diff --git a/include/swift/Frontend/Frontend.h b/include/swift/Frontend/Frontend.h
index a1e15c82654..395de845f6e 100644
--- a/include/swift/Frontend/Frontend.h
+++ b/include/swift/Frontend/Frontend.h
@@ -55,6 +55,10 @@ class SerializedModuleLoader;
 class MemoryBufferSerializedModuleLoader;
 class SILModule;
 
+namespace Lowering {
+class TypeConverter;
+}
+
 /// The abstract configuration of the compiler, including:
 ///   - options for all stages of translation,
 ///   - information about the build environment,
@@ -372,6 +376,7 @@ class CompilerInstance {
   SourceManager SourceMgr;
   DiagnosticEngine Diagnostics{SourceMgr};
   std::unique_ptr<ASTContext> Context;
+  std::unique_ptr<Lowering::TypeConverter> TheSILTypes;
   std::unique_ptr<SILModule> TheSILModule;
 
   std::unique_ptr<PersistentParserState> PersistentState;
@@ -422,8 +427,6 @@ class CompilerInstance {
 
   bool isWholeModuleCompilation() { return PrimaryBufferIDs.empty(); }
 
-  void createSILModule();
-
 public:
   // Out of line to avoid having to import SILModule.h.
   CompilerInstance();
@@ -448,6 +451,10 @@ public:
   SILOptions &getSILOptions() { return Invocation.getSILOptions(); }
   const SILOptions &getSILOptions() const { return Invocation.getSILOptions(); }
 
+  Lowering::TypeConverter &getSILTypes();
+
+  void createSILModule();
+
   void addDiagnosticConsumer(DiagnosticConsumer *DC) {
     Diagnostics.addConsumer(*DC);
   }
diff --git a/include/swift/SIL/SILModule.h b/include/swift/SIL/SILModule.h
index 089e3d07596..802bb85041b 100644
--- a/include/swift/SIL/SILModule.h
+++ b/include/swift/SIL/SILModule.h
@@ -260,7 +260,8 @@ private:
 
   // Intentionally marked private so that we need to use 'constructSIL()'
   // to construct a SILModule.
-  SILModule(ModuleDecl *M, SILOptions &Options, const DeclContext *associatedDC,
+  SILModule(ModuleDecl *M, Lowering::TypeConverter &TC,
+            SILOptions &Options, const DeclContext *associatedDC,
             bool wholeModule);
 
   SILModule(const SILModule&) = delete;
@@ -313,7 +314,7 @@ public:
   void serialize();
 
   /// This converts Swift types to SILTypes.
-  mutable Lowering::TypeConverter Types;
+  Lowering::TypeConverter &Types;
 
   /// Invalidate cached entries in SIL Loader.
   void invalidateSILLoaderCaches();
@@ -340,12 +341,14 @@ public:
   /// If a source file is provided, SIL will only be emitted for decls in that
   /// source file.
   static std::unique_ptr<SILModule>
-  constructSIL(ModuleDecl *M, SILOptions &Options, FileUnit *sf = nullptr);
+  constructSIL(ModuleDecl *M, Lowering::TypeConverter &TC,
+               SILOptions &Options, FileUnit *sf = nullptr);
 
   /// Create and return an empty SIL module that we can
   /// later parse SIL bodies directly into, without converting from an AST.
   static std::unique_ptr<SILModule>
-  createEmptyModule(ModuleDecl *M, SILOptions &Options,
+  createEmptyModule(ModuleDecl *M, Lowering::TypeConverter &TC,
+                    SILOptions &Options,
                     bool WholeModule = false);
 
   /// Get the Swift module associated with this SIL module.
diff --git a/include/swift/Subsystems.h b/include/swift/Subsystems.h
index d2ce73b6f14..c9784cbf066 100644
--- a/include/swift/Subsystems.h
+++ b/include/swift/Subsystems.h
@@ -69,6 +69,10 @@ namespace swift {
   class UnifiedStatsReporter;
   enum class SourceFileKind;
 
+  namespace Lowering {
+    class TypeConverter;
+  }
+
   /// Used to optionally maintain SIL parsing context for the parser.
   ///
   /// When not parsing SIL, this has no overhead.
@@ -254,11 +258,13 @@ namespace swift {
   /// The module must contain source files. The optimizer will assume that the
   /// SIL of all files in the module is present in the SILModule.
   std::unique_ptr<SILModule>
-  performSILGeneration(ModuleDecl *M, SILOptions &options);
+  performSILGeneration(ModuleDecl *M, Lowering::TypeConverter &TC,
+                       SILOptions &options);
 
   /// Turn a source file into SIL IR.
   std::unique_ptr<SILModule>
-  performSILGeneration(FileUnit &SF, SILOptions &options);
+  performSILGeneration(FileUnit &SF, Lowering::TypeConverter &TC,
+                       SILOptions &options);
 
   using ModuleOrSourceFile = PointerUnion<ModuleDecl *, SourceFile *>;
 
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index fffc5ed5171..0571a76fce4 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -148,11 +148,20 @@ SerializationOptions CompilerInvocation::computeSerializationOptions(
   return serializationOpts;
 }
 
+Lowering::TypeConverter &CompilerInstance::getSILTypes() {
+  if (auto *tc = TheSILTypes.get())
+    return *tc;
+  
+  auto *tc = new Lowering::TypeConverter(*getMainModule());
+  TheSILTypes.reset(tc);
+  return *tc;
+}
+
 void CompilerInstance::createSILModule() {
   assert(MainModule && "main module not created yet");
   // Assume WMO if a -primary-file option was not provided.
   TheSILModule = SILModule::createEmptyModule(
-      getMainModule(), Invocation.getSILOptions(),
+      getMainModule(), getSILTypes(), Invocation.getSILOptions(),
       Invocation.getFrontendOptions().InputsAndOutputs.isWholeModule());
 }
 
@@ -1074,6 +1083,7 @@ void CompilerInstance::performParseOnly(bool EvaluateConditionals,
 
 void CompilerInstance::freeASTContext() {
   PersistentState.reset();
+  TheSILTypes.reset();
   Context.reset();
   MainModule = nullptr;
   SML = nullptr;
diff --git a/lib/Frontend/ParseableInterfaceModuleLoader.cpp b/lib/Frontend/ParseableInterfaceModuleLoader.cpp
index 36e960c077b..be93b99a4cb 100644
--- a/lib/Frontend/ParseableInterfaceModuleLoader.cpp
+++ b/lib/Frontend/ParseableInterfaceModuleLoader.cpp
@@ -592,7 +592,8 @@ public:
 
       SILOptions &SILOpts = subInvocation.getSILOptions();
       auto Mod = SubInstance.getMainModule();
-      auto SILMod = performSILGeneration(Mod, SILOpts);
+      auto &TC = SubInstance.getSILTypes();
+      auto SILMod = performSILGeneration(Mod, TC, SILOpts);
       if (!SILMod) {
         LLVM_DEBUG(llvm::dbgs() << "SILGen did not produce a module\n");
         SubError = true;
diff --git a/lib/FrontendTool/FrontendTool.cpp b/lib/FrontendTool/FrontendTool.cpp
index d60866ee490..8f921df7e83 100644
--- a/lib/FrontendTool/FrontendTool.cpp
+++ b/lib/FrontendTool/FrontendTool.cpp
@@ -917,7 +917,7 @@ generateSILModules(CompilerInvocation &Invocation, CompilerInstance &Instance) {
   if (!opts.InputsAndOutputs.hasPrimaryInputs()) {
     // If there are no primary inputs the compiler is in WMO mode and builds one
     // SILModule for the entire module.
-    auto SM = performSILGeneration(mod, SILOpts);
+    auto SM = performSILGeneration(mod, Instance.getSILTypes(), SILOpts);
     std::deque<PostSILGenInputs> PSGIs;
     const PrimarySpecificPaths PSPs =
         Instance.getPrimarySpecificPathsForWholeModuleOptimizationMode();
@@ -930,7 +930,7 @@ generateSILModules(CompilerInvocation &Invocation, CompilerInstance &Instance) {
   // once for each such input.
   std::deque<PostSILGenInputs> PSGIs;
   for (auto *PrimaryFile : Instance.getPrimarySourceFiles()) {
-    auto SM = performSILGeneration(*PrimaryFile, SILOpts);
+    auto SM = performSILGeneration(*PrimaryFile, Instance.getSILTypes(), SILOpts);
     const PrimarySpecificPaths PSPs =
         Instance.getPrimarySpecificPathsForSourceFile(*PrimaryFile);
     PSGIs.push_back(PostSILGenInputs{std::move(SM), true, PrimaryFile, PSPs});
@@ -944,7 +944,7 @@ generateSILModules(CompilerInvocation &Invocation, CompilerInstance &Instance) {
       if (Invocation.getFrontendOptions().InputsAndOutputs.isInputPrimary(
               SASTF->getFilename())) {
         assert(PSGIs.empty() && "Can only handle one primary AST input");
-        auto SM = performSILGeneration(*SASTF, SILOpts);
+        auto SM = performSILGeneration(*SASTF, Instance.getSILTypes(), SILOpts);
         const PrimarySpecificPaths &PSPs =
             Instance.getPrimarySpecificPathsForPrimary(SASTF->getFilename());
         PSGIs.push_back(
diff --git a/lib/Immediate/REPL.cpp b/lib/Immediate/REPL.cpp
index 0ae6644162d..5d55c9f633c 100644
--- a/lib/Immediate/REPL.cpp
+++ b/lib/Immediate/REPL.cpp
@@ -874,7 +874,8 @@ private:
     if (!CI.getASTContext().hadError()) {
       // We don't want anything to get stripped, so pretend we're doing a
       // non-whole-module generation.
-      sil = performSILGeneration(*M->getFiles().front(), CI.getSILOptions());
+      sil = performSILGeneration(*M->getFiles().front(), CI.getSILTypes(),
+                                 CI.getSILOptions());
       runSILDiagnosticPasses(*sil);
       runSILOwnershipEliminatorPass(*sil);
       runSILLoweringPasses(*sil);
diff --git a/lib/RemoteAST/RemoteAST.cpp b/lib/RemoteAST/RemoteAST.cpp
index 506ec914ca4..ef02e490f8b 100644
--- a/lib/RemoteAST/RemoteAST.cpp
+++ b/lib/RemoteAST/RemoteAST.cpp
@@ -61,6 +61,7 @@ namespace {
 struct IRGenContext {
   IRGenOptions IROpts;
   SILOptions SILOpts;
+  Lowering::TypeConverter TC;
   std::unique_ptr<SILModule> SILMod;
   llvm::LLVMContext LLVMContext;
   irgen::IRGenerator IRGen;
@@ -69,7 +70,8 @@ struct IRGenContext {
 private:
   IRGenContext(ASTContext &ctx, ModuleDecl *module)
     : IROpts(createIRGenOptions()),
-      SILMod(SILModule::createEmptyModule(module, SILOpts)),
+      TC(*module),
+      SILMod(SILModule::createEmptyModule(module, TC, SILOpts)),
       IRGen(IROpts, *SILMod),
       IGM(IRGen, IRGen.createTargetMachine(), LLVMContext) {}
 
diff --git a/lib/SIL/SILModule.cpp b/lib/SIL/SILModule.cpp
index 76d224fc318..c6723e0b206 100644
--- a/lib/SIL/SILModule.cpp
+++ b/lib/SIL/SILModule.cpp
@@ -89,11 +89,13 @@ class SILModule::SerializationCallback final
   }
 };
 
-SILModule::SILModule(ModuleDecl *SwiftModule, SILOptions &Options,
-                     const DeclContext *associatedDC, bool wholeModule)
-    : TheSwiftModule(SwiftModule), AssociatedDeclContext(associatedDC),
+SILModule::SILModule(ModuleDecl *SwiftModule, TypeConverter &TC,
+                     SILOptions &Options, const DeclContext *associatedDC,
+                     bool wholeModule)
+    : TheSwiftModule(SwiftModule),
+      AssociatedDeclContext(associatedDC),
       Stage(SILStage::Raw), wholeModule(wholeModule), Options(Options),
-      serialized(false), SerializeSILAction(), Types(*SwiftModule) {
+      serialized(false), SerializeSILAction(), Types(TC) {
   // We always add the base SILModule serialization callback.
   std::unique_ptr<DeserializationNotificationHandler> callback(
       new SILModule::SerializationCallback());
@@ -118,10 +120,10 @@ SILModule::~SILModule() {
 }
 
 std::unique_ptr<SILModule>
-SILModule::createEmptyModule(ModuleDecl *M, SILOptions &Options,
+SILModule::createEmptyModule(ModuleDecl *M, TypeConverter &TC, SILOptions &Options,
                              bool WholeModule) {
   return std::unique_ptr<SILModule>(
-      new SILModule(M, Options, M, WholeModule));
+      new SILModule(M, TC, Options, M, WholeModule));
 }
 
 ASTContext &SILModule::getASTContext() const {
diff --git a/lib/SILGen/SILGen.cpp b/lib/SILGen/SILGen.cpp
index e3dc128e087..c384666ac90 100644
--- a/lib/SILGen/SILGen.cpp
+++ b/lib/SILGen/SILGen.cpp
@@ -1662,7 +1662,8 @@ void SILGenModule::emitSourceFile(SourceFile *sf) {
 //===----------------------------------------------------------------------===//
 
 std::unique_ptr<SILModule>
-SILModule::constructSIL(ModuleDecl *mod, SILOptions &options, FileUnit *SF) {
+SILModule::constructSIL(ModuleDecl *mod, TypeConverter &tc,
+                        SILOptions &options, FileUnit *SF) {
   SharedTimer timer("SILGen");
   const DeclContext *DC;
   if (SF) {
@@ -1672,7 +1673,7 @@ SILModule::constructSIL(ModuleDecl *mod, SILOptions &options, FileUnit *SF) {
   }
 
   std::unique_ptr<SILModule> M(
-      new SILModule(mod, options, DC, /*wholeModule*/ SF == nullptr));
+      new SILModule(mod, tc, options, DC, /*wholeModule*/ SF == nullptr));
   SILGenModule SGM(*M, mod);
 
   if (SF) {
@@ -1721,11 +1722,13 @@ SILModule::constructSIL(ModuleDecl *mod, SILOptions &options, FileUnit *SF) {
 }
 
 std::unique_ptr<SILModule>
-swift::performSILGeneration(ModuleDecl *mod, SILOptions &options) {
-  return SILModule::constructSIL(mod, options, nullptr);
+swift::performSILGeneration(ModuleDecl *mod, Lowering::TypeConverter &tc,
+                            SILOptions &options) {
+  return SILModule::constructSIL(mod, tc, options, nullptr);
 }
 
 std::unique_ptr<SILModule>
-swift::performSILGeneration(FileUnit &sf, SILOptions &options) {
-  return SILModule::constructSIL(sf.getParentModule(), options, &sf);
+swift::performSILGeneration(FileUnit &sf, Lowering::TypeConverter &tc,
+                            SILOptions &options) {
+  return SILModule::constructSIL(sf.getParentModule(), tc, options, &sf);
 }
diff --git a/tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp b/tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp
index 0ae7f8f68e9..230f055d450 100644
--- a/tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp
+++ b/tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp
@@ -1000,7 +1000,8 @@ ASTUnitRef ASTProducer::createASTUnit(
 
     if (auto SF = CompIns.getPrimarySourceFile()) {
       SILOptions SILOpts = Invocation.getSILOptions();
-      std::unique_ptr<SILModule> SILMod = performSILGeneration(*SF, SILOpts);
+      auto &TC = CompIns.getSILTypes();
+      std::unique_ptr<SILModule> SILMod = performSILGeneration(*SF, TC, SILOpts);
       runSILDiagnosticPasses(*SILMod);
     }
   }
diff --git a/tools/driver/modulewrap_main.cpp b/tools/driver/modulewrap_main.cpp
index bf871732043..886d7a62fba 100644
--- a/tools/driver/modulewrap_main.cpp
+++ b/tools/driver/modulewrap_main.cpp
@@ -24,6 +24,7 @@
 #include "swift/Option/Options.h"
 #include "swift/Serialization/Validation.h"
 #include "swift/SIL/SILModule.h"
+#include "swift/SIL/TypeLowering.h"
 #include "swift/Subsystems.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Bitcode/BitstreamReader.h"
@@ -177,7 +178,8 @@ int modulewrap_main(ArrayRef<const char *> Args, const char *Argv0,
                          true);
   ModuleDecl *M = ModuleDecl::create(ASTCtx.getIdentifier("swiftmodule"), ASTCtx);
   SILOptions SILOpts;
-  std::unique_ptr<SILModule> SM = SILModule::createEmptyModule(M, SILOpts);
+  std::unique_ptr<Lowering::TypeConverter> TC(new Lowering::TypeConverter(*M));
+  std::unique_ptr<SILModule> SM = SILModule::createEmptyModule(M, *TC, SILOpts);
   createSwiftModuleObjectFile(*SM, (*ErrOrBuf)->getBuffer(),
                               Invocation.getOutputFilename());
   return 0;
diff --git a/tools/sil-func-extractor/SILFunctionExtractor.cpp b/tools/sil-func-extractor/SILFunctionExtractor.cpp
index c2d878b1cc6..7c04d529c33 100644
--- a/tools/sil-func-extractor/SILFunctionExtractor.cpp
+++ b/tools/sil-func-extractor/SILFunctionExtractor.cpp
@@ -277,8 +277,7 @@ int main(int argc, char **argv) {
   if (Invocation.hasSerializedAST()) {
     assert(!CI.hasSILModule() &&
            "performSema() should not create a SILModule.");
-    CI.setSILModule(
-        SILModule::createEmptyModule(CI.getMainModule(), CI.getSILOptions()));
+    CI.createSILModule();
     std::unique_ptr<SerializedSILLoader> SL = SerializedSILLoader::create(
         CI.getASTContext(), CI.getSILModule(), nullptr);
 
diff --git a/tools/sil-llvm-gen/SILLLVMGen.cpp b/tools/sil-llvm-gen/SILLLVMGen.cpp
index e3fd63c679f..a8df48d756e 100644
--- a/tools/sil-llvm-gen/SILLLVMGen.cpp
+++ b/tools/sil-llvm-gen/SILLLVMGen.cpp
@@ -189,8 +189,7 @@ int main(int argc, char **argv) {
   if (Invocation.hasSerializedAST()) {
     assert(!CI.hasSILModule() &&
            "performSema() should not create a SILModule.");
-    CI.setSILModule(SILModule::createEmptyModule(
-        CI.getMainModule(), CI.getSILOptions(), PerformWMO));
+    CI.createSILModule();
     std::unique_ptr<SerializedSILLoader> SL = SerializedSILLoader::create(
         CI.getASTContext(), CI.getSILModule(), nullptr);
 
diff --git a/tools/sil-nm/SILNM.cpp b/tools/sil-nm/SILNM.cpp
index 3b1a6ed501a..04c754faebb 100644
--- a/tools/sil-nm/SILNM.cpp
+++ b/tools/sil-nm/SILNM.cpp
@@ -191,8 +191,7 @@ int main(int argc, char **argv) {
   if (Invocation.hasSerializedAST()) {
     assert(!CI.hasSILModule() &&
            "performSema() should not create a SILModule.");
-    CI.setSILModule(
-        SILModule::createEmptyModule(CI.getMainModule(), CI.getSILOptions()));
+    CI.createSILModule();
     std::unique_ptr<SerializedSILLoader> SL = SerializedSILLoader::create(
         CI.getASTContext(), CI.getSILModule(), nullptr);
 
diff --git a/tools/sil-opt/SILOpt.cpp b/tools/sil-opt/SILOpt.cpp
index 9561e5cd5bc..90c9260c760 100644
--- a/tools/sil-opt/SILOpt.cpp
+++ b/tools/sil-opt/SILOpt.cpp
@@ -389,8 +389,7 @@ int main(int argc, char **argv) {
   if (Invocation.hasSerializedAST()) {
     assert(!CI.hasSILModule() &&
            "performSema() should not create a SILModule.");
-    CI.setSILModule(SILModule::createEmptyModule(
-        CI.getMainModule(), CI.getSILOptions(), PerformWMO));
+    CI.createSILModule();
     std::unique_ptr<SerializedSILLoader> SL = SerializedSILLoader::create(
         CI.getASTContext(), CI.getSILModule(), nullptr);