[CS] Remove ReturnAllDiscoveredSolutions flag

This is now no longer used.

Author: hamishknight

lib/Sema/CSRanking.cpp

@@ -94,9 +94,6 @@ bool ConstraintSystem::worseThanBestSolution() const {
   if (getASTContext().TypeCheckerOpts.DisableConstraintSolverPerformanceHacks)
     return false;
 
-  if (retainAllSolutions())
-    return false;
-
   if (!solverState || !solverState->BestScore ||
       CurrentScore <= *solverState->BestScore)
     return false;

lib/Sema/CSSolver.cpp

@@ -70,13 +70,11 @@ Solution ConstraintSystem::finalize() {
 
   // Update the best score we've seen so far.
   auto &ctx = getASTContext();
-  if (!retainAllSolutions()) {
-    assert(ctx.TypeCheckerOpts.DisableConstraintSolverPerformanceHacks ||
-           !solverState->BestScore || CurrentScore <= *solverState->BestScore);
+  assert(ctx.TypeCheckerOpts.DisableConstraintSolverPerformanceHacks ||
+         !solverState->BestScore || CurrentScore <= *solverState->BestScore);
 
-    if (!solverState->BestScore || CurrentScore <= *solverState->BestScore) {
-      solverState->BestScore = CurrentScore;
-    }
+  if (!solverState->BestScore || CurrentScore <= *solverState->BestScore) {
+    solverState->BestScore = CurrentScore;
   }
 
   for (auto tv : getTypeVariables()) {
@@ -1311,8 +1309,7 @@ bool ConstraintSystem::solve(SmallVectorImpl<Solution> &solutions,
   // Filter deduced solutions, try to figure out if there is
   // a single best solution to use, if not explicitly disabled
   // by constraint system options.
-  if (!retainAllSolutions())
-    filterSolutions(solutions);
+  filterSolutions(solutions);
 
   // We fail if there is no solution or the expression was too complex.
   return solutions.empty() || getExpressionTooComplex(solutions);

lib/Sema/CSStep.h

@@ -228,8 +228,7 @@ class SolverStep {
   Optional<Score> getBestScore() const { return CS.solverState->BestScore; }
 
   void filterSolutions(SmallVectorImpl<Solution> &solutions, bool minimize) {
-    if (!CS.retainAllSolutions())
-      CS.filterSolutions(solutions, minimize);
+    CS.filterSolutions(solutions, minimize);
   }
 
   /// Check whether constraint solver is running in "debug" mode,

lib/Sema/ConstraintSystem.h

@@ -1004,24 +1004,20 @@ using ConstraintList = llvm::ilist<Constraint>;
 enum class ConstraintSystemFlags {
   /// Whether we allow the solver to attempt fixes to the system.
   AllowFixes = 0x01,
-  
-  /// If set, this is going to prevent constraint system from erasing all
-  /// discovered solutions except the best one.
-  ReturnAllDiscoveredSolutions = 0x04,
 
   /// Set if the client wants diagnostics suppressed.
-  SuppressDiagnostics = 0x08,
+  SuppressDiagnostics = 0x02,
 
   /// If set, the client wants a best-effort solution to the constraint system,
   /// but can tolerate a solution where all of the constraints are solved, but
   /// not all type variables have been determined.  In this case, the constraint
   /// system is not applied to the expression AST, but the ConstraintSystem is
   /// left in-tact.
-  AllowUnresolvedTypeVariables = 0x10,
+  AllowUnresolvedTypeVariables = 0x04,
 
   /// If set, constraint system always reuses type of pre-typechecked
   /// expression, and doesn't dig into its subexpressions.
-  ReusePrecheckedType = 0x20,
+  ReusePrecheckedType = 0x08,
 };
 
 /// Options that affect the constraint system as a whole.
@@ -2168,13 +2164,6 @@ class ConstraintSystem {
   bool hasFreeTypeVariables();
 
 private:
-  /// Indicates if the constraint system should retain all of the
-  /// solutions it has deduced regardless of their score.
-  bool retainAllSolutions() const {
-    return Options.contains(
-        ConstraintSystemFlags::ReturnAllDiscoveredSolutions);
-  }
-
   /// Finalize this constraint system; we're done attempting to solve
   /// it.
   ///