[ConstraintSystem] Convert DisjunctionChoices to a map vector & assert on duplicates

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -2384,8 +2384,7 @@ class ConstraintSystem {
 
   /// The set of remembered disjunction choices used to reach
   /// the current constraint system.
-  std::vector<std::pair<ConstraintLocator*, unsigned>>
-      DisjunctionChoices;
+  llvm::MapVector<ConstraintLocator *, unsigned> DisjunctionChoices;
 
   /// A map from applied disjunction constraints to the corresponding
   /// argument function type.
@@ -4903,7 +4902,10 @@ class ConstraintSystem {
   /// Record a particular disjunction choice of
   void recordDisjunctionChoice(ConstraintLocator *disjunctionLocator,
                                unsigned index) {
-    DisjunctionChoices.push_back({disjunctionLocator, index});
+    // We shouldn't ever register disjunction choices multiple times.
+    assert(!DisjunctionChoices.count(disjunctionLocator) ||
+           DisjunctionChoices[disjunctionLocator] == index);
+    DisjunctionChoices.insert({disjunctionLocator, index});
   }
 
   /// Filter the set of disjunction terms, keeping only those where the

lib/Sema/CSSolver.cpp

@@ -127,13 +127,6 @@ Solution ConstraintSystem::finalize() {
 
   // Remember all the disjunction choices we made.
   for (auto &choice : DisjunctionChoices) {
-    // We shouldn't ever register disjunction choices multiple times,
-    // but saving and re-applying solutions can cause us to get
-    // multiple entries.  We should use an optimized PartialSolution
-    // structure for that use case, which would optimize a lot of
-    // stuff here.
-    assert(!solution.DisjunctionChoices.count(choice.first) ||
-           solution.DisjunctionChoices[choice.first] == choice.second);
     solution.DisjunctionChoices.insert(choice);
   }
 
@@ -240,7 +233,7 @@ void ConstraintSystem::applySolution(const Solution &solution) {
 
   // Register the solution's disjunction choices.
   for (auto &choice : solution.DisjunctionChoices) {
-    DisjunctionChoices.push_back(choice);
+    DisjunctionChoices.insert(choice);
   }
 
   // Remember all of the argument/parameter matching choices we made.