Sema: Tighten invariant in ConstraintSystem::addConversionRestriction()

Author: slavapestov

lib/Sema/ConstraintSystem.cpp

@@ -276,10 +276,11 @@ void ConstraintSystem::addConversionRestriction(
     Type srcType, Type dstType,
     ConversionRestrictionKind restriction) {
   auto key = std::make_pair(srcType.getPointer(), dstType.getPointer());
-  bool inserted = ConstraintRestrictions.insert(
-      std::make_pair(key, restriction)).second;
-  if (!inserted)
+  auto pair = ConstraintRestrictions.insert({key, restriction});
+  if (!pair.second) {
+    ASSERT(pair.first->second == restriction);
     return;
+  }
 
   if (solverState) {
     recordChange(SolverTrail::Change::AddedConversionRestriction(