Use a SmallSetVector to eliminate duplicates

Author: DougGregor

include/swift/Sema/ConstraintSystem.h

@@ -2364,7 +2364,7 @@ class ConstraintSystem {
       caseLabelItems;
 
   /// The set of parameters that have been inferred to be 'isolated'.
-  llvm::SmallVector<ParamDecl *, 2> isolatedParams;
+  llvm::SmallSetVector<ParamDecl *, 2> isolatedParams;
 
   /// Maps closure parameters to type variables.
   llvm::DenseMap<const ParamDecl *, TypeVariableType *>

lib/Sema/CSSimplify.cpp

@@ -8999,7 +8999,7 @@ bool ConstraintSystem::resolveClosure(TypeVariableType *typeVar,
 
         // Note when a parameter is inferred to be isolated.
         if (contextualParam->isIsolated() && !flags.isIsolated() && paramDecl)
-          isolatedParams.push_back(paramDecl);
+          isolatedParams.insert(paramDecl);
 
         param =
             param.withFlags(flags.withInOut(contextualParam->isInOut())

lib/Sema/CSSolver.cpp

@@ -186,7 +186,8 @@ Solution ConstraintSystem::finalize() {
 
   solution.solutionApplicationTargets = solutionApplicationTargets;
   solution.caseLabelItems = caseLabelItems;
-  solution.isolatedParams = isolatedParams;
+  solution.isolatedParams.clear();
+  solution.isolatedParams.append(isolatedParams.begin(), isolatedParams.end());
 
   for (const auto &transformed : resultBuilderTransformed) {
     solution.resultBuilderTransformed.insert(transformed);
@@ -294,7 +295,7 @@ void ConstraintSystem::applySolution(const Solution &solution) {
   }
 
   for (auto param : solution.isolatedParams) {
-    isolatedParams.push_back(param);
+    isolatedParams.insert(param);
   }
 
   for (const auto &transformed : solution.resultBuilderTransformed) {