Sema: Fold ConstraintGraph::lookupNode() into ::operator[]

lookupNode() returned a pair but both callers only looked at the
first element of the pair.

Author: slavapestov

include/swift/Sema/ConstraintGraph.h

@@ -245,13 +245,7 @@ class ConstraintGraph {
   ConstraintSystem &getConstraintSystem() const { return CS; }
 
   /// Access the node corresponding to the given type variable.
-  ConstraintGraphNode &operator[](TypeVariableType *typeVar) {
-    return lookupNode(typeVar).first;
-  }
-
-  /// Retrieve the node and index corresponding to the given type variable.
-  std::pair<ConstraintGraphNode &, unsigned> 
-  lookupNode(TypeVariableType *typeVar);
+  ConstraintGraphNode &operator[](TypeVariableType *typeVar);
 
   /// Add a new constraint to the graph.
   void addConstraint(Constraint *constraint);

lib/Sema/ConstraintGraph.cpp

@@ -50,8 +50,8 @@ ConstraintGraph::~ConstraintGraph() {
 
 #pragma mark Graph accessors
 
-std::pair<ConstraintGraphNode &, unsigned>
-ConstraintGraph::lookupNode(TypeVariableType *typeVar) {
+ConstraintGraphNode &
+ConstraintGraph::operator[](TypeVariableType *typeVar) {
   // Check whether we've already created a node for this type variable.
   auto &impl = typeVar->getImpl();
   if (auto nodePtr = impl.getGraphNode()) {
@@ -60,7 +60,7 @@ ConstraintGraph::lookupNode(TypeVariableType *typeVar) {
            "Type variable mismatch");
     ASSERT(nodePtr->TypeVar == typeVar &&
            "Use-after-free");
-    return { *nodePtr, impl.getGraphIndex() };
+    return *nodePtr;
   }
 
   // Allocate the new node.
@@ -98,7 +98,7 @@ ConstraintGraph::lookupNode(TypeVariableType *typeVar) {
     bindTypeVariable(typeVar, fixed);
   }
 
-  return { *nodePtr, index };
+  return *nodePtr;
 }
 
 void ConstraintGraphNode::reset() {

lib/Sema/ConstraintSystem.cpp

@@ -1103,8 +1103,8 @@ TypeVariableType *ConstraintSystem::isRepresentativeFor(
     return nullptr;
 
   auto &CG = getConstraintGraph();
-  auto result = CG.lookupNode(typeVar);
-  auto equivalence = result.first.getEquivalenceClass();
+  auto &result = CG[typeVar];
+  auto equivalence = result.getEquivalenceClass();
   auto member = llvm::find_if(equivalence, [=](TypeVariableType *eq) {
     auto *loc = eq->getImpl().getLocator();
     if (!loc)