diff --git a/lib/Sema/CSBindings.cpp b/lib/Sema/CSBindings.cpp
index 7ac46bae1de65..77ae9f31ea653 100644
--- a/lib/Sema/CSBindings.cpp
+++ b/lib/Sema/CSBindings.cpp
@@ -25,22 +25,26 @@ Optional<ConstraintSystem::PotentialBindings>
 ConstraintSystem::determineBestBindings() {
   // Look for potential type variable bindings.
   Optional<PotentialBindings> bestBindings;
-  llvm::SmallDenseMap<TypeVariableType *, PotentialBindings> cache;
-
   // First, let's collect all of the possible bindings.
   for (auto *typeVar : getTypeVariables()) {
     if (typeVar->getImpl().hasRepresentativeOrFixed())
       continue;
 
+    if (Bindings.count(typeVar) > 0)
+      continue;
+
     if (auto bindings = getPotentialBindings(typeVar))
-      cache.insert({typeVar, std::move(bindings)});
+      Bindings.insert({typeVar, std::move(bindings)});
   }
 
   // Now let's see if we could infer something for related type
   // variables based on other bindings.
   for (auto *typeVar : getTypeVariables()) {
-    auto cachedBindings = cache.find(typeVar);
-    if (cachedBindings == cache.end())
+    if (typeVar->getImpl().hasRepresentativeOrFixed())
+      continue;
+
+    auto cachedBindings = Bindings.find(typeVar);
+    if (cachedBindings == Bindings.end())
       continue;
 
     auto &bindings = cachedBindings->getSecond();
@@ -62,8 +66,8 @@ ConstraintSystem::determineBestBindings() {
       if (!tv)
         continue;
 
-      auto relatedBindings = cache.find(tv);
-      if (relatedBindings == cache.end())
+      auto relatedBindings = Bindings.find(tv);
+      if (relatedBindings == Bindings.end())
         continue;
 
       for (auto &binding : relatedBindings->getSecond().Bindings) {
diff --git a/lib/Sema/CSSimplify.cpp b/lib/Sema/CSSimplify.cpp
index 638f8a6e8ed9c..8eab47b0cf280 100644
--- a/lib/Sema/CSSimplify.cpp
+++ b/lib/Sema/CSSimplify.cpp
@@ -1561,7 +1561,6 @@ ConstraintSystem::matchTypesBindTypeVar(
   }
 
   assignFixedType(typeVar, type);
-
   return getTypeMatchSuccess();
 }
 
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 73d3f1bed204c..5f609854da603 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -232,6 +232,10 @@ void ConstraintSystem::addTypeVariableConstraintsToWorkList(
                              constraint);
     constraint->setActive(true);
   }
+
+  // Invalidate pre-computed bindings associated
+  // with this type variable (if any).
+  invalidateBindings(typeVar);
 }
 
 /// Retrieve a dynamic result signature for the given declaration.
diff --git a/lib/Sema/ConstraintSystem.h b/lib/Sema/ConstraintSystem.h
index dd72e8708a4f5..cf8f11ab84afc 100644
--- a/lib/Sema/ConstraintSystem.h
+++ b/lib/Sema/ConstraintSystem.h
@@ -1213,6 +1213,7 @@ class ConstraintSystem {
     /// \param constraint The newly generated constraint.
     void addGeneratedConstraint(Constraint *constraint) {
       generatedConstraints.push_back(constraint);
+      CS.invalidateBindings(constraint->getTypeVariables());
     }
 
     /// \brief Erase given constraint from the list of generated constraints
@@ -2940,6 +2941,12 @@ class ConstraintSystem {
     }
   };
 
+  /// Maps type variables to their bindings. Bindings are invalidated
+  /// and have to be re-computed if new constraints are introduced or
+  /// in relation to a particular set of type variables or type variables
+  /// are assigned fixed types or merged together.
+  llvm::DenseMap<TypeVariableType *, PotentialBindings> Bindings;
+
   Optional<Type> checkTypeOfBinding(TypeVariableType *typeVar, Type type,
                                     bool *isNilLiteral = nullptr);
   Optional<PotentialBindings> determineBestBindings();
@@ -3228,6 +3235,28 @@ class ConstraintSystem {
                             SmallVectorImpl<unsigned> &Ordering,
                             SmallVectorImpl<unsigned> &PartitionBeginning);
 
+  void invalidateBindings(ArrayRef<TypeVariableType *> typeVars) {
+    llvm::SmallPtrSet<TypeVariableType *, 8> visitedVars;
+    for (auto *typeVar : typeVars) {
+      if (typeVar != typeVar->getImpl().getRepresentative(nullptr) ||
+          visitedVars.count(typeVar) > 0)
+        continue;
+
+      // If there was no binding, there is no need to disturb
+      // other type variables.
+      Bindings.erase(typeVar);
+      visitedVars.insert(typeVar);
+
+      for (auto *eqClassVar : CG[typeVar].getEquivalenceClass()) {
+        for (auto *adjacentVar : CG[eqClassVar].getAdjacencies()) {
+          auto *var = getRepresentative(adjacentVar);
+          if (visitedVars.insert(var).second)
+            Bindings.erase(var);
+        }
+      }
+    }
+  }
+
   LLVM_ATTRIBUTE_DEPRECATED(
       void dump() LLVM_ATTRIBUTE_USED,
       "only for use within the debugger");
diff --git a/validation-test/Sema/type_checker_perf/fast/rdar30596744_3.swift.gyb b/validation-test/Sema/type_checker_perf/fast/rdar30596744_3.swift.gyb
new file mode 100644
index 0000000000000..0deb3d139b296
--- /dev/null
+++ b/validation-test/Sema/type_checker_perf/fast/rdar30596744_3.swift.gyb
@@ -0,0 +1,15 @@
+// RUN: %scale-test --begin 1 --end 20 --step 1 --select NumLeafScopes %s
+// REQUIRES: OS=macosx
+// REQUIRES: asserts
+
+% array_elements = 20
+
+let _ = [
+%for i in range(0, N):
+  ${i} : [
+    %for j in range(array_elements):
+      "e${j}",
+    %end
+  ],
+%end
+]
diff --git a/validation-test/Sema/type_checker_perf/slow/rdar30596744_2.swift.gyb b/validation-test/Sema/type_checker_perf/slow/rdar30596744_2.swift.gyb
index f706934b1ef8d..9580d897a00f4 100644
--- a/validation-test/Sema/type_checker_perf/slow/rdar30596744_2.swift.gyb
+++ b/validation-test/Sema/type_checker_perf/slow/rdar30596744_2.swift.gyb
@@ -1,4 +1,4 @@
-// RUN: %scale-test --invert-result --begin 1 --end 5 --step 1 --select NumLeafScopes %s --expected-exit-code 1
+// RUN: %scale-test --invert-result --begin 1 --end 4 --step 1 --select NumLeafScopes %s --expected-exit-code 1
 // REQUIRES: OS=macosx
 // REQUIRES: asserts