Merge pull request swiftlang#35775 from hborla/solver-active-disjunction-choices

[ConstraintSystem] Tweak disjunction selection (again) to avoid inadvertently increasing the branching factor

Author: hborla

lib/Sema/CSSolver.cpp

@@ -2287,12 +2287,14 @@ Constraint *ConstraintSystem::selectDisjunction() {
   auto cs = this;
   auto minDisjunction = std::min_element(disjunctions.begin(), disjunctions.end(),
       [&](Constraint *first, Constraint *second) -> bool {
+        unsigned firstActive = first->countActiveNestedConstraints();
+        unsigned secondActive = second->countActiveNestedConstraints();
         unsigned firstFavored = first->countFavoredNestedConstraints();
         unsigned secondFavored = second->countFavoredNestedConstraints();
 
         if (!isOperatorBindOverload(first->getNestedConstraints().front()) ||
             !isOperatorBindOverload(second->getNestedConstraints().front()))
-          return first->countActiveNestedConstraints() < second->countActiveNestedConstraints();
+          return firstActive < secondActive;
 
         if (firstFavored == secondFavored) {
           // Look for additional choices that are "favored"
@@ -2305,17 +2307,19 @@ Constraint *ConstraintSystem::selectDisjunction() {
           secondFavored += secondExisting.size();
         }
 
-        firstFavored = firstFavored ? firstFavored : first->countActiveNestedConstraints();
-        secondFavored = secondFavored ? secondFavored : second->countActiveNestedConstraints();
-
         // Everything else equal, choose the disjunction with the greatest
         // number of resoved argument types. The number of resolved argument
         // types is always zero for disjunctions that don't represent applied
         // overloads.
         if (firstFavored == secondFavored) {
-          return first->countResolvedArgumentTypes(*this) > second->countResolvedArgumentTypes(*this);
+          if (firstActive != secondActive)
+            return firstActive < secondActive;
+
+          return (first->countResolvedArgumentTypes(*this) > second->countResolvedArgumentTypes(*this));
         }
 
+        firstFavored = firstFavored ? firstFavored : firstActive;
+        secondFavored = secondFavored ? secondFavored : secondActive;
         return firstFavored < secondFavored;
       });