[CSStep] Don't retain multiple copies of the same bindings just for printing

Author: xedin

include/swift/Sema/ConstraintSystem.h

@@ -5826,6 +5826,9 @@ class TypeVarBindingProducer : public BindingProducer<TypeVariableBinding> {
         TypeVar(bindings.TypeVar),
         Bindings(bindings.Bindings.begin(), bindings.Bindings.end()) {}
 
+  /// Retrieve a set of bindings available in the current state.
+  ArrayRef<Binding> getCurrentBindings() const { return Bindings; }
+
   Optional<Element> operator()() override {
     // Once we reach the end of the current bindings
     // let's try to compute new ones, e.g. supertypes,

lib/Sema/CSStep.cpp

@@ -446,13 +446,15 @@ void TypeVariableStep::setup() {
     PO.PrintTypesForDebugging = true;
     auto &log = getDebugLogger();
 
+    auto initialBindings = Producer.getCurrentBindings();
     log << "Initial bindings: ";
-    interleave(InitialBindings.begin(), InitialBindings.end(),
-               [&](const Binding &binding) {
-                 log << TypeVar->getString(PO)
-                     << " := " << binding.BindingType->getString(PO);
-               },
-               [&log] { log << ", "; });
+    interleave(
+        initialBindings.begin(), initialBindings.end(),
+        [&](const Binding &binding) {
+          log << TypeVar->getString(PO)
+              << " := " << binding.BindingType->getString(PO);
+        },
+        [&log] { log << ", "; });
 
     log << '\n';
   }

lib/Sema/CSStep.h

@@ -479,9 +479,9 @@ class ComponentStep final : public SolverStep {
 template <typename P> class BindingStep : public SolverStep {
   using Scope = ConstraintSystem::SolverScope;
 
+protected:
   P Producer;
 
-protected:
   /// Indicates whether any of the attempted bindings
   /// produced a solution.
   bool AnySolved = false;
@@ -569,10 +569,6 @@ class TypeVariableStep final : public BindingStep<TypeVarBindingProducer> {
   using Binding = ConstraintSystem::PotentialBinding;
 
   TypeVariableType *TypeVar;
-  // A set of the initial bindings to consider, which is
-  // also a source of follow-up "computed" bindings such
-  // as supertypes, defaults etc.
-  SmallVector<Binding, 4> InitialBindings;
 
   /// Indicates whether source of one of the previously
   /// attempted bindings was a literal constraint. This
@@ -583,8 +579,7 @@ class TypeVariableStep final : public BindingStep<TypeVarBindingProducer> {
 public:
   TypeVariableStep(ConstraintSystem &cs, BindingContainer &bindings,
                    SmallVectorImpl<Solution> &solutions)
-      : BindingStep(cs, {cs, bindings}, solutions), TypeVar(bindings.TypeVar),
-        InitialBindings(bindings.Bindings.begin(), bindings.Bindings.end()) {}
+      : BindingStep(cs, {cs, bindings}, solutions), TypeVar(bindings.TypeVar) {}
 
   void setup() override;
 
@@ -593,8 +588,7 @@ class TypeVariableStep final : public BindingStep<TypeVarBindingProducer> {
   void print(llvm::raw_ostream &Out) override {
     PrintOptions PO;
     PO.PrintTypesForDebugging = true;
-    Out << "TypeVariableStep for " << TypeVar->getString(PO) << " with #"
-        << InitialBindings.size() << " initial bindings\n";
+    Out << "TypeVariableStep for " << TypeVar->getString(PO) << '\n';
   }
 
 protected: