[ConstraintSystem] Sort the designated types based on actual argument…

… types.

In cases where we have multiple designated types, sort the types that
were designated for this operator based on any information we can
gather about actual argument types at usage sites.

We can consider extending this further in a future commit to ignore
designated types when we have concrete type information that we are
confident of.

lib/Sema/CSSolver.cpp

@@ -1683,14 +1683,91 @@ getOperatorDesignatedNominalTypes(Constraint *bindOverload) {
   return operatorDecl->getDesignatedNominalTypes();
 }
 
+void ConstraintSystem::sortDesignatedTypes(
+    SmallVectorImpl<NominalTypeDecl *> &nominalTypes,
+    Constraint *bindOverload) {
+  auto *tyvar = bindOverload->getFirstType()->castTo<TypeVariableType>();
+  llvm::SetVector<Constraint *> applicableFns;
+  getConstraintGraph().gatherConstraints(
+      tyvar, applicableFns, ConstraintGraph::GatheringKind::EquivalenceClass,
+      [](Constraint *match) {
+        return match->getKind() == ConstraintKind::ApplicableFunction;
+      });
+
+  // FIXME: This is not true when we run the constraint optimizer.
+  // assert(applicableFns.size() <= 1);
+
+  // We have a disjunction for an operator but no application of it,
+  // so it's being passed as an argument.
+  if (applicableFns.size() == 0)
+    return;
+
+  // FIXME: We have more than one applicable per disjunction as a
+  //        result of merging disjunction type variables. We may want
+  //        to rip that out at some point.
+  Constraint *foundApplicable = nullptr;
+  SmallVector<Optional<Type>, 2> argumentTypes;
+  for (auto *applicableFn : applicableFns) {
+    argumentTypes.clear();
+    auto *fnTy = applicableFn->getFirstType()->castTo<FunctionType>();
+    ArgumentInfoCollector argInfo(*this, fnTy);
+    // Stop if we hit anything with concrete types or conformances to
+    // literals.
+    if (!argInfo.getTypes().empty() || !argInfo.getLiteralProtocols().empty()) {
+      foundApplicable = applicableFn;
+      break;
+    }
+  }
+
+  if (!foundApplicable)
+    return;
+
+  // FIXME: It would be good to avoid this redundancy.
+  auto *fnTy = foundApplicable->getFirstType()->castTo<FunctionType>();
+  ArgumentInfoCollector argInfo(*this, fnTy);
+
+  size_t nextType = 0;
+  for (auto argType : argInfo.getTypes()) {
+    auto *nominal = argType->getAnyNominal();
+    for (size_t i = nextType + 1; i < nominalTypes.size(); ++i) {
+      if (nominal == nominalTypes[i]) {
+        std::swap(nominalTypes[nextType], nominalTypes[i]);
+        ++nextType;
+        break;
+      }
+    }
+  }
+
+  if (nextType + 1 >= nominalTypes.size())
+    return;
+
+  for (auto *protocol : argInfo.getLiteralProtocols()) {
+    auto defaultType = TC.getDefaultType(protocol, DC);
+    auto *nominal = defaultType->getAnyNominal();
+    for (size_t i = nextType + 1; i < nominalTypes.size(); ++i) {
+      if (nominal == nominalTypes[i]) {
+        std::swap(nominalTypes[nextType], nominalTypes[i]);
+        ++nextType;
+        break;
+      }
+    }
+  }
+}
+
 void ConstraintSystem::partitionForDesignatedTypes(
     ArrayRef<Constraint *> Choices, ConstraintMatchLoop forEachChoice,
     PartitionAppendCallback appendPartition) {
 
-  auto designatedNominalTypes = getOperatorDesignatedNominalTypes(Choices[0]);
-  if (designatedNominalTypes.empty())
+  auto types = getOperatorDesignatedNominalTypes(Choices[0]);
+  if (types.empty())
     return;
 
+  SmallVector<NominalTypeDecl *, 4> designatedNominalTypes(types.begin(),
+                                                           types.end());
+
+  if (designatedNominalTypes.size() > 1)
+    sortDesignatedTypes(designatedNominalTypes, Choices[0]);
+
   SmallVector<SmallVector<unsigned, 4>, 4> definedInDesignatedType;
   SmallVector<SmallVector<unsigned, 4>, 4> definedInExtensionOfDesignatedType;
 

lib/Sema/ConstraintSystem.h

@@ -3227,6 +3227,12 @@ class ConstraintSystem {
   typedef std::function<void(SmallVectorImpl<unsigned> &options)>
       PartitionAppendCallback;
 
+  // Attempt to sort nominalTypes based on what we can discover about
+  // calls into the overloads in the disjunction that bindOverload is
+  // a part of.
+  void sortDesignatedTypes(SmallVectorImpl<NominalTypeDecl *> &nominalTypes,
+                           Constraint *bindOverload);
+
   // Partition the choices in a disjunction based on those that match
   // the designated types for the operator that the disjunction was
   // formed for.

validation-test/Sema/type_checker_perf/fast/rdar17024694.swift

@@ -1,4 +1,4 @@
-// RUN: %target-typecheck-verify-swift -solver-expression-time-threshold=1
+// RUN: %target-typecheck-verify-swift -solver-expression-time-threshold=1 -swift-version 5 -solver-disable-shrink -disable-constraint-solver-performance-hacks -solver-enable-operator-designated-types
 // REQUIRES: tools-release,no_asserts
 
 _ = (2...100).reversed().filter({ $0 % 11 == 0 }).map {