar1) == CS.getRepresentative(typeVar2) &&
"type representatives don't match");
// Retrieve the node for the representative that we're merging into.
auto typeVarRep = CS.getRepresentative(typeVar1);
auto &repNode = (*this)[typeVarRep];
// Retrieve the node for the non-representative.
assert((typeVar1 == typeVarRep || typeVar2 == typeVarRep) &&
"neither type variable is the new representative?");
auto typeVarNonRep = typeVar1 == typeVarRep? typeVar2 : typeVar1;
// Record the change, if there are active scopes.
if (CS.isRecordingChanges()) {
CS.recordChange(
SolverTrail::Change::ExtendedEquivalenceClass(
typeVarRep,
repNode.getEquivalenceClass().size()));
}
// Merge equivalence class from the non-representative type variable.
auto &nonRepNode = (*this)[typeVarNonRep];
repNode.addToEquivalenceClass(nonRepNode.getEquivalenceClassUnsafe());
}
void ConstraintGraph::bindTypeVariable(TypeVariableType *typeVar, Type fixed) {
assert(!fixed->is<TypeVariableType>() &&
"Cannot bind to type variable; merge equivalence classes instead");
auto &node = (*this)[typeVar];
llvm::SmallPtrSet<TypeVariableType *, 4> referencedVars;
fixed->getTypeVariables(referencedVars);
for (auto otherTypeVar : referencedVars) {
if (typeVar == otherTypeVar)
continue;
auto &otherNode = (*this)[otherTypeVar];
otherNode.addReferencedBy(typeVar);
node.addReferencedVar(otherTypeVar);
// Record the change, if there are active scopes.
if (CS.isRecordingChanges())
CS.recordChange(SolverTrail::Change::RelatedTypeVariables(typeVar, otherTypeVar));
}
}
void ConstraintGraph::introduceToInference(TypeVariableType *typeVar, Type fixed) {
(*this)[typeVar].introduceToInference(fixed);
}
void ConstraintGraph::unrelateTypeVariables(TypeVariableType *typeVar,
TypeVariableType *otherTypeVar) {
auto &node = (*this)[typeVar];
auto &otherNode = (*this)[otherTypeVar];
otherNode.removeReferencedBy(typeVar);
node.removeReference(otherTypeVar);
}
void ConstraintGraph::inferBindings(TypeVariableType *typeVar,
Constraint *constraint) {
(*this)[typeVar].getCurrentBindings().infer(constraint);
}
void ConstraintGraph::retractBindings(TypeVariableType *typeVar,
Constraint *constraint) {
(*this)[typeVar].getCurrentBindings().retract(constraint);
}
#pragma mark Algorithms
/// Perform a depth-first search.
///
/// \param cg The constraint graph.
/// \param typeVar The type variable we're searching from.
/// \param preVisitNode Called before traversing a node. Must return \c
/// false when the node has already been visited.
/// \param visitConstraint Called before considering a constraint. If it
/// returns \c false, that constraint will be skipped.
/// \param visitedConstraints Set of already-visited constraints, used
/// internally to avoid duplicated work.
static void depthFirstSearch(
ConstraintGraph &cg,
TypeVariableType *typeVar,
llvm::function_ref<bool(TypeVariableType *)> preVisitNode,
llvm::function_ref<bool(Constraint *)> visitConstraint,
llvm::SmallPtrSet<Constraint *, 8> &visitedConstraints) {
// Visit this node. If we've already seen it, bail out.
if (!preVisitNode(typeVar))
return;
// Local function to visit adjacent type variables.
auto visitAdjacencies = [&](ArrayRef<TypeVariableType *> adjTypeVars) {
for (auto adj : adjTypeVars) {
if (adj == typeVar)
continue;
// Recurse into this node.
depthFirstSearch(cg, adj, preVisitNode, visitConstraint,
visitedConstraints);
}
};
// Walk all of the constraints associated with this node to find related
// nodes.
auto &node = cg[typeVar];
for (auto constraint : node.getConstraints()) {
// If we've already seen this constraint, skip it.
if (!visitedConstraints.insert(constraint).second)
continue;
if (visitConstraint(constraint))
visitAdjacencies(constraint->getTypeVariables());
}
// Visit all of the other nodes in the equivalence class.
auto repTypeVar = cg.getConstraintSystem().getRepresentative(typeVar);
if (typeVar == repTypeVar) {
// We are the representative, so visit all of the other type variables
// in this equivalence class.
visitAdjacencies(node.getEquivalenceClass());
} else {
// We are not the representative; visit the representative.
visitAdjacencies(repTypeVar);
}
// Walk any type variables related via fixed bindings.
visitAdjacencies(node.getReferencedBy());
visitAdjacencies(node.getReferencedVars());
}
llvm::TinyPtrVector<Constraint *> ConstraintGraph::gatherConstraints(
TypeVariableType *typeVar, GatheringKind kind,
llvm::function_ref<bool(Constraint *)> acceptConstraintFn) {
llvm::TinyPtrVector<Constraint *> constraints;
// Whether we should consider this constraint at all.
auto shouldConsiderConstraint = [&](Constraint *constraint) {
// For a one-way constraint, only consider it when the left-hand side of
// the binding is one of the type variables currently under consideration,
// as only such constraints need solving for this component. Note that we
// don't perform any other filtering, as the constraint system should be
// responsible for checking any other conditions.
if (constraint->isOneWayConstraint()) {
auto lhsTypeVar = constraint->getFirstType()->castTo<TypeVariableType>();
return CS.isActiveTypeVariable(lhsTypeVar);
}
return true;
};
auto acceptConstraint = [&](Constraint *constraint) {
return shouldConsiderConstraint(constraint) &&
acceptConstraintFn(constraint);
};
llvm::SmallPtrSet<TypeVariableType *, 4> typeVars;
llvm::SmallPtrSet<Constraint *, 8> visitedConstraints;
if (kind == GatheringKind::AllMentions) {
// If we've been asked for "all mentions" of a type variable, search for
// constraints involving both it and its fixed bindings.
depthFirstSearch(
*this, typeVar,
[&](TypeVariableType *typeVar) {
return typeVars.insert(typeVar).second;
},
[&](Constraint *constraint) {
if (acceptConstraint(constraint))
constraints.push_back(constraint);
// Don't recurse into the constraint's type variables.
return false;
},
visitedConstraints);
return constraints;
}
// Otherwise only search in the type var's equivalence class and immediate
// fixed bindings.
// Local function to add constraints.
auto addTypeVarConstraints = [&](TypeVariableType *adjTypeVar) {
if (!typeVars.insert(adjTypeVar).second)
return;
for (auto constraint : (*this)[adjTypeVar].getConstraints()) {
if (visitedConstraints.insert(constraint).second &&
acceptConstraint(constraint))
constraints.push_back(constraint);
}
};
auto &reprNode = (*this)[CS.getRepresentative(typeVar)];
auto equivClass = reprNode.getEquivalenceClass();
for (auto typeVar : equivClass) {
if (!typeVars.insert(typeVar).second)
continue;
auto &node = (*this)[typeVar];
for (auto constraint : node.getConstraints()) {
if (visitedConstraints.insert(constraint).second &&
acceptConstraint(constraint))
constraints.push_back(constraint);
}
for (auto adjTypeVar : node.getReferencedBy()) {
addTypeVarConstraints(adjTypeVar);
}
for (auto adjTypeVar : node.getReferencedVars()) {
addTypeVarConstraints(adjTypeVar);
}
}
return constraints;
}
namespace {
/// A union-find connected components algorithm used to find the connected
/// components within a constraint graph.
class ConnectedComponents {
ConstraintGraph &cg;
ArrayRef<TypeVariableType *> typeVars;
/// A mapping from each type variable to its representative in a union-find
/// data structure, excluding entries where the type variable is its own
/// representative.
mutable llvm::SmallDenseMap<TypeVariableType *, TypeVariableType *>
representatives;
// Figure out which components have unbound type variables and/or
// constraints. These are the only components we want to report.
llvm::SmallDenseSet<TypeVariableType *> validComponents;
/// The complete set of constraints that were visited while computing
/// connected components.
llvm::SmallPtrSet<Constraint *, 8> visitedConstraints;
/// Describes the one-way incoming and outcoming adjacencies of
/// a component within the directed graph of one-way constraints.
struct OneWayComponent {
/// The (uniqued) set of type variable representatives to which this
/// component has an outgoing edge.
TinyPtrVector<TypeVariableType *> outAdjacencies;
/// The (uniqued) set of type variable representatives from which this
/// component has an incoming edge.
TinyPtrVector<TypeVariableType *> inAdjacencies;
};
// Adjacency list representation of the directed graph of edges for
// one-way constraints, using type variable representatives as the
// nodes.
llvm::SmallDenseMap<TypeVariableType *, OneWayComponent> oneWayDigraph;
public:
using Component = ConstraintGraph::Component;
/// Compute connected components for the given set of type variables
/// in the constraint graph.
ConnectedComponents(ConstraintGraph &cg,
ArrayRef<TypeVariableType *> typeVars)
: cg(cg), typeVars(typeVars)
{
auto oneWayConstraints = connectedComponents();
// If there were no one-way constraints, we're done.
if (oneWayConstraints.empty())
return;
// Build the directed one-way constraint graph.
buildOneWayConstraintGraph(oneWayConstraints);
}
/// Retrieve the set of components.
SmallVector<Component, 1> getComponents() const {
// The final return value.
SmallVector<Component, 1> flatComponents;
// We don't actually need to partition the graph into components if
// there are fewer than 2.
if (validComponents.size() < 2 && cg.getOrphanedConstraints().empty())
return flatComponents;
// Mapping from representatives to components.
llvm::SmallDenseMap<TypeVariableType *, Component> components;
SmallVector<TypeVariableType *, 4> representativeTypeVars;
// Capture the type variables of each component.
for (auto typeVar : typeVars) {
// Find the representative. If we aren't creating a type variable
// for this component, skip it.
auto rep = findRepresentative(typeVar);
if (validComponents.count(rep) == 0)
continue;
auto pair = components.insert({rep, Component(components.size())});
if (pair.second)
representativeTypeVars.push_back(rep);
// Record this type variable in the set of type variables for its
// component.
pair.first->second.typeVars.push_back(typeVar);
}
// Retrieve the component for the given representative type variable.
auto getComponent = [&](TypeVariableType *rep) -> Component& {
auto component = components.find(rep);
assert(component != components.end());
return component->second;
};
auto &cs = cg.getConstraintSystem();
// Assign each constraint to its appropriate component.
// Note: we use the inactive constraints so that we maintain the
// order of constraints when we re-introduce them.
for (auto &constraint : cs.getConstraints()) {
auto constraintTypeVars = constraint.getTypeVariables();
if (constraintTypeVars.empty())
continue;
TypeVariableType *typeVar;
if (constraint.isOneWayConstraint()) {
// For one-way constraints, associate the constraint with the
// left-hand type variable.
typeVar = constraint.getFirstType()->castTo<TypeVariableType>();
} else {
typeVar = constraintTypeVars.front();
}
auto rep = findRepresentative(typeVar);
getComponent(rep).addConstraint(&constraint);
}
// If we have any one-way constraint information, compute the ordering
// of representative type variables needed to respect one-way
// constraints while solving.
if (!oneWayDigraph.empty()) {
// Sort the representative type variables based on the disjunction
// count, so
std::sort(representativeTypeVars.begin(), representativeTypeVars.end(),
[&](TypeVariableType *lhs, TypeVariableType *rhs) {
return getComponent(lhs).getNumDisjunctions() >
getComponent(rhs).getNumDisjunctions();
});
representativeTypeVars =
computeOneWayComponentOrdering(representativeTypeVars);
// Fill in one-way dependency information for all of the components.
for (auto typeVar : representativeTypeVars) {
auto knownOneWayComponent = oneWayDigraph.find(typeVar);
if (knownOneWayComponent == oneWayDigraph.end())
continue;
auto &oneWayComponent = knownOneWayComponent->second;
auto &component = getComponent(typeVar);
for (auto inAdj : oneWayComponent.inAdjacencies) {
if (validComponents.count(inAdj) == 0)
continue;
component.recordDependency(getComponent(inAdj));
}
}
}
// Flatten the set of components.
flatComponents.reserve(
representativeTypeVars.size() + cg.getOrphanedConstraints().size());
for (auto rep: representativeTypeVars) {
assert(components.count(rep) == 1);
flatComponents.push_back(std::move(getComponent(rep)));
}
// Gather orphaned constraints; each gets its own component.
for (auto orphaned : cg.getOrphanedConstraints()) {
flatComponents.push_back(Component(flatComponents.size()));
flatComponents.back().addConstraint(orphaned);
}
// Create component ordering based on the information associated
// with constraints in each step - e.g. number of disjunctions,
// since components are going to be executed in LIFO order, we'd
// want to have smaller/faster components at the back of the list.
// When there are one-way constraints, we can't reorder them, so only
// sort the orphaned constraints at the back. In the absence of
// one-way constraints, sort everything.
if (components.size() > 1) {
auto sortStart = oneWayDigraph.empty()
? flatComponents.begin()
: flatComponents.end() - cg.getOrphanedConstraints().size();
std::sort(sortStart, flatComponents.end(),
[&](const Component &lhs, const Component &rhs) {
return lhs.getNumDisjunctions() > rhs.getNumDisjunctions();
});
}
return flatComponents;
}
/// Find the representative for the given type variable within the set
/// of representatives in a union-find data structure.
TypeVariableType *findRepresentative(TypeVariableType *typeVar) const {
// If we don't have a record of this type variable, it is it's own
// representative.
auto known = representatives.find(typeVar);
if (known == representatives.end() || known->second == typeVar)
return typeVar;
// Find the representative of the parent.
auto parent = known->second;
auto rep = findRepresentative(parent);
representatives[typeVar] = rep;
return rep;
}
private:
/// Perform the union of two type variables in a union-find data structure
/// used for connected components.
///
/// \returns true if the two components were separate and have now been
/// joined, \c false if they were already in the same set.
bool unionSets(TypeVariableType *typeVar1, TypeVariableType *typeVar2) {
auto rep1 = findRepresentative(typeVar1);
auto rep2 = findRepresentative(typeVar2);
if (rep1 == rep2)
return false;
// Reparent the type variable with the higher ID. The actual choice doesn't
// matter, but this makes debugging easier.
if (rep1->getID() < rep2->getID()) {
validComponents.erase(rep2);
representatives[rep2] = rep1;
} else {
validComponents.erase(rep1);
representatives[rep1] = rep2;
}
return true;
}
/// Perform the connected components algorithm, skipping one-way
/// constraints.
///
/// \returns the set of one-way constraints that were skipped.
TinyPtrVector<Constraint *> connectedComponents() {
TinyPtrVector<Constraint *> oneWayConstraints;
auto &cs = cg.getConstraintSystem();
// Perform a depth-first search from each type variable to identify
// what component it is in.
for (auto typeVar : typeVars) {
// If we've already assigned a representative to this type variable,
// we're done.
if (representatives.count(typeVar) > 0)
continue;
// Perform a depth-first search to mark those type variables that are
// in the same component as this type variable.
depthFirstSearch(
cg, typeVar,
[&](TypeVariableType *found) {
// If we have already seen this node, we're done.
auto inserted = representatives.insert({found, typeVar});
assert((inserted.second || inserted.first->second == typeVar) &&
"Wrong component?");
if (inserted.second)
if (!cs.getFixedType(found))
validComponents.insert(typeVar);
return inserted.second;
},
[&](Constraint *constraint) {
// Record and skip one-way constraints.
if (constraint->isOneWayConstraint()) {
oneWayConstraints.push_back(constraint);
return false;
}
return true;
},
visitedConstraints);
}
for (auto &constraint : cs.getConstraints()) {
if (constraint.getKind() == ConstraintKind::Disjunction ||
constraint.getKind() == ConstraintKind::Conjunction) {
for (auto typeVar : constraint.getTypeVariables()) {
auto rep = findRepresentative(typeVar);
if (validComponents.insert(rep).second)
ASSERT(cs.getFixedType(typeVar));