[ConstraintSystem] Don't attempt to rollback state and scope from incorrect state

Author: xedin

Diff for: lib/Sema/CSSolver.cpp

@@ -422,6 +422,11 @@ ConstraintSystem::SolverState::~SolverState() {
          "Expected constraint system to have this solver state!");
   CS.solverState = nullptr;
 
+  // If constraint system ended up being in an invalid state
+  // let's just drop the state without attempting to rollback.
+  if (CS.inInvalidState())
+    return;
+
   // Make sure that all of the retired constraints have been returned
   // to constraint system.
   assert(!hasRetiredConstraints());
@@ -513,6 +518,10 @@ ConstraintSystem::SolverScope::SolverScope(ConstraintSystem &cs)
 }
 
 ConstraintSystem::SolverScope::~SolverScope() {
+  // Don't attempt to rollback from an incorrect state.
+  if (cs.inInvalidState())
+    return;
+
   // Erase the end of various lists.
   while (cs.TypeVariables.size() > numTypeVariables)
     cs.TypeVariables.pop_back();

Diff for: lib/Sema/ConstraintGraph.cpp

@@ -37,7 +37,14 @@ using namespace constraints;
 ConstraintGraph::ConstraintGraph(ConstraintSystem &cs) : CS(cs) { }
 
 ConstraintGraph::~ConstraintGraph() {
-  assert(Changes.empty() && "Scope stack corrupted");
+#ifndef NDEBUG
+  // If constraint system is in an invalid state, it's
+  // possible that constraint graph is corrupted as well
+  // so let's not attempt to check change log.
+  if (!CS.inInvalidState())
+    assert(Changes.empty() && "Scope stack corrupted");
+#endif
+
   for (unsigned i = 0, n = TypeVariables.size(); i != n; ++i) {
     auto &impl = TypeVariables[i]->getImpl();
     delete impl.getGraphNode();
@@ -412,6 +419,11 @@ ConstraintGraphScope::ConstraintGraphScope(ConstraintGraph &CG)
 }
 
 ConstraintGraphScope::~ConstraintGraphScope() {
+  // Don't attempt to rollback if constraint system ended up
+  // in an invalid state.
+  if (CG.CS.inInvalidState())
+    return;
+
   // Pop changes off the stack until we hit the change could we had prior to
   // introducing this scope.
   assert(CG.Changes.size() >= NumChanges && "Scope stack corrupted");