diff --git a/lib/Serialization/SerializeSIL.cpp b/lib/Serialization/SerializeSIL.cpp
index 72f8fe06ff195..0a6deac3158f9 100644
--- a/lib/Serialization/SerializeSIL.cpp
+++ b/lib/Serialization/SerializeSIL.cpp
@@ -167,6 +167,9 @@ namespace {
                          << " for layout " << Layout::Code << "\n");
     }
 
+    // TODO: this is not required anymore. Remove it.
+    bool ShouldSerializeAll;
+
     /// Helper function to update ListOfValues for MethodInst. Format:
     /// Attr, SILDeclRef (DeclID, Kind, uncurryLevel, IsObjC), and an operand.
     void handleMethodInst(const MethodInst *MI, SILValue operand,
@@ -202,8 +205,8 @@ namespace {
 
   public:
     SILSerializer(Serializer &S, ASTContext &Ctx,
-                  llvm::BitstreamWriter &Out)
-      : S(S), Ctx(Ctx), Out(Out) {}
+                  llvm::BitstreamWriter &Out, bool serializeAll)
+      : S(S), Ctx(Ctx), Out(Out), ShouldSerializeAll(serializeAll) {}
 
     void writeSILModule(const SILModule *SILMod);
   };
@@ -1694,23 +1697,28 @@ void SILSerializer::writeSILBlock(const SILModule *SILMod) {
   // FIXME: Resilience: could write out vtable for fragile classes.
   const DeclContext *assocDC = SILMod->getAssociatedContext();
   for (const SILVTable &vt : SILMod->getVTables()) {
-    if (vt.getClass()->isChildContextOf(assocDC))
+    if (ShouldSerializeAll &&
+        vt.getClass()->isChildContextOf(assocDC))
       writeSILVTable(vt);
   }
 
-  // Write out WitnessTables.
+  // Write out WitnessTables. For now, write out only if EnableSerializeAll.
   for (const SILWitnessTable &wt : SILMod->getWitnessTables()) {
-    if (wt.getConformance()->getDeclContext()->isChildContextOf(assocDC))
+    if (ShouldSerializeAll &&
+        wt.getConformance()->getDeclContext()->isChildContextOf(assocDC))
       writeSILWitnessTable(wt);
   }
 
   // Go through all the SILFunctions in SILMod and write out any
   // mandatory function bodies.
   for (const SILFunction &F : *SILMod) {
-    if (shouldEmitFunctionBody(F))
+    if (shouldEmitFunctionBody(F) || ShouldSerializeAll)
       writeSILFunction(F);
   }
 
+  if (ShouldSerializeAll)
+    return;
+
   // Now write function declarations for every function we've
   // emitted a reference to without emitting a function body for.
   for (const SILFunction &F : *SILMod) {
@@ -1724,10 +1732,10 @@ void SILSerializer::writeSILModule(const SILModule *SILMod) {
   writeIndexTables();
 }
 
-void Serializer::writeSIL(const SILModule *SILMod) {
+void Serializer::writeSIL(const SILModule *SILMod, bool serializeAllSIL) {
   if (!SILMod)
     return;
 
-  SILSerializer SILSer(*this, M->getASTContext(), Out);
+  SILSerializer SILSer(*this, M->getASTContext(), Out, serializeAllSIL);
   SILSer.writeSILModule(SILMod);
 }